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  • 1.
    Alam, M. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, SE-100 44 Stockholm, Sweden.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander F. H.
    Luleå University of Technology.
    Häggblad, Hans-Åke
    Luleå University of Technology.
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, no 6, p. 1936-1945Article in journal (Refereed)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 2.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, no 10, p. 2246-2258Article in journal (Refereed)
    Abstract [en]

    Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations

  • 3.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part I2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.

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  • 4.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
    Abstract [en]

    Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.

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  • 5.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Geometrical aspects of the fatigue behaviour of laser hybrid fillet welds2009In: Proceedings of the Fatigue Design Conference, Cetim , 2009Conference paper (Refereed)
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  • 6.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds2009In: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla: Laser institute of America , 2009, p. 38-46Conference paper (Refereed)
    Abstract [en]

    The geometrical aspects of laser hybrid welding before, during and after the process differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the microgeometry, i.e. the surface ripples can be more critical than the macrogeometry of the weld surface and even than lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface the tendency to LOF can be explained. Stress analysis was carried out by FEA for the complex joint geometry and bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

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  • 7.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    High-pressure compaction modelling of calcite (CaCO3) powder compact2011In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, no 3, p. 259-268Article in journal (Refereed)
    Abstract [en]

    Numerical simulation of manufacturing processes with working conditions at high pressure (above 1 GPa) requires constitutive data of the powder for the whole range of pressure and density. Most of the test apparatuses commonly used to obtain such data is only working in the lower pressure regions. Because of the absence of high-pressure data, many parameters have to be guessed or extrapolated. A material used in high-pressure applications is Calcite (CaCO3). The material can be used as an insulator in high-pressure capsules it is also a common material in the earth core. An apparatus often used to generate high pressure during compaction is the Bridgman anvil apparatus. In this work experimental tests with a Bridgman anvil set-up using Calcite powder discs with different thicknesses were done. A nonlinear elastic-plastic cap model was developed to model the behaviour of powder material from low pressure and loose state to high pressure and solid state. The constitutive model was implemented in a finite element code. The constitutive data were identified by optimization of experimental data. Validation was done by numerically reproduce the mechanical behaviour of uni-axially pressing Calcite to different pressure (up to 5 GPa) including unloading. The load-displacement curves, density distribution and the surface displacement were measured and compared to the finite element results. The results of the compaction simulations agree reasonably well with the experimental results.

  • 8. Berg, Sven
    et al.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental characterisation of CaCO3 powder mix for high-pressure compaction modelling2010In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, no 2, p. 198-205Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of powders at high pressures are difficult to measure and therefore such data are rarely reported in open literature. Available test equipment mainly operates in the low-pressure region, 0-200 MPa. Calcite (CaCO3) is a mineral suitable for high-pressure processes, e.g. sintering of diamond compacts. It is also a very common material in the earth core and therefore of interest for geoscientists. In order to model the processes in the high-pressure region (above 1 GPa), knowledge of the mechanical properties of the powder in the entire pressure range is needed. Experimental studies have been conducted to investigate the pressure-density relationship of a CaCO3 powder and also to correlate the relative density to elastic and strength properties using experimental results. Further, a methodology has been introduced to provide a foundation for an elastic-plastic constitutive model. The mechanical behaviour of a CaCO3 powder mix has been investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The experiments showed increasing elastic modulus and strength with increasing density. An empirical expression of the dependence of the bulk modulus on density has also been introduced.

  • 9.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental characterization of CaCO3powder for use in compressible gaskets up to ultra-high pressure2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 215-216, p. 124-131Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to investigate the compaction properties for a CaCO3 powder mix up to ultra-high pressure (10GPa) and how these properties affect the gasket behaviour. Different parameters of the powder are investigated, i.e. initial density and internal moisture. A set-up, supporting the outer diameter of the compact, commonly used for gaskets in the belt apparatus was also investigated. The experimental results are in terms of pressure instrumentation in the Bridgman anvil apparatus together with load–displacement curves of the powder compacts. The instrumentation is done so that it can be used to calibrate constitutive models.

  • 10.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Carlson, Johan E.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    High pressure characterization and modelling of CaCO3 powder mix in the Bridgman anvil apparatus2012In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 32, no 4, p. 490-508Article in journal (Refereed)
    Abstract [en]

    For investigating high pressure sintering processes, numerical models can be used. This will demand material models which give realistic mechanical response throughout the whole parameter space of the actual process. As the pressures become higher, the material density approaches its full theoretical value and the elastic part of the material properties becomes increasingly important. In this investigation, Poisson's ratio was determined using ultrasonic pulse-echo measurements. A new elastic model and an improved plasticity model were implemented into a user-defined material subroutine in a finite element (FE) code. To experimentally investigate the load displacement response and pressure distribution in powder compacts during pressing, a pressure instrumented Bridgman anvil apparatus was used. Validation of the FE model was conducted against experimental data from pressing experiments using two different start densities. The results show that the simulation model is indeed capable of reproducing load–thickness curves and pressure profiles reasonable close to the experimental curves.

  • 11.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Frictional behaviour of CaCO3 powder compacts2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 228, p. 429-434Article in journal (Refereed)
    Abstract [en]

    During powder compaction processes friction has an influence on the final shape and properties of components. It is therefore important to understand how the friction influences the compaction process. Since detailed friction measurements of the powder compact-tool interface are rare, simulation models of the powder compaction process often involve a more accurate description of the frictional behaviour. This limits the accuracy of the simulated results. More accurate numerical models can give improved results, especially in regards to the evolution of density and its distribution within the powder compacts.This study is as a step towards more advanced friction models for powder compaction simulations. A universal tribometer has been used to investigate the frictional behaviour of contact interfaces between a carbide counter surface and CaCO3 powder compacts with different densities. Both static and dynamic frictional properties were measured in a variety of conditions to build a fundamental foundation for friction modelling in powder compaction simulations.The results show that increasing the powder compact density decreases the dynamic friction coefficient but that the static friction coefficient remains fairly constant. The measured friction coefficient can be used to improve the simulation of a powder compact process. Also investigated is the change in friction coefficient that occurs in the compaction process when the surfaces are worn such that loose powder appears in the interface between the tool and the powder compact. This behaviour is important to take into account to accurately describe the compaction process.

  • 12.
    Cante, J.
    et al.
    E.T.S. d’Enginyeries Industrial i Aeronáutica de Terrassa, Technical University of Catalonia (UPC), Campus Terrassa UPC.
    Dávalos, C.
    International Center for Numerical Methods in Engineering (CIMNE), C/. Gran Capitan s/n, 08034 , Barcelona.
    Hernández, J.A.
    E.T.S. d’Enginyeries Industrial i Aeronáutica de Terrassa, Technical University of Catalonia (UPC), Campus Terrassa UPC.
    Oliver, J.
    E.T.S. d’Enginyers de Camins, Canals i Ports de Barcelona, Technical University of Catalonia (UPC), Campus Nord UPC.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustafsson, Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    PFEM-based modeling of industrial granular flows2014In: Computational Particle Mechanics, ISSN 2196-4378, Vol. 1, no 1, p. 47-70Article in journal (Refereed)
    Abstract [en]

    The potential of numerical methods for the solution and optimization of industrial granular flows problems is widely accepted by the industries of this field, the challenge being to promote effectively their industrial practice. In this paper, we attempt to make an exploratory step in this regard by using a numerical model based on continuous mechanics and on the so-called Particle Finite Element Method (PFEM). This goal is achieved by focusing two specific industrial applications in mining industry and pellet manufacturing: silo discharge and calculation of power draw in tumbling mills. Both examples are representative of variations on the granular material mechanical response—varying from a stagnant configuration to a flow condition. The silo discharge is validated using the experimental data, collected on a full-scale flat bottomed cylindrical silo. The simulation is conducted with the aim of characterizing and understanding the correlation between flow patterns and pressures for concentric discharges. In the second example, the potential of PFEM as a numerical tool to track the positions of the particles inside the drum is analyzed. Pressures and wall pressures distribution are also studied. The power draw is also computed and validated against experiments in which the power is plotted in terms of the rotational speed of the drum.

  • 13.
    Carbonell, Josep Maria
    et al.
    Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE) Universitat Politècnica de Catalunya (UPC) Campus Norte UPC, 08034 Barcelona, Spain.
    Oñate, Eugenio
    Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE) Universitat Politècnica de Catalunya (UPC) Campus Norte UPC, 08034 Barcelona, Spain.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modelling of finished surfaces produced by large deformation processes with the Particle Finite-Element Method (PFEM)2019In: VI International Conference on Particle-Based Methods: Fundamentals and Applications, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2019Conference paper (Refereed)
  • 14.
    Casellas, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics. Eurecat, Centre Tecnològic de Catalunya, Manresa, Spain.
    Frómeta, D.
    Eurecat, Centre Tecnològic de Catalunya, Manresa, Spain.
    Parareda, S.
    Eurecat, Centre Tecnològic de Catalunya, Manresa, Spain.
    Grifé, L.
    Eurecat, Centre Tecnològic de Catalunya, Manresa, Spain.
    Tarhouni, I.
    Eurecat, Centre Tecnològic de Catalunya, Manresa, Spain.
    Sandin, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    When fracture toughness becomes essential for Lightweighting: Understanding cracking behaviour in high strength sheets2022In: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Conference paper (Refereed)
  • 15.
    Casellas, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Frómeta, David
    Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Lara, Toni
    undació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Molas, Silvia
    undació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Golling, Stefan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A fracture mechanics approach to develop high crash resistant microstructures by press hardening2017In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 101-107Conference paper (Refereed)
    Abstract [en]

    Crashworthiness is a relevant engineering property for car parts. However it is not easy to measure at laboratory scale and complex impact tests have to be carried out to determine it. Crash resistance for high strength steel is commonly evaluated in terms of cracking pattern and energy absorption in crashed specimens. Accordingly, the material resistance to crack propagation, i.e. the fracture toughness, could be used to rank crashworthiness. It has been proved in a previous work by the authors, so the measure of fracture toughness, in the frame of fracture mechanics in small laboratory specimens, would allow determining the best microstructure for crash resistance parts. Press hardening offers the possibility to obtain a wide range of microstructural configurations, with different mechanical properties. So the aim of this work is to evaluate the fracture toughness following the essential work of fracture methodology for ferrite-pearlite, bainite, ferrite-bainite, martensite and martensite-bainite microstructures. Results showed that bainitic microstructures have high fracture toughness, similar to TWIP and CP steels, which allows pointing them as potential candidates for obtaining high crash resistance in parts manufactured by press hardening.

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  • 16. Coube, O.
    et al.
    Chen, Y.
    Imbault, D.
    Doremus, P.
    Maassen, R.
    Federzoni, L.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Tweed, J.
    Gethin, D.
    Rolland, S.
    Computer simulation of die compaction: guidelines and an example from the European dienet project2004In: Conference proceedings: Euro PM 2004, Powder Metallurgy World Congress & Exhibition : Austria Centre, Vienna, Austria, 17 - 21 October 2004 / [ed] Herbert Danninger, Shrewsbury: European powder metallurgy association , 2004Conference paper (Refereed)
  • 17. Coube, O.
    et al.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kraft, T.,
    Chen, Y.
    Imbault, D.
    Doremus, P.
    Gethin, D.
    Rolland, S.
    Federzoni, L.
    Numerical simulation of die compaction: case studies and guidelines from the European dienet project2005In: PM in Prague, new opportunities in a new Europe: Euro PM 2005 congress and exhibition, European powder metallurgy association , 2005, p. 313-319Conference paper (Refereed)
  • 18.
    Coube, Olivier
    et al.
    EPMA.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Case studies: discussion and guidelines2007In: Modelling of Powder Die Compaction, London: Encyclopedia of Global Archaeology/Springer Verlag, 2007, p. 197-222Chapter in book (Other academic)
  • 19.
    Forsström, Dan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Calibration and validation of a large scale abrasive wear model by coupling DEM-FEM: Local failure prediction from abrasive wear of tipper bodies during unloading of granular material2016In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 66, p. 274-383Article in journal (Refereed)
    Abstract [en]

    Handling of granular materials like rocks, pebbles and sand can expose equipment to abrasive wear that can result in local failure. In some cases this can have far reaching economic significance such as the costs of replacement, the costs from machine downtime and lost production. Models for predicting wear can be found from lab scale tests, but are difficult to apply in large scale applications. An important property is the flow behaviour of granular material during its transportation in a granular material handling system. In order to effectively predict abrasive wear in large scale applications, models for solid structure, granular material flow and wear behaviour have to be coupled. In this work; the finite element method is used to model the structure of the tipper body and the discrete element method is used to model the granular material. To couple the structure response to granular flow behaviour a contact model is used. A calibration of the wear constant in Archard's wear law is obtained from measurement data of rotating drum tests, using the representative material combination used in a tipper unloading case. This wear model is then used in a full scale tipper body simulation to predict the absolute wear and validated against field measurement. A good agreement between numerical calculation and field measurement regarding the spatial position and size of wear areas were found. This combination of numerical methods gives new possibilities to understand the wear process and is one step towards more physically correct models for large scale predictions between tipper bodies and granular material. Numerical tools can give future opportunities to optimise material selections and geometry with the intension to increase functionality, life of large scale wear applications and avoid local failure.

  • 20.
    Forsström, Dan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Load intensity calculations on tipper body using DEM FEM coupling2014In: 11th World Congress on Computational Mechanics (WCCM XI) 5th European Conference on Computational Mechanics (ECCM V) 6th European Conference on Computational Fluid Dynamics (ECFD VI) / [ed] Eugenio Oñate; Xavier Oliver; Antonio Huerta, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2014, Vol. 3, p. 1612-1621Conference paper (Refereed)
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  • 21.
    Forsström, Dan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustafsson, Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Granular flow model for large scale wear prediction2015Conference paper (Refereed)
    Abstract [en]

    To predict abrasive wear in industrial bulk material, couplings between granular material flow and wear calculation have to be developed. It would also be desirable to include both sliding and impact wear in such model. The emptying of a tipper loaded with a rock mass of approximately 20 tonnes was modelled. The rock was modelled using two different numerical techniques: the discrete element method (DEM) and the finite element method (FEM). The purpose of the simulations was to study the coupling between the two numerical techniques and to compare their usefulness in wear calculation. The tipper emptying model had previously been used in calculating abrasive wear during unloading. A tipper body [1], protected with SSAB Hardox 450 steel, was modelled with FEM using and a piecewise linear plasticity model for the material behaviour. For the numerical model labelled DEMFEM, the rocks were modelled with spherical discrete elements with rolling friction and damping parameters applied to simulate non-spherical rocks. Another numerical model labelled FEM-FEM, to mimic arbitrary shape rocks used two slightly different simplified shapes, round and prism like kinds. To compare the numerical approaches the pressure on the tipper body was studied at two times during the unloading. The first measurement occasion was defined when the rock mass had been dropped into the tipper and had come to rest and the second when the tipping had started and approximately half of the load had been unloaded. When the two approaches were compared it could be seen that the calculated pressure field agreed fairly well both initially with the rock mass at rest and during emptying with the rock mass in motion.

  • 22.
    Forsström, Dan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lindbäck, Torbjörn
    Conex Engineering.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prediction of wear in a dumper truck body by coupling SPH-FEM models2013Conference paper (Refereed)
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  • 23.
    Forsström, Dan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lindbäck, Torbjörn
    Conex Engineering.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prediction of wear in dumper truck body by coupling SPH-FEM2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 2, p. 111-115Article in journal (Refereed)
    Abstract [en]

    Abrasive wear is largely involved in many industries processes, and can cause serious problems and economic loss. A number of theoretical models and numerical models have been established to study wear phenomena. However, simulation and prediction of wear at large scale are seldom presented. Sliding abrasive wear of steel plates from interaction with granular material is here studied with numerical simulations. Abrasive wear of unloading of two different dumper body geometries are studied with the smoothed particle hydrodynamics method coupled to the finite element method. These numerical tools are of interest as they can reproduce interaction between solid and granular material. Wear pattern on the dumper bodies obtained from numerical simulation shows a reasonably good correspondence to experimental measurements. An advanced analysis tool that takes into account both the actual material flows, coupled with wear calculation model would be a new tool to design and optimise handling equipment against wear.

  • 24.
    Frómeta, D.
    et al.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Spain.
    Parareda, S.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Spain.
    Lara, A.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Spain.
    Molas, S.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Spain.
    Casellas, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Spain.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Calvo, J.
    Universitat Politècnica de Catalunya, Spain.
    Identification of fracture toughness parameters to understand the fracture resistance of advanced high strength sheet steels2020In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 229, article id 106949Article in journal (Refereed)
    Abstract [en]

    The fracture toughness of four advanced high strength steel (AHSS) thin sheets is evaluated through different characterization methodologies, with the aim of identifying the most relevant toughness parameters to describe their fracture resistance. The investigated steels are: a Complex Phase steel, a Dual Phase steel, a Trip-Aided Bainitic Ferritic steel and a Quenching and Partitioning steel. Their crack initiation and propagation resistance is assessed by means of J-integral measurements, essential work of fracture tests and Kahn-type tear tests. The results obtained from the different methodologies are compared and discussed, and the influence of different parameters such as specimen geometry or notch radius is investigated. Crack initiation resistance parameters are shown to be independent of the specimen geometry and the testing method. However, significant differences are found in the crack propagation resistance values. The results show that, when there is a significant energetic contribution from necking during crack propagation, the specific essential work of fracture (we) better describes the overall fracture resistance of thin AHSS sheets than JC. In contrast, energy values obtained from tear tests overestimate the crack propagation resistance and provide a poor estimation of AHSS fracture performance. we is concluded to be the most suitable parameter to describe the global fracture behaviour of AHSS sheets and it is presented as a key property for new material design and optimization.

  • 25.
    Frómeta, David
    et al.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, Manresa 08243, Spain.
    Parareda, Sergi
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, Manresa 08243, Spain.
    Lara, Antoni
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, Manresa 08243, Spain.
    Casellas, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, Manresa 08243, Spain.
    Pujante, Jaume
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, Manresa 08243, Spain.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Golling, Stefan
    Gestamp R&D, Box 929, 97 125 Luleå, Sweden.
    Sieurin, Henrik
    SCANIA AB, Materials Technology Department SE-151 87 Södertälje, Sweden.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Fracture Toughness Evaluation of Thick Press Hardened 22MnB5 Sheets for High Crash Performance Applications in Trucks2019In: Hot sheet metal forming of high-performance steel: Proceedings / [ed] Mats Oldenburg, Jens Hardell, Daniel Casellas, Wissenschaftliche Scripten , 2019, p. 113-121Conference paper (Refereed)
    Abstract [en]

    The present work investigates the fracture toughness of a thick press hardened 22MnB5 steel sheet, in order to assess its applicability for truck safety parts. The fracture toughness is evaluated in the frame of the elastic plastic fracture mechanics (EPFM), in terms of essential work if fracture (EWF) and J-integral. Digital Image Correlation (DIC) measuring techniques are used to measure crack tip opening displacement and crack extension. It is shown that EWF presents some limitations for thick high strength metal sheet applications, making necessary the use of conventional EPFM procedures. Digital image analysis has shown to be very useful in fracture toughness characterization of thick press hardened steel sheets. The differences observed between different methodologies are discussed and results are compared to toughness values of different AHSS grades.

  • 26.
    Golling, Stefan
    et al.
    Gestamp R&D, Box 828, 97 125 Luleå.
    Frometa, David
    Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spain.
    Casellas, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spain.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Influence of microstructure on the fracture toughness of hot stamped boron steel2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 743, p. 529-539Article in journal (Refereed)
    Abstract [en]

    The automotive industry's desire for weight reduction while maintaining crashworthiness demands development of materials and material properties within the economic framework of consumers. The industrial process of hot stamping provides a technique to utilize steel in an efficient way. In hot stamping, microstructural characteristics of a steel blank are influenced by controlling the cooling rate. Hot stamping has become a prevalent method for lightweight solutions in car bodies without sacrificing passenger safety. The process of hot stamping applies sequential forming and quenching in a single production step. During the cooling of the blank, various microstructures can be formed depending on the cooling rate or holding temperature. Special tooling allows the application of different cooling rates within the same blank. Thus, the microstructure and mechanical properties can be influenced in designated areas of a blank.

    Fracture toughness properties of sheet metal are necessary to better understand fracture initiation and crack propagation during crash loading as well as improve crashworthiness predictions. This paper focus on fracture toughness of low-alloyed boron steel sheet common in the automotive industry. A heat treatment process is used to form different microstructures, predominately consisting of one single phase or mixed microstructures with two distinct phases. The fracture toughness of the present microstructures is evaluated using the Essential Work of Fracture methodology. Results are discussed in terms of the different microstructures obtained and the consequent part performance.

    Results show a strong connection between microstructure and fracture toughness. The bainitic grade shows favorable fracture toughness while a mixed microstructure of bainite and martensite shows a very brittle fracture behavior. A post heat treatment in the form of paint bake curing shows a negligible effect on fracture toughness of martensite.

  • 27.
    Golling, Stefan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Frómeta, David
    Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Casellas, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Granström, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Determination of the essential work of fracture at high strain rates2017In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 261-269Conference paper (Refereed)
    Abstract [en]

    During the last decades, the use of ultra-high strength steel (UHSS) has increased as its favorable ratio between strength and mass allows the design of lighter body-in-white while maintaining passenger safety. Modeling impact loads of components made of UHS steel requires reliable descriptions of the material deformation and fracture behavior.

    Traditional stress or strain based fracture criteria are used in finite element modeling. A different approach in modeling fracture in components uses the fracture energy as a model parameter.

    Fracture toughness is difficult to measure in thin sheets; a method termed Essential Work of Fracture (EWF) provides the possibility to determine the fracture toughness in sheet metal. With knowledge of the fracture toughness the understanding of fracture behavior and crack propagation in ultra-high strength steel can be increased. The obtained EWF is related to the fracture energy and can be used in numerical models as a material parameter.

    In the present work results from preliminary testing are shown and a discussion on cross-head speed and strain rate in the critical specimen cross section is given. The use of digital image correlation provides information about the displacement field in the vicinity of the notch and hence about the strain- and strain rate distribution. Furthermore, the difficulties in reliable measurement of force and elongation in high speed tensile testing machines are elucidated. Issues encountered during the development of the high-speed DENT specimen are not limited to the specific geometry presented in this paper.

    The present work aims at the development of a test specimen to obtain the Essential Work of Fracture (EWF) at high test speed. This work contributes to the overall goal to model fracture behavior and crack propagation, dependent on the strain rate. For the investigation, a high-speed tensile testing machine equipped with an in-house developed load cell and an optical elongation measurement system was used with a high-speed camera to obtain data for digital image correlation.

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  • 28.
    Golling, Stefan
    et al.
    Gestamp R&D, Luleå.
    Frómeta, David
    Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Casellas, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. Fundació CTM Centre Tecnològic, Plaça de la Ciència 2, 08243 Manresa, Spai.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Investigation on the Influence of Loading-Rate on Fracture Toughness of AHSS Grades2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 726, p. 332-341Article in journal (Refereed)
    Abstract [en]

    The automotive industry is striving for light body-in-white structures while maintaining or improving passenger safety. The aim of this paper is to investigate the influence of the loading rate on the fracture toughness of thin steel sheet metal of three advanced high strength steels. Although steel is a heavy material it plays a significant role for lightweight solutions in car bodies. Three different advanced high strength steel (AHSS) grades, namely dual-phase (DP), quench-partitioning (Q&P) and TRIP-assisted bainitic-ferritic (TBF), are investigated in the present paper. For crash relevant components it is of importance to know the material response under high loading velocities i.e. high strain rates. A standard tensile test system is used for low loading rates, a high-speed tensile testing setup is used to obtain high loading rates. The fracture toughness of the three AHSS grades is evaluated using the methodology of the Essential Work of Fracture (EWF). The tensile specimen used in the present work is the double edge notched tensile (DENT) geometry with a pre-developed crack. High-speed imaging is applied to verify the validity of the evaluation method Essential Work of Fracture at high rates of loading. Results from this work show that knowledge of fracture toughness would improve the understanding of fracture and crack propagation mechanisms for third generation high strength steels used for automotive components

  • 29.
    Gustafsson, David
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Parareda, S.
    Eurecat, Centre Tecnologic de Catalunya, Spain.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Effect Of Cutting Clearance And Sandblasting On Fatigue Of Thick CP800 Steel Sheets2022In: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Conference paper (Refereed)
  • 30.
    Gustafsson, David
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Parareda, Sergi
    Eurecat, Plaça de la ciència 2, 08242 Manresa; CIEFMA, EEBE, Universitat Politècnica de Catalunya-BarcelonaTech, 08019 Barcelona, Spain.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Effect of cutting clearance and sandblasting on fatigue of thick CP800 steel sheets for heavy-duty vehicles2022In: Hot Sheet Metal Forming of High-Performance Steel: proceedings / [ed] Mats Oldenburg; Jens Hardell; Daniel Casellas, Wissenschaftliche Scripten , 2022, p. 315-322Conference paper (Refereed)
    Abstract [en]

    Effect from manufacturing processes on fatigue properties of high-strength thick steel sheets have gained increased attention the recent years, due to new demands on the heavy-duty vehicle (HDV) industry to reduce the carbon footprint. The aim of this study is to add knowledge of the effect of shear cutting clearance on the fatigue behaviour of complex phase CP800 thick steel sheets. In addition, sandblasting and its effect on the fatigue properties are studied. Service loads are fluctuating loads acting on chassis component making fatigue an important failure mode. The fatigue strength usually follows the yield strength of the material and hence weight could in theory be saved by using steels of higher strength. However, in the presence of edge defects this relation does not necessarily hold, this leads to large safety factors of the design and under-utilization of the high-strength material. Thus, an increased knowledge about the effect from manufacturing processes on fatigue properties is important for the quest to achieve weight reduction. This is particularly true for thick sheets which, to the best of our knowledge, are less investigated than their thinner counterparts, but of high importance for the HDV development.

     

    In this paper, empirical results from fatigue testing of complex phase steel CP800, subjected to punching and trimming, are presented. Results for different cutting clearances are compared as well as the effect of sandblasting. A fast fatigue testing method called Rapid fatigue test based on stiffness evolution is utilized. The results show the improvement obtained by using sandblasting as well as illustrating the effect of different cutting clearances. These results can be used as a guidance for design and production of HDV components, where cutting clearance is set. Furthermore, the results can be used as an input for discussions whether the extra costs associated with sandblasting is motivated or not for components made from high strength, thick steel sheets.

  • 31. Gustafsson, Gustaf
    et al.
    Cante, Juan Carlos
    Escola Tècnica Superior d'Enginyeries Industrial i Aeronàutica de Terrassa.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Weyler, Rafael
    Escola Tècnica Superior d'Enginyeries Industrial i Aeronàutica de Terrassa.
    Comparison of smoothed particle method and particle finite element method in applied granular flow problems2009In: Particle-Based Methods: Fundamentals and Applications / [ed] Eugenio Oñate; Roger Owen, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2009, p. 204-207Conference paper (Refereed)
    Abstract [en]

    Traditionally, discrete element (DE) method and finite element (FE) method are used in numerical simulation of granular flow problems. A drawback with the (DE) method is the limitations in modelling the extreme large number of particles, which normally are in real granular flow problems. With a numerical method based on continuum mechanics modelling like the FE-method, the problems can be solved with less computation particles. However, the limitations of the FE-method have been pointed out to be when extremely large deformation needs to be captured. Granular flow problem motions produce large distortions of the mesh and ruin the convergence of the problem. The purpose of this paper is to compare two alternative continuum based methods, the Particle Finite Element Method (PFEM) and the Smoothed Particle (SP) method, to model two different granular flow problems.

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  • 32.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Characterization modelling and validation of a two-point loaded iron ore pellet2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 235, p. 126-135Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different stresses, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental and numerical work to investigate the mechanical properties of blast furnace iron ore pellets. To study the load deformation behaviour and the fracture of iron ore pellets, a number of point load tests are carried out and analysed. Material parameters for an elastic–plastic constitutive model with linear hardening for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. Two finite element models are developed for different purposes. For the material parameter determination, a perfectly spherical model is used. The constitutive model is validated with a finite element model based on a representative optically scanned iron ore pellet. The proposed constitutive model is capturing the force displacement relation for iron ore pellets in a two-point load test. A stress based fracture criterion which takes the triaxiality into account is suggested and calculated as the maximum equivalent effective stress dependent on the three principal stresses at fracture. The results of this study show that the equivalent effective stress in the vicinity of the centre of an irregular model of an iron ore pellet is very close to the results of a model of a perfectly spherical iron ore pellet. The proposed fracture criterion indicates fracture in the representative iron ore pellet model coincident with the location of the crack developed during the test of the optically scanned iron ore pellet.

  • 33.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modelling and simulation of iron ore pellets2013Conference paper (Refereed)
    Abstract [en]

    Transportation and storage are important parts in the process chain for producers of iron ore pellets. Knowledge and optimization of these processes are very important for further efficiency progress and increased product quality. The existence of a numerical simulation tool with accurate material characteristics will significantly increase the possibility to predict critical forces in developing new and existing transportation and storing systems and thereby decrease the amount of damaged, fractured or crushed pellets (fines). In this work modelling and simulation of iron ore pellets are carried out at different length scales. An elastic plastic granular continuum flow model for iron ore pellets using smoothed particle (SP) method is presented [1]. The model is used to model iron ore pellets silo flow. A finite element (FE) model of single iron ore pellets is also worked out with statistical data for an elastic plastic constitutive model with a fracture criterion [2]. The model is used to simulate loading and fracture on single iron ore pellets and is validated with a two point load test. In order to find the relation between the behaviour of iron ore pellets at different length scales, e.g. compare the stresses in a silo to the critical stress inside a single iron ore pellet, modelling of iron ore pellets on an intermediate length scale is established. A multi particle finite element model (MPFEM) consisting of individual discretized models of the iron ore pellets is here presented [3]. An instrumented confined compression tests is developed for measuring the global response on a limited amount of iron ore pellets [4]. The experiment is used to validate the MPFEM model in terms of the amount of broken pellets.

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  • 34.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Multi-particle finite element modelling of the compression of iron ore pellets with statistically distributed geometric and material data2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 239, p. 231-238Article in journal (Refereed)
    Abstract [en]

    The multi-particle finite element method (MPFEM) is used to simulate confined compression of iron ore pellets. The confined compression test consists of a cylindrical steel tube and two compressive platens. The iron ore pellets are confined by the tools and compressed. In the MPFEM model of the test, the iron ore pellets are represented by 1680 finite element (FE) discretised particles (7-16 mm). The size, shape and material properties of the pellets are statistically distributed. The contacts are modelled using the penalty stiffness method and Coulomb friction. The compression is simulated in two steps. In the first step, the iron ore pellet models are sparsely placed in the computational model of the steel tube and a gravity-driven simulation is conducted to make the pellets arrange themselves randomly. In a second step, the compression is simulated by a prescribed motion of the upper compressive platen. From the MPFEM simulation, the stresses inside the individual pellet models are evaluated, and the fracture probability of the iron ore pellets is derived and compared with experimental data. In addition, data on the global axial and radial stresses and axial displacement are presented and compared with experimental confined compression test data. The MPFEM model can reproduce the fracture ratio of iron ore pellets in uniaxial confined compression and is a feasible method for virtual fracture experiments of iron ore pellets.

  • 35.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation of stresses in iron ore pellets for confined compression-tests using the multi particle finite element method2011Conference paper (Refereed)
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  • 36.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Simulation of stresses in iron ore pellets for confined compression-tests using the multi particle finite element method2011Conference paper (Refereed)
    Abstract [en]

    Numerical simulation of the compaction of granular materials is an area of active research. One approach is to use deformable discrete elements of the individual particles using a 2D finite element (FE) mesh, see e.g. [1] and [2]. In this work, the axial compression of iron ore pellets inside a steel cylinder is studied and the individual particles are discretized with a coarse FE mesh in 3D. One possibility of this model is to study the stresses and strains inside the granular particles. Experiment and simulation of iron ore pellets in a confined compression test are done. The experiment consists of an upper and lower piston of thick circular steel plates surrounded by a 2 mm steel cylinder containing the iron ore pellets. The total mass of the iron ore pellets is 46.0kg. During a test, an axial load is applied on the lower piston to a certain level and then unloaded. Measured data are the force and displacement of the lower piston. In addition, strain gauges are measuring the circumferential strain in the middle of the steel membrane. Experimental compression tests between two plates of 18 randomly chosen iron ore pellets were done in order to characterize the load displacement behaviour of the individual pellets. FE models of the experimental tested pellets were carried out and simulated. Each pellet was discretized with an eight-node FE mesh. An elasto-plastic material model with linear hardening is used. The Young’s modulus, the plastic hardening modulus, and the yield stress of the material model were found by inverse modelling. Different material parameters were tested systematically in the FE model and compared with the experimental results until the same load displacement curve was obtained. A multi particle finite element model (MPFEM) was used to simulate the confined compression test. The iron ore pellets are represented in a quarter-model of the real experimental setup by 4756 discretized particles (7-16 mm) with a normal distribution measured from size distribution in the experiment. The contacts are modelled with the penalty stiffness method. The pistons are considered rigid in the simulation and the steel cylinder is modelled with thin elastic shell elements. The compression is simulated in two steps. In the first step, the iron ore pellets models are randomly sparse placed the cylinder and a gravity driven simulation is carried out where the pellets are arranged in the cylinder. In the second step, the compression is simulated by a prescribed displacement of the upper piston. Compared data from the experiment and simulation are; fill density, force-displacement curve and circumferential strain. A relation between the global stress state from the loading of the piston and the maximum stresses inside the individual iron ore pellets was carried out from the simulation. References [1] A.T. Procopio, A. Zavaliangos. “Simulation of multi-axial compaction of granular media from loose to high relative densities”, Journal of the Mechanics and Physics of Solids, 53 pp. 1523-1551, 2005. [2] D.T. Gethin, R.S. Ransing, R.W. Lewis, M. Dutko, A.J.L. Crook, “Numerical comparison of a deformable discrete element model and an equivalent continuum analysis for the compaction of ductile porous material”, Computers and Structures, 79 pp. 1287-1294, 2001.

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  • 37.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Determination of bulk properties and fracture data for iron ore pellets using instrumented confined compression experiments2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 241, p. 19-27Article in journal (Refereed)
    Abstract [en]

    In this work, an experimental method for measuring the bulk properties and fracture loading relations for iron ore pellets is presented. Knowledge on the bulk behaviour and fracture data for iron ore pellets is of great importance for improving the material transportation systems and to increase the product quality. Trustworthy numerical simulations of iron ore pellets also demand reliable materials data for the models. Here, instrumented confined compression tests are carried out at different load levels. Measurement data of the axial and radial stresses and the axial displacement are recorded for each test. Measurements of fractured iron ore pellets are carried out at different loads giving rise to crushing up to 20% of the total material. From the measured data, the Poisson´s ratio, the bulk modulus and a plastic strain hardening function are determined. In addition, friction measurements of iron ore pellets are carried out at different loads and configurations. In conclusion, the test method developed here is usable for the determination of the bulk properties and fracture characteristics of iron ore pellets.

  • 38.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan, Nagoya Institute of Technology.
    High-rate behaviour of iron ore pellet2015In: EPJ Web of Conferences, E-ISSN 2100-014X, Vol. 94, article id 5003Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In the transportation from the pelletizing plants to the customers, the iron ore pellets are exposed to different loading situations, resulting in degradation of strength and in some cases fragmentation. For future reliable numerical simulations of the handling and transportation of iron ore pellets, knowledge about their mechanical properties is needed. This paper describes the experimental work to investigate the dynamic mechanical properties of blast furnace iron ore pellets. To study the dynamic fracture of iron ore pellets a number of split Hopkinson pressure bar tests are carried out and analysed

  • 39.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical Prediction of Fracture in Iron Ore Pellets During Handling and Transportation2017In: / [ed] Barry Wills, 2017Conference paper (Refereed)
    Abstract [en]

    Iron ore pellets are sintered, centimetre-sized spheres of ore with high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. During transportation and handling of iron ore pellets they are exposed to different loads, resulting in degradation of the strength and in some cases fragmentation. The aim of this work is to increase the knowledge of how to design the handling systems for iron ore pellets to decrease the amount of fractured materials in the flows. A numerical finite element model for iron ore pellets fracture probability analysis is presented with a stress based fracture criterion. The model is used to simulate different flows of iron ore pellets hitting guide plates and to predict the proportion of fractured iron ore pellets in the flow. The amount of fractured iron ore pellets are predicted at different flow velocities, showing good agreement with experimental measurements.

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  • 40.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Msahiro
    Nagoya Institute of Technology, Gokisocho, Showa-ku, Aichi.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Fracture probability modelling of impact-loaded iron ore pellets2017In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 102, p. 180-186Article in journal (Refereed)
    Abstract [en]

    Blast furnace iron ore pellets are sintered, centimetre-sized ore spheres with a high iron content. Together with carbonized coal, iron ore pellets are used in the production of steel. In transporting pellets from pelletizing plants to customers, iron ore pellets are exposed to different static and dynamic loading situations, resulting in strength degradation and, in some cases, fragmentation. This can lead to a reduced gas flow in the blast furnace, which causes reduced quality in steel production. Reliable numerical simulations that can predict the ability of the pellets to endure their handling are important tools for optimizing the design of equipment for iron ore handling. This paper describes the experimental and numerical work performed to investigate the impact fracture behaviour of iron ore pellets at different strain rates. A number of split Hopkinson pressure bar tests with different striker velocities are carried out and analysed to investigate the strain rate dependency of the fracture strength of iron ore pellets. Fracture data for iron ore pellets are derived and expressed in terms of statistical means and standard deviations. A stress based, strain-rate dependent fracture model that takes triaxiality into account is suggested. The fracture model is used and validated with impact tests of iron ore pellets. In the validation experiment, iron ore pellets are fired against a steel plate, and the percentage of fractured pellets at different impact velocities are measured. Finite element simulations of the experiment are carried out and the probability of pellets fracturing during impact are calculated and compared with the experimental results. The agreement between the experiments and numerical simulations shows the validity of the model.

  • 41.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Smoothed particle simulation and validation of powder filling2015Conference paper (Refereed)
    Abstract [en]

    Powder pressing is often a complicated process as the behaviour of the powder material changes with increasing density. Manufactures tend to produce components with more complicated shapes which demand complex pressing equipment and methods. Mechanical properties of powder materials changes dramatically from the beginning to the end of the compaction phase. Previous investigations have shown that powder transfer and high powder flow during filling affects the strength of the final component significantly. Experimental studies combined with simulations is likely to improve the understanding of the filling stage, e.g. to explain the non-homogeneity of the density of powder pressed parts. This work covers both experimental measurements and umerical modelling of powder filling. Experimental measurements with digital speckle photography (DSP) is used to study the powder behaviour and for the characterisation of the die filling as part of the process in powder pressing. TheDSP measurements are carried out by recording the powder filling process with a high speed video camera. The image series are then evaluated using an image correlation technique. By this, field data during the filling process can be visualised such as velocity fields and strain fields. These measurements are also supporting the development of a numerical model of the process. In this workthe smoothed particle method (SPH) is used to model the powder filling process. The numerical results are compared with the DSP measurements. The validated model is then used to study the process in more detail, e.g. to evaluate the density distribution after filling. The comparison of DPS measurements and simulations gives similar flow characteristics. Experimental measurements with DSP together with numerical simulation with the SP method are powerful tools to increase the knowledge of powder filling and to improve the process in the future is concluded.

  • 42.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kato, Hidinori
    Nagoya Institute of Technology.
    Nishida, Masahiro
    Nagoya Institute of Technology.
    Modelling and simulation of high velocity loaded iron powder2012Conference paper (Refereed)
    Abstract [en]

    High velocity compaction is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. The dynamic testing is performed using a modified split Hopkinson pressure bar (SHPB). A specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of an input bar creating elastic wave propagation. This process is modelled and simulated by using finite element method. The stress and strain history in the specimen during impact are compared with the evaluated experimental values from the strain measured on the input and output bars. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite and 0.6% Kenolube. In order to model the impact process a constitutive relation describing the powder behaviour taking into account the strain-rate and density variations are proposed. In conclusion, the proposed material model captures the increase in yield stress due to higher strain rates.

  • 43.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kato, Hidinori
    Nagoya Institute of Technology.
    Ogura, Takashi
    Nagoya Institute of Technology.
    Nishida, Masahiro
    Nagoya Institute of Technology.
    Strain Rate Dependent Constitutive Model with Failure for Impact Loading of Metal Powder2013Conference paper (Refereed)
    Abstract [en]

    Few studies have been conducted to investigate the strain rate behavior of metal powders. To achieve better understanding of the strain rate dependency of metal powders, it's necessary to conduct dynamic experiments and numerical simulations e.g. using finite element method. High strain rate experiments of iron powder material have been conducted using the split Hopkinson pressure bar method [1]. The dynamic testing is performed using a modified split Hopkinson pressure bar (Kolsky bar). A specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of an input bar creating elastic wave propagation. The powder material used for the experiments was a press-ready premix containing Distaloy AE, 0.5% graphite and 0.6% Kenolube. This process is modeled and simulated by using finite element method. In order to model the impact process a constitutive relation describing the powder behavior taking into account the strain-rate and density variations are proposed [2]. The stress and strain history in the specimen during impact is validated against the experimental measurements. To capture the global response caused by cracking during impact, a failure criterion is implemented. In conclusion, the proposed material model captures the increase in yield stress due to higher strain rates and the decrease in stress due to cracking.

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  • 44.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kato, Hidinori
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Ogura, Takashi
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Japan.
    Experimental studies and modelling of high-velocity loaded iron-powder compacts2014In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 268, p. 293-305Article in journal (Refereed)
    Abstract [en]

    A production technique with the capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts is high-velocity compaction (HVC). To extend the usage of the HVC method, detailed knowledge of the HVC process is important. To facilitate the development of production processes, numerical simulations can be utilised. In the development of high-precision simulation models, constitutive data of HVC specimens at high strain rates are required. In this study, the dynamic compressive properties of cylindrical specimens made by HVC were measured using a split Hopkinson pressure bar (Kolsky bar) assembly. For this technique, a specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of the input bar and generates elastic-wave propagation.The powder material used for the experiments is a press-ready iron-based premix. Among specimens made by HVC and conventional compaction (CC), the effects of the specimen density and the strain rate on the compressive properties, such as failure stress, Young´s modulus and failure behaviour, are investigated. During dynamic compression, the failure behaviour of the specimens was also recorded using a high-speed video camera. The difference in the mechanical behaviour between HVC-pressed specimens and conventionally pressed specimens are also investigated. The stress–strain curves of HVC-pressed specimens are identical to those of conventionally pressed specimens, but the failure behaviour differs are concluded.A well-established numerical method for forming simulations also conducted for powder compaction is the finite element method (FEM). The impact loading of the powder is modelled and simulated using nonlinear three-dimensional FEM. To model the impact process, a constitutive relation for the powder behaviour is proposed, taking into account the strain rate and density variations. To capture the global response caused by cracking during impact, a damage model is implemented. The numerical results in terms of the stress and strain history in the specimen during impact are compared with the experimental measurements. In conclusion, the proposed material model captures the increase in the yield stress due to the higher strain rates and the decrease in stress due to cracking.

  • 45.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Nishida, Masahiro
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan.
    Ito, Yoshikata
    Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Takayama, Tetsuo
    Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
    Todo, Mitsugu
    Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan.
    Mechanical characterization and modelling of the temperature-dependent impact behaviour of a biocompatible poly(L-lactide)/poly(ε-caprolactone) polymer blend2015In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 51, p. 279-290Article in journal (Refereed)
    Abstract [en]

    Poly(ε-caprolactone) (PCL) is a ductile, bioabsorbable polymer that has been employed as a blend partner for poly(L-lactic acid) (PLLA). An improvement of the material strength and impact resistance of PLLA/PCL polymer blends compared to pure PLLA has been shown previously. To use numerical simulations in the design process of new components composed of the PLLA/PCL blend, a constitutive model for the material has to be established. In this work, a constitutive model for a PLLA/PCL polymer blend is established from the results of compressive tests at high and low strain rates at three different temperatures, including the body temperature. Finite element simulations of the split Hopkinson pressure bar test using the established constitutive model are carried out under the same condition as the experiments. During the experiments, the changes in the diameter and thickness of the specimens are captured by a high-speed video camera. The accuracy of the numerical model is tested by comparing the simulation results, such as the stress, strain, thickness and diameter histories of the specimens, with those measured in the experiments. The numerical model is also validated against an impact test of non-homogenous strains and strain rates. The results of this study provide a validated numerical model for a PLLA/PCL polymer blend at strain rates of up to 1800 s−1 in the temperature range between 22 °C and 50 °C.

  • 46.
    Hammarberg, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Modeling of Ultra High Strength Steel Sandwiches with Lightweight Cores2019In: Hot sheet metal forming of high-performance steel: Proceedings / [ed] Mats Oldenburg, Jens Hardell, Daniel Casellas, Wissenschaftliche Scripten , 2019, p. 313-320Conference paper (Refereed)
    Abstract [en]

    Legislation, du to greenhouse gas emissions, is forcing the automotive industry to reduce emissions and energy consumption. High-performance lightweight materials and structures are essential for meeting these demands. In this work, two types of lightweight sandwich materials are investigated and developed; one intended for crash applications (Type I) and another for stiffness applications (Type II). In order to predict the final properties of the sandwich materials, numerical modeling strategies are established. To achieve reasonable computational time, homogenization is adopted to overcome the complex core geometries of the sandwich materials. Type I, based on press-hardened boron steel, consists of a perforated core between two face plates. Evaluation of energy absorption during crash is conducted by utilizing numerical deformation models of a hat-profile geometry. The intention is to compare the energy absorption of the hat-profile based on the Type I sandwich to a hat-profile based on solid steel with equivalent weight. Type II, based on press-hardened boron steel, consists of a bidirectionally corrugated core between two face plates. The geometry of the bidirectional core requires a large amount of finite elements for precise discretization, causing impractical simulation times. This is adressed by suggesting an equivalent material formulation, to reduce the computational time. The results from Type I indicate an increased specific energy absorption capacity of 20 % as compared to solid steel. From the equivalent material procedure of Type II, it is found that the computational cost is reduced by 95 % with a maintained accuracy for structural stiffness. Validation is carried out by subjecting the sandwich to three-point bending. Good agreement is found between numerical and experimental data. Thus, this work shows that sandwich materials are an interesting and promising approach for reducing weight of vehicle components while maintaining performance, in terms of stiffness and crashworthiness.   

  • 47.
    Hammarberg, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Ultra high strength steel sandwich for lightweight applications2020In: SN Applied Sciences, ISSN 2523-3963, E-ISSN 2523-3971, Vol. 2, no 6, article id 1040Article in journal (Refereed)
    Abstract [en]

    Methods for reducing weight of structural elements are important for a sustainable society. Over the recent years ultra high strength steel (UHSS) has been a successful material for designing light and strong components. Sandwich panels are interesting structural components to further explore areas where the benefits of UHSS can be utilized. The specific properties of sandwich panels make them suitable for stiffness applications and various cores have been studied extensively. In the present work, bidirectionally corrugated UHSS cores are studied experimentally and numerically. A UHSS core is manufactured by cold rolling and bonded to the skins by welding. Stiffness is evaluated experimentally in three-point bending. The tests are virtually reproduced using the finite element method. Precise discretization of the core requires large amounts of computational power, prolonging lead times for sandwich component development, which in the present work is addressed by homogenization, using an equivalent material formulation. Input data for the equivalent models is obtained by characterizing representative volume elements of the periodic cores under periodic boundary conditions. The homogenized panel reduces the number of finite elements and thus the computational time while maintaining accuracy. Numerical results are validated and agree well with experimental testing. Important findings from experimental and simulation results show that the suggested panels provide superior specific bending stiffness as compared to solid panels. This work shows that lightweight UHSS sandwiches with excellent stiffness properties can be manufactured and modeled efficiently. The concept of manufacturing a UHSS sandwich panel expands the usability of UHSS to new areas.

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  • 48.
    Hammarberg, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Moshfegh, Ramin
    Lamera AB, Odhners gata 17, 42130 Västra Frölunda, Sweden.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Calibration of orthotropic plasticity- and damage models for micro-sandwich materials2022In: SN Applied Sciences, ISSN 2523-3963, E-ISSN 2523-3971, Vol. 4, no 6, article id 182Article in journal (Refereed)
    Abstract [en]

    Sandwich structures are commonly used to increase bending-stiffness without significantly increasing weight. In particular, micro-sandwich materials have been developed with the automotive industry in mind, being thin and formable. In the present work, it is investigated if micro-sandwich materials may be modeled using commercially available material models, accounting for both elasto-plasticity and fracture. A methodology for calibration of both the constitutive- and the damage model of micro-sandwich materials is presented. To validate the models, an experimental T-peel test is performed on the micro-sandwich material and compared with the numerical models. The models are found to be in agreement with the experimental data, being able to recreate the force response as well as the fracture of the micro-sandwich core.

  • 49.
    Hammarberg, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Moshfegh, Ramin
    Lamera AB, A Odhners Gata 17, 421 30 Västra Frölunda, Sweden.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Solid Mechanics.
    Novel Methodology for Experimental Characterization of Micro-Sandwich Materials2021In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 16, article id 4396Article in journal (Refereed)
    Abstract [en]

    Lightweight components are in demand from the automotive industry, due to legislation regulating greenhouse gas emissions, e.g., CO2. Traditionally, lightweighting has been done by replacing mild steels with ultra-high strength steel. The development of micro-sandwich materials has received increasing attention due to their formability and potential for replacing steel sheets in automotive bodies. A fundamental requirement for micro-sandwich materials to gain significant market share within the automotive industry is the possibility to simulate manufacturing of components, e.g., cold forming. Thus, reliable methods for characterizing the mechanical properties of the micro-sandwich materials, and in particular their cores, are necessary. In the present work, a novel method for obtaining the out-of-plane properties of micro-sandwich cores is presented. In particular, the out-of-plane properties, i.e., transverse tension/compression and out-of-plane shear are characterized. Test tools are designed and developed for subjecting micro-sandwich specimens to the desired loading conditions and digital image correlation is used to qualitatively analyze displacement fields and fracture of the core. A variation of the response from the material tests is observed, analyzed using statistical methods, i.e., the Weibull distribution. It is found that the suggested method produces reliable and repeatable results, providing a better understanding of micro-sandwich materials. The results produced in the present work may be used as input data for constitutive models, but also for validation of numerical models.

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  • 50.
    Hammarberg, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kajberg, Jörgen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindkvist, Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Evaluation of Perforated Sandwich Cores for Crash ApplicationsManuscript (preprint) (Other academic)
1234 1 - 50 of 175
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