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  • 51.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A study of sample withdrawal for lubricated systems: Part 1: Influence of flow characteristics, sampling techniques and locations2001Ingår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 53, nr 1, s. 22-31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The wear of a machine element, whether it is due to fatigue or abrasive wear, will add contaminants in the form of particulates to the system. If a machine element is starting to wear out it will produce a large amount of particles and it will finally break down. Since this can be very costly, one can establish the need to monitor the system so that one can foresee failure. There are many different ways to monitor a system, e.g. measurements of the temperature, pressure, vibrations and the degree of contamination. The purpose of contamination control is to extend the life of a component and thereby save money. When monitoring a system it is very important that the monitoring control instrument should give the right output. One important factor in achieving this is the withdrawal of a representative oil sample. In this paper an investigation of where and how to take a representative sample is performed using Stokes' law and the migration of spheres in a channel. A generalised sedimentation chart for diffe rent oils and particles is introduced. Sampling routines for proper sample withdrawal are also presented

  • 52.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A study of sample withdrawal for lubricated systems: Part 2: practical sample withdrawal and selection of proper sampling methods2001Ingår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 53, nr 3, s. 97-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims to use some of the sampling techniques and sampling routines, mentioned in Part 1 of the article, to perform practical tests to determine their differences in withdrawing samples. Uses two different types of systems, a hydraulic system and a gear system, together with some of the investigated sampling techniques. In order to find out the optimum sampling method for each of the two systems, uses a specification of requirements and a systematic approach, together with practical sample withdrawal from the two systems. For the hydraulic system, uses an on-line particle counter and bottle samples from valves, and for the gear system, applies drain-plug and vacuum pump sampling. It was found that for hydraulic systems on-line sampling is the most appropriate, if information on the elements is not required. If information on the elements is required, bottle sampling from a valve together with flushing of the valve should be performed. For the gear system no difference was seen between the samples taken with a vacuum pump and those taken from the drain-plug, and therefore an alternative method is suggested to improve the reliability of the sampling.

  • 53.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Ultra high-pressure compaction of powder2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Sintering at high-pressure improves the properties of the material, either through new sintering aids becoming available or through improving intergranular bonding. This gives the manufactured products potential advantages like faster cut rates, and more precise and cleaner production methods that add up to cost efficiency and competitive edge. The production of synthetic diamond products demands tooling that can achieve high pressures and deliver it with a high degree of certainty. The common denominator for almost all high-pressure systems is to use capsules where a powder material encloses the core material. Numerical analysis of manufacturing processes with working conditions that reach ultra high pressure (above 10 GPa) requires a constitutive model that can handle the specific behaviours of the powder from a low density to solid state. The work in this thesis deals with characterization and simulation of the material behaviour during high-pressure compaction in powder pressing. Some of the work was focused on investigating the material when used as compressible gasket in high-pressure systems. The aim was to increase the knowledge of the high-pressure pressing process. This includes a better understanding of how mean stress develops in the compact during pressing and an insight into the development material models concerning highpressure materials. Both experimental and numerical investigations were made to gain knowledge in these fields. The mechanical behaviour of a CaCO3 powder mix was investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The aim of the experimental work was to provide a foundation for numerical simulation of CaCO3 powder compaction at higher pressures. Friction measurements of the powder were also conducted. From the experimental investigations, density dependent material parameters were found. An elasto-plastic Cap model was developed for ultra high-pressure powder pressing. To improve the material model, density dependent constitutive parameters were included. The model was implemented as a user-defined material subroutine in a nonlinear finite element program. The model was validated against pressure measurements using phase transitions of Bismuth. The measurements were conducted in a Bridgman anvil apparatus. The simulations showed that thin discs with small radial extrusion generate a plateau at a low-pressure level, while thick discs with large radial extrusion generate a pressure peak at a high-pressure level. The results showed that FE-results can be used to engineer pressure peaks needed to seal HPHT-systems. For compressible gaskets, it was found that diametral support increases the phase transformation load. Higher initial density of the powder compact and diametral support generate higher pressure per unit thickness. The results from the validation using pressure measurements showed that the simulation model was indeed capable of reproducing load–thickness curves and pressure profiles, up to 9 GPa, close to the experimental curves.

  • 54.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Byheden, Åke
    Luleå tekniska universitet.
    A wear investigation in the FZG spur gear rig with particular matter contaminated oils2002Ingår i: Lubricants, materials and lubrication engineering : January 15 - 17, 2002: 13th International Colloquium Tribology. Technische Akademie Esslingen / [ed] Wilfried Bartz, Ostfildern: Techn. Akad. Esslingen , 2002, s. 1139-1143Konferensbidrag (Refereegranskat)
  • 55.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    High-pressure compaction modelling of calcite (CaCO3) powder compact2011Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, nr 3, s. 259-268Artikel i tidskrift (Refereegranskat)
    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.

  • 56. Berg, Sven
    et al.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental characterisation of CaCO3 powder mix for high-pressure compaction modelling2010Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, nr 2, s. 198-205Artikel i tidskrift (Refereegranskat)
    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.

  • 57.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental characterization of CaCO3powder for use in compressible gaskets up to ultra-high pressure2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 215-216, s. 124-131Artikel i tidskrift (Refereegranskat)
    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.

  • 58.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    High pressure characterization and modelling of CaCO3 powder mix in the Bridgman anvil apparatus2012Ingår i: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 32, nr 4, s. 490-508Artikel i tidskrift (Refereegranskat)
    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.

  • 59.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jungmar, Ulf
    Bodycote Materials Testing AB, Linköping.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Vähäoja, Pekka
    Department of Mechanical Engineering, University of Oulu.
    Investigation of the measurement precision of oil analysis instruments, using fully formulated oils: Part 1: Spectroscopic instruments2011Ingår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 63, nr 6, s. 404-411Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose - The aim of this study is to determine the variation of the different oil analysis instruments in terms of standard deviation and CV-values, when measuring samples of fully formulated hydraulic and gear oils taken from working systems. Design/methodology/approach - In this investigation, two different spectrometric techniques, inductively coupled plasma-optical emission spectrometers (ICP-OES) and rotating disk electrode-optical emission spectrometers (RDE-OES), have been studied to determine the instruments' precision of measurement and ability to measure the absolute level of contamination. The study was based on a series of measurements using artificial contamination mixed with oil. Findings - The ICP has better precision of measurement of the two instruments, but cannot predict the absolute values of contamination when oil samples are only treated by organic solvent dilution if the samples include large or dense particles. It is therefore not too good, with the sample pre-treatment method used, at detecting wear processes that produce dense/large particles, such as pitting failure. For instance, microwave-assisted acid digestion could be used for sample pre-treating to obtain accurate results in that case. It should, however, be able to detect wear mechanisms that produce small particles such as abrasive wear in any case. The ICP has a repeatability value of r=3 percent and a reproducibility value of R=12 percent for contamination levels of between 50 and 400 ppm and r=0.6 and R=2 ppm, respectively, at values below 50 ppm. The RDE cannot predict the absolute value of contamination if this includes large or dense particles if proper sample pre-treatment is not used. It is therefore not good at detecting wear mechanisms that produces dense/large particles (if the oil samples are not pre-treated properly) such as pitting but should be able to detect abrasive wear and similar processes that produce small particles in any case. The RDE's precision of measurement is not as good as the ICP, with a reproducibility variation of R=r=25 percent for contamination levels between 20 and 500 ppm and R=r=6 ppm for contamination level below 20 ppm. Research limitations/implications - Only the effects from lubricating oils are studied. Practical implications - This study will significantly increase the industrial knowledge concerning measurement precision in particle contamination measurement systems. Originality/value - No similar study is found

  • 60.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jungmar, Ulf
    Bodycote Materials Testing AB, Linköping.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Vähäoja, Pekka
    Department of Mechanical Engineering, University of Oulu.
    Investigation of the measurement precision of oil analysis instruments, using fully formulated oils: Part 2: Contamination-measuring instruments2011Ingår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 63, nr 6, s. 412-419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose - The aim of this study is to determine the variation of the different oil analysis instruments in terms of standard deviation and CV-values, when measuring samples of fully formulated hydraulic and gear oils taken from working systems. Design/methodology/approach - In this investigation two different spectrometric techniques, ICP-OES and RDE-OES, have been studied to determine the instruments' precision of measurement and ability to measure the absolute level of contamination. Findings - The ICP has better precision of measurement of the two instruments, but cannot predict the absolute values of contamination when oil samples are only treated by organic solvent dilution if the samples include large or dense particles. It is therefore not too good, with the sample pre-treatment method used, at detecting wear processes that produce dense/large particles, such as pitting failure. For instance, microwave-assisted acid digestion could be used for sample pre-treating to obtain accurate results in that case. It should, however, be able to detect wear mechanisms that produce small particles such as abrasive wear in any case: the ICP has a repeatability value of ITr/IT=3 per cent and a reproducibility value of ITR/IT=12 per cent for contamination levels of between 50-400 PPM and ITr/IT=0.6 PPM and ITR/IT=2 PPM, respectively, at values below 50 PPM; the RDE cannot predict the absolute value of contamination if this includes large or dense particles if proper sample pre-treatment is not used. It is therefore not good at detecting wear mechanisms that produce dense/large particles (if the oil samples are not pre-treated properly) such as pitting but should be able to detect abrasive wear and similar processes that produce small particles in any case; the RDE's precision of measurement is not as good as the ICP, with a reproducibility variation of ITR/IT=ITr/IT=25 per cent for contamination levels between 20-500 PPM and ITR/IT=ITr/IT=6 PPM for contamination level below 20 PPM. Research limitations/implications - Measuring only on fully formulated oils from hydraulic and gear systems. Practical implications - The study will be of significant support regarding industrial interpretation of measurement results from the most common oil particle measurement methods. Originality/value - No other similar studies are known

  • 61.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rheological properties of contaminated oil2000Ingår i: Proceedings of the International Tribology Conference: ITC Nagasaki 2000 ; October 29 - November 2, 2000, Tokyo: Japan Society of Tribologists , 2000, s. 1239-1243Konferensbidrag (Refereegranskat)
  • 62.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Frictional behaviour of CaCO3 powder compacts2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 228, s. 429-434Artikel i tidskrift (Refereegranskat)
    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.

  • 63. Berglund, Daniel
    et al.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundbäck, Andreas
    Three-dimensional finite element simulation of laser welded stainless steel plate2001Ingår i: Simulation of materials processing: theory, methods and applications : proceedings of the 7th International conference on numerical methods in industrial forming processes - NUMIFORM 2001 / [ed] Ken-ichiro Mori, Lisse: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 2001, s. 1119-1124Konferensbidrag (Refereegranskat)
  • 64.
    Bergman, Greger
    et al.
    SSAB HardTech.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A finite element model for thermomechanical analysis of sheet metal forming2004Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 59, nr 9, s. 1167-1186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to model simultaneous forming and quenching of thin-walled structures. A staggered approach is used for coupling the thermal and mechanical analysis, wherein each analysis is performed with different time step sizes. The implementation includes a thermal shell element with linear temperature approximation in the plane and quadratic in the thickness direction, and contact heat transfer. The material behaviour is described by a temperature-dependent elastic-plastic model with a non-linear isotropic hardening law. Transformation plasticity is included in the model. Examples are presented to validate and evaluate the proposed model. The model is evaluated by comparison with a one-sided forming and quenching experiment

  • 65. Bergman, Greger
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermo-mechanical analyses of forming and quenching of thin steel plates1999Ingår i: Proceedings of the 2nd ESAFORM Conference on Material Forming, 1999Konferensbidrag (Refereegranskat)
  • 66. Bergman, Greger
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Verification of thermomechanical material models by thin-plate quenching simulations1997Ingår i: Journal of thermal stresses, ISSN 0149-5739, E-ISSN 1521-074X, Vol. 20, nr 7, s. 679-695Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A computational model for quenching simulations of thin plates has been developed. The model is examined by comparisons with experiments with one-sided water spray cooling. With this experiment, the thermomechanical behavior of the material can be monitored throughout the time history of the test. Experiments have been performed with a material that undergoes only martensitic transformation during quenching. For the conditions examined the plate exhibits permanent deformation after quenching. In the stress calculation, transformation plasticity is included in the effective-stress-function (ESF) algorithm as an additional strain component related to the stress and to the progress of transformation. Analyses of the present experiments show that the permanent deformation of the plate is exclusively due to transformation plasticity

  • 67. Bergman, Greger
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jeppsson, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Integration of a product design system and nonlinear finite element codes via a relational database1995Ingår i: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, Vol. 12, nr 5, s. 439-449Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A database for finite element models and related data is developed and incorporated into a prototype system for integration of non-linear finite element codes with a product design system. In the prototype system, the database is used as a link for integrating commercial, public domain as well as in-house codes. In the present system, the public domain finite element codes NIKE2D, NIKE3D, DYNA2D, DYNA3D and TOPAZ2D are integrated with the CIM-system I-DEAS. The prototype system is primarily intended as a platform in research projects for development of integrated environments tuned for simulations of specific manufacturing processes such as quenching, welding, hot rolling, metal powder compaction and hot isostatic pressing

  • 68.
    Börjesson, Lars
    et al.
    Luleå tekniska universitet.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Residual stresses and microstructure computation for multipass [multirun] welding1997Ingår i: The Fifth International Conference on Residual Stresses - ICRS-5 / [ed] Torsten Ericsson; Magnus Odén; Aneth Andersson, Linköping: Linköping University Electronic Press, 1997, Vol. 1, s. 189-194Konferensbidrag (Refereegranskat)
    Abstract [en]

    Residual stress studies (by centre-hole drilling and finite element analysis) and microstructural computations (using temperature measurements) were carried out on multirun butt welded steel plates. The plates, 200 mm thickness, were in SIS 2134 material (0.12%C, 1.42%Mn, 0.044%V, 0.014%Ti, 0.038%Al). Welding was by submerged arc welding using ESAB OK AUTROD 12.10 filler material and ESAB OK FLUX 10.80 flux

  • 69.
    Börjesson, Lars
    et al.
    Luleå tekniska universitet.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of multipass welding using mixture rules for prediction of material properties1998Ingår i: Simulation of materials processing : theory, methods and applications: international conference on numerical methods in industrial forming processes, NUMIFORM '98 / [ed] J. Huétink; F.P.T Baaijens, Rotterdam: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1998, s. 351-357Konferensbidrag (Refereegranskat)
    Abstract [en]

    Multipass butt welding of two 0.2 m thick steel plates has been investigated. The purpose of the project is to evaluate the residual stresses by experiment and simulations. Temperature dependent material properties were assumed in previous studies. We account for the dependency on temperature history in this work. This has been done by computing the microstructure evolution. This is combined with mixture rules for computing material properties.

  • 70.
    Börjesson, Lars
    et al.
    Luleå tekniska universitet.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of multipass welding with simultaneous computation of material properties2001Ingår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 123, nr 1, s. 106-111Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multipass butt welding of two 0.2 m thick steel plates has been investigated. The objective is to calculate residual stresses and compare them with measured residual stresses. The material properties depend on temperature and temperature history. This dependency is accounted for by computing the microstructure evolution and using this information for computing material properties. This is done by assigning temperature dependent material properties to each phase and applying mixture rules to predict macro material properties. Two different materials have been used for the microstructure calculation, one for the base material and one for the filler material

  • 71.
    Calleecharan, Yogeshwarsing
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Contributions to the electromechanics of unbalanced magnetic pull in a synchronous hydropower generator2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Misalignment between the rotor geometrical axis and the geometrical stator axis in a hydropower generator is usually present at standstill and when the machine is under operation. Now, rotor-stator eccentricity in a rotating electrical machine is a harbinger to abnormal operating conditions of the machine. This rotor-stator eccentricity gives rise to a phenomenon called the unbalanced magnetic pull (UMP). Though the topic of UMP has been studied for more than a century, little attention has been paid to another phenomenon which is whirling and more specifically to non-synchronous whirling. Whereas the rotor-stator standstill misalignment can be cured to an acceptable level, a rotor when under operation normally entails whirling as well. Whirling is a reality in hydropower generators which are vertical machines and the latter are studied in this thesis work. It turns out that studying the effects of whirling in conjunction with the UMP can lift off pre-conceived ideas and hence provide a more qualitative and quantitative assessment of the effects of the nature and consequences of having a hydropower generator operating with UMP present. This thesis work provides simple theoretical conceptualisations that capture the phenomena of whirling and of the UMP, and purports to provide mechanical and electrical engineers with information on the necessity of studying these two phenomena simultaneously. With only the rotor eccentricity type considered in this work, the contributions are limited to mechanical dynamic simulations in the first part of the research work in addition to electromagnetic (EM) simulations in the second part of the research work. The validity of these EM simulations has been verified with an actual reported measurement. As for the mechanical dynamic analyses that cover the first part of the research work and which concern in essence one case of rotor eccentricity, valuable information such as the maximum rotor centre displacements inside the stator of the generator together with stability characteristics of the rotor motion are arrived at. These analyses indicate how stable the hydropower generator is under operation when UMP is present due to rotor eccentricity. It shows that one needs to consider both components of the UMP which are the radial UMP and the tangential UMP. Leaving out the tangential UMP component and/or considering a simplified whirling-independent model of the radial UMP lead(s) to a false representation of the dynamics of the generator when treated as a mechanical system. The analyses are new as a model that is used cares for both components of the UMP. In the second part of the research work, an electromechanics approach is preferred and emphasis is put on showing that important EM parameters such as force or the UMP, currents and ohmic losses are affected when non-synchronous whirling exists. The consideration of whirling as intimately linked to the UMP leads in the last stages of the research work to a robust and reliable method to compute the steady state UMP magnitude(s) up to sufficiently large eccentricities when two primary types of eccentricities, which are a purely static eccentricity and a purely dynamic eccentricity, co-exist. This novel computation method is of utmost importance and is a breakthrough in this area for four reasons: Firstly, there is no other work in the literature that has looked at mixed eccentricities motion of the geometric centre of the rotor in conjunction with simultaneous consideration of the UMP and the whirling phenomena. Secondly, it is fast as it is a semi-analytical method that rests on some previously done EM simulations which can be obtained with certain commercial EM field modelling software packages. Thirdly, it dispenses the analyst to have one of the rare contemporary commercial EM software products that can handle such intricate rotor centre motion since the proposed method rests upon less complicated EM simulations. And fourthly, it enables an analyst to obtain very good estimates of the UMP for a rotor centre motion that better mimics the true motion occurring in practice inside the stator of a hydropower generator. Altogether, the contributions in this thesis work can profoundly shape the strategies for better machine designs and analysis of the UMP without discounting previous knowledge that has been amassed since the end of the nineteenth century in this field. It is hoped that the research work carried out will help in the long interdisciplinary pursuit and allegiance to honing hydropower technology through creating an awareness of the need to study non-synchronous whirling effects as opposed to only looking at the usual synchronous whirling motion.

  • 72.
    Calleecharan, Yogeshwarsing
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    On the dynamics of an hydropower generator subjected to unbalanced magnetic pull: characterisation and analysis2010Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in rotating electrical machines is a significant concern in industry. The UMP arises due to magnetic flux crossing the air-gap between the rotor and stator, and can be more intense than the useful peripheral force that the machine develops. Electric machines are the workhorses of any modern society and for over a century, the UMP phenomenon has been studied and this mainly by electrical engineers. Though, several refinements have been made in the equations describing this electromagnetic force to account for the effects such as saturation of iron parts and parallel circuits in the machine armature, the treatment of UMP is scarce in literature, and its characterisation and analysis remains a conundrum, and stays a subject of current research in electrical machinery design. Until a few years back, the UMP was thought to consist only of one component which acts in the radial direction. Though theoretical and mathematical developments have advanced to a very high level and are still forthcoming, there is generally no agreed model. The UMP model that tends to be utilised in industry only assumes the existence of the radial UMP and further simplifies the analysis by considering the maximum radial UMP stiffness to be applicable at all whirling angular velocities of the rotor. The present work comes in as furnishing two original contributions with emphasis on the understanding of the dynamics in lieu of considering both mechanical and electrical parameters that would create hard-to-analyse abstractions. First, it is shown that the simple model currently being used in industry may be fraught with risks. A new corrected model that accounts for both UMP components is thereby proposed in this work. This model is cast into stiffness terms and the separate effects of the radial UMP and that of the tangential UMP as well as their combined effects are explored quantitatively. So as to have tangible results that can be explained and the dynamics understood, a symmetrical Jeffcott rotor is used to simulate the newly proposed UMP model. Other pertinent simplifications include the use of a combined damping value for the rotor and bearings, the exclusion of unbalance force on the rotor due to mass eccentricity effect, the omission of the effects of saturation in the magnetic circuits together with assumption of linear behaviour of the UMP curves with eccentricity for low eccentricity values. Several important results surface from the analysis. It is found that the new UMP model is sensitive to forcing frequency in the rotor movements and that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur.The second contribution in this thesis lays ground for stability consideration which is a cornerstone in the sound understanding of the design and operation of any machinery. Stability analysis is indispensable as disturbances do exist in real-life that can drive machines away from an equilibrium operating point. For the system at hand, it becomes essential to investigate the effect(s) of non-synchronous whirling on the stability of the system. Eigenvaluebased stability analysis is performed on the simple Jeffcott model and results show that damping, and stiffness of the rotor and of the bearings are important when non-synchronous whirling of the rotor comes into play. The original contributions in this work as depicted above comes primarily from the formulation and use of an UMP model that accounts for both the radial and the tangential UMP components. This allows unprecedented results to be arrived at that can be expected to be part of a crucial milestone in the generation of better rotor design parameters which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors. This influential contribution will help in the long interdisciplinary pursuit and allegiance to honing hydropower technology.

  • 73.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Dynamics of a hydropower generator subjected to unbalanced magnetic pull2011Ingår i: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 225, nr 9, s. 2076-2088Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: a radial component and a tangential one. Models that are used in industry tend to include the radial component alone. In this article, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterizing the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Secondly, it is found that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Thus, it becomes interesting to be able to account for the UMP stiffness contribution in order to curb machine malfunction which might result from these UMP forces

  • 74.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    On the dynamics of an hydropower generator subjected to unbalanced magnetic pull2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this paper, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Moreover, complex dynamics in the displacements of the rotor are observed for some forcing frequencies and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Eigenvalue-based stability analysis is performed and shows that damping of the rotor and of the bearings are important when non-synchronous whirling of the rotor is considered. Accounting for both components of UMP is an important cornerstone in the generation of better rotor design parameters which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors to the betterment of hydropower technology.

  • 75.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    On the dynamics of an hydropower generator subjected to unbalanced magnetic pull2011Ingår i: The Institution of Engineering and Technology 8th International Conference on Computation in Electromagnetics: (CEM 2011), Wroclaw, Poland, 11-14 April 2011, 2011, s. 50-51Konferensbidrag (Refereegranskat)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this paper, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Moreover, complex dynamics in the displacements of the rotor are observed for some forcing frequencies and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Eigenvalue-based stability analysis is performed and shows that damping of the rotor and of the bearings are important when non-synchronous whirling of the rotor is considered. Accounting for both components of UMP is an important cornerstone in the generation of better rotor design parameters which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors to the betterment of hydropower technology.

  • 76.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Stability analysis of an hydropower generator subjected to unbalanced magnetic pull2011Ingår i: IET Science, Measurement & Technology, ISSN 1751-8822, E-ISSN 1751-8830, Vol. 5, nr 6, s. 231-243Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: A radial component and a tangential one. Models that are used in industry currently tend to include the radial component alone. In this study, a Jeffcott rotor model together with a new UMP model that incorporates both the radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterising the UMP as springs permits the proposed model to inherit UMP stiffness contribution. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements and secondly, that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed for some forcing frequencies and system stiffnesses. Eigenvalue-based stability analysis is performed and shows that damping and stiffness of the rotor and of the bearings are important when non-synchronous whirling of the rotor comes into play. Accounting for both UMP components is an important cornerstone in the generation of better rotor designs which can help to curb rotor-stator malfunction and can contribute in the design of long lasting rotors.

  • 77.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Brauer, J.P
    No-load electromagnetic simulations of a hydropower generator considering the effect of rotor whirling2015Ingår i: Balkan Journal of Electrical and Computer Engineering, ISSN 2147-284X, Vol. 3, nr 3, s. 124-134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electromagnetic (EM) analysis of hydropower generators iscommon practice but there is little emphasis on studying the effect of rotorwhirling in the analysis. This paper explores the effect on electromagneticanalysis as the rotor is allowed to whirl both in forward and inbackward directions under no-load conditions. As a hydropower generatorrotor shaft can experience whirling when under eccentric operation,the objective is to examine how whirling can affect the unbalancedmagnetic pull (UMP), flux densities, damper currents, and ohmic lossesin a synchronous hydropower generator. These results are obtained ina commercial FEM-based EM field modelling software package thatallows various degrees of freedom in motion types and multiple motioncomponents to be set. It is seen that backward whirling tends to inducehigher eddy currents than forward whirling does.

  • 78.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jauregui, Ricardo
    DEE Universitat Politècnica de Catalunya , El Grupo de Compatibilidad Electromagnética GCEM, Barcelona.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Estimating forces in mixed eccentricities motion for purley dynamic eccentric rotor centre motion in a hydropower generator and their validation against EM simulations2015Ingår i: Balkan Journal of Electrical and Computer Engineering, ISSN 2147-284X, Vol. 3, nr 2, s. 78-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electromagnetic analysis of hydropower generators is commonpractice but there is little emphasis on studying the effect ofrotor whirling in the analysis. This paper demonstrates the use ofthe unbalanced magnetic pull (UMP) curves based on purely dynamiceccentricity motion for a wide range of whirling frequencies in theprediction of the steady state UMP in the case of mixed eccentricitiesmotion. The latter motion type is more realistic in practice. Actualelectromagnetic (EM) simulations are also carried out for these mixedeccentricities motion cases in order to verify the proposed method. Goodagreement between the UMP from the actual EM simulations and theUMP predictions are made when low eccentricities exist. The proposedmethod is thus very useful since firstly, very few EM software packagescan handle mixed eccentricities motion and secondly, since actual EMsimulations of intricate rotor centre motion are time-consuming, theproposed method is a big time saver. A modified feature selective validation(FSV) method, the FSV-UPC, is also applied to assess the similarities andthe differences in the force computations.

  • 79.
    Calleecharan, Yogeshwarsing
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jauregui, Ricardo
    DEE Universitat Politècnica de Catalunya , El Grupo de Compatibilidad Electromagnética GCEM, Barcelona.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Towards a general method for estimating the unbalanced magnetic pull in mixed eccentricities motion including sufficiently large eccentricities in a hydropower generator and their validation against EM simulations2013Ingår i: European Physical Journal: Applied physics, ISSN 1286-0042, E-ISSN 1286-0050, Vol. 63, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electromagnetic (EM) analysis of hydropower generators is common practice but rotor whirling is little studied. This paper suggests a novel semi-analytical method for estimating the steady state unbalanced magnetic pull (UMP) when the rotor centre is undergoing mixed eccentricities motion. The ability to estimate the UMP for mixed eccentricities motion in finite element method (FEM)-based modelling software packages is rare. The proposed methodology in its formulation takes advantage of the fact that a purely dynamic eccentricity motion including non-synchronous whirling and a purely static eccentricity motion can be more amenable to implement in existing FEM-based EM modelling software products for UMP estimation. After these initial separate UMP results are obtained, the proposed method can be applied for virtually any mixed eccentricities motion cases up to sufficiently large eccentricities for quick analysis instead of running the mixed eccentricities simulations directly in a FEM-based software package. Good agreement between the UMP from the actual EM mixed eccentricities motion simulations in a commercial FEM-based software package and the UMP estimations by the novel method is made for a wide range of eccentricities that may commonly occur in practice. A modified feature selective validation (FSV) method, the FSV-UPC, is applied to assess the similarities and the differences in the UMP computations

  • 80.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gustafsson, Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    PFEM-based modeling of industrial granular flows2014Ingår i: Computational Particle Mechanics, ISSN 2196-4378, Vol. 1, nr 1, s. 47-70Artikel i tidskrift (Refereegranskat)
    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.

  • 81. Carlsson, J.
    et al.
    Lundberg, Bengt
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Determination of force, particle velocity and related quantities in a dynamically loaded non-uniform rod from strain histories at two cross sections1990Ingår i: Experimental mechanics : 9th International conference : Papers., Lyngby: Technical University of Denmark , 1990Konferensbidrag (Refereegranskat)
  • 82.
    Carlsson, J.
    et al.
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundberg, Bengt
    Luleå tekniska universitet.
    Method for determination of in-hole dynamic force-penetration data from two-point strain measurement on a percussive drill rod1990Ingår i: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, ISSN 0148-9062, E-ISSN 1879-2073, Vol. 27, nr 6, s. 553-558Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the present investigation is to establish a testing method suited for determination of in-hole dynamic force-penetration data for non-uniform standard percussive drill rod-bit configurations. The method is based on a version of the method of two-point strain measurement, which permits non-uniform rods, i.e. rods with variable characteristic impedance. This version allows normal force and particle velocity to be evaluated at an arbitrary cross-section of a homogenous non-uniform elastic rod from strain measurements performed at two different cross-sections of the same rod. The main problem of this investigation is to assess whether the influence of threads can be considered insignificant. As a part of the study force-penetration relationships have been determined for the penetration of a standard Sandvik Rock Tools button bit into Swedish Bohus granite.

  • 83.
    Casellas, Daniel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    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 tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Golling, Stefan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A fracture mechanics approach to develop high crash resistant microstructures by press hardening2017Ingår i: 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, s. 101-107Konferensbidrag (Refereegranskat)
    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.

  • 84.
    Casellas, Daniel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lara, Antoni
    Fundació CTM Centre Tecnològic, Manresa.
    Frómeta, David
    Fundació CTM Centre Tecnològic, Manresa.
    Gutiérrez, David
    Fundació CTM Centre Tecnològic, Manresa.
    Molas, Silva
    Fundació CTM Centre Tecnològic, Manresa.
    Pérez, Lluís
    Fundació CTM Centre Tecnològic, Manresa.
    Rehrl, Johannes
    Voestalpine Stahl GmbH, Linz.
    Suppan, Clemens
    Voestalpine Stahl GmbH, Linz.
    Fracture Toughness to Understand Stretch-Flangeability and Edge Cracking Resistance in AHSS2017Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, nr 1, s. 86-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The edge fracture is considered as a high risk for automotive parts, especially for parts made of advanced high strength steels (AHSS). The limited ductility of AHSS makes them more sensitive to the edge damage. The traditional approaches, such as those based on ductility measurements or forming limit diagrams, are unable to predict this type of fractures. Thus, stretch-flangeability has become an important formability parameter in addition to tensile and formability properties. The damage induced in sheared edges in AHSS parts affects stretch-flangeability, because the generated microcracks propagate from the edge. Accordingly, a fracture mechanics approach may be followed to characterize the crack propagation resistance. With this aim, this work addresses the applicability of fracture toughness as a tool to understand crack-related problems, as stretch-flangeability and edge cracking, in different AHSS grades. Fracture toughness was determined by following the essential work of fracture methodology and stretch-flangeability was characterized by means of hole expansions tests. Results show a good correlation between stretch-flangeability and fracture toughness. It allows postulating fracture toughness, measured by the essential work of fracture methodology, as a key material property to rationalize crack propagation phenomena in AHSS.

  • 85.
    Casellas, Daniel
    et al.
    Fundació CTM Centre Tecnològic / Universitat Politècnica de Catalunya, Universitat Politècnica de Catalunya, Fundació CTM Centre Tecnològic, Avda.
    Lara, Antoni
    Fundació CTM Centre Tecnològic.
    Molas, Silvia
    Fundació CTM Centre Tecnològic.
    Gironès, Anna
    Fundació CTM Centre Tecnològic.
    Golling, Stefan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Fracture resistance of tailor tempered microstructures obtained by different press hardening conditions2015Ingår i: Hot Sheet Metal Forming of High-Performance Steel 5th International Conference: May 31-June 3, Toronto, Canada : Proceedings / [ed] Kurt Steinhoff; Mats Oldenburg; Braham Prakash, Auerbach: Verlag Wissenschaftliche Scripten , 2015, s. 221-229Konferensbidrag (Refereegranskat)
    Abstract [en]

    Tailored tempering can produce different amounts of martensite, upper and lower bainite and ferrite depending on the press hardening conditions are usually obtained. The tensile properties of such microstructures are quite well known, but the intrinsic fracture properties, as fracture toughness, have not yet been characterized. This is mainly related the experimental difficulty to measure fracture toughness in thin sheets. Recently, the authors have proposed to measure it through the application of the Essential Work of Fracture methodology. The knowledge of facture toughness would give valuable information to increase their applicability in automotive components and would also allow a further understanding of fracture and crack propagation mechanisms in B steel hardened at different cooling conditions. Thus the aim of this paper is to determine the fracture toughness in microstructures of a 22MnB5 steels obtained by tailored tempering. Results indicate that the EWF methodology can be applied to measure fracture toughness and the energy for crack initiation in ferrite-pearlite and ferrite-bainite microstructures. Fracture initiation energy is the same in ferrite-pearlite and ferrite-bainite microstructures, which will indicate that ferrite has a clear effect on fracture initiation. Moreover, fractography results reveal the effect of inclusion content on fracture energies

  • 86.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Karlsson, Thommy
    Interdisciplinary research in full-scale hydropower machines at Porjus, Jokkmokk, Sweden2005Ingår i: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 57, nr 12, s. 40-44Artikel i tidskrift (Övrigt vetenskapligt)
  • 87.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, Ida
    Jourak, Amir
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Porjus U9A full-scale hydropower research facility2008Ingår i: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.

  • 88.
    Charles, Corinne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermal driving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles. The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents’ fractions. This makes it possible to apply the model efficiently for large computational models of general thermo-mechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding- wire feed additive manufacturing processes.Four quantities are calculated in the model: the volume fraction of α phase, assumed interpreted to be Widmanstätten α, grain boundary α, and martensite α. The phase transformations are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless α martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used also for the α to β transformation upon heating. An added variable, grain size indicator of assumed Widmanstätten α, has also been tested through the implementation of a simple Arrhenius law after parameter calibration.The coupling with physically based constitutive model gives first steps towards a more comprehensive and predictive model of the properties that evolve during processing.

  • 89.
    Charles, Corinne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling microstructure evolution of weld deposited Ti-6Al-4V2008Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The microstructure and consequently the mechanical properties of titanium alloys are highly dependent on the temperature history endured by the material. The manufacturing process of metal deposition induces repetitive cooling and heating in the material determining a specific microstructure. The presented study is devoted to developing and implementing a microstructure model for Ti-6Al-4V intended to be coupled to a thermo- mechanical model of the metal deposition process. Microstructural analysis of the metal deposited samples was first performed to understand the formed microstructure. A set of representative parameters for microstructure modelling were then selected as representative for the known impact of Ti-6Al-4V microstructure on mechanical properties. Evolution equations for these parameters were implemented for thermal finite element analysis of the process. Six representative state variables are modelled: the phase volume fraction of total alpha, beta, Widmanstätten alpha, grain boundary alpha, martensite alpha, and the alpha lath thickness. Heating, cooling and repeated re-heating involved in the process of metal deposition are taken into account in the model. The phase transformations were modelled based on a diffusionnal theory described by a Johnson-Mehl-Avrami formulation, as well as diffusionless transformations for the martensite alpha formation and the beta reformation during reheating. The Arrhenius equation is applied as a simplification to model temperature dependent alpha lath size calculation. Grain growth is not included in the present formulation, but would have to be added for capturing alpha lath coarsening during long term heat treatment. The temperature history during robotised tungsten inert gas deposition welding is simulated together with the microstructure. The implementation of the model handles well the complex cyclic thermal loading from the metal deposition process. A particular banded structure observed in the metal deposited microstructure is partially explained using the proposed microstructure model. It is concluded that although qualitatively interesting results have been achieved, further calibration testing over a wider range of temperature histories must be performed to improve the transformation kinetic parameters for reliable quantitative predictions of the microstructure.

  • 90. Coccoz, G.
    et al.
    Bellet, M.
    Lécot, R.
    Ackermann, L.
    Häggblad, Hans-åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Cold compaction of iron powder: experiments and simultation.1994Ingår i: PM '94 : Congrès Mondial de Métallurgie des Poudres - Powder Metallurgy World Congress, Paris, 6 - 9 juin 1994: Société Française de Métallurgie et de Matériaux; European Powder Metallurgy Association, Les Ulis: Ed. de Physique , 1994Konferensbidrag (Refereegranskat)
  • 91.
    Cocks, Alan C F
    et al.
    University of Oxford.
    Gethin, David T
    University of Swansea.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kraft, Torsten
    Fraunhofer IWM.
    Coube, Olivier
    Plansee SE.
    Compaction models2007Ingår i: Modelling of powder die compaction, London: Encyclopedia of Global Archaeology/Springer Verlag, 2007, s. 43-64Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 92. Coube, O.
    et al.
    Chen, Y.
    Imbault, D.
    Doremus, P.
    Maassen, R.
    Federzoni, L.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Tweed, J.
    Gethin, D.
    Rolland, S.
    Computer simulation of die compaction: guidelines and an example from the European dienet project2004Ingår i: 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 , 2004Konferensbidrag (Refereegranskat)
  • 93. Coube, O.
    et al.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    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 project2005Ingår i: PM in Prague, new opportunities in a new Europe: Euro PM 2005 congress and exhibition, European powder metallurgy association , 2005, s. 313-319Konferensbidrag (Refereegranskat)
  • 94.
    Coube, Olivier
    et al.
    EPMA.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Case studies: discussion and guidelines2007Ingår i: Modelling of Powder Die Compaction, London: Encyclopedia of Global Archaeology/Springer Verlag, 2007, s. 197-222Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 95.
    Deng, Liang
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Investigation and simulation of tool wear in press hardening2014Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Due to the requirements of higher strength components and lower carbon dioxide emission, press hardening becomes prevalent in the automotive industry. Heating a boron alloyed steel blank to obtain the austensite phase at high temperature and quenching it to martensitic phase enhances the strength of the products and still allows complex shapes. However, the stamping tool has to endure severe temperature changes, impacts of the counterpart and sliding processes. The wear including material transfer, surface scuffing and complicated reactions between coatings and superficial oxide layers not only shortens the service-life of tools but also decreases the productivity and the quality of the manufacturing process. Furthermore, the harsh contact conditions between the stamping tools and the work-piece, regarded as the reason for the wear, are difficult to measure in situ. The fundamental study on the tool wear in the press hardening receives insufficient attention. The present work aims at establishing an understanding of tribological characteristics in press hardening and at developing a predictive wear model by establishing a relationship between the contact conditions and the wear process. Based on these results, the extension of the service life of stamping tools through adjustment of process parameters can be possible. Sliding wear, as the dominant wear phenomenon taking place during press hardening processes, causes formation of wear particles and transfer of material fragments to the tool surface. Since the wear process is dependent on the contact conditions, finite element (FE) simulations based on thermo-mechanical calculations are used to investigate the contact conditions in a given press hardening process. Based on the results from the FE--simulations, reciprocating tests and tribolgical tests are conducted respectively under press hardening conditions to evaluate the wear coefficients of the Archard's wear model. A modified wear model is implemented in the FE--simulations to predict wear depths on the stamping tools. It is noted that most wear concentrates on the tool radius and that it correlates with the sliding distance. The correlation between the experimental set-ups and the wear predictions are analysed. An industrial experimental set-up for validation of the wear model predictions has been developed. The future work on this study is outlined.

  • 96.
    Deng, Liang
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling of wear and galling in press hardening simulations2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Implementation of press hardened parts in automobile responses to the requirement of reduced carbon dioxide emission because the press hardened part has very high ratio of strength to weight. Furthermore, ultra high-strength steels (press hardened parts) increases the vehicle safety. The press hardening processes are prevalently applied in global automotive industries. However, the press hardening processes corresponding to heating, forming, and cooling processes result in harsh contact conditions such as cyclic pressures, high temperatures and complex reactions between coatings and tool steels. Consequently, these harsh contact conditions increase the tool maintenance due to abrasive wear and adhesive wear. In order to study tribological behaviours in the press hardening, two kinds of the tribological experiments have been developed and used. Firstly, a reciprocating test, also called SRV test, is performed at elevated temperatures to study the wear mechanisms under press hardening conditions. However, the discrepancy between the press hardening and SRV test is obvious. To overcome the disadvantage, a sliding tribometer, also called tribolgoical test, is used as the second tribological test. A unidirectional sliding process is running under the corresponding pressures, temperatures, velocities and sliding distances. These test parameters are based on press hardening simulations. According to the present study, the abrasive wear is the predominant wear mechanism in the uncoated interface of the press hardening processes. When Al-Si coated workpieces are applied in the press hardening, severe adhesive wear, also called galling, substantially occurs in the stamping tool. The modelling of the abrasive and adhesive wear is derived from the Archard wear model in which the specific coefficients for the wear are calibrated by the tribological tests. The wear predictions implemented in the press hardening simulation have been validated by a press hardening experiment, which represents a typical geometry of vehicle components.

  • 97.
    Deng, Liang
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Mozgovoy, Sergej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Development of a Tribological Test Programme Based on Press Hardening Simulations2017Ingår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, nr 2, artikel-id 43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Press hardening is widely utilized to form ultra-high-strength steels characterized by a high strength-to-weight ratio for automotive components. Press hardening processes include heating boron–manganese steels to austenite phase, forming the steels at a high temperature, and cooling the formed blanks until the martensite phase is reached . However, press hardening processes lead to severe contact conditions between the blank and the tools including contact pressure, relative sliding, and high temperatures, which result in tool wear and increased maintenance cost. The contact conditions that occur in the stamping tool are difficult to study on site. Additionally, simplified tests, such as pin on disc and ball on disc, are insufficient to reproduce press hardening conditions in laboratory environments . The aim of this study includes developing a tribological test with press hardening conditions in which tool steel pins continuously slide on fresh and hot boron–manganese steel strips. The test programme mimics press hardening conditions with respect to sliding distance, sliding velocity, contact pressure, and surface temperature that were studied based on finite element (FE) simulations of a press hardening experiment. Furthermore, a FE simulation of the tribological test is established and it provides contact temperature in the pin tip with a high accuracy. A tribological test is used to study friction and mass loss with variational pressures and velocities that represented typically variational contact conditions in the press hardening. The tribological test is also used to obtain correlations between the tribological behaviours and process parameters in press hardening including pressure and sliding velocity.

  • 98.
    Deng, Liang
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Mozgovoy, Sergej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Implementation of wear models for stamping tools under press hardening conditions based on laboratory tests2014Ingår i: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 1063, s. 339-342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tool wear occurring in press hardening processes receives insufficient attention since its corresponding measurements and full-scale experiments are complicated and expensive. This paper presents a study of tool wear in press hardening based on laboratory experiments and FE-simulations. Two experimental laboratory setups depending on the contact conditions in press hardening build the base for the wear models implemented in the FE-simulation to predict wear depths. The highest wear depth is found at the radius of the stamping tool and the discrepancies in wear predictions based on the two different laboratory test setups are analyzed.

  • 99.
    Deng, Liang
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Mozgovoy, Sergej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical study of contact conditions in press hardening for tool wear simulation2017Ingår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 10, nr 5, s. 717-727Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the press hardening industry, industrial and academic efforts are being directed toward predicting tool wear to realize an economical manufacturing process. Tool wear in press hardening is a tribological response to contact conditions such as pressure and sliding motion. However, these contact conditions are difficult to measure in-situ. Furthermore, press hardening involves high temperatures, and this increases the complexity of the tribo system. The present work investigated the contact conditions of press hardening with a commercial FE code (LS-DYNA) as a base for tool wear simulation. A press hardening experiment was established in industrial environments and evaluated through FE simulations. The numerical model was set up so as to approximate the manufacturing conditions as closely as possible, and the sensitivity with respect to the friction coefficients was examined. The influence of numerical factors such as the penalty value and mesh size on the contact conditions is discussed. The implementation of a modified Archard’s wear model in the FE simulation proved the possibility of tool wear simulation in press hardening. Finally, a comparison between the tool wear simulation and the measured wear depth is presented. 

  • 100.
    Deng, Liang
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Mozgovoy, Sergej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Press-hardening thermo-mechanical conditions in the contact between blank and tool2013Ingår i: 4th International Conference Hot Sheet Metal Forming of High-performance Steel CHS: June 9-12, Luleå, Sweden : Proceedings / [ed] Mats Oldenburg; Braham Prakash; Kurt Steinhoff, Auerbach: Verlag Wissenschaftliche Scripten , 2013, s. 293-300Konferensbidrag (Refereegranskat)
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