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  • 51.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nilsson, Larsgunnar
    Luleå tekniska universitet.
    Oldenburg, Mats
    Implementation of substructure technique in the finite element program FEMP1986Rapport (Övrigt vetenskapligt)
  • 52.
    Häggblad, Hans-Åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nishida, Masahiro
    Nagoya Institute of Technology.
    Cillia, Mathieu De
    IFMA Clermont-Ferrand.
    Jonsén, Pär
    Oldenburg, Mats
    Strain rate effects on constitutive properties of iron powder2009Ingår i: Euro PM2009, European powder metallurgy association , 2009, Vol. 3, s. 15-20Konferensbidrag (Refereegranskat)
  • 53.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    A model for the influence of lubricants on the pressing behaviour of iron powder1996Ingår i: Modelling in materials science and processing : COST 512: MMSP '96 General Workshop, Davos, Switzerland, 29 September - 2 October 1996 / [ed] Michel Rappaz, Luxembourg: Office for official publications of the European communities , 1996Konferensbidrag (Refereegranskat)
  • 54.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Modelling and simulation of metal powder die pressing with use of explicit time integration1994Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 2, nr 4, s. 893-911Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The pressing of hard metal components is analyzed with numerical methods. The analyzed components are selected from produced components for which the density distribution in the material after pressing has been measured. The expected results from the analyses are the density distribution and the springback after unloading and ejection of the components. The highly non-linear quasistatic problem is analyzed with the use of explicit integration of the equations of motion. A contact constraint method based on direct integration of the equations of the contact interface is used in the analyses. The contact and friction algorithms have been developed in earlier work and are further verified by analyses of a test problem that has an analytical solution. The behaviour of the powder is described by a special cap plasticity material model developed for powder applications. In one example the results obtained using the cap model are compared with results obtained with a multisurface plasticity model. The parameters of the constitutive models are fitted to triaxial experimental data through optimization methods. The presented methods are evaluated by comparing the results with experimental data from density measurements where a technique based on gamma ray absorption is used. The density distributions are qualitatively in good agreement with experimental results. The springback obtained in the simulation of unloading and ejection is in good agreement with measured values.

  • 55.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Numerical simulation of powder compaction for two multilevel ferrous parts, including powder characterisation and experimental validation2002Ingår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 45, nr 4, s. 335-344Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents a summary of two case studies that were carried out by the scientific team in the Thematic Network PM Modnet. During the life of this project, the compaction of complex multilevel ferrous components was investigated. These formed a vehicle to explore methods to characterise the yield and friction properties of the powder, perform simulation of the compression stage of the forming process, complete experimental trials, and compare experimental and simulated results. Density comparisons were made with results from Archimedes, quantitative metallography, and computerised tomography and force levels were compared with recordings from the pressing trials. The results highlight differences between equipment and experimental techniques used in characterising powders. They also show that hardness, metallographic analysis, and computerised tomography may be used to measure density variations throughout the compact. The prediction of density variation was reasonably consistent when using different simulations, whereas punch force prediction showed good consistency. It was found that predicted and measured density distributions agree within 0·05 to 0·5 g cm-3 and that punch force levels may be predicted within 10 to 30%. The study effectively establishes a benchmark with which to compare and improve future simulations.

  • 56.
    Häggblad, Hans-åke
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Larsson, Hans
    On nonlinear constitutive models: including numerical experiments1983Rapport (Övrigt vetenskapligt)
  • 57. Häggblad, Hans-åke
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Wikman, Bengt
    Bengtsson, S.
    Design and evaluation of die pressing experiments for inverse modelling2000Ingår i: Proceedings of 2000 Powder Metallurgy World Congress : November 12 - 16, 2000, Kyoto International Conference Hall, Japan: organized by Japan Society of Powder and Powder Metallurgy, Japan Powder Metallurgy Association. / [ed] Koji Kosuge; Hiroshi Nagai, Tokyo: Japan Society of Powder and Powder Metallurgy , 2000Konferensbidrag (Refereegranskat)
  • 58. Isaksson, Erik
    et al.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Correlation of vehicle crash model parameters to car properties in low-speed collisions: a design of experiments approach2010Ingår i: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 15, nr 3, s. 241-249Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the current study, a methodology for relating model parameters in a one dimensional Mass Spring Damper (MSD) model to global properties of a car, e.g. axial stiffness, bending stiffness and mass, is presented. It is shown that these three vehicle properties affect the vehicle's crash performance in low-speed collision tests used for industrial verification of bumper system performance. Based on information of the properties for a vehicle under development, parameters in the MSD model can be adjusted to give the correct boundary conditions for a finite element (FE) crash simulation with a candidate bumper design. In the FE simulations, the MSD model is then coupled to the FE mesh of candidate bumper design to find a bumper that meets the crash performance requirements of a car under development. The methodology is based on Design of Experiments (DOE) and FE simulations on a public domain model of a Ford Taurus. The knowledge gained from this study gives a valuable tool to use in design and development of bumper systems for the automotive industry.

  • 59.
    Jeppsson, Peter
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A neutral database for preparation of computer controlled coordinate measurements1993Ingår i: Computer integrated manufacturing: proceedings of the 2nd international conference ; 6 - 10 September 1993, Singapore / [Second International Conference on Computer Integrated Manufacturing], Singapore: World Scientific and Engineering Academy and Society, 1993Konferensbidrag (Refereegranskat)
  • 60.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Golling, Stefan
    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.
    Casellas, Daniel
    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 mechanics based modelling of failure in advanced high strength steels2017Ingår 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. 15-23Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the last decade, the favorable properties of the press hardening process for advanced high strength steel (AHSS) have increased the demands concerning passenger safety and lightweight design. AHSS show excellent mechanical properties from e.g. tensile test measurements, but it has previously been shown that results from tensile elongation or energy calculation of un-notched and smooth specimen are not appropriate to classify the crash behavior of steel grades. This is because they completely underestimate the post-uniform region from start of necking to failure. Another issue, the mechanical behavior of a notched or cracked component is different than a smooth and un-notched component. If the mechanical behavior in some loading is dominated by crack propagation, it should be rationalized in terms of the materials crack propagation resistance. Therefore, the evolution of the material property that controls crack propagation, i.e. the fracture toughness, is an interesting approach to evaluate loading and deformation of AHSS. Process modelling including fracture toughness depending properties gives valuable information and additional understanding of fracture behavior and crack propagation mechanisms in AHSS components. Fracture toughness in thin sheets can be readily measured through the application of the Essential Work of Fracture (EWF) methodology. The damage evolution law can be specified in terms of fracture energy (per unit area) or in terms of equivalent plastic failure strain as a function of triaxiality and lode angle. In this work, DENT test samples have been experimentally evaluated and finite element simulations of the DENT tests have been performed. By this approach the numerical study includes mechanical response of AHSS specimen including sharp cracks. In the numerical model, the J-integral was evaluated using the virtual crack-tip extension (VCE) method. From the comparison of the numerical and experimental results of load-displacement for different ligament length cases it is obvious that there are in agreement. Also, the numerically obtained value of fracture toughness Jc, is in agreement with the experimentally measured value of essential work of fracture we.

     

    When finite element based fracture mechanics is applied to practical design, the fracture toughness can be used as design criteria. One appealing property of the evaluation of the J-integral is that it can be evaluated from the far field solution, which facilitates computation as many numerical errors arise close to the crack tip. Evolution of stress- and strain field, plastic zone, J-integral value and other mechanical properties is interesting to study with the combination of experimental and numerical investigations.

  • 61.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Isaksson, Erik
    Luleå University of Technology.
    Sundin, Karl-Gustaf
    Oldenburg, Mats
    Identification of lumped parameter automotive crash models for bumper system development2009Ingår i: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 14, nr 6, s. 533-541Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the design and development process of bumper systems for the automotive industry, information about the future car model is limited. Normally, iterative finite element (FE) analyses of different crash loading tests are used to find an appropriate bumper system to the coming car model. Because of the lack of information, only a rough model of the car is normally utilised in the FE simulations. This leads to uncertainties in the bumper design since the dynamic response of the car is dependent on the load case and the properties of the actual bumper system. This paper presents a method for identification of lumped parameter models based on results from crash tests of a Volvo S40. The ability to predict the measured results for models with different number of degrees of freedom (DOF) is investigated. Also, a validation of the model together with an FE mesh of the bumper system is presented. The results clearly show that a linear mass spring damper model with 2 DOF can be used to predict the response from the measurements in case of symmetric loading. Further increase of the number of DOF only causes small or no improvements of the agreement between the predicted and measured crash response.

  • 62.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Svanberg, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Ramirez, Giselle
    Eurecat, Centre Tecnològic de Catalunya.
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Eurecat, Centre Tecnològic de Catalunya.
    Hernández, Ricardo
    Eurecat, Centre Tecnològic de Catalunya.
    Marth, Stefan
    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.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A Novel Method for Modelling of Cold Cutting of Microstructurally Tailored Hot Formed Components2019Ingår i: CHS² 2019 - 7th International Conference on Hot Sheet Metal Forming of High Performance Steel, 2019 / [ed] Mats Oldenburg, Jens Hardell, Daniel Casellas, 2019, Vol. 7, s. 645-652Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the last decade, hot metal forming of advanced high strength steel (AHSS) have improved passenger safety and open possibilities for lightweight design. Hot metal forming can be applied to locally tailor the microstructure of components and gradual vary mechanical properties to improve crash resistance behaviour and optimized weight for e.g. safety related parts. Sometimes post punching or trimming must be done on hardened parts. Such conditions induce damage and fractures in the trimmed edge. Another issue is that high pressures are required in cutting operations due to the high yield stress of press hardened parts, which accelerate wear and produce premature fracture in tools. Optimizing cutting operations to minimize damage and wear are essentials and numerical simulations of cutting operations can be of good assistance. One of the main challenges in the numerical modelling consists of numerically be able to treat the extremely large deformation occurring in the cutting zone. A second challenge is to find suitable failure models. In this work, the punching process of soft and hard microstructures obtained by press hardening is experimentally studied, but also modelled with a combination of smoothed particle Galerkin (SPG) method and finite element method (FEM). Laboratory punching tests with different clearance values were carried out using sheets of different fracture strengths. All experimental cases are numerically modelled. Validation is conducted by comparing numerical results with experimental measurements of punch force and displacement. In addition, morphology of the final cutting edges from both real and virtual are compared. Numerical results show good agreement against experimental measurements. Furthermore, the combined method gives robust-ness and stability as it can handle large deformations efficiently.

  • 63. Karjalainen, L.P.
    et al.
    Somani, M.C.
    Porter, D.A.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Physical simulation, a tool for improving the modelling of thermomechanical processing2001Ingår i: Proceedings of the International Conference on High Technologies in Advanced Metal Science and Engineering / [ed] G. Kodjaspirov, 2001Konferensbidrag (Refereegranskat)
  • 64.
    Lindkvist, Göran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Ahlin, Hans
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Hot Stamping of Tailored Component: Experiments and Numerical Analysis2015Ingår 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. 755-763Konferensbidrag (Refereegranskat)
    Abstract [en]

    This study is concerned with plasticity and ductile fracture modelling aspects of press hardened steels, where multiple phases of different yield strength, work hardening and ductility are present. Macroscopic constitutive properties are determined using a semi-analytical approach termed Mean Field Homogenization (MFH), based on the properties of individual phases and micro-topology. This is combined with a phenomenological ductile fracture initiation criterion formulated in stress space at the microscopic scale. Localization enhanced kinematics are introduced at the macro-scale when instability is signaled by a local bifurcation analysis of the homogenized material. Discontinuities in the strain field are introduced into a quadrilateral shell based on the weak discontinuity approach. Fracture properties and flow curves up to large strains are determined from single phase tensile experiments using digital image correlation. The predictions of the integrated MFH and fracture model is compared with experimental results on steel sheets with different thermal histories, in terms of fracture prediction and and overall mechanical properties

  • 65.
    Lindkvist, Göran
    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.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical prediction of failure in high temperature formblowing and hardening2011Ingår i: Hot sheet metal forming of high-performance steel, CHS2: 3rd international conference, Proceedings. Kassel, Germany, June 13-17, 2011 / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Prakash, Auerbach: Verlag Wissenschaftliche Scripten , 2011, s. 57-64Konferensbidrag (Refereegranskat)
    Abstract [en]

    The process studied in this work is high temperature formblowing and hardening (HTFH). Bursting failure is an irrecoverable failure mode present in the HTFH process. The main objective was to determine if a ductile fracture criterion would be possible to use as pre-bursting failure indicator in finite element (FE) simulations of the forming process. The failure criterion was implemented in the utilised FE code. Calibration was performed by the use of analytical forming limit curves (FLC:s). The FLC:s were derived from experimentally obtained stress-strain curves for different temperatures using theory for localised necking. Experiments with the HTFH process in the form of burst tests were performed. Experimental data and output from thermomechanical FE simula-tions of the process were compared. Results indicated that the implemented numerical criterion predicted failure prior to irrecoverable experimental failure. It is concluded that the implemented fracture criterion can be used as a failure indicator in FE simulations of the HTFH process.

  • 66.
    Lindkvist, Göran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Oldenburg, Mats
    Thermo-mechanical simulation of high temperature formblowing and hardening2009Ingår i: Hot sheet metal forming of high-performance steel, CHS2: 2nd international conference, June 15-17 2009, Luleå, Sweden. Proceedings / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Parkash, Bad Harzburg: GRIPS media , 2009, s. 247-254Konferensbidrag (Refereegranskat)
  • 67.
    Marth, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Golling, Stefan
    Gestamp R&D, Box 828, 97 125 Luleå, Sweden.
    Östlund, Rickard
    Gestamp R&D, Box 828, 97 125 Luleå, Sweden.
    Barrero Pijoan, Anna
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, 08243 Manresa, Spain.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Failure Modelling and Experimental Evaluation of a Press-Hardened Laboratory Scale Component with Multi-Phase Microstructure2019Ingår i: CHS² 2019 - 7th International Conference on Hot Sheet Metal Forming of High Performance Steel, 2019 / [ed] Mats Oldenburg, Jens Hardell, Daniel Casellas, 2019, Vol. 7, s. 39-50, artikel-id B1Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hot stamping of boron alloyed steel has become a standard in the automotive industry for safety relevant body in white components. This process allows the design of complex geometries with superior mechanical properties. Special tool design enables to manufacture components with special properties based on varying microstructures in designated areas. This is a challenge for finite element (FE) simulations of deformation and failure for multi-phase microstructure components.

    In the present work, a laboratory scale test component with multi-phase microstructure is studied from blank to fractured component. Using different tool temperatures and adding an air-cooling step before transfer to the press hardening tool, the microstructure of the component is varied. By this, components with four different multi-phase microstructures are produced. These components are tested under tensile deformation until fracture, where force, elongation and the strain field on the components surface are measured.

    The laboratory scale test component is evaluated using FE-modelling. The complete production process is modelled starting with the pre-cut austenitized blank, subsequent transfer, air-cooling, forming operation, and the final post-cooling. The resulting multi-phase micro structures are evaluated using manual optical microscope image analysis and compared with the simulated phase composition. Furthermore, the deformation and fracture of the manufactured component under tensional loading is studied using a mean-field homogenization scheme for the multi-phase composition combined with the OPTUS failure model. This finite element investigation is conducted taking the microstructure composition, shape and thickness deviations from the forming simulation into account.

    The present work shows the feasibility of modelling methods of the complete process chain for press-hardened components with multi-phase microstructures, from blank to fractured component.

  • 68.
    Marth, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Golling, Stefan
    Gestamp R&D, Luleå, Sweden.
    Östlund, Rickard
    Gestamp R&D, Luleå, Sweden.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    From Blank to Fractured Component: Numerical and Experimental Results of a Laboratory Scale Component2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hot stamping of boron alloyed steel has become a standard in the automotive industry for safety relevant chassis components. Hot stamping of ultra-high strength steel allows the design of complex geometries with superior mechanical properties. In the present work, a laboratory scale test component is followed up from blank to fractured component. The production process starts with a pre-cut blank, which then is austenitized, transferred to the press hardening tool, formed and quenched and ends with post-cooling to room temperature. These components are tested under tensile deformation until fracture, where force, elongation and the strain field on the components surface are measured. The strain field measurements are performed by using digital image correlation (DIC). The laboratory scale test component is evaluated using finite element modelling. The production process is modelled starting with a pre-cut austenitized blank, subsequent transfer and forming operation, and ends with post-cooling. Furthermore, the deformation and fracture under tension/bending is studied using the OPTUS damage model. The as-produced component is measured using a three dimensional scanning system. Shape deviation and thickness change are compared to in the forming simulation predicted geometry after post-cooling. A finite element investigation on the deformation and fracture under tensional/bending loading is conducted applying shape and thickness deviations in the model. The majority of industrial components undergo paint curing before they are included in an assembly. Paint baking is a heat treatment at relatively low temperatures and causes relaxation in a martensitic microstructure. The effect of paint baking on the mechanical response of the laboratory scale test component is investigated. In the present work the reliability of modelling tools from blank to fractured component is shown. The possibility is shown to predict the failure of the component, with the specific phase composition after the hot stamping process obtained from simulations. Furthermore, the influence of the paint baking process on the mechanical properties is presented.

  • 69.
    Marth, Stefan
    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.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A comparison between Stepwise Modelling and Inverse Modelling methods for characterization of press hardened sheet metals2017Ingår 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. 281-288Konferensbidrag (Refereegranskat)
    Abstract [en]

    The demand for weight reduction of cars has increased the number of press hardened sheet metal parts used in the automotive industry. This leads to an increased demand on the precision of simulations of press hardened sheet metals. An accurate prediction of the post-necking behaviour of materials is therefore needed to increase the precision of computer simulations with large deformations, as for example in forming simulations and crash simulations. Especially fracture simulations of press hardened steel parts with tailored properties have a huge demand on precise material models.

    Inverse modelling is a common engineering tool to characterize the elasto-plastic behaviour of materials.  Taking experimental data, such as force and displacement data, the material model parameters are optimised until the simulated output reaches a target function.  Then inverse modelling is highly time demanding and needs nonlinear hardening material models. 

    Lately a new fast method for post necking characterisation of sheet metals, called the Stepwise Modelling Method (SMM), was presented. This method uses full field measurements to obtain the strain field on the surface of sheet metal tensile specimens.  Furthermore, the stepwise modelling method models an experimental hardening curve in a stepwise process.  This hardening curve is a piecewise linear curve and not restricted to any specific material model.

    In this paper SMM is used to characterize the hardening behaviour for thermally treated boron steel.  These results are compared with the results of inverse modelling. Three different material models are used. The comparison shows a minor deviation in the resulting hardening relations between stepwise modelling and inverse modelling. Since the efficiency is an important factor in product development calculation times are taken into account.  Comparing calculation time using SMM is considerably more efficient than using inverse modelling. Furthermore another advantage of SMM is shown in the fact that the piecewise linear hardening curves can be fitted to almost any material model without computational costs.

  • 70.
    Marth, Stefan
    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.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Östlund, Rickard
    Post necking characterisation for sheet metal materials using full field measurement2016Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 238, s. 315-324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    precise prediction of the post-necking behaviour of materials is needed to increase the precision of computer simulations with large deformations. Applications in which this need is encountered include crash, forming, and failure simulations. By using an optical full-field measurement of the localised deformation field, an effective and computationally fast method is presented to determine the relationship between true stress and true plastic strain, including post-necking behaviour. The presented stepwise modelling method is used to characterise heat-treated boron steel using thin sheet metal specimens. These results are validated with the results determined by a method based on inverse modelling. It can be concluded that the stepwise modelling method is considerably faster than the compared inverse modelling method. The method is also suitable for effectively determining element size dependency due to regularisation of the hardening behaviour needed for finite element analysis with strain localisation, e.g., for crash simulations

  • 71.
    Mozgovoy, Sergej
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Deng, Liang
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel2013Konferensbidrag (Refereegranskat)
  • 72.
    Mozgovoy, Sergej
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Deng, Liang
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel2014Ingår i: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, nr 2, s. 65-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s−1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.

  • 73.
    Mozgovoy, Sergej
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Deng, Liang
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Simulative High Temperature Friction and Wear Studies for Press Hardening Applications2015Ingår 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. 167-175Konferensbidrag (Refereegranskat)
    Abstract [en]

    Press hardening is employed in automotive industry to produce advanced high-strength steel components for safety and structural applications. In this hot forming process, the dimensional accuracy of produced components relies not only on an optimum friction level for the deformation of the workpiece, but it also gets affected by wear of the forming tools, which reduces the service life of the tool as well. It is desirable to enhance the durability of the tools by understanding the influence of contact conditions on tool wear. However, this is difficult to achieve in conventional tribological testing equipment. With this in view, the tribological behaviour of tool-workpiece material pairs at elevated temperatures has been studied in a newly developed experimental set-up simulating the conditions prevalent during interaction of the hot workpiece with the tool surface. The coefficients of friction of uncoated and Al-Si coated 22MnB5 steel decreased when the normal load increased. The influence of sliding velocity on the coefficient of friction was negligible for uncoated and Al-Si coated 22MnB5 steel. In the case of Al-Si coated 22MnB5 steel, adhesive material transfer of the Al-Si coating onto the tool steel surface was the main wear mechanism and this was also the reason for the higher and unstable friction coefficient when compared to uncoated 22MnB5 steel. In the case of uncoated 22MnB5 steel, adhesion was the main wear mechanism.

  • 74.
    Mozgovoy, Sergej
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Deng, Liang
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Tribological Behavior of Tool Steel under Press Hardening Conditions Using Simulative Tests2018Ingår i: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 140, nr 1, artikel-id 011606Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Press hardening is employed in the automotive industry to produce advanced high-strength steel components for safety and structural applications. This hot forming process depends on friction as it controls the deformation of the sheet. However, friction is also associated with wear of the forming tools. Tool wear is a critical issue when it comes to the dimensional accuracy of the produced components and it reduces the service life of the tool. It is therefore desirable to enhance the durability of the tools by studying the influence of high contact pressures, cyclic thermal loading, and repetitive mechanical loading on tool wear. This is difficult to achieve in conventional tribological testing devices. Therefore, the tribological behavior of tool-workpiece material pairs at elevated temperatures was studied in a newly developed experimental setup simulating the conditions prevalent during interaction of the hot sheet with the tool surface. Uncoated 22MnB5 steel and aluminum-silicon (Al-Si)-coated 22MnB5 steel were tested at 750 °C and 920 °C, respectively. It was found that higher loads led to lower and more stable friction coefficients independent of sliding velocity or surface material. The influence of sliding velocity on the coefficient of friction was only marginal. In the case of Al-Si-coated 22MnB5, the friction coefficient was generally higher and unstable due to transfer of Al-Si coating material to the tool. Adhesion was the main wear mechanism in the case of uncoated 22MnB5

  • 75.
    Nilsson, L.
    et al.
    Luleå tekniska universitet.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    On tensile fracture and wave propagation in granular materials1983Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 12, nr 6, s. 299-301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the analysis the material is treated as plastic fracturing. A continuum approach to tensile fracturing is related to fracture mechanical concepts. The rate of strain-softening is obtained from the rate of fracture energy being released. Material anisotropy due to the formation of crack-planes is accounted for. The proposed strain-softening tensile fracturing model is implemented in a finite element program for wave propagation analysis. The strain-softening model is compared to an ideal brittle model in analysis of wave propagation in a concrete rod.

  • 76. Nilsson, L.
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    On the numerical simulation of tensile fracture1985Ingår i: Finite Element Methods for Nonlinear Problems: proceedings of the Europe-US Symposium ; the Norwegian Institute of Technology, Trondheim, Norway, August 12-16, 1985 / [ed] Pal G. Bergan; K.J. Bathe, Norges tekniske högskola , 1985Konferensbidrag (Refereegranskat)
  • 77. Nilsson, L.
    et al.
    Zhong, Z.-H.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Analysis of shell structures subjected to contact-impact1989Ingår i: Analytical and computational models of shells :: Symposium entitled "Analytical and computational models for shells" : Winter annual meeting : Papers. / [ed] Ahmed K. Noor; Ted Belytschko; Juan C Simo, American Society of Mechanical Engineers , 1989Konferensbidrag (Refereegranskat)
  • 78.
    Nilsson, Larsgunnar
    et al.
    Luleå tekniska universitet.
    Häggblad, Hans-åke
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    FEMP: an interactive, graphic finite element program for small and large computer systems : verification and demonstration manual1983Rapport (Övrigt vetenskapligt)
  • 79. Nilsson, Larsgunnar
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nonlinear wave propagation in plastic fracturing materials: a constitutive modelling and finite element analysis1983Ingår i: Nonlinear deformation waves: symposium, Tallinn, Estonian SSR, USSR, August 22-28, 1982 / [ed] Uno Nigul ; Jüri Engelbrecht, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1983, s. 209-217Konferensbidrag (Refereegranskat)
  • 80.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Hertzman, J.
    Forming Group, OSAS, Industrial Development Centre in Olofström AB.
    Thilderkvist, P.
    Forming Group, OSAS, Industrial Development Centre in Olofström AB.
    Merklein, M.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Kuppert, A.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Stöhr, B.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Lechler, J.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermo-mechanical sheet metal forming of aero engine components in Ti-6Al-4V: Part 1: Material characterisation2013Ingår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 6, nr 3, s. 391-402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ti-6Al-4V is one of the most frequently used titanium alloy in aerospace applications such as for load carrying engine structures, due to their high strength to weight ratio in combination with favourable creep resistance at moderate operating temperatures. In the virtual development process of designing suitable thermo-mechanical forming processes for titanium sheet metal components in aero engine applications numerical finite element (FE) simulations are desirable to perform. The benefit is related to the ability of securing forming concepts with respect to shape deviation, thinning and strain localisation. The reliability of the numerical simulations depends on both models and methods used as well as on the accuracy and applicability of the material input data. The material model and related property data need to be consistent with the conditions of the material in the studied thermo-mechanical forming process. In the present work a set of material tests are performed on Ti-6Al-4V at temperatures ranging from room temperature up to 560°C. The purpose is to study the mechanical properties of the specific batch of alloy but foremost to identify necessary material model requirements and generate experimental reference data for model calibration in order to perform FE-analyses of sheet metal forming at elevated temperatures in Ti-6Al-4V.

  • 81. Odenberger, Eva-Lis
    et al.
    Jansson, M.
    Engineering Research Nordic AB.
    Thilderkvist, P.
    Olofström School of Automotive Stamping.
    Gustavsson, H.
    Volvo Aero Corporation.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A short lead time methodology for design, compensation and manufacturing of deep drawing tools for Inconel 7182008Ingår i: Conference Best in Class Stamping, June 16 - 18, 2008, Olofström, Sweden: [proceedings] / IDDRG, International Deep Drawing Research Group / [ed] Nader Asnafi, Olofström: Industriellt utvecklingscentrum i Olofström AB , 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a systematic methodology for the design and manufacturing of deep drawing tools generating high quality components at an extremely short lead time. Prototype tools for five different super alloy Inconel 718 sheet metal components were designed, manufactured and tested in 15 weeks. Two of these prototype tools (A, B) are the topics of this paper. The methodology is based on virtual tool design in which the tool concepts are secured and optimized with respect to sheet metal formability and shape deviation using FE-analyses. Tool surfaces are compensated for springback, if necessary, using the *INTERFACE_COMPENSATED_NEW capability in LS-DYNA v971 (B).The compensated FE tool surfaces are used as reference to generate high quality surfaces suitable for the milling process. Laser scanning was used to determine shape deviation. The CAD-evaluation revealed a minor shape deviation within tolerance of component (A) and a small over-compensation of the final geometry of component (B). The maximum shape deviation was however in the order of the sheet thickness. The work presented in this paper substantiate the idea that it is possible to realize development projects for new applications in Inconel 718 accurately, which is of outmost importance when developing tools at a short lead time. The key is consistent studies according to the systematic methodology in which FEanalyses were used for the virtual tool design and compensation.

  • 82.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Niklasson, Fredrik
    GKN Aerospace Engine Systems Sweden.
    Direct-hit development of manufacturing processes: Thermo-mechanical forming of Titanium aero engine structures2013Ingår i: Book of Abstracts for the 4:th CEAS Conference, 2013, Linköping: Linkoping University Electronic Press , 2013, s. 175-Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to increase the competitiveness of the Swedish aerospace industry, alternative manufacturing processes for static load carrying aero engine structures are desired. Presently, these components mainly consist of large-scaled single castings. To increase the in-house level of processing, the Swedish aero engine industry focus on fabricated alternatives by introducing new manufacturing processes and create relations with adjacent sub-suppliers. Theconcept of fabrication involves forgings, sheet metals and small ingots assembled by welding. The possibility to reduce weight, i.e. fuel consumption and product cost also exists. In the aerospace industry extremely highdemands on safety and reliability exists which requires precise knowledge regarding the influence on the material and its properties through the whole fabrication chain. The advanced Finite Element (FE) technology makes precise analyses possible assuming that proper material descriptions are used. Analyses of sheet metal forming provides with information of formability, thinning, springback, resultant mechanical properties and residual stress state which are important input to analyses of subsequent welding and heat treatments. One challenge in producing complete structures based on fabrication isrelated to the accuracy in numerical predictions of shape deviation using FE-analyses, in order to effectively compensate forming tools forspringback and accumulated shape distortions. By fundamental research on and development of thermo-mechanical processes for hot sheet metal forming of titanium, this project shall result in that a few SME can further developtheir processes for product and process development. The project gather competence from the Swedish aero engine industry GKN Aerospace, acknowledged R&D within forming processes, FE-modelling and SME withexperience of forming. The aims of the project are:Development of methodologies for thermomechanical material characterisation of Ti-6Al- 4V and FE-models for hot sheet metal forming. Suggestion of forming procedures suitable for production of titanium components in which resultant geometry and properties are secured.Activities where Swedish SME takes necessary development steps, in order to produce desired titanium sheet metal parts and develop into new sub-suppliers for the Aero engine industry. This presentation summarise results obtained inpresent and previous research and development projects regarding short lead time design, compensation and manufacturing of deep drawing tools of titanium and super alloys. The research funding by VINNOVA - NFFP 4 and 5for SME, BFS and GKN Aerospace Sweden are gratefully acknowledged.

  • 83.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thilderkvist, P.
    Forming Group, OSAS, Industrial Development Centre in Olofström AB.
    Stoehr, T.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Lechler, J.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Merklein, M.
    Manufacturing Technology, University of Erlangen-Nuremberg.
    Tool development based on modelling and simulation of hot sheet metal forming of Ti-6Al-4 V titanium alloy2011Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, nr 8, s. 1324-1335Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the aero engine industry alternative manufacturing processes for load carrying aero engine structures imply fabrication. The concept of fabrication involves simple forgings, sheet metals and small ingots of e.g. titanium alloys which are welded together and heat treated. In the concept phase of the product development process, accurate evaluations of candidate manufacturing processes with short lead times are crucial. In the design of sheet metal forming processes, the manual die try out of deep drawing tools is traditionally a time consuming, expensive and inexact process. The present work investigates the possibility to design hot forming tools, with acceptable accuracy at short lead times and with minimal need for the costly die try out, using finite element (FE) analyses of hot sheet metal forming in the titanium alloy Ti-6Al-4 V. A rather straightforward and inexpensive approach of material modelling and methods for material characterisation are chosen, suitable for early evaluations in the concept phase. Numerical predictions of punch force, draw-in and shape deviation are compared with data from separate forming experiments performed at moderately elevated temperatures. The computed responses show promising agreement with experimental measurements and the predicted shape deviation is within the sheet thickness when applying an anisotropic yield criterion. Solutions for the hot forming tool concept regarding heating and regulation, insulation, blank holding and tool material selection are evaluated within the present work.

  • 84.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Division Materials and Production, RISE IVF ABRISE Research Institutes of Sweden, Olofström.
    Pederson, Robert
    Division of Subtractive and Additive Manufacturing, University West, Trollhättan.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Finite element modeling and validation of springback and stress relaxation in the thermo-mechanical forming of thin Ti-6Al-4V sheets2019Ingår i: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, a hot forming procedure is developed using computer-aided engineering (CAE) to produce thin Ti-6Al-4V sheet components in an effective way. Traditional forming methods involve time- and cost-consuming furnace heating and subsequent hot sizing steps. A material model for finite element (FE) analyses of sheet metal forming and springback at elevated temperatures in Ti-6Al-4V is calibrated and evaluated. The anisotropic yield criterion proposed by Barlat et al. 2003 is applied, and the time- and temperature-dependent stress relaxation behavior for elastic and inelastic straining are modeled using a Zener–Wert–Avrami formulation. Thermo-mechanical uniaxial tensile tests, a biaxial test, and uniaxial stress relaxation tests are performed and used as experimental reference to identify material model parameters at temperatures up to 700 °C. The hot forming tool setup is manufactured and used to produce double-curved aero engine components at 700 °C with different cycle times for validation purposes. Correlations between the predicted and measured responses such as springback and shape deviation show promising agreement, also when the forming and subsequent holding time was as low as 150 s. The short cycle time resulted in elimination of a detectable alpha case layer. Also, the tool surface coating extends the tool life in combination with a suitable lubricant. 

  • 85.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Pederson, Robert
    Volvo Aero Corporation, Trollhättan.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermo-mechanical material response and hot sheet metal forming of Ti-62422008Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 489, nr 1-2, s. 158-168Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The thermo-mechanical response of a Ti-6242 alloy has been studied in elevated temperature compression tests (CT) together with cold and hot sheet metal forming tests (FT) to evaluate the suitability of different cold and hot sheet metal forming processes. The CT are designed to function as input for the estimation of material model parameters such as the parameters of constitutive equations. Furthermore, results from the FT will be used in correlation of finite element (FE) models for the prediction of sheet metal forming. Experiments were performed in a broad range of temperatures and strain rates. In CT at 400-900 °C and strain rates 0.05-1 s-1. In FT at 20-1000 °C in both isothermal and non-isothermal forming, at forming velocities of 5 and 10 mm/s. The microstructures of as-received material and deformed specimens were examined using optical microscopy. Experimental results of the CT show that initial material hardening was followed by specimen failure where cracks have formed in deformation bands or by flow softening, depending on the temperature. Compressive logarithmic strains of 10-50% were achieved. The FT reveals that optimal forming conditions are a combination of forming velocity, temperature and holding time. Hence increasing forming temperatures alone does not necessary imply better forming characteristics. A change in spring-back characteristics occurred at elevated temperatures. It can be concluded that, under the current conditions in this study, Ti-6242 is suitable to be formed by hot sheet metal forming.

  • 86.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Component Manufacturing, Swerea IVF AB, Olofström.
    Pérez Caro, Lluís
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Component Manufacturing, Swerea IVF AB, Olofström.
    Åhlin, Hans
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermo-mechanical Material Characterization and Stretch-bend Forming of AA60162018Ingår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 418, artikel-id 012022Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lightweight design has become increasingly in focus for the manufacturing industry. Global environmental challenges, goals and legislations imply that lighter and sustainable products are imperative to remain competitive. One example is stamped products made of aluminum alloys which are of interest to the automotive industry, where lightweight designs are essential. In order to increase formability and to produce more complex geometries in stamped aluminum components there is a need to develop hot forming techniques. The Finite Element Method (FEM) has enabled important advances in the study and design of competitive manufacturing procedures for metal parts. Predicting the final geometry of a component is a complex task, especially if the forming procedure occurs at elevated temperatures. This work presents selected results from thermo-mechanical material testing procedures, FE-analyses and forming validation tests in AA6016 material. The material tests are used to determine the thermo-mechanical anisotropic properties, strain rate sensitivity and formability (Forming Limit Curves, FLC) at temperatures up to 490°C. Stretch-bending tests are performed to compare predicted results with experimental observations such as punch force, strain levels, thinning, forming temperatures, springback and failure. It was found that the heat-treatment and forming at elevated temperatures substantially increased formability and that measured responses could in general be predicted if care was taken to model the initial blank temperatures, heat transfer and thermo-mechanical material properties. The room temperature case confirms the importance of considering anisotropy.

  • 87.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Schill, M.
    DYNAmore Nordic AB.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thermo-mechanical sheet metal forming of aero engine components in Ti-6Al-4V: Part 2 : Constitutive modelling and validation2013Ingår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 6, nr 3, s. 403-416Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work constitutive models suitable for thermo-mechanical forming of the titanium alloy Ti-6Al-4V are evaluated. A tool concept for thermo-mechanical forming of a double-curved sheet metal component in Ti-6Al-4V is proposed. The virtual tool design is based on finite element (FE) analyses of thermo-mechanical sheet metal forming in which two different anisotropic yield criteria are evaluated and compared with an isotropic assumption to predict global forming force, draw-in, springback and strain localisation. The shape of the yield surface has been found important and the accuracy of the predicted shape deviation could be slightly improved by including the cooling procedure. The predicted responses show promising agreement with the corresponding experimental observations when the anisotropic properties of the material are considered

  • 88.
    Odenberger, Eva-Lis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Thilderkvist, Per
    Industrial Development Centre in Olofstrom AB.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Springback and stress relaxation in thermo-mechanical forming of thin Ti-6Al-4v sheets2014Konferensbidrag (Refereegranskat)
  • 89.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Finite element analysis of tensile fracturing structures1985Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 90.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Finite element analysis of thin-walled structures subjected to impact loading1988Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis is devoted to the numerical solution of dynamic problems involving thin-walled structures. Special consideration is paid to the effects of contact-impacts. Thus, the main effort is concentrated on studies, development and computer program implementations of efficient algorithms for analysis of dynamically loaded shell structures, including contact-impacts and severe structural deformation. Recent developments in the formulation of efficient finite elements for dynamically loaded shell structures are studied. A program implementation of a low-order four-node shell element with uniformly reduced integration is performed. The efficiency and the behaviour of this element type are compared with existing shell and solid elements implemented in the same program system. Hourglass resisting algorithms are reviewed and formulated, and parameter studies are carried out. A new contact interface algorithm for dynamic analysis with explicit integration is presented. The development of the defence node algorithm permits contact constraints based on the Lagrange multiplier method to be introduced in dynamic analysis with explicit integration. Numerical tests show the good performance of the developed algorithms. A new global search method for general contacting systems is developed and implemented in a computer program together with the abovementioned contact interface algorithm. The concept of position codes for efficient global contact searching and the local search procedure used are presented. Numerical experiments are performed in order to examine the behaviour of the algorithms in different aspects.

  • 91.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Low-order elements for dynamic analysis of shell structures1991Ingår i: Proceedings of the International Conference on Mechanics of Solids and Structures: Nanyang Technological University ; 11 - 13 September 1991 / [ed] Daniel T Lwin, Singapore: World Scientific and Engineering Academy and Society, 1991Konferensbidrag (Refereegranskat)
  • 92.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Warm forming of steels for tailored microstructure2014Ingår i: Encyclopedia of Thermal Stresses, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2014, s. 6469-6479Kapitel i bok, del av antologi (Refereegranskat)
  • 93.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    A contact constraint method with friction for explicit analysis applied to powder compaction problems1992Ingår i: Numerical methods in engineering '92 :: proceedings of the first European Conference on Numerical Methods in Engineering, 7 - 11 September 1992, Brussels, Belgium, Elsevier, 1992Konferensbidrag (Refereegranskat)
  • 94.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Compaction simulation of a hard metal powder component with verification by density measurements using gamma-ray absorption techniques1993Ingår i: Proceedings of 1993 Powder Metallurgy World Congress :: July 12 - 15, 1993, Kyoto International Conference Hall, Japan / [ed] Yoshichika Bando; Koji Kosuge, Kyoto :: Japan Society of Powder and Powder Metallurgy , 1993Konferensbidrag (Refereegranskat)
  • 95.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Material parameter fitting in an integrated environment for analysis of iron powder pressing1994Ingår 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 , 1994, s. 693-696Konferensbidrag (Refereegranskat)
    Abstract [en]

    An analysis of powder processing requires accurate material models of the various powder mixes that are available. The set of material parameters for a given material model in metal powder pressing simulations is extensive. In order to model the behaviour of an Fe powder, a fitting of the parameters to experimental data has to be made. In this work, optimization methods are used to fit the parameters of material models to triaxial load test data of Fe powder. A prototype material database is developed where data describing material behaviour based on tests are separated from the material parameters of specific material models. The tools for fitting of material parameters operate on the material database. With this concept, the material parameter fitting can be performed and evaluated at the time of the analysis and can be based on e.g. the expected range in strains, temperatures or timescale. The material database is incorporated is a system with integrated product design and non-linear finite element codes

  • 96.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Simulation of the cold pressing of a hard metal powder component using explicit integration methods1993Ingår i: Advances in engineering plasticity and its applications : proceedings of the Asia-Pacific Symposium on Advances in Engineering Plasticity and its Applications -: AEPA' 92 / [ed] W.B. Lee, Elsevier, 1993Konferensbidrag (Refereegranskat)
  • 97.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Wikman, Bengt
    A friction model for iron powder pressing based on a tribological approach1996Ingår i: Advances in powder metallurgy & particulate materials - 1996: proceedings of the 1996 World Congress on Powder Metallurgy & Particulate Materials ..., June 16 - 21, Washington, DC / [ed] Terry M. Cadle, Princeton, NJ: Metal powder industries federation , 1996, Vol. 7, s. 329-340Konferensbidrag (Refereegranskat)
    Abstract [en]

    The global behaviour of the cold pressing process of iron powder is dependent on the material response in the powder as well as the friction between the powder and the tool walls. Both the behaviour with respect to the material response and the friction effects are dependent on the lubricant used in the powder mixture. Normally, solid phase lubricants are mixed into the iron powder. It is assumed that the local heat generated in the microscopic contact areas between the powder and the tool walls is partly responsible for the functionality of the lubricant. The microscopic interaction between powder, lubricant and tool wall at the point of contact is described by relations between the friction coefficient and a combination of state variables, e.g. relative velocity, pressure and powder density. The relations are established by use of tribological classifications of the lubricant as well as the mixture of lubricant and iron powder. Finite element simulations of pressing experiments are used for studying the influence of the frictional relations on the global pressing behaviour.

  • 98.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-åke
    Wikman, Bengt
    Material model parameter estimation by inverse analysis of a closed die experiment2002Ingår i: Process modeling in powder metallurgy & particulate materials: proceedings of the 2002 International Conference on Process Modeling in Powder Metallurgy & Particulate Materials, [held October 28 - 29, 2002, Newport Beach, California] / [ed] Alan Lawley, Prinecton; NJ: Metal powder industries federation , 2002Konferensbidrag (Refereegranskat)
  • 99.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindkvist, Göran
    Micro-structure evolution in the press hardening process with respect to tool and contact thermal properties2010Ingår i: Proceedings of the 13th International Conference on Metal Forming: September 19 - 22, 2010, Hotel Nikko Toyohashi, Toyohashi, Japan / [ed] K. Mori; M. Pietrzyk; J. Kusiak; J. Majta; P. Hartley; J. Llin, Weinheim: Wiley-VCH Verlagsgesellschaft, 2010, s. 865-868Konferensbidrag (Refereegranskat)
  • 100.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindkvist, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Tool thermal conditions for tailored material properties2011Ingår i: HTM: Journal of Heat Treatment and Materials: Zeitschrift für Werkstoffe, Wärmebehandlung, Fertigung, ISSN 0341-101X, Vol. 66, nr 6, s. 329-334Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With the press hardening technology it is possible to produce components with tailor- made material properties. The present work is based on a comprehensive thermo-mechanical material model for simulation of press hardening and similar processes. The model accounts for and predicts time dependent and timeindependent phase transformations, mechanical and thermal properties as well as transformation plasticity during the complete cooling and deformation process from 900 °C to room temperature. The model predicts the microstructure evolution during the complete process as well as the final fractions. The thermal contact properties and the thermal properties in the tools have influence on the final material state. Solutions for tool heating and cooling for manufacturing of components with soft zones are studied. Based on the results from the press hardening simulations, thermal properties of special tool materials are taken into account in order to optimise the manufacturing thermal cycle.

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