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Sökning: hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Maskinteknik) > Oldenburg Mats

  • Resultat 1-10 av 158
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1.
  • Bergman, Greger, et al. (författare)
  • Integration of a product design system and nonlinear finite element codes via a relational database
  • 1995
  • Ingår i: Engineering computations. - : Emerald. - 0264-4401 .- 1758-7077. ; 12:5, s. 439-449
  • Tidskriftsartikel (refereegranskat)abstract
    • 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
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2.
  • Casellas, Daniel, et al. (författare)
  • A fracture mechanics approach to develop high crash resistant microstructures by press hardening
  • 2017
  • Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 101-107
  • Konferensbidrag (refereegranskat)abstract
    • Crashworthiness is a relevant engineering property for car parts. However it is not easy to measure at laboratory scale and complex impact tests have to be carried out to determine it. Crash resistance for high strength steel is commonly evaluated in terms of cracking pattern and energy absorption in crashed specimens. Accordingly, the material resistance to crack propagation, i.e. the fracture toughness, could be used to rank crashworthiness. It has been proved in a previous work by the authors, so the measure of fracture toughness, in the frame of fracture mechanics in small laboratory specimens, would allow determining the best microstructure for crash resistance parts. Press hardening offers the possibility to obtain a wide range of microstructural configurations, with different mechanical properties. So the aim of this work is to evaluate the fracture toughness following the essential work of fracture methodology for ferrite-pearlite, bainite, ferrite-bainite, martensite and martensite-bainite microstructures. Results showed that bainitic microstructures have high fracture toughness, similar to TWIP and CP steels, which allows pointing them as potential candidates for obtaining high crash resistance in parts manufactured by press hardening.
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3.
  • Golling, Stefan, et al. (författare)
  • A comparative study of different failure modeling strategies on a laboratory scale test component
  • 2017
  • Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 37-46
  • Konferensbidrag (refereegranskat)abstract
    • Ultra-high strength steel (UHSS) has become a common material in the automotive industry during the last decades. The technique of press hardening allows modifying and tailoring the material properties of the blank in accordance with desired performance.In the present work, a laboratory scale test component is developed. On basis of tests on the component it is intended to investigate the deformation and fracture behavior of a boron alloyed steel after different heat treatments. The tooling is developed to allow the production of single phase microstructures like martensite and bainite as well as mixed microstructures containing ferrite. Testing of the component is performed in a standard tensile testing machine with additional digital speckle measurements to determine the strain to fracture in the critical cross section. The initial geometry shape introduces bending in the critical cross-section during tensile loading of the specimen.The aim of this work is to compare different material models on a component like level, including the prediction of failure. A finite element model of a laboratory scale component is analyzed using LS-Dyna. To compare different failure modeling approaches a set of damage models is calibrated to full hardened, martensitic steel. The deformation and fracture behavior of the component is presented in terms of load-displacement, plastic strain-stress triaxiality as well as in principal strain space.
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4.
  • Golling, Stefan, et al. (författare)
  • Determination of the essential work of fracture at high strain rates
  • 2017
  • Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 261-269
  • Konferensbidrag (refereegranskat)abstract
    • During the last decades, the use of ultra-high strength steel (UHSS) has increased as its favorable ratio between strength and mass allows the design of lighter body-in-white while maintaining passenger safety. Modeling impact loads of components made of UHS steel requires reliable descriptions of the material deformation and fracture behavior.Traditional stress or strain based fracture criteria are used in finite element modeling. A different approach in modeling fracture in components uses the fracture energy as a model parameter.Fracture toughness is difficult to measure in thin sheets; a method termed Essential Work of Fracture (EWF) provides the possibility to determine the fracture toughness in sheet metal. With knowledge of the fracture toughness the understanding of fracture behavior and crack propagation in ultra-high strength steel can be increased. The obtained EWF is related to the fracture energy and can be used in numerical models as a material parameter.In the present work results from preliminary testing are shown and a discussion on cross-head speed and strain rate in the critical specimen cross section is given. The use of digital image correlation provides information about the displacement field in the vicinity of the notch and hence about the strain- and strain rate distribution. Furthermore, the difficulties in reliable measurement of force and elongation in high speed tensile testing machines are elucidated. Issues encountered during the development of the high-speed DENT specimen are not limited to the specific geometry presented in this paper.The present work aims at the development of a test specimen to obtain the Essential Work of Fracture (EWF) at high test speed. This work contributes to the overall goal to model fracture behavior and crack propagation, dependent on the strain rate. For the investigation, a high-speed tensile testing machine equipped with an in-house developed load cell and an optical elongation measurement system was used with a high-speed camera to obtain data for digital image correlation.
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5.
  • Golling, Stefan, et al. (författare)
  • Modeling of multi-phase microstructures in press hardened components plastic deformation and fracture in different stress states
  • 2017
  • Ingår i: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596.
  • Tidskriftsartikel (refereegranskat)abstract
    • Hot stamping or press hardening is an industrialized technique with the aim of improving material properties by heat treatment and forming of a component in a single production stage. Within the field of press hardening the method of tailored material properties evolved. Components with tailored material properties possess different mechanical properties in designated areas. This paper presents an approach for modeling the mechanical response of mixed microstructures under different stress states. A homogenization method is used to predict the hardening of the material; the strain decomposition provides the possibility of applying a fracture criterion per phase. To validate the modeling approach for different stress states a set of samples with different notch and hole geometries as well as microstructural composition are produced. The combination of a homogenization method and a fracture criterion show good agreement with experimental results. The homogenization method is suitable to predict the hardening of the material with good accuracy. Fracture for different microstructural compositions is well predicted over a range of stress triaxialities relevant for sheet metal applications. It is concluded that the use of a homogenization method combined with a fracture model can be used to predict the mechanical response of mixed microstructures for a range of different stress states.
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8.
  • Jonsén, Pär, et al. (författare)
  • Fracture mechanics based modelling of failure in advanced high strength steels
  • 2017
  • Ingår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS<sup>2</sup>. - Warrendale, PA : Association for Iron & Steel Technology, AIST. - 9781935117667 ; , s. 15-23
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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9.
  • Oldenburg, Mats, et al. (författare)
  • Experiments with one-sided spray-cooling of steel plates for evaluation of thermo-mechanical material models
  • 1996
  • Ingår i: Quenching and the control of distortion. - Materials Park, Ohio : ASM International. - 0871705842 ; , s. 267-273
  • Konferensbidrag (refereegranskat)abstract
    • The quenching process of thin plates is studied. In many industrial applications of quenching, there is a need for simple tests for evaluation of analysis methods and material models for simulations. The presented study is part of a program for the simulation of the combined pressing and quenching process of thin-walled structures. This type of manufacturing process is used in, e.g., the production of side-impact protection beams for cars. By the use of an experiment with one-sided spray-cooling of a thin strip, large deformations can be studied and followed in time. The prediction of the deformation of the strip can be regarded as a one-dimensional problem where the curvature of the strip is sought. The thermo-mechanical behavior of the material can be evaluated throughout the time-history of the tests. In order to match the deformation of the plate, the material model must predict the temperature distribution through the thickness of the plate in each point in time, the phase transformations taking place in each layer of the thin plate and the stress and strain components in each layer. Experiments have been performed with a material (Inconel 600) without phase transformations in the actual temperature and time scale and with a material with only martensitic transformations. Analyses with a thermo-elastic-plastic material model with transformation plasticity included have been performed
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10.
  • Gavelin, Anders, et al. (författare)
  • Modelling and simulation of seat-integrated safety belts including studies of pelvis and torso responses in frontal crashes
  • 2007
  • Ingår i: International Journal of Crashworthiness. - Abingdon : Taylor & Francis. - 1358-8265 .- 1754-2111. ; 12:4, s. 367-379
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of the present study is to investigate how the physical properties influence the interaction of the seat back frame and the safety belt. Seat-integrated 3- and 4-point configurations with both non-rigid and rigid seat back frames were compared with common 3-point configurations with anchor points on the car body. The LS-DYNA FE-analysis software was used in order to perform frontal crash simulations with a belted 50th percentile Hybrid III FE-dummy model as occupant. The belt-webbing distribution between the lap and the torso belts via a slip-ring and in combination with a non-rigid seat back frame increases the ride-down efficiency compared to a system with no belt-webbing distribution. No tendencies of pelvis submarining were observed regardless of belt configuration. The dynamic response of the seat back frame has some influence on the ride-down efficiency.
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