Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1998
A finite element (FE)-based computational model is developed for the calculation of residual stre... more A finite element (FE)-based computational model is developed for the calculation of residual stresses in steel as induced by a local thermal shock. Subroutines to handle phase transformations and constitutive behaviour including volumetric expansion and transformation-induced plasticity are added to a commercial FE code. Sliding contact problems with application to railway technology are studied. Six examples of wheel flat formation are investigated in detail. In all of them rather high tensile stresses are found in the wheel rim in a domain below the top layer of phase transformations. For those combinations of train speed, wheel load and sliding duration, where the brittle martensite phase is found, surface cracks are likely. The predicted tensile stresses may propagate these cracks further into the rim material and thus cause spalling.
The engineering design of a floor pan structure to meet existing requirements on torsion and bend... more The engineering design of a floor pan structure to meet existing requirements on torsion and bending stiffness of a reference steel floor while reducing its weight by 50% and the number of parts by 70% is discussed here. The crashworthiness of the composite floor pan design is evaluated by means of the commercial PAMCRASH explicit Finite Element software package by reproducing the same loading and support conditions of the EuroNCAP pole side impact crash test. The numerical results are then compared against the experimental data from two crash tests and the results confirm that a good degree of confidence can be used in the numerical simulation of the crash behaviour of textile composites.
ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust ... more ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1998
A finite element (FE)-based computational model is developed for the calculation of residual stre... more A finite element (FE)-based computational model is developed for the calculation of residual stresses in steel as induced by a local thermal shock. Subroutines to handle phase transformations and constitutive behaviour including volumetric expansion and transformation-induced plasticity are added to a commercial FE code. Sliding contact problems with application to railway technology are studied. Six examples of wheel flat formation are investigated in detail. In all of them rather high tensile stresses are found in the wheel rim in a domain below the top layer of phase transformations. For those combinations of train speed, wheel load and sliding duration, where the brittle martensite phase is found, surface cracks are likely. The predicted tensile stresses may propagate these cracks further into the rim material and thus cause spalling.
Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 1999
Extensive field experiments (the ‘Silinge wheel flat experiments’) with a moving train have been ... more Extensive field experiments (the ‘Silinge wheel flat experiments’) with a moving train have been designed, performed (at Silinge) and evaluated. More than 200 wheel flats were formed under controlled conditions involving different wheel loads, train speeds and sliding durations, and the friction coefficient between the wheel and the rail was also varied (and indirectly measured). Samples extracted from flats of the tested wheels have been metallographically examined with respect to phase transformations and cracks. A numerical model for wheel flat prediction has been qualitatively verified and quantitatively calibrated. In the experiments, martensite was found beneath all flats and cracks were observed in most cases. It is concluded that the risk for future spalling should be considered for all wheelsets with flats. A damaged wheelset should be taken out of service as quickly as possible. When reprofiling the wheels, all martensite and an additional layer of several millimetres shou...
The engineering design of a floor pan structure to meet existing requirements on torsion and bend... more The engineering design of a floor pan structure to meet existing requirements on torsion and bending stiffness of a reference steel floor while reducing its weight by 50% and the number of parts by 70% is discussed here. The crashworthiness of the composite floor pan design is evaluated by means of the commercial PAMCRASH explicit Finite Element software package by reproducing the same loading and support conditions of the EuroNCAP pole side impact crash test. The numerical results are then compared against the experimental data from two crash tests and the results confirm that a good degree of confidence can be used in the numerical simulation of the crash behaviour of textile composites.
ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust ... more ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.
ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust ... more ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.
International Journal of Mechanical Sciences, 2014
ABSTRACT Prediction of failure in metal sheets is an important topic for the sheet forming commun... more ABSTRACT Prediction of failure in metal sheets is an important topic for the sheet forming community, as well as for the automotive crash community. The word ‘failure’ can have different meaning for different individuals within these communities. Methods for failure prediction within this area can either focus on the prediction of plastic instability (necking), or on the actual fracture phenomenon. The pros and cons of these approaches are discussed in this paper. The current authors have chosen to favour methods for necking prediction. The traditional method for necking prediction is to use a limit curve in the principal strain space (FLD). The great disadvantage of this approach is that it is only applicable for linear strain paths. In fact, the necking phenomenon can be shown to be strongly strain path dependent. In the current report, four different numerical methods for instability prediction are discussed, and compared in applications to some simple problems involving broken strain paths. It is shown that these methods can yield dramatically different results in some particular cases. Based on the findings of this study, the paper concludes with some recommendations for how the failure prediction problem best can be handled in industrial sheet forming and crash simulations.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1998
A finite element (FE)-based computational model is developed for the calculation of residual stre... more A finite element (FE)-based computational model is developed for the calculation of residual stresses in steel as induced by a local thermal shock. Subroutines to handle phase transformations and constitutive behaviour including volumetric expansion and transformation-induced plasticity are added to a commercial FE code. Sliding contact problems with application to railway technology are studied. Six examples of wheel flat formation are investigated in detail. In all of them rather high tensile stresses are found in the wheel rim in a domain below the top layer of phase transformations. For those combinations of train speed, wheel load and sliding duration, where the brittle martensite phase is found, surface cracks are likely. The predicted tensile stresses may propagate these cracks further into the rim material and thus cause spalling.
The engineering design of a floor pan structure to meet existing requirements on torsion and bend... more The engineering design of a floor pan structure to meet existing requirements on torsion and bending stiffness of a reference steel floor while reducing its weight by 50% and the number of parts by 70% is discussed here. The crashworthiness of the composite floor pan design is evaluated by means of the commercial PAMCRASH explicit Finite Element software package by reproducing the same loading and support conditions of the EuroNCAP pole side impact crash test. The numerical results are then compared against the experimental data from two crash tests and the results confirm that a good degree of confidence can be used in the numerical simulation of the crash behaviour of textile composites.
ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust ... more ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 1998
A finite element (FE)-based computational model is developed for the calculation of residual stre... more A finite element (FE)-based computational model is developed for the calculation of residual stresses in steel as induced by a local thermal shock. Subroutines to handle phase transformations and constitutive behaviour including volumetric expansion and transformation-induced plasticity are added to a commercial FE code. Sliding contact problems with application to railway technology are studied. Six examples of wheel flat formation are investigated in detail. In all of them rather high tensile stresses are found in the wheel rim in a domain below the top layer of phase transformations. For those combinations of train speed, wheel load and sliding duration, where the brittle martensite phase is found, surface cracks are likely. The predicted tensile stresses may propagate these cracks further into the rim material and thus cause spalling.
Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 1999
Extensive field experiments (the ‘Silinge wheel flat experiments’) with a moving train have been ... more Extensive field experiments (the ‘Silinge wheel flat experiments’) with a moving train have been designed, performed (at Silinge) and evaluated. More than 200 wheel flats were formed under controlled conditions involving different wheel loads, train speeds and sliding durations, and the friction coefficient between the wheel and the rail was also varied (and indirectly measured). Samples extracted from flats of the tested wheels have been metallographically examined with respect to phase transformations and cracks. A numerical model for wheel flat prediction has been qualitatively verified and quantitatively calibrated. In the experiments, martensite was found beneath all flats and cracks were observed in most cases. It is concluded that the risk for future spalling should be considered for all wheelsets with flats. A damaged wheelset should be taken out of service as quickly as possible. When reprofiling the wheels, all martensite and an additional layer of several millimetres shou...
The engineering design of a floor pan structure to meet existing requirements on torsion and bend... more The engineering design of a floor pan structure to meet existing requirements on torsion and bending stiffness of a reference steel floor while reducing its weight by 50% and the number of parts by 70% is discussed here. The crashworthiness of the composite floor pan design is evaluated by means of the commercial PAMCRASH explicit Finite Element software package by reproducing the same loading and support conditions of the EuroNCAP pole side impact crash test. The numerical results are then compared against the experimental data from two crash tests and the results confirm that a good degree of confidence can be used in the numerical simulation of the crash behaviour of textile composites.
ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust ... more ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.
ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust ... more ABSTRACT In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.
International Journal of Mechanical Sciences, 2014
ABSTRACT Prediction of failure in metal sheets is an important topic for the sheet forming commun... more ABSTRACT Prediction of failure in metal sheets is an important topic for the sheet forming community, as well as for the automotive crash community. The word ‘failure’ can have different meaning for different individuals within these communities. Methods for failure prediction within this area can either focus on the prediction of plastic instability (necking), or on the actual fracture phenomenon. The pros and cons of these approaches are discussed in this paper. The current authors have chosen to favour methods for necking prediction. The traditional method for necking prediction is to use a limit curve in the principal strain space (FLD). The great disadvantage of this approach is that it is only applicable for linear strain paths. In fact, the necking phenomenon can be shown to be strongly strain path dependent. In the current report, four different numerical methods for instability prediction are discussed, and compared in applications to some simple problems involving broken strain paths. It is shown that these methods can yield dramatically different results in some particular cases. Based on the findings of this study, the paper concludes with some recommendations for how the failure prediction problem best can be handled in industrial sheet forming and crash simulations.
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Papers by Johan Jergéus