A reaction-injection molding (RIM) material was selected for the rear bumper fascia of the Ford GT. As part of its performance criteria, the rear bumper fascia is required to withstand a 1.5 mph corner pendulum impact without sustaining permanent damage. Finite element modeling of this component was undertaken to predict whether the designed bumper fascia would meet the impact criteria. The mechanical properties of the material were required as input to the model, including the yield point and a representation of high strain rate behavior. The elastic limit for painted RIM material was determined in tension at 45deg to the extrusion direction at a nominal strain rate of 1 s(exp-1). With 'zero' permanent strain defined as 0.2% strain after 30 minutes of recovery as measured with an extensometer that has a system noise level of 0.1%-0.14% strain, yield occurs at approximately 14.0% strain and 20.7 MPa. If 'zero' permanent strain is defined as a 0.5% strain reading, which is a more practical level in the context of the bumper impact test criteria, then the elastic limit would extend to approximately 15.5% strain. The corresponding yield stress would be 21.1 MPa. When tested beyond the elastic limit, it was observed that cracks or blemishes in the paint become visible to the naked eye at approximately 25.8% strain. The ultimate tensile strength and failure strain are approximately 25.5 MPa and 80% respectively. Painted and unpainted specimens at 45deg orientation have the same response within the elastic limit, for the 1 s(exp-1) rate considered. Beyond the elastic limit, there is still no apparent difference in response between painted and unpainted specimens, with the exception of one unpainted specimen having significantly greater ductility and consequently higher ultimate strength. Beyond the elastic limit, a reduction in strength and ductility may exist in painted specimens oriented at 90deg to the extrusion direction compared to those at 45deg. More testing would be required to determine the validity and statistical significance of this observation. Unpainted specimens at 180deg showed the same response within the elastic region as unpainted specimens at 45deg. Tests were not conducted beyond the elastic region on unpainted specimens 180deg (parallel) to the extrusion direction. To account for the strain rate sensitivity of this material, the Johnson-Cook material model represents the experimental data better than the Cowper-Symonds or Zerilli-Armstrong models. Based on the data generated in this study and the CAE analyses conducted by the GT team using an appropriate material model to represent the strain rate sensitivity of the RIM behavior, the fascia was predicted to pass the 1.5 mph bumper impact test (NHTSA (49 CFR) Part 581 Bumper Standard). The fascia successfully passed the physical test in July 2003.


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    Title :

    Material behavior for modeling bumper impact


    Contributors:


    Publication date :

    2004


    Size :

    5 Seiten, 9 Bilder, 2 Tabellen, 1 Quelle




    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




    Material Behavior for Modeling Bumper Impact

    Rehkopf, Jackie D. | SAE Technical Papers | 2004


    Material Behavior for Modeling Bumper Impact

    Rehkopf, J. D. / Society of Automotive Engineers | British Library Conference Proceedings | 2004


    Material behavior for modeling bumper impact

    Rehkopf,J.D. / Ford Motor,US | Automotive engineering | 2004


    Material Behavior for Modeling Bumper Impact

    Rehkopf, J. D. / Society of Automotive Engineers | British Library Conference Proceedings | 2004


    2004-01-0010 Material Behavior for Modeling Bumper Impact

    Rehkopf, J. D. / Society of Automotive Engineers | British Library Conference Proceedings | 2004