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The paper presents a method of analysis based on the theory of damage mechanics to quantify the degree of damage in an engineering structure under load. The method is incorporated into a Ford in-house finite element program called FCRASH that is applied to analyze the cumulative damage in a bumper under multiple low speed impacts. The numerical results calculated at the peak value of the contact force are compared with the test results. The FEA results are used to identify the locations of the hotspot in the bumper system and the predicted location where a potential crack would initiate. The microscopic observations showed damage in the area predicted with the finite element program after the specified number of impacts.

An important basis of the technology strategy of the Partnership of a New Generation of Vehicles (PNGV), is the assumption that major advances in a number of different technologies must be made, before the realization of most of the challenging goals of the new generation of vehicles. One of those technologies is the reliance on lightweight alternative materials in order to produce lightweight components to achieve the projected fuel economy increases. However, this push toward lightweight components should not be on the basis of sacrificing vehicle performance, handling, reliability or safety. Toward this objective, engineers frequently are relying on super-fast computers as well as new approaches to achieve a new generation of designs of automotive components, based on some form of optimization techniques. These techniques however, usually imply increasing the number of constraints imposed on a particular design objective, which is the weight of the vehicle in this case.

To design a cost, weight, and energy efficient bumper foam energy absorber, it is important to consider optimizing the shape of coring employed in the design of the system. In this paper, a number of foam coring patterns are studied by both empirical and analytical methods. The size and shape of proposed core designs are studied in detail with consideration given to several different densities of expanded polypropylene (EPP) foam. Using the finite element method of structural analysis, it is possible to have an inside look at the stress distribution during deformation of foam structures. An optimization study using the finite element method is conducted using the energy absorption ratio as an efficiency parameter. Several coring patterns are studied and recommended for bumper foam core design based on high energy absorption efficiency and low tear stress.