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This paper gives an overview of an ongoing program of work aimed at developing a new life assessment methodology for bonded and weld bonded automotive structures. The approach involves the integration of three key requirements: environmental resistance, fatigue behavior in fracture mechanics terms and finite element analysis of joint design. A relatively simple laboratory fatigue test, suitable for typical automotive sheet materials, has been developed to assess the interaction of fatigue loading with environmental effects. From this, data are derived to: (a) compare the effects of various environmental conditions on adhesive systems, and (b) provide fundamental fracture mechanics data that can be used in the analysis of structures. The required fracture mechanics parameters for structures are obtained using finite element analysis (FEA). Validation of the method has been carried out by correlating the measured fatigue life of model automotive structures with the predicted behavior.

A key challenge in engineering design with elastomers for automotive applications, such as chassis suspension mounts and engine mounts, is to integrate fatigue life calculations into the design process. This will be required for life cycle engineering but is a difficult and complex task and this paper will outline some recent progress that has been made using a fracture mechanics approach together with a new finite element code, FLEXPAC, developed especially for this purpose. Finite element analysis enables the fracture mechanics approach to be generalised in principle to any geometry. In practice, however there have been serious difficulties in obtaining numerical solutions when rubber components containing internal cracks, whose surfaces are in contact, are modelled with large deformations and non linear elasticity properties. The overall problem has been approached in three parts. First, materials models are input for elasticity, stress softening and fatigue crack growth behaviour.