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Traditionally, vehicle durability cracks have been treated to be local problems as a result of poor designs of notches, welds, holes, corners or reinforcements. The problems were usually found and fixed at a late design stage which often resulted in weight and cost penalties for a vehicle program. However, in many instances, the local problems mentioned above are simply the consequence of a poor global design. The global problems can generally be grouped into three categories: stress induced fatigue problems due to excessive global stresses as a result of body structural discontinuities, load induced fatigue problems due to excessive loads input to a body as a result of suspension designs, and vibration induced fatigue problems due to unfavorable structural resonance. The current paper presents a CAE analysis process which can be used at the upfront design stage to assess vehicle durability performances from a global design point of view.

Due to several indeterminate factors, the assessment of the durability performance of a vehicle body is traditionally accomplished using test methods. An analytical fatigue life prediction method (four-step durability process) that relies mainly on numerical techniques is described in this paper. The four steps comprising this process include the identification of high stress regions, recognizing the critical load types, determining the critical road events and calculation of fatigue life. In addition to utilizing a general purpose finite element analysis software for the application of the Inertia Relief technique and a previously developed fatigue analysis program, two customized programs have been developed to streamline the process into an integrated, user-friendly tool. The process is demonstrated using a full body, finite element model.