Design enhancements for stress relaxation in automotive multi-shell-structures

Recent attempt to enhance the safety against collision has reshaped the simple single-shell structure into the integrated multi-shell structure. Moreover, due to various regulations continuously tightened for environment, weight reduction of automobile becomes an increasingly important issue. Weight reduction is mainly accomplished by better redesign, adoption of lighter materials, and small-sizing of auto (parts). Focusing on the local redesign among three, we suggest local patching methods. We also present, as another way, a method of determining thicknesses of subpart-shells in an integrated multi-shell structure. Those redesign methods successfully bring a preset amount of stress relaxation. More specifically, we first select a cross member as local patching model. Based on the finite element stress calculations, we relieve the stress of cross member by patching in two ways-non-uniform thickness patching and optimized uniform thickness patching. The latter is more effective and practical. Selecting a box type subframe as other redesign model, we determine the thickness of each subpart-shell by axiomatic design approach. The patching methods and the axiomatic approach of this work can be extended to the other multi-shell structures such as center member and lower control arm.