On Duty Simulation of a Trimmed Body Under Dynamic Loads: Modal Superposition Approach to Evaluate Fatigue Life

The prediction of fatigue induced failures on thin metal sheet structures subjected to random dynamic loads is a challenging task to perform through CAE tools; with this aim an integrated numerical methodology has been developed to evaluate the durability of a trimmed car body and the related damage distribution during fatigue tests. The method firstly evaluates the interaction between the dynamic behavior of the structure and the load spectrum, checking for potential overlapping among the structure natural frequencies and the loads main frequencies, with possible occurrence of resonance phenomena. Then the time-dependent stresses are computed combining in a transient analysis the stress mode shapes and the modal influence coefficients, superposing the static stresses induced by constant loads, thus obtaining the stress/strain time-histories needed in a high-cycle fatigue life evaluation.