New Approaches to Modal Transient Fatigue Analysis

Fatigue life estimates of automotive structures are often obtained using stress estimated from static solution methods such as inertia relief [1, 2]. This approach can provide reliable results if the natural frequencies of the system are at least twice that of the highest loading frequency. Direct and modal transient fatigue approaches would include dynamic effects but are not practical due to increased computer resource requirements.

This paper outlines a modified modal superposition based transient method. In this method, modal stress is obtained using a commercial FEA code. The transient solution is then obtained externally to significantly reduce computer requirements. Additionally, a numerical procedure is outlined which is capable of incorporating non-zero initial conditions for increased accuracy.