Multi-time scale fatigue FEA

Cylinder heads in truck engines are subject to thermo-mechanical fatigue during their operational life (Fig. 1). Investigating this phenomenon with conventional finite element (FE) analysis is computationally expensive due to the large number of cycles typically encountered in such a problem (Fig. 2).



MSc student: Maurice Beusink
Daily supervisors: Dr. ir. Ron Peerlings, Dr. ir. Varvara Kouznetsova, Ir. Juan-Carlos Pina
Project supervisor: Prof. dr. ir. Marc Geers

Dual-time scale FE methods split the single time scale t into a coarse time scale N (defined in terms of cycles) and a fine time scale τ (defined within one cycle) and compute the response of the model at hand with respect to the coarse time scale (Fig. 3).

In this thesis two dual-time scale methods are investigated in terms of efficiency and accuracy. The first is a wavelet based finite element (FE) method with implicit cycle scale time integration (CSTI). This is derived from literature and allows a number of displacement coefficients nnec to be dropped from the updating procedure and integrates with cycle scale time steps ΔN. The second method uses only this last feature, i.e. CSTI, and incorporates it in a conventional FE framework.

Several problems were simulated with both methods and the efficiency was compared (Fig. 4). For problems that consisted of large amounts of elements, the wavelet based method was up to 8 times faster than the conventional method with implicit CSTI. However it was prone to convergence issues when nnec and ΔN were not carefully adjusted to each other.