도시형 전동차 언더프레임 피로균열성장 해석

초록

A fatigue crack, initiated at an under-frame of electric multiple unit(EMU), will be propagated if proper maintenance action has not been performed. In this research, we predict the critical crack size and the fatigue crack growth rate of cracked under-frame of EMU by applying linear elastic fracture mechanics. For this purpose, we build a FE model of car-body which has a virtual crack in the center sil to calculate the stress intensity factor. The virtual cracks with various size are modeled at the cross section between center sil and cross beam. The critical crack size and crack growth rate under the normal operating condition are calculated. The critical crack size at the critical point of center sill with given loading condition is calculated as 90.00 mm. Fatigue crack growth rate is predicted by measuring the dynamic stress amplitude at the critical point during normal operation in commercial line and performed fatigue crack growth analyses until an initial crack reaches the critical crack. We can calculate that an initial crack size as 30 mm takes 7.6 years(with HAZ material), 4.6 years(with post tempered HAZ material) to reach the critical crack size, respectively