Estimation of the fatigue life and failure probability of welded joints in the railway bogie frames using the partial safety factor method (JIS B 9955–2017)

The present study aimed to clarify the relationship between the fatigue life under in-service conditions and the failure probability of welded joints in a railway bogie frame. Considering the effects of the stress ratio and weld toe radius, the authors determined the P–S–N curves by applying the fatigue data of cruciform as-welded joints to the Smith Watson Topper method. An estimation method for the probability of fatigue failure was proposed based on the partial safety factor method (JIS B 9955, 2017, JSME S 018, 2018). Subsequently, the following two concepts were introduced to the fatigue failure issue: one employed the accumulated fatigue damage and its criterion as an evaluation parameter, and the other employed the interval estimation of the scatter of the aforementioned damages based on the t-distribution. Therefore, the proposed method enabled the consideration of the deviation of the in-service cyclic stress. The method was applied to a vehicle using the modified Miner’s rule and the aforementioned P–S–N curves. Consequently, the failure probability increased with an increase in the mileage of the vehicle, and the relationship between the failure probability and the mileage varied because of the deviation of the in-service stress.