Fatigue life analysis of fillet weld with root gap in bogie tie rod seat under road traffic load

The results of failure analysis on the fillet welds of the tie rod seat in HDX2 type vehicle showed that size of root gap around cracks was usually larger than that observed in the region without cracks. Dynamic strain gauges were used to measure the time-strain curve of the zone surrounding the fillet weld in the locomotive traveling process. Then, a transfer matrix was utilized to calculate the time-strain curve of fillet welds and then a rainflow counting method was adopted to obtain hierarchical load spectra in the traveling process, which was used for predicting fatigue damage of fillet welds and safe service mileage. To reveal the influence of the root gap on the fatigue life of fillet welds, a three-factor and five-level orthogonal scheme was designed by taking the height, width and length of the root gap as variables. The calculation results based on road traffic loads indicated that: (1) When there is no gap at the root of fillet weld, the safe service mileage can meet standard requirements; when there is a gap at the root of the fillet weld, the safe service mileage is significantly shortened; (2) When the width, height or length of the root gap of fillet weld increases, the safe service mileage decreases monotonously. Given the same change in size, effect of the change in height of root gap on safe service mileage is the most significant among the three variables considered; (3) The maximum stress at straight line section of weld path was significantly greater than that at the corner section; (4) An inspection and maintenance program for root gaps of various sizes was developed.