Strength and life assessment of TC4 titanium alloy welded frame for high-speed railway vehicles

The hardness distribution, basic mechanics and high cycle fatigue properties of TC4 titanium alloy base metal and welded joint were obtained by TIG arc welding test. The finite element simulation model of titanium alloy welded bogie frame with pseudo-axis was established, and the static and fatigue strength of the new TC4 titanium alloy and the existing S355 weathering steel frame was checked respectively. Based on the experimental fatigue load spectrum and Miner linear fatigue cumulative damage theory, the fatigue life of TC4 titanium alloy and S355 weathering steel bogie frames was evaluated respectively. The results show that the safety factor of the minimum static strength of titanium alloy and weathering steel bogie frame is 2.8 and 1.5 respectively, which are both greater than the safety factor threshold and meet the design requirements. Both the critical safety location of titanium alloy and weathering steel bogie frame were within the envelope range of modified Goodman fatigue limit diagram, which meets the design requirements. In addition, the envelope space of TC4 titanium alloy Goodman fatigue limit diagram was much larger than S355 weathering steel. Under typical level 8 load spectrum, if the annual operation is estimated to be 30 × 10⁷ km, all critical location of the bogie frame could meet the design requirements of 35 years of service life, and the estimated life of TC4 titanium alloy bogie frame is about 2 times than that of S355 weathering steel bogie frame. The research can provide scientific basis for the strength and structure design of bogie frame with higher speed and safety level.