REMAINING LIFE ASSESSMENT OF HOOK TAIL FRAME IN RAILWAY HEAVY-HAUL WAGON BASED ON REAL LOADING SPECTRUM

With the increase in the operation scale and frequency of China heavy-haul railroad wagons, the failure fracture problem of hook tail frame is becoming more and more serious. In this work, domestic 16/17 type hook tail frame (forged E-grade steel) was used as a research object, the basic mechanical properties and fracture performances of forged E-grade steel were firstly obtained by systematic material tests; secondly, a finite element model of the hook tail frame with initial crack defects was established; finally, the remaining life prediction of the damaged hook frame was calculated by using the NASGRO equation based on the measured loading spectrum. The results show that when the crack shape ratio of 0.8, 0.5, 0.3, the calculated remaining life of the hook tail frame gradually decreases, and the calculated remaining life of the fatigue crack propagation from 2 mm to 20 mm is 360000 km, 320000 km and 260000 km, respectively, all of which are less than one depot maintenance period; the remaining life ratios of the three profile ratios are small after crack expansion to 12 mm, which are only 4.7%, 4.0%, and 2.2% of the total remaining serviceable mileage. Therefore, it is reasonable to take 12 mm as the damage tolerance of the hook tail frame for stopping crack. To investigate the effect of near threshold area on crack propagation life, reducing the initial crack size to 0.5 mm with a shape ratio of 0.5, when the crack is near the crack propagation threshold area, the calculated remaining service mileage increases to 1.56 million km, which is 4.9 times of the initial crack of 2 mm, including three maintenance periods. These results can provide a basic reference for the optimization and strategy of the inspection interval of the hook tail frame widely used for railway heavy-haul railroad wagons.