Accurate prediction of remaining fatigue life and formulation of condition repair procedure of high-speed train body

In order to reduce the cost of high-speed train operation and maintenance, improve operational safety, and extend the service life of structure, high-speed train service deterioration factors were considered. The method of vehicle system dynamics was adopted to calculate and formulate the load spectrum for the remaining life prediction of train body. A finite element model of train body and a proxy model of crack extension driving force at the focus points were established to achieve the mapping of the load spectrum of deterioration to the dynamic driving force of crack. Based on the advanced CJP model, a crack extension model considering the crack tip closure effect and stress ratio was established, and the relationship between the ranges of CJP stress intensity factor and conventional stress intensity factor was fitted. The Kriging agent model was used to accurately integrate the crack extension life, which further improved the accuracy of life prediction. On the basis of the remaining life prediction of train body, the modal strain energy was used as an indicator to monitor the crack state of high-speed train body. In addition, a condition level function was constructed to establish the corresponding relationship between the remaining life and the crack state. According to the crack monitoring results, the condition level was evaluated, and the consequences of continuous operation were predicted through risk assessment. The most economical repair strategy and repair procedure for high-speed train body were formulated according to the risk level. Research results show that the minimum and maximum values of load amplitudes after deterioration on the left and right sides of air spring are 107 and 122 kN. The maximum value of the load spectrum at the maximum degradation level increases by 6.16%. The structural stresses at the air conditioning mount (focus point 1) on the roof and the door corner position (focus point 2) have the same changing trend, increasing from 12.4 MPa to 15.8 MPa. This indicates that the stresses at the focus points increase with the deterioration of component performance, causing a great probability of failure. Based on the parameters in the CJP model and the International Institute of Welding (IIW) criteria, the calculated shortest remaining life mileages are both located at the connection position between the underframe beam and the longitudinal profile at the first end of train body (focus point 3), which are 6.781×10⁶ and 1.128×10⁷ km, respectively. This suggests that the remaining life calculated by the CJP model is more conservative. Through the systematic research on the service performance deterioration, structural life evolution, and condition course deterioration of high-speed trains, the mapping relationship between the remaining life and the fatigue state is established, and the method formulating the condition repair procedure of train body by combining the remaining life of train body with the operation and maintenance strategy is put forward, which is of great scientific significance for promoting the transformation of high-speed train maintenance mode from plan-based maintenance, fault-based maintenance to condition-based maintenance.