Failure analysis and design improvement of high-pressure seal cone head for vehicle hydrogen engine

Abstract

As hydrogen energy vehicle technology advances, the performance requirements of vehicle hydrogen engine components become increasingly stringent. The high-pressure sealing cone head is a vital connection of the vehicle's hydrogen engine, however, it is easily fractured during the loading test. To address this issue, this research combines finite element modeling and material characterization methodologies to perform failure analysis and re-optimization design of the sealing cone head. First, the parameters for the CL toughness fracture criteria and the Johnson-Cook constitutive model were obtained by the inversion technique and the tensile test, respectively. On the cold heading formation process of the cone head, finite element analysis and microstructure analysis were performed. The results show that machining defects on the outer surface are the root cause of failure. Fatigue cracking is the main failure mechanism, and the crack gradually expands under the effect of alternating loads, which eventually causes a fracture of the cone head. At the same time, there are bending-type folding defects caused by the instability of the cone head under pressure. Second, the critical structural and process factors that impact the mechanical behavior of the components are investigated, and the orthogonal experiment optimization method is utilized to find the optimal process parameters, using the damage value as the evaluation index. According to the findings, the die angle has a major impact on the damage value, but the eligible die angle that is too small would negatively affect the force of the cone head and nut. Finally, a multi-station cold heading procedure for the high-pressure seal cone head was innovatively presented, and its mechanism of action was unveiled. The aforementioned defects were effectively addressed by the optimized process, and as compared to the pre-optimization, the maximum principal stress of the optimized component in the C-region was reduced by 27%, which did not exceed the tensile strength. At the same time, the spindle load was decreased by 25% and the maximum damage value was decreased by 48%, reaching the safe range. The optimized process effectively improves the performance of the part and increases the quality stability.