超高压容器典型裂纹自由表面处应力强度因子的计算方法改进

The stress intensity factor at the free surface is a core calculation parameter in the typical crack propagation and life prediction process of ultra-high-pressure vessels. Based on the segmented linear interpolation method, an improved method based on high-order polynomial fitting calculation was proposed. With blind bottom cracks as an example, stress data under different collected data volumes were fitted by means of polynomials of different orders; The stress intensity factors at the free surface of different cracks was calculated with this method, and the effects of polynomial orders and data amounts on the calculation results were explored; At different crack depth to length ratios, the differences between this method and the recommended linear interpolation method in previous literatures and the finite element method, were compared and analyzed. The results indicate that, as the polynomial order increases, the calculation results show a gradually approaching and converging trend. The minimum relative error of the calculation results for conventional cubic and high-order polynomial fitting is about -30%; As the collected data amount continues to increase, the calculation results gradually converge towards a stable value. Comparison of calculation results between the cases with less and more data shows that, the maximum relative error can reach about 11%. This method, with its calculation results, is basically consistent with the linear interpolation method in the previous literatures and the finite element method, and is suitable for dynamic crack propagation and life prediction processes.