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采用断裂力学方法和已知应力强度因子的标准试件，测定出待测试件的裂纹扩展速率和应力强度因子，用数学回归分析方法测定出Ｐａｒｉｓ公式中的材料系数，采用工程实际构件，通过试验得出了裂纹扩展速率随裂纹深度的变化规律。利用Ｐａｒｉｓ公式求出应力强度因子幅值ΔＫ，最后求出应力强度因子因数，比较了不同预紧力情况下应力强度因子因数的大小，得到的对应最小值时的预紧力，即最佳预紧力。
The crack growth rate and stress intensity factor of the test piece were measured by the method of fracture mechanics and the known stress intensity factor. The coefficient of material in the Paris formula was determined by the mathematical regression analysis method. By using the actual engineering components, The change rule of crack propagation rate with crack depth was obtained. The Paris formula is used to calculate the magnitude of stress intensity factor ΔK. Finally, the factor of stress intensity factor is calculated, and the factors of stress intensity factor under different preload conditions are compared. The pre-tightening force corresponding to the minimum value is obtained, Tight.