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使用James-Anderson方法,通过实验得到了抽油杆杆头螺纹段带预紧力情况下螺纹根部部分椭圆表面裂纹最深点和表面点的应力强度因子表达式。实验过程中,把20CrMo钢5/8英寸抽油杆杆头螺纹段带预紧力的试件,用应变片控制施加的预紧力使之满足工程实际,然后用降载勾线技术描绘出了螺纹根部横截面上缺陷源的疲劳扩展线,由此取得了一系列疲劳裂纹扩展速率数据,并结合疲劳断裂力学标准试样测定的材料性能,得出试件螺纹段螺纹根部部分椭圆表面裂纹最深点和表面点的应力强度因子幅值。再引入这二点应力强度因子正则系数Ya、Ys,又得出一系列相对于顿裂纹形状a/c,和相对深度a/r的Ya、Ys数据。再用拟合法得到函数Ya(a/r,a/c),于是得出应力强度因子表达式。将表达式用于估算试件的疲劳寿命,估算表明,与实验结果符合。证明表达式的正确性,可以在工程上实用。
By using the method of James-Anderson, the stress intensity factor expression of the deepest point and the surface point of the oval surface crack in the root part of the root of the sucker rod rod under the condition of pre-tightening is obtained. During the experiment, the specimen with 20% pre-tensioned on the threaded section of the 5/8 "sucker rod of 20CrMo steel was controlled by the strain gauge to make it meet the requirements of engineering practice. Then, A series of fatigue crack growth rate data were obtained from the fatigue extension line of the defect source on the root section of the thread. Combined with the material properties measured by the standard specimen of fatigue fracture mechanics, the elliptical surface crack at the root of the thread section of the specimen was obtained The deepest point and surface stress intensity factor amplitude. After introducing these two regularity factors Ya, Ys of stress intensity factor, a series of Ya, Ys data about the shape of a crack c / a and the relative depth a / r are obtained. Then the function Ya (a / r, a / c) is obtained by the fitting method, so the stress intensity factor expression is obtained. The expression is used to estimate the fatigue life of the specimen, and the estimation shows that it is in good agreement with the experimental result. Prove the correctness of expressions can be practical in engineering.