抽油杆螺纹段表面裂纹应力强度因子实验研究

AN INVESTIGATION ON STRESS INTENSITY FACTOR INSUCKER ROD THREAD SECTION WITH SURFACE CRACK

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 James-Anderson＇s method, we obtained experimentally the expression of stress intensity factor on the deepest point and surface point of partly elliptical surface crack on the root of thread section of sucker rod head in the case of pre-stressing. During the experiment, samples of 20CrMo steel 5/8＂sucker rod head thread section with pre-stressing were used and the pre-stress applied to the samples were controlled by a strain gage to model neads of enginerring Then, by using marking techniques to delineate the fatigue crack propagation of the source of defect on the cross section of a thread root, a series of data on crack fatigue ceack growth rates were obtained. By combining them with material properties with standard specimens in arfatigue fracture mechanics testing, the stress intensity factor amplitudes on the deepest point and surface point of a partialy elliptical surface crack of thread section root of the samples were obtained. We introduced the normalized coefficient Y_a, Y_s of stress intensity factor on the two points to obtain, a series of data Y_2, Y_s corresponding to surface crack shapes a/c and relative depth a/r. Finaslly, by means of matching technique the functions Y_a (a/r, a/c) , Y_s (a/r, a/c)were obtained.The expressions used for estimating the fatigue life of the samples, and the estimate agrees with experimental results. The expressions of stress intensity factor obtained in this paper are reasonable, and can be applied to engineering practice.