关键词: 抽油杆, 裂纹应力强度因子, 表面裂纹, 拉伸圆杆, 表面缺陷, 近似式, 裂纹形状, 自由表面边界, 影响系数, 杆体

Abstract: This article suggess a free surface boundary influence coefficient M in a sucker rod string, the partial surface defect is simplified to a partially elliptical surface crack. On the basis of an exact analytical solution of the stress intensity factor of an infinite elastic tension body with flat elliptical crack, the problem of a sucker rod string with partial surface defect is simplified to a problem of a round tension rod with partially elliptical surface crack. Assuming that the deformation of the surface crack in the round tension rod is a partial ellipsoid,the relation between M and center opening displacement Δ₀ of surface crack mouth are obtained.It is called simply as a M-Δ₀ equation. The coefficient functtion M (a/r, a/c) is obtained by using marking techniques in fatigue crack growth to delineate the different crack shanes, determining their corresponding displacement by experiments,computing the corresponding values M by M-Δ₀ equation, and making regression on data M in different crack shapes. Thus we get an approximate expression of the stress intensity factor of a sucker rod string with partial surface crack. A comparison of the numerical values on the deepest point of corresponding surface crack shape with the results in literature shows that they are somewhat con-sistant to each other.