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本文以拉伸无限体中椭圆片裂纹应力强度因子的精确解析解为基础,引入抽油杆杆体自由表面边界影响系数M,并将抽油杆杆体局部表面缺陷简化为部份椭圆表面裂纹,于是就将有局部表面缺陷的抽油杆杆体问题简化为有部份椭圆表面裂纹的拉伸圆杆问题。在假设拉伸圆杆部份椭圆表面裂纹的变形为“部份椭球”的条件下,得到了M与该表面裂纹嘴中心张开位移Δ_0之间的关系,简称M-Δ_0公式,用变载勾线法勾画不同裂纹形状,用实验测定相应Δ_0,用M-Δ_0公式计算相应的M值,将不同裂纹形状下的M数据进行数学回归,得到了系数M(a/r,a/c)函数,从而得到了抽油杆杆体局部表面裂纹应力强度因子近似式。将对应的表面裂纹形状最深点的数值与文献的结果进行了比较,比较表明,二者大体一致。
Based on the exact analytical solution of the stress intensity factor of the elliptical crack in the infinite body, the influence coefficient M on the free surface boundary of sucker rod body is introduced and the partial surface defects of sucker rod body are reduced to some elliptical surface cracks. The problem of the sucker rod body with local surface defects is reduced to the stretch rod problem with the partial oval surface cracks. Under the assumption that the deformation of the oval surface crack of the extended round bar is “partial ellipsoid”, the relationship between M and the open center displacement Δ_0 of the surface crack nozzle is obtained, which is called M-Δ_0 formula, Load line method is used to sketch different crack shapes, the corresponding Δ_0 is determined experimentally, the corresponding M value is calculated by M-Δ_0 formula, and the M data under different crack shapes are mathematically obtained. The coefficients M (a / r, a / c ) Function, the approximate formula of the stress intensity factor of the local surface crack of sucker rod body is obtained. The corresponding values of the surface crack shape at the deepest point are compared with the results of the literature. The comparison shows that the two are generally in agreement.