Assessment method of COD for a surface flaw at a structural discontinuity

我们首先建立了单边裂纹板(SC)的弹塑性COD，它是表面裂纹的横截面，受拉(Sigma_M)，由中心裂纹板(CC)的COD和偏心受弯曲应力(m*)的单边裂纹板的COD叠加得到。结果表明，应力为Sigma_m+0.75m*的Cc的COD与应力为m*的Sc的COD叠加得到Sc的Sigma_m的COD。在上述处理中，m*/sigma_m是sigma_m/sigma_y(sigma_y：屈服应力)的函数，当出现总屈服时，m*/sigma_m随sigma_m增加到零而减小。然后，根据表面裂纹工作张力和弯曲最深处的K值，得到表面裂纹横截面的工作拉应力和弯曲应力。采用简化梁理论，给出了混凝土在拉弯联合作用下的孔洞屈服应力计算方法，并将该方法应用于海洋结构T型管节点冠部表面缺陷的计算。表面中心的化学需氧量估计值与实验值吻合较好。结果表明，对于三点弯曲CTOD试验，由缺口尖端R端位移定义的CTOD在高工作应力情况下往往比Dugdale模型和铰链模型所定义的CTOD更小。

We invested at first that elasto-plastic COD's for a single edge cracked sheet(SC), which is a cross section of a surface crack, subjected to tension(sigma_m) were given by some superposition of COD's for a center cracked sheet(CC) subjected to tension and COD's for a single edge cracked sheet subjected to bending stress(m*) by eccentricity. As a result, COD's for SC by sigma_m are obtained by superposition of COD's for CC subjected to tens ion which stress is sigma_m plus 0.75m* and COD's for SC subjected to m*. In above treatment,m*/sigma_m is a function of sigma_m/sigma_y(sigma_y:yield stress) and decreases as sigma_m increases to zero when gross yield occurs.Then working tension stress and bending stress for a cross section of a surface crack are obtained by K value at the deepest point of a surface crack working tension and bending. By adapting a simplified beam theory, aperient yield stress for SC due to bending in case of combined tension and bending is introduced.This estimating method of COD's is applied to a surface flaw in a crown part of T tubular joint of an offshore structure. Estimated COD's at a center of a surface are in good agreement with experimental ones. As a result, it becomes clear that CTOD defined by the displacement of R end of a notch tip is tend to give smaller value in case of high working stress than CTOD defined by Dugdale model and hinge model for 3 point bending CTOD testing .