厚度与分层耦合效应对X60管线钢断裂韧性的影响

EFFECTS OF THICKNESS AND DELAMINATION ON FRACTURE TOUGHNESS OF X60 PIPELINE STEEL

通过对厚度分别为 ３， ６， ９， １２和 １５ ｍｍ的 ＣＴ试样的断裂韧性实验和微观断口分析，研究了 Ｘ６０高韧性管线钢的断裂韧性和裂纹扩展阻力曲线的厚度与分层裂纹耦合效应．结果表明，分层裂纹与厚度方向的离面应力存在约束互相作用，厚度增加，分层开裂加剧，局部有效厚度并未增加，导致断裂过程中裂纹端部的三维应力约束总是近平面应力的低约束状态，表观断裂韧性不随厚度变化．在有分层裂纹出现时，无法靠增加试样厚度获得材料的平面应变断裂韧性．由于分层与厚度的耦合作用与裂纹扩展方向与厚度方向的相对方位密切相关，应用穿透裂纹的表观断裂韧性数据进行管道结构的安全评定并不完全可靠研究还表明，塑性区修正的有效应力强度因子与弹塑性Ｊ积分参量在失稳扩展前保持良好的等效性。

The effects of thickness and delamination on the fracture toughness of X60 pipeline steel were investigated experimentally by using of compact tension specimens with thicknesses of 3, 6, 9, 12 and 15 mm. The couple effect of delamination cracks and out-of-plane stress constraint was discovered. Delamination became serious as thickness increasing, and the three-dimensional stress constraint near the crack-tip is nearly low-constraint plane stress state during fracture. Appearance fracture toughness is independent on thickness. It is impossible to attain plane strain fracture toughness by increasing specimen thickness when delamination cracks turn up. Because the couple effect of thickness and delamination is related closely with the relative direction of crack growth and thickness, the safe assessment of pipeline by using test data from through-thickness crack is not very reliable, The plasticity modified stress intensity factor K-e and J integral were found to be equivalent in description of the cracking growth of such ductile steel.