Abstract: The fracture characteristics of X 60 steel pipeline were investigated experimentally by using CT specimens with thickness of 3mm, 6mm, 9mm, 12 mm and 15mm.The results indicate that the appearance toughness of X 60 steel is independent on the thickness of specimen due to the couple effect of delamination cracks and out-of-plane stress constraint in direction of specimen thickness.It is impossible to attain plane strain fracture toughness by increasing specimen thickness.The safety assessment on cracked pipeline by using test data of thickness of penetrated crack is not reliable.The plasticity modified stress intensity factor K_e and Jintegral were found to be equivalent in description of the crack growth on steel pipeline.The effects of thickness on the fatigue crack growth rates of X 60 pipeline steel were investigated experimentally by using CT specimen with thickness of 2mm, 4mm and 14 mm.The results indicate that effect of thickness on the fatigue crack growth rates is notable.The effect of thickness on fatigue crack growth rate is obvious when the thickness of specimen is less than 4mm.

Key words: pipeline, specimen thickness, lamination crack, fracture toughness, fatigue crack propagation, 3-D stress constraint

摘要： 对厚度分别为3mm、6mm、9mm、12mm、1mm的紧凑拉伸(CT)试样进行了断裂韧性试验,研究了X60管线钢的断裂特性.研究结果表明,由于试件厚度与分层裂纹间有强烈的耦合效应,表观断裂韧性不随厚度的变化而变化,靠增加试样厚度无法获得材料的平面应变断裂韧性,应用穿透裂纹的表观断裂韧性数据进行管道的安全评定不可靠;考虑塑性区修正的有效应力强度因子K_e与弹塑性J积分参量K_J在失稳扩展前保持了良好的等效性.对厚度分别为2mm、4mm和14mm的CT试样的疲劳裂纹扩展试验表明,高韧性管道钢的疲劳裂纹扩展存在显著的厚度效应,厚度效应敏感区在4 mm以内.

关键词: 管线, 试样厚度, 分层裂纹, 断裂韧性, 疲劳裂纹扩展, 三维应力约束