加载历史对聚乙烯管道损伤演化的影响

Influence of Loading History on Damage Evolution of Polyethylene Pipes

采用两步实验法研究了加载历史对聚乙烯管道力学性能和损伤演化规律的影响。在第1步实验中,通过单轴拉伸、蠕变和疲劳3种加载模式将聚乙烯缺口管道环式样拉伸到预先设定的预应变值。2个月后,第2步实验采用加载速度为0. 001 mm/min的单轴拉伸实验表征管道环式样力学性能的变化。实验结果表明:聚乙烯管道的屈服应力和切线模量随着第1步实验预应变的增大而减小,但残余塑性应变随着预应变的增大而增大。基于实验测得的切线模量的变化建立了聚乙烯管道的损伤演化方程,实验发现力学性能的衰减程度和损伤演化与第1步实验的加载模式(单轴拉伸,蠕变或者疲劳加载)和加载速度有关。

A novel two-step test method was developed to investigate the effects of loading history on mechanical properties and damage evolution of polyethylene(PE)pipe.In the first-step of test,each notched pipe ring specimen is stretched to a predetermined prestrain values using various loading histories,including monotonic tensile,creep and fatigue loading conditions.The second-step is to apply a monotonic tensile tests at a crosshead speed of 0.001 mm/min to characterize the correspondence change in mechanical properties two months after the first-step test.Experimental results show that yield stress and tangent modulus decrease and residual plastic strain increases with the increase of prestrain introduced in the first-step.The variation of experimentally measured tangent modulus was used to establish damage evolution law for PE pipe.It was also found that the deterioration of mechanical properties and damage evolution depend on loading mode(tensile,creep or fatigue)and loading speed(1 mm/min and 10 mm/min).