聚乙烯压力管道裂纹快速扩展性及止裂性分析.docx

中文摘要
聚乙烯(PE)压力塑料管道目前应用已经十分广泛,但由于其低温时易出现裂纹快速扩展,而且其破坏一般都具有突发性的特点,难以预防。所以对其裂纹扩展和止裂的研究就显得十分重要。
本文对几种测试裂纹扩展的方法作了陈述与比较,并对小尺寸试验方法的试验装置作了详细的介绍,同时采用小尺寸稳态(S4)的试验方法,测试了在不同温度下裂纹扩展长度随压强的变化情况,同时也测试了在不同压强下裂纹扩展长度随温度的变化情况。并通过计算分析确定了裂纹快速扩展的临界压强和临界温度。给出了影响该试验结果的一些因素如温度、压力、介质、裂纹扩展速度、及裂纹尖端的流体减压等。
本文陈述了几种与裂纹快速扩展和止裂相关的动态断裂理论,对裂纹扩展和止裂的判断准则作了讨论,给出了管道开裂的机理。管道中裂纹能否扩展主要是由裂纹扩展驱动力G和裂纹扩展阻力G。决定。裂纹扩展驱动力可通过有限元节点力释放的方法和能量平衡理论求解,而裂纹扩展阻力只与材料性能有关。
因为塑料管道的开裂是很难绝对避免的,所以对裂纹扩展后的止裂研究就显得尤其重要。文中对止裂相关的三种止裂观点即静态观点、动态观点和能量观点作了介绍,指出止裂的唯一途径就是降低裂纹扩展驱动力或增加裂纹扩展阻力。并通过试验测试了焊缝以及套筒对塑料管道开裂的影响。最后给出了塑料管道在实际运行中的一些具体的止裂措施如在某些截面施加外压力、或是加进韧性较大的管段、改变轧制方向等,这些都会提高抵抗裂纹扩展的特性。
关键词:聚乙烯 裂纹快速扩展 小尺寸稳态流体减压 止裂 裂纹扩展驱动力
动态断裂阻力 轧制方向 韧性
ABSTRACT
At present,Polyethylene(PE)pressurized plastic pipelines have been extensively used,but at lower temperature,rapid crack propagation(RCP)will happen easily. Furthermore the destructive effect is abrupt and very dimcult to the
research on rapid crack propagation and arrest is very important.
This paper makes some statements parisons of several test methods measuring crack propagation,and gives a detailed introduction about test device of small scale steady state(S4),at the same time adopting S4 test method,testing how crack propagation length changes with the pressure at different temperature,and how it changes with the temperature at different the critical pressure and the critical temperature of RCP by calculation and illustrating such factors influencing this experiment as temperature,pressure,medium,crack propagation velocity and fluid pression ahead ofthe crack tip.
Several dynamic analysis theories relating to rapid crack propagation and arrest are presented in this paper,and the criteria for crack propagation and arrest has been discussed,then explaining the crack propagation mechanics of plastic pipelines.
Whether the crack Can propagate is mainly determined by crack driving force G and
dynamic fracture resistance driving force G