基于延性耗竭的蠕变损伤模型预测含缺陷聚乙烯管接头长期性能

聚乙烯（PE）燃气管常因热熔对接接头中存在焊接缺陷而发生事故，给城市公共安全带来了严重隐患，但迄今没有方法可以有效预测各种焊接缺陷对PE管热熔对接接头长期性能的影响。基于延性耗竭的蠕变损伤模型可能是较好的方法，可是模型中的多轴蠕变延性因子是基于空洞幂律长大理论建立的，并未考虑PE管蠕变损伤产生银纹的影响，因而不能直接用于PE管。本项目拟以PE管热熔对接接头为研究对象，通过蠕变试验，建立与应力水平相关的蠕变本构和蠕变延性模型，根据测出的单轴蠕变延性和多轴蠕变延性修正多轴蠕变延性因子，进而建立适用于PE管的基于延性耗竭的蠕变损伤模型，把建立的模型耦合到有限元软件模拟含焊接缺陷试样的蠕变断裂试验，与试验结果对比，验证模型的准确性。通过建立的基于延性耗竭的蠕变损伤模型，可以模拟预测各种焊接缺陷对PE管热熔对接接头长期性能的影响，为含焊接缺陷PE管热熔对接接头长期性能的安全评定提供理论模型。

Accidents usually occur in butt fusion welded joints for polyethylene (PE) gas pipes due to the existence of welding defects. These affect seriously the city public security. However, there is currently no way to effectively predict the effects of all kinds of welding defects on the long-term performance for butt fusion welded joints of PE pipes. The creep damage model based on the ductility exhaustion is possibly an effective method, but multi-axis creep ductility factor in the model is derived based on the void growth controlled by power-law and does not take into account the craze which appears in the crack of PE materials when creep damage occurs. Therefore, the creep damage model based on the ductility exhaustion cannot be directly used for PE pips. In this project, butt fusion welded joints of PE pipes were researched. The creep constitutive and creep ductility model related to the stress level were established by creep test. Based on the measured uniaxial and multi-axial creep ductility, the multi-axis creep ductility factor was modified to the calculate the multi-axis creep ductility of PE pipes, and then the creep damage model based on the ductility exhaustion was established. The creep damage model was coupled into the finite element software to simulate the creep rupture test. The simulated results were compared with the test results to verify the accuracy of the creep damage model. Based on the established creep damage model, effects of all kinds of welding defects on the long-term performance for butt fusion welded joints of PE pipes can be predicted. Therefore, this project can provide the theoretical model for the safety assessment of the long-term performance for butt fusion welded joints of PE pipes with welding defects.