Environmental stress crack resistance of structural polyethylene: modelling long-term material performance

本提案解决了聚乙烯（PE）在建筑行业中材料适用性背景下的失效建模。为了安全使用PE和类似聚合物作为建筑材料，PE的长期性能可能是需要解决的最关键问题。PE的长期性能和失效（慢裂纹扩展、蠕变破裂或屈服）与其环境应力抗裂性（ESCR）直接相关，而ESCR是在实验室条件下确定的。然而，在实际条件下，ESCR与聚乙烯结构性能之间的关系尚不清楚。拟开展的研究包括：1)从影响各类试验的物理现象方面对ESCR试验方法进行分析和评价；2)根据ESCR试验结果和PE的分子结构确定合理的失效准则；3)将这些失效准则纳入宏观力学时效本构公式；4)将本构公式纳入有限元分析程序。该研究将通过在分子、微观和宏观力学水平上检查蠕变、塑性变形和破坏的力学来完成。建立微观与宏观的关系。这些目标将通过一个全面的研究计划来实现，这将包括实验室测试（化学和机械）以及聚合物材料的理论力学模型的发展。该研究项目是滑铁卢大学开展的一项更大的研究计划的一部分，该计划的重点是将聚合物的化学和机械特性联系起来。目标是开发合理的本构配方，这是聚合物在结构中的实际应用所必需的，并在已知所需（期望）机械性能时指定适当的制造和成型工艺，从而为特定应用生产改进的材料。

This proposal addresses modelling of failure of polyethylene (PE) in the context of the applicability of this material for the construction industry.  Long term performance of PE is likely the most critical issue that needs to be addressed in order to safely use PE and similar polymers as construction materials. Long term performance and failure (slow crack growth, creep rupture or yield) of PE are directly related to its environmental stress crack resistance (ESCR), which is determined in laboratory conditions. However, the relationship between ESCR and the structural performance of polyethylene in real conditions is not well understood.The proposed research will involve: 1) analysis and evaluation of ESCR testing methods in terms of the physical phenomena influencing each type of test, 2) determination of rational failure criteria based on ESCR test results and molecular structure of PE, 3) implementation of these failure criteria into macromechanical time-dependent constitutive formulations, and 4) implementation of the constitutive formulations into finite element analysis procedures. The study will be done by examining mechanics of creep, plastic deformations and failure on the molecular, micro-mechanical and macro-mechanical levels.  The relationship between micro- and macro-levels will be established.  The objectives will be realized by a comprehensive research program, which will include laboratory testing (both chemical and mechanical) as well as the development of theoretical mechanical modelling for polymeric materials.  The proposed research project is part of a larger research initiative carried out at the University of Waterloo that focuses on linking chemical and mechanical properties of polymers.  The goals are developing rational constitutive formulations, necessary for practical utilization of polymers in structures and specifying appropriate manufacturing and molding processes when the required (desired) mechanical properties are known, allowing to produce improved materials for specific applications.