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

本建议针对聚乙烯(PE)材料在建筑行业中的适用性对其失效进行建模。为了安全地将PE和类似聚合物用作建筑材料，PE的长期性能可能是需要解决的最关键的问题。PE的长期性能和失效(慢裂纹扩展、蠕变断裂或屈服)直接关系到其环境应力抗裂性(ESCR)，这是在实验室条件下测定的。然而，ESCR与聚乙烯在实际条件下的结构性能之间的关系还没有得到很好的理解。建议的研究将包括：1)根据影响每种测试的物理现象来分析和评价ESCR测试方法；2)根据ESCR测试结果和PE的分子结构确定合理的失效准则；3)将这些失效准则应用于宏观力学时间相关本构方程；以及4)将本构方程应用于有限元分析程序。这项研究将通过在分子、微观机械和宏观力学水平上研究蠕变、塑性变形和破坏的机理来完成。我们将建立微观和宏观水平之间的关系。这些目标将通过一个全面的研究计划来实现，该计划将包括实验室测试(化学和机械)以及发展聚合物材料的理论力学模型。建议的研究项目是滑铁卢大学开展的一个更大的研究计划的一部分，该计划侧重于将聚合物的化学和力学性能联系起来。其目标是开发合理的本构配方，这对于聚合物在结构中的实际应用是必要的，并在已知所需(所需)机械性能的情况下指定适当的制造和成型工艺，从而能够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.