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

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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.