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Numerical Analysis of Creep Fracture Behaviour of Medium Density Polyethylene

The increasing application of polymeric materials, especially of polyethylene, as structural materials demands new methodologies for assessing the material capability to withstand loads. The use of medium density polyethylene (MDPE) pipes for water and gas distribution is one of the most common examples. An accurate modelling of fracture and viscoelastic material responses of such structures represents a key to the prediction of structural integrity. Since polyethylene structures are mostly subjected to creep loadings, the present paper is concerned with the numerical modelling of creep fracture mechanisms by slow crack growth in MDPE [1]. The failure assessment philosophy for polymers is similar to philosophies for metals. Moreover, the J-integral equations can be used in principle to estimate the C*-integral by replacing the strain with the strain rate [2]. Based on the experimental data by Ben Hadj Hamouda et al. [3] and an analogy between plasticity and creep, the paper discusses a method used to develop an efficient computational strategy for modelling creep fracture mechanisms by slow crack growth in MDPE pipes. The derived algorithm is applied to the material point level of the available finite elements in the code ABAQUS [4] by using the user subroutine CREEP. The computational strategy is based on the time hardening integration approach. In order to check the accuracy of the derived algorithm, the creep simulation is performed on an axisymmetrically cracked specimen denoted as a full notched crack tensile (FNCT) specimen. A realistic material model of a FNCT specimen and a thick-walled MDPE pipe with an external axial surface crack subjected to internal pressure is employed for the calculation and estimation of the C*-integral.

finite element analysis; polyethylene; creep; C*-integral

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