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The Creep and Fracture Behaviour of the Polyethylene PE100

The pipes for water and gas distribution are mainly made of polyethylene. An accurate modelling of the nonlinear and time-dependent material responses of such structures represent a key for the prediction of structural integrity and reliability, as well as their design and optimization process. In the present paper the creep fracture mechanisms by slow crack growth in polyethylene PE100 are investigated, both experimentally and numerically. Experimental tests have been performed on the standard specimen type 1BA and axisymmetrically cracked specimen denoted as a full-notched crack tensile (FNCT) specimen [1]. Based on the experimental results, the primary/secondary creep constitutive model is proposed. It is shown that the crucial fracture mechanics parameter for determination of the lifetime of a PE100 material is steady-state creep C*-integral [2]. In addition, the Failure Assessment Diagram in the form of C*–integral versus time to failure is proposed [1]. Computational algorithm for the integration of the primary/secondary creep constitutive law is derived [3] and implemented at the material point level in the finite element code ABAQUS by using the user subroutine CREEP [4]. In order to check the accuracy of the derived algorithm, the creep simulation on a FNCT specimen is performed. Furthermore, the detailed finite element solutions for the C*-integral values are obtained for a thick-walled polyethylene gas pipe with an external axial surface crack.

Polyethylene; Creep; Experiment; Finite element analysis; C-integral

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