Effect of the weld-joint on fracture behaviour of polymer material

abstract

English

Polyethylene pipeline for gas energy distribution should be carefully constructed to prevent an explosive gas from leaking, and the rate of failure should be very low. Therefore, there is a pressing need for reliable test procedures to evaluate the mechanical properties of welded joints. These tests are carried out either on coupons cut from the welded joint or on the complete weld, and can be either short-term or long-term. However, since the weld is more likely to fail in the long-term in service, it is important that the results from short term tests should be correlated with those from long term tests. Up to now, little work has been done to correlate results from short-term tests with those from long-term tests in the case of welded polymer pipes. To do this we need to understand the kinetics of crack initiation and its growth particularly through the welded joint. The first step is to study fracture behaviour of a polymer structure with a crack growing in or through the weld and estimate corresponding fracture mechanics parameters. The welded materials have relatively complicated structure depending on the welding method and upon the conditions of making it. Basically the weld joint non-uniformity can be modelled by continuous change of the material properties from those corresponding to the base material of the pipe to parameters corresponding to the heat affected zone of the weld. Based on experimental data, the change of mechanical properties (especially of Young modulus) for weld-joint is estimated and than implemented to the structure corresponding to numerical model of the weld. Weld-joint is modelled as an area of graded elastic material and calculations are performed by finite element method. The interaction between crack and the weld-joint will be focused mainly on two, from the practical point of view, important cases: crack propagating in the middle of the weld and the crack propagating perpendicularly to the weld. The results can help for more accurate estimation of weld-joint effect on the fracture behaviour of the PE pipeline.

crack, polymer, weld, fracture, FEM

HUTAŘ, P.; ŠEVČÍK, M.; KNÉSL, Z.; NEZBEDOVÁ, E.; LACH, R.

1. 9. 2009

Dortmund

173

173

1