Analysis of the Strain Hardening test for polyethylene

Abstract

The Strain Hardening test is a promising method to reduce testing times for predicting the lifetime of polyethylene pipes used in the Dutch natural gas distribution network significantly. The Strain Hardening test measures the resistance to disentanglement of the polymer chains, and thus the resistance to slow crack growth. In this study, the influence of the testing temperature, tensile speed, test specimen thickness, thermal history and molecular orientation on the strain hardening modulus were investigated. The strain hardening modulus decreased with testing temperature and increased with tensile speed. The thermal history seemed to influence the strain hardening modulus too, but the test specimen thickness did not. Also it was found that test specimens prepared in axial pipe direction had a significantly larger strain hardening modulus than those prepared in tangential pipe direction.