Viscoelastic Characterization Of Fusion Processing In Bimodal Polyethylene Blends

Polyethylene is an advantageous material for the construction of buried pipelines. It is corrosion resistant, seismic tolerant, and utilizes low cost installation methods. Pipe sections are often joined using thermal fusion processes. The strength of the joint is related to the ability of the polyethylene chains to inter-diffuse and form inter-crystalline tie-chains across the two polyethylene surfaces. Testing the strength of the fusion bond is difficult and a number of different destructive and non-destructive tests have been developed, but it is not possible to understand the impact of the fusion process on the local microstructure from these tests. In this work, instrumented indentation with a flat punch is used to measure the local viscoelastic behavior of five different polyethylene resins used for pipe manufacturing at short times. High strain behavior related to slow crack growth is measured using a strain hardening measurement under tension. The impact of thermal processing is investigated by imposing three different thermal cooling histories (0.4, 9, and 100 degrees C/min) on the polyethylenes. The goal is to determine if short-term creep under indentation is capable of accurately measuring; (a) bulk creep behavior, (b) impact of resin architecture, and (c) the impact of thermal processing. The results show that indentation using a flat punch is capable of measuring creep within the range of bulk creep behavior, but not sensitive to the slow crack growth resistance of the resin.