Stress crack resistance of unaged high-density polyethylene geomembrane fusion seams

Abstract

The stress crack resistance (SCR) of high density polyethylene (HDPE) geomembrane (GMB) fusion seams is examined for two 1.5 mm HDPE GMBs and a range of welding parameters. Results are reported for both unnotched and notched seams as well as their corresponding sheet material. Unnotched seam SCR specimens are shown to preferentially initiate craze formation at the terminating edge of the squeeze-out bead, while incorporating potentially degraded areas, such as the seams heat-affected zone (HAZ), within the slow crack growth region of the specimen. In the short-term, little variation was observed between the majority of seams for the nine welding parameter combinations examined, with an average normalized seam SCR value (normalized with respect to the unnotched sheet SCR) of 0.3 ± 0.1, or about 30% of the SCR of the unnotched sheet. It is shown that squeeze-out geometry plays an important role in the SCR of fusion seams. Seams with weld track rippling, a known qualitative indication of overheating, were found to have average unnotched SCR values 45% lower than smooth weld track seams. Deleterious squeeze-out geometries are identified to provide a framework through which CQA engineers and researchers can more readily identify ‘higher risk’ seams with respect to stress cracking.