A Tensile Strain Hardening Test Indicator of Environmental Stress Cracking Resistance

• Published in: Journal of macromolecular science. Part A, Pure and applied chemistry Vol. 45; no. 8; pp. 599 - 611
• Main Authors: Cheng, Joy J., Polak, Maria A., Penlidis, Alexander
• Format: Journal Article
• Language: English
• Published: Colchester Taylor & Francis Group 01.08.2008; Taylor & Francis
• Subjects: Applied sciences; environmental stress cracking resistance; Exact sciences and technology; high density polyethylene; Mechanical properties; natural drawing ratio; Organic polymers; Physicochemistry of polymers; polyethylene resin comparison; Properties and characterization; strain hardening test; tensile test; strain hardening test; Strain rate sensitivity; High density ethylene polymer; Mechanical properties; Liquid medium; natural drawing ratio; Experimental study; Crack propagation resistance; Tension test; Mechanical test; environmental stress cracking resistance; high density polyethylene; tensile test; polyethylene resin comparison; Reproducibility; Measurement method
• ISSN: 1060-1325; 1520-5738
• DOI: 10.1080/10601320802168728

Environmental stress cracking resistance (ESCR) is an important indicator of performance for high density polyethylene (HDPE) in structural and polymer pipe applications. The commonly used test for determining ESCR of HDPE can be time consuming and rather imprecise. A tensile strain hardening test was recently proposed to offer a faster way to characterize ESCR of polyethylene. In this paper, a practical approach is adopted whereby the test is extended to room temperature and shown to relate reliably to the ESCR of HDPE. Several HDPE resins (including pipe-grade resins) are analyzed at strain rates of 0.5 mm/min and 7 mm/min to compare the effect of strain rate. Comparisons between the conventional ESCR test method and the strain hardening test show that strain hardening can be used to rank ESCR of HDPE in a reliable fashion. In our study the more direct measure of "hardening stiffness" is used to compare resins instead of strain hardening modulus. Because no true stress-strain measurement is needed, this is a much simpler test method than other methods previously suggested. In addition, the use of the natural drawing ratio (NDR) as ESCR ranking indicator is examined. Results show that NDR can also be employed as a strain rate-independent indicator of ESCR of HDPE. The test proposed herein is practical, simple and precise, and hence a more reliable indicator of ESCR performance of HDPE.