Using strain hardening to predict the stress crack resistance of unaged and aged smooth black HDPE geomembranes

The correlation between the single-point notched constant tensile load-stress crack resistance (SP-NCTL SCR) Test (ASTM D5397; Appendix) of smooth high density polyethylene (HDPE) geomembranes and their strain hardening modulus is investigated for both unaged and aged specimens. The strain hardening modulus was calculated based on the (force-elongation) raw data from the tensile strength test conducted at room temperature using Type IV and/or Type V specimens (as described in ASTM D638) at a test speed of 7 mm/min. Three different approaches are used to define the strain hardening modulus and to compare the representative strain hardening modulus with the SP-NCTL SCR. It is shown that the high test speed of 7 mm/min performed at room temperature provides a good correlation with the SP-NCTL SCR of different smooth black HDPE geomembranes. Additionally, the proposed method using Type V specimens predicts the SCR values during oxidative degradation close to those observed using the SP-NCTL SCR test. For the resins and conditions examined, the proposed method provides a quick assessment of the SP-NCTL SCR of unaged geomembranes when the SP-NCTL SCR takes long testing times (e.g., >1000 h) or in jurisdictions in which the use of surfactants becomes prohibited to allow conducting the SP-NCTL SCR tests.