Impact of test speed on the thermo-mechanical behavior of various types of geomembranes

Geomembranes in hydraulic structures are often in exposed conditions; the ambient temperature can vary significantly and hence influence their mechanical behavior. To determine their tensile behavior at various temperatures, unidirectional tensile tests can be performed in temperature-controlled chambers. However, the test speeds recommended by the main standards are high. Considering the elasto-visco-plastic behavior of geomembranes, the test speed has a double effect; the first comes from the viscous component and the second comes from temperature variation, due to the self-heating of the tested specimen during test. This study aims to investigate the effect of the test speed on the mechanical behavior of various geomembranes by decoupling the viscous effect and the self-heating effect. Through various unidirectional tensile tests performed on a wide range of test speeds, from 0.01 mm/min to 500 mm/min, it was found that for various tested geomembranes (HDPE, EPDM, PVC, FPO, Bituminous), the higher the test speed, the greater the tensile force at various strain levels and the greater the change in internal temperature of the specimen. Regarding the temperature effect, it was shown that for test speeds less than or equal to 10 mm/min, no self-heating of the specimen was observed for all geomembranes.