Adiabatic effects on the temperature and rate dependency of the fracture toughness of an ethylene-fluoroethylene film

In this work, the essential work of fracture (EWF) test has been applied to determine the temperature and strain-rate dependency of the fracture toughness of ethylene-fluoroethylene (ETFE) thin films. EWF tests were conducted at different temperatures (23, 50 and 80 °C) and different cross-head rates (1, 10, and 100 mm/min). At 23 °C, the specific essential work of fracture (w e ) values slightly increase as the strain rate increases, while at 50 °C and 80 °C w e values decrease. This trend is associated to an increase of the specific essential work for crack propagation (w e,prop ) while the specific essential work for crack initiation (w e,init ) decreases with strain rate with a magnitude related to the testing temperature. Thermal observations with an infrared camera revealed an increase of the temperature at the crack tip for the highest strain rate, thus suggesting, for the sample tested at the lowest temperature, the concurrent effects of strain-rate embrittlement and adiabatic heating. Digital image correlation (DIC) analysis revealed an ovoid shape of the outer plastic zone (OPZ) prior to the start of the crack propagation. DIC also indicated that the extension of the OPZ increases linearly with the square of the ligament length.