Transient heat generation and thermo-mechanical response of epoxy resin under adiabatic impact compressions

• Localization of adiabatic temperature increase in epoxy resin is photographed.
• Transient deformations of epoxy under impact compression are observed.
• Post-yield response under impact depends on adiabatic-heating softening behavior.
• Simple constitutive relationship for post-yield and adiabatic softening is obtained.

This investigation examines transient heat generation and the thermal-mechanical response of epoxy resin subjected to quasi-static and dynamic compression. High-speed optical and infrared imaging systems are used to obtain visual and thermo-graphic images during dynamic tests. It is found that the post-yield response of epoxy resin depends on whether the loading is quasi-static or dynamic. Results from quasi-static compression show that yield is followed by post-yield softening, plastic flow and final hardening. An obvious difference for high-rate compression is that post-yield softening persists without a final hardening phase. From the high-speed infrared images, localizations of adiabatic heating and temperature distribution were identified morphologically in high strain rate compressions. Dynamic mechanical analysis (DMA) and quasi-static data for elevated temperatures confirm the temperature sensitivity of epoxy resin. By calculating the different pixel numbers in infrared images at the different temperature values, the inelastic heat fraction is estimated to be about 0.45 for the epoxy. A simple constitutive relationship that describes the mechanical behavior of the polymer, such as elasticity–plasticity, post-yield softening and final strain hardening for quasi-static loading, as well as adiabatic-heating softening for dynamic loading, is proposed.