Thermal Exchanges and Thermomechanical Couplings in Amorphous Polymers

Abstract

During mechanical loading, the strain process can be accompanied by thermal effects generated by thermomechanical couplings. The aim of this work was the determination of energy (heat sources, mechanical energy, internal dissipated energy) during a mechanical test on polymer materials by observing strain and thermal data fields. Heat sources were calculated by establishing the heat equation using concepts of the classical thermodynamics of irreversible processes and applied to polymer materials. With a simple experimental set-up, we show that the thermal exchanges and the thermal losses in polymer samples are mainly induced by conduction and convective. The temperature at the surface was assumed to be equal to the average temperature in the thickness. We show that it is possible to obtain heat source values quantitatively without knowing their position and dimension along the thickness. It can also be difficult to calculate heat sources correctly because of lack of knowledge of the polymer property values involved in the heat equation (thermal conductivity, specific heat and heat transfer coefficient). So we present a procedure to determine these thermal parameters easily in our environmental conditions of work without making a mechanical hypothesis, and without knowing the heat source distribution because we analyse thermal data as soon as the heat source is switched off. In conclusion, we show an application involving a large strain mechanical test on a specimen of PC. The strain field is obtained by a mark tracking method. The energy balance has been calculated and associated with the volumetric deformation, showing the macroscopic and microscopic behaviour.