Complete balance of energy during necking in polymeric glasses and its strain-rate dependence

Abstract

Some polymeric glasses, e.g., polycarbonate, deform heteregeneously after yielding by forming a neck. The boundary between two zones with different strains λ′ and λ″ propagates at constant stress with a valocity v _n over the sample, changing the deformation of the material from λ′ to λ″. This process is accompanied by an exchange of mechanical work and heat. At low v _n both quantities are measured in a stretching calorimeter. At higher v _n, we observe the sample in the stretching device with an infrared camera. Comparison of the measured temperature pattern on the surface of the sample with a calculation using the differential equation of heat conduction including heat sources and heat loss results in the strength of the sources and, therefore, to the heat produced by the transition. The mechanical work shows a small increase with v _n. The heat is constant at low v _n and increases at v _n≈2 · 10⁻⁴ m/s until the entire work is transformed into heat.