FULL-FIELD STRAIN AND TEMPERATURE MEASUREMENTS IS STATIC AND DYNAMIC TENSILE TESTS

Tensile tests at low and high strain rates in which full-field strain and full-field temperature are measured simultaneously on the surface of the specimen during the test are presented. Various testing methods are used (including the tensile Split Hopkinson Bar for testing at high strain rates) for loading the specimens. Strain measurements are done using the Digital Image Correlation (DIC) technique and temperatures are measured with a high-speed IR camera. The experiments provide details of the strain and temperature during the uniform deformation before the initiation of necking, and in the necking region during the necking. Results from testing several metals (stainless steel, titanium, aluminum) show a uniform temperature rise during the uniform deformation which is higher with increasing strain rate and a significant increase in the strain rate and temperature during the necking in the necking region. The strain rate in the necking area can be three times the nominal strain rate and, at a high strain rate test, the temperature in the necking area can increase by 300°C. The data from these experiments is of great importance. It can be used for the determination of the fraction of the plastic work that is converted to heat and its dependence on strain rate and plastic strain. In addition, the experiments provide data that can be used to obtain more accurate constitutive models for plasticity. Constitutive models for plastic deformation are written in a form that accounts for the effects of strain hardening, temperature and strain rate. Having temperature measurement in addition to stress and strain provides mean for determining the uncoupled values of the parameters in the models.