Analysis of the work-to-heat conversion beyond the necking onset in non-isothermal tensile tests

When metals undergo plastic deformation at sufficiently high speed, the plastic work dissipated as heat can cause material self-heating, influencing the material's mechanical behavior. This phenomenon is particularly critical during localized deformation. The present study proposes two methods for investigating the work-to-heat conversion during the post-necking phase of tensile tests on cylindrical dog-bone samples. One method directly applies the heat equation and is developed for adiabatic conditions only; the other method requires iterative thermal-structural finite element simulations but is also applicable to non-adiabatic conditions. Both methods involve recording the tests with optical and infrared cameras with adequate temporal and spatial resolution to fully exploit the heterogeneous fields and to improve the reliability of the results. A key distinction from other studies is the avoidance of using Digital Image Correlation technique, opting instead for a method based on necking silhouettes, which reduces experimental complexity and avoids issues related to speckle damage. Both the direct and iterative approaches, after being successfully tested against numerical benchmarks, were applied to an experimental case study. The material tested was 17–4PH martensitic stainless steel, known for its moderate strain rate sensitivity and substantial self-heating due to low thermal conductivity. Tests were conducted at room temperature and at nominal strain rates of 1, 10, and 1000 s⁻¹. The results demonstrated the practical applicability of the proposed methods, suggesting their potential for investigating the work-to-heat conversion up to large strains by exploiting the post-necking phase of tensile tests with limited experimental complexity.