Determination of the Heat Dissipated from a Specimen Undergoing Cyclic Plasticity by a Hybrid Numerical/Experimental Method

Abstract : When a metallic specimen is deformed plastically, the bulk of the irreversible work is dissipated in the form of heat. It is generally accepted that the remaining part of the input energy is consumed by the change in the material's internal energy. Such internal energy changes can be attributed to phase changes, development of residual stresses, translation of dislocations; and the creation and/or enlargement of internal surfaces such as voids. Recent interests in deformation heating have primarily been motivated by metal forming processes where the substantial heat generation greatly influences the formability. A combined experimental/numerical approach is taken to decompose the hysteresis energy of a tensile specimen undergoing fully reversed plastic cycling into heat generation and internal energy in accordance with the first law of thermodynamics and the one dimensional diffusion equation with internal sources. Because of the difficulties in determining accurate boundary conditions and the sensitivity of the solution to the boundary conditions, the finite difference method was complemented with Lagrange multipliers. The sum of the square of the difference between the measured temperature and the predicted temperature at specific points along the specimen axis were minimized subject to the constraint of the finite difference template used. Results from preliminary tests indicate that when a critical energy density is reached failure occurs.