Heat dissipation measurements in low stress cyclic loading of metallic materials: From internal friction to micro-plasticity

Study and validation of a variational theory of thermo-mechanical coupling in finite visco-plasticity

Determination of the fraction of plastic work converted into heat in metals

The energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, was recently proposed as fatigue damage index, and it was successfully applied to rationalise fatigue data obtained by carrying out stress-controlled and strain-controlled fatigue tests on AISI 304 L stainless steel plain and hole specimens. In this paper, it is shown that the Q parameter is independent on thermal and mechanical boundary conditions occurring during experiments. After that, additional stress-controlled fatigue tests on plain and notched specimens characterised by smaller notch tip radii than those tested previously have been performed. Present data have been compared with previous ones, and it was found that all available results can be synthesised in terms of the energy parameter Q into a unique scatter band, independently on the testing conditions (stress-controlled or strain-controlled) and on the specimens' geometry (plain or notched). About 100 data were included in the statistical analysis to characterise the energy-based scatter band of the material. Finally, some limitations of applicability of the experimental technique adopted in the present paper are discussed.

A synthesis of the push‐pull fatigue behaviour of plain and notched stainless steel specimens by using the specific heat loss

The use of the specific heat loss to analyse the low- and high-cycle fatigue behaviour of plain and notched specimens made of a stainless steel

The fraction of plastic work converted to heat is typically measured either by nearly isothermal experiments, in which the thermal energy is measured during a deformation experiment with a calorimeter, or by adiabatic experiments, in which the thermal energy is determined from the temperature rise, measured either during the test or immediately after the test by dropping the sample into a calorimeter. In the present work, the temperature is measured with a single fine-wire thermocouple. The restriction to adiabatic loadings is relaxed by using a hybrid method that combines the measurements with finite difference simulations to calculate the heat losses that occur during the test. These heat losses are then accounted for in the final energy balance to determine the fraction of plastic work converted to heat. The method is applied to annealed 302 stainless steel. The results show that the fraction of plastic work converted to heat is a decreasing function ranging from 0.7 to 0.4 over a tensile strain range of 0 to 0.15. An analysis of the restrictions to this method and of the potential errors is given.

E. Babinsky

Papers

Hybrid Method for Determining the Fraction of Plastic Work Converted to Heat