Comparison between the thermal properties of fully dense and porous Ni-Ti SMAs

In this paper the results and methodology for evaluating the dependence of the thermal properties of porous and fully dense NiTi SMAs on temperature and porosity using an experimental-numerical approach is reported. In the experimental work a cylindrical NiTi sample was uniformly heated at one side and temperature histories at different positions recorded. A variety of heating rates ranging from 10 to 100 K/s and maximum temperature values of 400 K or 1400 K at the top of the NiTi sample were used to carry out experiments. The numerical code based on the 1D unsteady heat diffusion equation considers the sample as a solid featured by the average density depending on its porosity and permits the evaluation of the effective thermal properties. The total heat capacity of each sample is defined on the basis of the transformation latent heat and data reported in literature, while the thermal conductivity is obtained by comparison of the numerical results to the experimental curves. Samples featuring porosity levels of 0%, 30%, 48%, 68% have been tested and the total heat capacity and thermal conductivity dependence on temperature and porosity are defined in the temperature range from 300 K up to 1400 K.