THE COMPUTER MODELLING OF FUNCTIONAL-MECHANICAL BEHAVIOR OF POROUS SHAPE MEMORY ALLOY SAMPLES

The authors proposed a model for the description of the functional and mechanical behavior of a sample of the porous shape memory alloy, the structural elements of which were approximated by flat slotted springs. These springs, in their turn, consist of beams. During the deformation process, beams oriented perpendicular to the loading direction contribute significantly to the sample macroscopic strain.

The authors investigated the influence of beam supporting conditions on the modeling results. Two types of boundary conditions are considered – hinge support and rigid fixing. Within the methods of the strength of materials for the specified types of supports, the authors solved the static problems; found the stresses in the most strained area and beam deflections. To calculate the anelastic deformation arising from the martensitic transformation in the shape memory alloys, the microstructural model allowing describing the functional properties of these materials was used. Basing on the analysis of microphotography of porous TiNi alloy, the geometrical parameters of beams were chosen. The authors carried out the simulation of the behavior of the porous shape memory alloy sample during the isothermal compression at various temperatures when the shape memory alloy is in austenitic and martensitic states. The deformation of a sample during the cooling and heating under the constant stress was calculated, in this case, the transformation plasticity and shape memory effects occur. It is shown, that the selection of boundary conditions has the important significance when modeling porous shape memory alloy behavior. The application of fixed-ended structural elements leads to the lower stresses in the modeled object and allows obtaining better correspondence between the calculation results and experimental data.