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Simulation of alternating deformation of the TiNi alloy sample in isothermal and adiabatic regimes
Summary
This materials science study developed theoretical models for the alternating deformation behavior of TiNi shape memory alloys under isothermal and adiabatic cycling conditions. Researchers validated their model against experimental data relevant to designing vibration-damping devices from these materials. This is a functional materials engineering study with no connection to environmental microplastic research.
Shape memory alloys belong to the class of functional materials with unique properties that make them useful in many engineering applications. Since in the austenitic state, due to the pseudoelasticity effect, such alloys have a significant damping capacity, and one of the possible applications is vibro-protection devices. Working elements of damping devices made of shape memory alloys are used in the conditions of cyclically varying stresses and/or temperature. The theoretical models adequately describing such behavior make it possible to advance the efficiency of damping devices. The paper aims at the microstructural modeling of alternating deformation of the sample of TiNi shape memory alloy. Phase transformations in the materials with the martensite channel of inelasticity take place with the release and absorption of heat, which can lead to a shift in the working temperatures of the element and the change in its functional properties. Consequently, when theoretically describing the mechanical behavior of the material, the authors considered heat release at the direct transformation and heat absorption at the reverse transformation. Within this study, the authors implemented such consideration for the adiabatic regime of alternating deformation and compared the obtained data with the results of modeling of isothermal alternating deformation. When calculating, the authors took into account the irreversible strain accumulation at cycling, which, in the real device, can cause the change in its working characteristics and operational life loss. The study showed that taking into account the latent transformation heat during cycling in the strain-controlled regime increases the maximum stresses in the cycle and reduces the volume fraction of the resulting martensite. When taking into account the microplastic strain, the deformation loop evolves. In this case, in the adiabatic regime in the first cycles, the temperature increases, later on, about by the seventh cycle, the temperature increase slows down, and the average temperature ceases to change markedly.