Macro- and Mesoscale Simulation of Superelastic Damping in Miniature Devices

We present a macroscale and mesoscale dynamic analysis of the forced vibration of a free-standing bridge of superelastic shape memory alloy TiNiFe for novel miniature scale applications. Damping and shock absorption have gained increasing importance in engineering of novel lightweight technical structures as well as smart miniature systems. Examples are novel handheld systems carrying sensible opto-mechanical, fluidic or electronic components and portable devices (cameras, smartphones) being sensitive to human motion. A thermodynamics-based finite element model is used to simulate the evolution of martensite phase fraction during load-induced martensitic phase transformation [1]. At the macroscale, the effects of pre-straining and excitation load are investigated in order to define an optimum operation point for a SMA bridge damper device. The analysis is performed under non-isothermal conditions by taking into account the heat transfer and the rate-dependence of release and absorption of latent heat [2]. At optimum pre-strain, the damping capacity of 0.2 per loop is obtained. During harmonic loading at resonance, we observe a shift of minimum deflection for progressing loading cycles, which is caused by incomplete reversible transformation and accumulation of martensite due to a self-heating effect. At the mesoscopic length scale, maximum energy dissipation and self-heating occur in the bridge center, while martensite accumulation occurs near the fixations of the SMA bridge.

[1] F. Wendler, H. Ossmer, C. Chluba, E. Quandt, M. Kohl, Acta Materialia 136, 105–117 (2017).

[2] S. Ahmadi, K. Jacob, F. Wendler, M. Kohl, International Journal of Smart and Nano Materials 9, 199-215 (2018).