Critical Frequency of Self-Heating in a Superelastic Ni-Ti Belleville Spring: Experimental Characterization and Numerical Simulation.

Emmanuel Ferreira De Souza,Carlos José De Araújo,Antonio Gilson Barbosa De Lima,Estephanie Nobre Dantas Grassi,Paulo César Sales Da Silva

doi:10.3390/s21217140

Emmanuel Ferreira De Souza, Carlos José De Araújo + Show 3 more

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https://doi.org/10.3390/s21217140

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Abstract

The mechanical loading frequency affects the functional properties of shape memory alloys (SMA). Thus, it is crucial to study its effect for the successful use of these materials in dynamic applications. Based on the superelastic cyclic behavior, this work presents an experimental methodology for the determination of the critical frequency of the self-heating of a NiTi Belleville conical spring. For this, cyclic compressive tests were carried out using a universal testing machine with loading frequencies ranging from 0.5 Hz to 10 Hz. The temperature variation during the cyclic tests was monitored using a micro thermocouple glued to the NiTi Belleville spring. Numerical simulations of the spring under quasi-static loadings were performed to assist the analysis. From the experimental methodology applied to the Belleville spring, a self-heating frequency of 1.7 Hz was identified. The self-heating is caused by the latent heat accumulation generated by successive cycles of stress-induced phase transformation in the material. At 2.0 Hz, an increase of 1.2 °C in the average temperature of the SMA device was verified between 1st and 128th superelastic cycles. At 10 Hz, the average temperature increase reached 7.9 °C and caused a 10% increase in the stiffness and 25% decrease in the viscous damping factor. Finally, predicted results of the force as a function of the loading frequency were obtained.

Highlights

IntroductionShape memory alloys (SMA) are smart metallic materials with the ability to reverse considerable mechanical deformation (in the order of 10% in tension for NiTi alloys), even under substantial mechanical loading [1]
Shape memory alloys (SMA) are smart metallic materials with the ability to reverse considerable mechanical deformation, even under substantial mechanical loading [1]
The shape recovery can occur through two distinct phenomena: shape memory effect (SME), taking place when heating is applied after a pseudoplastic deformation; and superelasticity (SE), an isothermal loading/unloading cycle leading to a pseudoelastic deformation

Summary

Introduction

Shape memory alloys (SMA) are smart metallic materials with the ability to reverse considerable mechanical deformation (in the order of 10% in tension for NiTi alloys), even under substantial mechanical loading [1]. The shape recovery can occur through two distinct phenomena: shape memory effect (SME), taking place when heating is applied after a pseudoplastic deformation; and superelasticity (SE), an isothermal loading/unloading cycle leading to a pseudoelastic deformation. Both SME and SE are associated with energy dissipation, observable through a mechanical hysteresis between loading and unloading curves. The stress to mechanically trigger the phase transformation in SMA increases linearly with temperature, following a Clausius–Clapeyron law [2,3,4]. The generated latent heat might accumulate if the loading frequency is sufficiently high, which in turn causes the material to stiffen as loading progresses due to the Clausius–Clapeyron relation

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