Thermomechanical response of flexinol actuator wires subjected to isostress, isothermal and dynamic load temperature coupling using induction heating method

Thermomechanical analysis of Shape Memory Alloy (SMA) actuators under different load-temperature coupling are important to tune the actuator response according to the changes in temperature, altitude and airspeed, thus making them more adaptive like the birds. SMA actuators can directly react to load and temperature changes with reduced mechanical complexity as the active element is in the wire or spring form. This coupling effect allows SMA to be integrated as sensors, actuator or components to enhance the actuation control, damping, vibration control, and adaptive autonomy control. However, the dynamic environmental nature especially, aeronautics and space realms vary temperature and pressure simultaneously. These changes drive the needs for understanding the SMA behaviour to fit specific requirements or applications. Hence, present study investigates the thermomechanical response of Flexinol actuator wire subjected to different loading conditions using induction heating method. A heat control chamber comprises induction heating technique was developed to provide a regulated temperature control with high precision. The SMA actuation performances were analysed under isostress, isothermal and dynamics disturbances loading. For isostress loading, thermal loading was applied and the response of the wire was evaluated in terms of the phase transformation temperatures, thermal hysteresis and the generated strains. Meanwhile for isothermal loading, a mechanical tensile loading-unloading was applied on the actuator wire and the response was assessed in terms of phase transformation stresses, stresses during phase transformation and mechanical hysteresis. Predictive mathematical equations were developed using response surface methodology (RSM) to evaluate the effect of stress and temperature on strain response of the wire under isostress and isothermal loading. For dynamic disturbances loading, combination of mechanical-induced and thermal-induced vibration were evaluated in terms of the actuation characteristics such as mean stress and means strain as well as the frequency of dynamic system. Isostress loading results showed that the phase transformation temperatures and transformation strain increased while, the thermal hysteresis decreased with increasing preloads. The transformation strains range was 3.02% to 3.97%. While, results for isothermal showed that with increasing temperature, the phase transformation stresses, stresses during phase transformation and mechanical hysteresis increasing with the transformation strain in the range of 2.7% to 3.6%. Here, predictive experimental-derived mathematical equations were developed and were further verified within the investigated range which provide high accuracy of the predicted strains above 98%. For dynamic disturbances loading, the mean strain is proportional to mean stress during heating-cooling cycle, whereas the frequency decreasing with increasing dynamic disturbances loading. The maximum and minimum total strain of wire under dynamic disturbances loading were 3.74% and 1.39% respectively. Herein, stroke performance increased by 0.23% and 1.63% for maximum and minimum total strain respectively in isostress loading. Meanwhile, for isothermal loading, the maximum stroke of wire showed 0.16% reduction, while the minimum stroke showed 1.31% increase. Therefore, the stroke performance is dependent on the method of actuation, whether it is thermally or mechanically derived. So, it is important to establish a comprehensive map of static and dynamic aspect of SMA specific to the thermomechanical response.

Text FK 2024 44 - Declaration Form.pdf Restricted to Repository staff only Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (669kB) Text FK 2024 44 - Full Text.pdf Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (9MB) Text FK 2024 44.pdf Restricted to Repository staff only Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (9MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/19009

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