Design and development of modern compliant, shape-adaptive or so-called morphing structures requires the successful combination of new materials with conventional ones to achieve enhanced capabilities that may combine adequate actuation rate, low developed stresses, low power requirements, slim profiles etc. Shape Memory Alloys (SMAs) are a class of metallic materials that present a number of different phenomena compared with conventional alloys due to the diffusionless, solid state transformation that takes place when the high temperature parent phase of Austenite changes to the lower temperature, product phase of Martensite. Such phenomena include but are not limited to the Shape Memory Effect (SME), pseudo-elasticity, thermo-mechanical coupling and memory associated with partial transformation loops, i.e. partially transforming between the pure phases.

 

Recent research studies report that operating SMA actuators in partial transformation greatly enhances their time response, power requirements and reduces developed stresses that might have a considerable impact on the fatigue life of the actuator component. To this end, accurate and efficient constitutive modeling of SMA partial transformation behaviour might be proved a highly important numerical tool to be used for the development of novel and robust design techniques that take into account the material characteristics. Considering the response of the SMA actuator known, the morphing capabilities can be further assessed and the whole system setup is developed based on the interaction between the host-passive structure and the active-actuator element.

 

Morphing strips are an indicative example of shape adaptive systems that consist of such a passive sub-structure and an active element, i.e. the SMA. Some possible application fields include aerospace industry, wind turbine blades, industrial switches/regulators, biomechanics, robotics etc. The strip system investigated herein is envisioned for aerospace and wind turbine applications. More specifically it is assumed to be either part of a larger morphing array of chevrons placed on civil aircraft jet engines intended for noise reduction or for local adaptation of the trailing edge of large wind turbine blades to achieve active load alleviation control.

 

In this paper, the design of the system is briefly discussed while particular focus is made on the response of the SMA ribbon actuator. Evaluation of the concept is performed by comparing the predicted response in terms of produced displacements (morphing shape), developed stresses and material internal state using two formulations of a phenomenological, thermodynamically consistent constitutive model: one that accounts for partial transformation behaviour and one that neglects it. Finally, relevant numerical results are presented followed by appropriate discussion.


Design of Morphing Strips Using SMA Actuators Under Partial Phase Transformation Operation

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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