A Bi-State Shape Memory Material Composite Soft Actuator

Ramprasad Rajagopalan,Andrew J Petruska,David Howard

doi:10.3390/act11030086

Ramprasad Rajagopalan, Andrew J Petruska + Show 1 more

Open Access

https://doi.org/10.3390/act11030086

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Abstract

Shape memory materials have been widely used as programmable soft matter for developing multifunctional hybrid actuators. Several challenges of fabrication and effective modelling of these soft actuating systems can be addressed by implementing novel 3D printing techniques and simulations to aid the designer. In this study, the temperature-dependent recovery of an embedded U-shaped Shape Memory Alloy (SMA) and the shape fixity of a 3D-printed Shape Memory Polymer (SMP) matrix were exploited to create a bi-state Shape Memory Composite (SMC) soft actuator. Electrical heating allowed the SMA to achieve the bi-state condition, undergoing phase transformation to a U shape in the rubbery phase and a flat shape in the glassy phase of the SMP. A COMSOL Multiphysics model was developed to predict the deformation and recovery of the SMC by leveraging the in-built SMA constitutive relations and user-defined material subroutine for the SMP. The bi-state actuation model was validated by capturing the mid-point displacement of the 80 mm length × 10 mm width × 2 mm-thick 3D-printed SMC. The viability of the SMC as a periodic actuator in terms of shape recovery was addressed through modelling and simulation. Results indicated that the proposed COMSOL model was in good agreement with the experiment. In addition, the effect of varying the volume ratio of the SMA wire in the SMC on the maximum and recovered deflection was also obtained. Our model can be used to design SMC actuators with various performance profiles to facilitate future designs in soft robotics and wearable technology applications.

Highlights

Smart materials responding to an external stimuli can be used to fabricate smart actuators for applications ranging from wearable technology to self-folding aerospace structures [1–3]
As the Shape Memory Polymer (SMP) exhibited an elasto-plastic behaviour at room temperature, the strain value was limited close to 1% to demonstrate the behaviour of the actuator in the small strain linear region
The main objective of this research was to design a bi-state shape memory material composite soft actuator that combined the strengths of the Shape Memory Alloy (SMA) and SMP and provided a tunable performance profile

Summary

Introduction

Smart materials responding to an external stimuli can be used to fabricate smart actuators for applications ranging from wearable technology to self-folding aerospace structures [1–3]. Extensive research in robotics has been carried out to utilise such devices to address the common challenges faced by rigid robots such as adaptable locomotion within a complex environment and safe interaction with human beings [4]. The emergence of soft robotics at the intersection of smart materials, advanced fabrication techniques, and computational design addresses these challenges by drawing inspiration from biological organisms [5]. The structural design of biological organisms is composed of soft and hard materials, with associated synchronised neuromechanical control. In order to develop robots mimicking such organisms, flexible actuation to deliver continuous deformation and embodiment of stiffness modulation through environmental interaction are essential [6]. The advent of additive manufacturing technologies, progress in material science, and advances in soft material simulation software support the design and fabrication of such complex metamaterial soft actuation structures

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