Influence of temperature on the SMA-PDMS interfacial bond behavior and its modeling with temperature dependent trapezoidal cohesive law

Abstract

Soft actuators composed of shape memory alloy (SMA) wires embedded in polydimethylsiloxane (PDMS) matrix are potential in shape-morphing structures and soft robots. However, the SMA-PDMS interface is inevitably subjected to high temperatures during actuation due to Joule heating of the SMA, which affects its bond properties. However, knowledge of how temperature impacts SMA-PDMS interfacial bond properties is still insufficient. This paper conducted fiber pull-out experiments at various interface temperatures to monitor and trace the debonding process with high-speed camera. Results show that the maximum debonding load, critical debonding displacement, and friction load are in exponential decay with interface temperature. Notably, interfacial strength degradation exceeds 50 % when the interface temperature increases from 25 °C to 100 °C, and the traction-separation behavior of SMA-PDMS interface shifts from trapezoidal to triangular as the interface temperature increases. A finite element model was developed to simulate the debonding behavior of SMA-PDMS, in which the interface was modeled using the cohesive zone model with temperature-dependent trapezoidal constitutive law. Simulation results agree well with experiments. Stress distribution during the interface debonding process was also analyzed and discussed. The work demonstrates the importance of accounting for interface bond strength degradation caused by temperature in the design of SMA-PDMS soft actuators.