Coiled nylon actuator is an important field of actuators in soft robotics due to its negative thermal expansion, large actuation stroke and high force output. Coiled nylon actuators are easily manufactured and an inexpensive material. They are produced by attaching one end to a rotating motor and at the bottom to a suspended mass. The bottom end is constrained to prevent rotation in the axial direction. After coiling, it is annealed to reduce any internal strain. Its means of actuation is due to the torqueing behavior when heated which is induced by nylons thermal expansion, but by constraining the rotation, its response is to displace in the negative axial direction. The goal in this study is to capture the displacement and force output of the nylon actuator using COMSOL Multiphysics with the thermomechanical properties, heat and suspended mass (force) being the inputs of the model. The model will heavily rely on the classical lamination theory where the on-axis thermomechanical properties are obtained first and then the off-axis reduced stiffness matrix and effective coefficient of thermal expansion is obtained. The COMSOL Multiphysics displacement and force output results will be compared to experimentally obtained results. The experimental results will be obtained using a TA Instrument Dynamic Mechanical Analysis (DMA) which will be used to perform a strain controlled dynamic temperature scan at a frequency of 1 Hz on the nylon actuator. Temperature will be scanned from room temperature 24°C to 150°C at 1 °C/min.
The multiple-shape-memory ionic polymer-metal composite (MSM-IPMC) actuator can demonstrate complex 3D
deformation. The MSM-IPMC have two characteristics, which are the electro-mechanical actuation effect and the
thermal-mechanical shape memory effect. The bending, twisting, and oscillating motions of the actuator could be
controlled simultaneously or separately by means of thermal-mechanical and electro-mechanical transactions. In our
study, we theoretically modelled and experimentally investigated the MSM-IPMC. We proposed a new physical
principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSMIPMC
was developed. It is based on the assumption that the multiple shape memory effect is caused by the thermal stress
and each individual Young’s modulus is ‘memorized’ during the previous programming process. As the MSM-IPMC
was reheated to each temperature, the corresponding thermal stress was applied on the MSM-IPMC, and the Young’s
modulus was recovered, which result in the shape recovery of the MSM-IPMC. To verify the model, a MSM-IPMC
sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the
experimental results, both results have a good agreement. The current study is beneficial for the better understanding of
the underlying physics of MSM-IPMC.