This works investigates in detail the electro-thermo-mechanical properties of a Shape Memory Composite (SMC) during shape memory cycles in which the heating is a result of resistive heating. The SMC is a covalently cross-linked poly(ε-caprolactone) network filled with 3 wt% of multiwall carbon nanotubes. The characterization is performed with the help of a custom-made tensile test bench that is able to couple the mechanical characterization with the thermal and electrical ones. A PI (Proportional Integral) controller using the lambda tuning method is used in order to control the temperature achieved by resistive heating of the SMC. The electrical resistivity of the SMC shows a non-linear and non-monotonic dependence on temperature and strain. The resistivity is also found to vary among successive shape memory cycles, suggesting that a (first) training cycle is necessary not only to stabilize the mechanical but also the electrical properties of the SMC. A fuzzy logic controller for constant load control is also used to investigate the strain variation with temperature related to the two-way shape memory effect of the SMC. The results give evidence of the strong interplay between the electrical and (thermo-)mechanical characteristics of electroactive SMCs.

This work investigates in detail the Joule resistive heating phenomenon of electroactive Shape Memory Composites (SMC) when an electric current is injected at constant power. The SMC is a covalent poly(ε-caprolactone) network filled with 3 wt% of multiwall carbon nanotubes. The resistive heating of the SMC is studied by means of surface temperature measurements, analytical formulas and a coupled 3D thermo-electric numerical model. Analytical expressions are derived for the 2D temperature distribution within a parallelepipedic SMC, either with constant or linearly-dependent electrical resistivity. These analytical expressions can be used to investigate the influence of geometrical and material parameters in the steady-state temperature and its distribution across the sample. The results also allow one to identify the parameters that are crucial for predicting the temperature rise due to resistive heating: the temperature dependence of the resistivity has little effect on the steady-state temperature, whereas the thermal conductivity plays a significant role. The time-dependent temperature is shown to be related to the particular temperature dependence of heat capacity. Furthermore, the presence of external objects (clamps or grips) used during the shape memory cycle must be taken into consideration for a certain temperature to be reached since they result in a lower steady-state temperature and a slower resistive heating phenomenon. With the findings presented in this work, accurate resistive heating can be predicted for a SMC upon the injection of an electric current at constant power.