Shape Recovery Behavior of Carbon Nanopaper Shape Memory Polymer Composite

Abstract

This thesis presents analytical, experimental and modeling studies of the shape recovery behavior of electrically activated Carbon Nanopaper (CNP) Shape Memory Polymer (SMP) composite. The composite structure studied consists of a CNP layer sandwiched by two SMP layers where the CNP layer acts as a flexible electrical heater when a voltage difference is applied. The behavior of CNP/SMP composite presents a coupled electrical-thermal-structural problem. The governing equations for the multiphysics behavior are derived. Derived parameters as a result of multiphysics analysis and effects of these parameters on the shape recovery behavior are investigated. The mechanical properties of the carbon nanopaper and viscoelastic properties of the shape memory polymer are characterized. A nonlinear, fully coupled electrical-thermal-structural finite element model is developed, and shape recovery experiments are carried out to validate multiphysics analysis and finite element model of the shape recovery of the CNP/SMP composite. Finite element model captures the general behavior of shape recovery, but overpredicts shape fixity and shape recovery rate.

Toward thermal stimulation of shape memory polymer composite bistable tape springs

“…In the context of strain-energy-deployed space structures, stiffness relaxation plays a significant role in the deployment dynamics of the structures as they are typically folded and stored for extended periods onboard a spacecraft before being deployed into their operational shape [29,30]. An analytical shell model is used in [17] to study the viscoelastic (VE) behavior of BiTSs which has been folded up to 10 h. Experimental studies on VE characterization of nonreinforced isotropic TSs have shown that the Young's modulus decreases with time [31][32][33][34][35]. In addition, the relaxation of the shear modulus and transversal Young's modulus play significant roles in the time-dependent behavior of BiTSs fabricated from unidirectional plies [29].…”

“…A Maxwell-Wiechert model (Prony series) is typically used to predict the VE properties of TSs after long-term stowage [14,32,33,[36][37][38]. Rose et al [30] assumed that a Prony series derived from matrix material properties could be sufficient for predicting relaxation of a carbon fiber reinforced polymer (CFRP).…”

“…At temperatures above T g the material exhibits dramatically reduced stiffnesses due to significant softening of the resin [3]. Kwok et al [31][32][33][34][35][39][40][41] used Prony series to predict the strain energy relaxation in the TSs, e.g. at 27 • C, 30 • C, 40 • C.…”

“…The empirical method in [38,53] were chosen to obtain the shifting values as function of temperature for the present SMPC, in figure 5. Williams-Landel-Ferry (WLF) and Arrhenius fitting equations are used to fit a curve to the shift factors, at temperatures below and above the glass transition temperature, respectively [30,33,[36][37][38]. For the MP-5510 SMP material which is used in current study, log 10 a T were fitted to the WLF equation, (2) successfully in [33]:…”

“…The in-plane shear modulus, G 12 , was defined from the DMA results as the instantaneous shear modulus, G 12 = G 120 = 6.8 ± 0.5 GPa. The Poisson's ratio for the same SMP material has been measured to be ν = 0.45 in [33].…”