Abstract
Shape memory composites (SMCs) based on shape memory alloys (SMAs) and shape memory polymers (SMPs) allow many design possibilities due to their controllable temperature-dependent mechanical properties. The complementary characteristics of SMAs and SMPs can be utilized in systems with shape recovery created by the SMA and shape fixity provided by the SMP. In this research, three SMC operating regimes are identified and the behavior of SMC structures is analyzed by focusing on composite shape fixity and interfacial stresses. Analytical models show that SMPs can be used to adequately fix the shape of SMA actuators and springs. COMSOL finite element simulations are in agreement with analytical expressions for shape fixity and interfacial stresses. Analytical models are developed for an end-coupled linear SMP-SMA two-way actuator and the predicted strain is shown to be in good agreement with experimental test results.
Highlights
Shape memory polymers (SMPs) are polymeric smart materials that undergo large deformation when heated above their glass transition temperature Tg, fix their deformed shape when cooled below Tg, and subsequently recover their original shape when reheated above Tg
shape memory composites (SMCs) OPERATING REGIMES This paper focuses on examining maximum interfacial stresses, composite shape fixity, and actuation strain, which do not occur during phase transitions, but within operating regimes
Three regimes of SMC operation have been identified that capitalize on the characteristic shape fixity of shape memory polymers (SMPs) and the shape recovery of shape memory alloys (SMAs)
Summary
Shape memory polymers (SMPs) are polymeric smart materials that undergo large deformation when heated above their glass transition temperature Tg, fix their deformed shape when cooled below Tg, and subsequently recover their original shape when reheated above Tg. CASE I: SMP MATRIX WITH AN EMBEDDED SMA WIRE The purpose of Case I is to analyze interfacial stresses by considering the maximum strain that results from the transition from. Where the constants C1 and C2 are obtained by applying the boundary conditions σA = −σ0 at x = ± L/2 (with L the length of the composite), FIGURE 2 | (A) Unloaded SMC and deformation in x –z view (shear lag model), and (B) free body diagram of a wire element and shear strain in the matrix. For the cases of the SMP radius equal to the beam half-thickness Rt and half-width Rw, the 8% strain corresponds to applied stresses of σ0 = 5.67 GPa and σ0 = 5.91 GPa, respectively These large axial stresses were used for the shear lag model to replicate a limiting strain condition when examining the interfacial shear stress. The Poisson’s ratios of the SMA wire and the SMP matrix are 0.3 and 0.35, respectively
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