Characterization of shear deformation and strain recovery behavior in shape memory polymers

The large strain deformation behavior of a styrene-based shape memory polymer (SMP) has been investigated in tensile- and shear-loading conditions with the aim of characterizing the mechanical properties. Of particular interest is the recovery behavior, which is critical for the development of new SMP-based applications, and the effect of filler-loading. Magnetite and iron spherical nano-particles have been used as fillers. The magnetite-filled samples were prepared to allow the investigation of magnetic induction-based heating to serve as a trigger for the thermally activated SMP. Very favorable response times were observed using this technique. The iron-filled samples were prepared to confer electrical conductivity to the polymer. Testing of the materials was performed in tensile and shear test conditions at room and elevated temperatures. Following tensile and shear deformation to lock-in plastic strain, the SMP exhibited a rapid rise in the recovery force following the application of a thermal trigger. However, full recovery of shear strain has not been recorded. This experimentation will yield data critical for SMP-based actuator design. Furthermore, the study will also provide insight on matrix-filler interaction and permit constitutive modeling through an investigation of the elastic, inelastic and recovery deformation response of the SMP.