<p style="text-align: justify">Shape memory polymers (SMPs) are a class of smart materials that have the ability to retain multiple temporary shapes and recover original shapes as they exhibit deformation in response to external stimuli. The shape change in these polymers can be triggered using different stimuli like temperature, light, water, pH, magnetism, and their mechanisms can be easily altered. SMPs are capable of displaying multiple temporary and one permanent shape by either creating a multiphase system or by undergoing a very broad thermal transition. The temporary shapes involved can be very complex but SMPs can recover large amounts of strains as compared to other smart materials. SMPs and their composites are also easy to manufacture and complex structures can be 3D printed with multimaterials by controlling the geometric parameters such as volume fraction and fiber’s position in space. Their applications are diverse and found in various fields such as transportation, energy generation, deployable structures, clothing and healthcare with tissue engineering, biological sutures, stents, bladder sensors, etc. Hence, there is an increasing need to model their behavior. This work discusses the behavior of a thermally activated subclass of SMPs in which the temporary shape is fixed by a crystalline phase and a light activated subclass of SMPs in which the temporary shape is fixed by photo-reversible covalent crosslinks. The return to original shape is either due to the transition of the crystalline phase or due to the cleaving of covalent crosslinks. Light activated SMPs not only remove the temperature limitations faced by thermally activated SMPs but also bring the added advantage of remote activation leading to even more possible applications. Their thermo-mechanical behavior is simulated using a framework based on the theory of multiple natural configurations while incorporating the viscoelastic effects in a rate type model. The model is applied to different boundary value problems related to homogeneous deformation such as uniaxial extension of dual and triple shape memory polymers under controlled stress and strain conditions. The effects of parameters such as temperature, external stress, crystallinity, shear modulus and relaxation time on the nonlinear deformation have also been studied. The results are found to be consistent with the experimental data and show how the complicated thermo-mechanical behavior and shape memory effects are influenced by these parameters. Furthermore, various shape memory cycles involving multiple transitioning mechanisms have been investigated where the same polymer has a crystallizable component as well as a photosensitive functional group.</p>

Constitutive Modeling of Viscoelastic Photo-Adaptable Thermally Activated Shape Memory Polymers

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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