Light-activated polymers are an exciting class of materials that respond mechanically when irradiated at particular
wavelengths. Recent demonstrations include two novel polymers developed by Scott et al (2006) and Lendlein et al
(2005). In these polymers, photochemistry alters the microstructure of the cross-linked polymer network, which is
further translated as light-induced deformation and when properly used light-induced shape memory effect. In this work,
we develop a model framework to simulate the photomechanical response of light-activated polymer systems. This
framework breaks down the observed macroscopic photomechanical phenomenon into four coupled sets of underlying
physics, which occur throughout the material during irradiation and mechanical deformation. In the context of this
framework, a basic photomechanical phenomenon involves simultaneously modeling photophysics, photochemistry,
chemomechanical coupling, and mechanical behavior. Furthermore, network alteration are accounted for through the
parallel decomposition of the cross-linked network into two components, an original network and a photochemically
altered network, which allows to capture the observed photomechanical behaviors demonstrated in these materials. One
of the principal strengths of this model framework is its generality as it can be applied to light activated polymer systems
with fundamentally different of photophysics, photochemistry, and chemomechanical behaviors simply by choosing
different field equations for the four sets of physics specific to a material system.
Seamless skins for morphing vehicles have been demonstrated as feasible but establishing robust fastening methods for
morphing skins is one of the next key challenges. Skin materials previously developed by Cornerstone Research Group
and others include high-performance, reinforced elastomeric and shape memory polymer (SMP)-based composites.
Recent focus has shifted to improving performance and increasing the technology readiness level of these materials.
Cycling of recently demonstrated morphing skins has determined that an abrupt interface between rigid and soft
materials leads to localized failure at the interface over time. In this paper, a fundamental understanding between skin
material properties and transition zone design are combined with advanced modeling techniques. A thermal gradient
methodology is simulated to predict performance benefits. Experimental testing and simulations demonstrated
improvement in morphing component performance for a uniaxial case. This work continues to advance development to
eliminate fastening as the weak link in morphing skin technology and provides tools for use in morphing structure
design.
Shape memory polymers (SMPs) are polymers that can recover a large pre-deformed shape in response to environmental
stimuli, such as temperatures, light, etc. For a thermally induced amorphous shape memory polymer, the pre-deformation
and recovery of the shape require the material to traverse the glassy transition temperature Tg under constrained or free
conditions. In this paper, effects of thermal rates to mechanical behaviors of SMP under constrained condition were
investigated. The stress-temperature behavior demonstrates a faster stress decrease than thermal contraction during
cooling and a characteristic stress overshoot during constrained reheating. These observations were explained by a one
dimensional (1D) model that considers the non-equilibrium structure relaxation and viscoelastic behavior of the material.
Shape memory polymers (SMPs) are receiving increasing attention because of their ability to store a temporary shape
for a prescribed period of time, and then when subjected to an environmental stimulus, recover an original programmed
shape. They are attractive candidates for a wide range of applications in microsystems, biomedical devices, deployable
aerospace structures, and morphing structures. In this paper we investigate the thermomechanical behavior of shape
memory polymers due to instrumented indentation, a loading/deformation scenario that represents complex multiaxial
deformation. The SMP sample is indented using a spherical indenter at a temperature T1 (>Tg). The temperature is then
lowered to T2 (g) while the indenter is kept in place. After removal of the indenter at T2, an indentation impression
exists. Shape memory is then activated by increasing the temperature to T1 (>Tg); during free recovery the indentation
impression disappears and the surface of the SMP recovers to its original profile. A recently-developed three-dimensional
finite deformation constitutive model for the thermomechanical behavior of SMPs is then used with the
finite element method to simulate this process. Measurement and simulation results are compared for cases of free and
constrained recovery and good agreement is obtained, suggesting the appropriateness of the simulation approach for
complex multiaxial loading/deformations that are likely to occur in applications.
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