Simulation of shape memory cycle of a polymeric beam undergoing large deflection using a simple incremental approach

Shape memory polymers are a group of polymers which can store a temporary shape at a relatively cold temperature and recover when heated above its glass transition temperature. Various constitutive models exist in literature to simulate the uniaxial shape memory cycle. One such popular model is based on the concept of multiple natural configurations. In the present work, the stress-strain-based model is adapted for bending application by converting it into a scalar moment-curvature-based relationship. The adapted model is used in a numerical framework for large deflection of beams to simulate the shape memory cycle. The employed numerical framework is based on linearising the non-linear governing differential equation and subsequently solving it in steps by numerical integration. The results are presented in suitable non-dimensional form for generality. Since coefficient of thermal expansion plays a minimal role in bending, it is found that the bending results are considerably different from their uniaxial counterpart. The approach may be claimed to be computationally economic as compared to finite element method because here large matrix inversion is avoided.

Triple Shape Memory Polymers: Constitutive Modeling and Numerical Simulation

Recently, triple shape memory polymers (TSMPs) have been discovered; these materials can be programmed to switch between three distinct shapes. Previously, we introduced a model to describe the mechanical behavior of TSMPs; however, the earlier study was limited in scope to simple cases of uniaxial deformation. In this work, we build upon our prior work, and develop robust numerical methods and constitutive equations to model complex mechanical behavior of TSMPs in inhomogeneous deformations and loading conditions using a framework based on the theory of multiple natural configurations. The model has been calibrated to uniaxial experiments. In addition, the model has been implemented as a user material subroutine (UMAT) in the finite element package abaqus. To demonstrate the applicability of the developed constitutive model, we have numerically simulated two cases of three-dimensional bodies undergoing triple-shape cycles; triple-shape recovery response of a complex TSMP geometry and the triple-shape recovery response of a stent when it is inserted in an artery modeled as a compliant elastomeric tube.

Modeling Circular Shear in Shape Memory Polymers With Triple Shape Effect Subjected to Crystallization Under Constant Shear

The capacity of a material to sense its environment and to change its shape on demand in a predefined way has tremendous technological significance for a wide variety of application areas. Shape memory polymers (SMPs) belong to this category of smart materials as they have the ability to undergo a shape change in a predetermined manner under the influence of an external stimulus. SMPs can recover their permanent shape after undergoing large deformation to a temporary shape on exposure to external triggers such as light, PH values and heat. Thermally induced SMPs are first generation SMPs and have been widely recognized. Crystallizable SMPs are a class of thermally induced SMPs whose temporary shape is due to formation of crystalline phases, and they will revert back to their permanent shape when the crystallization phase is melted through heating. Traditional crystallizable SMPs can only perform dual-shape memory cycles and this limits applications of crystallizable SMPs. Recently SMPs with triple shape effect have been reported that can switch from a second temporary shape to the first temporary shape and from there to the permanent shape under stimulation by heat. Our research focuses on modeling the mechanical behavior of these SMPs with triple-shape effect. The framework used in developing the model is built upon the theory of multiple natural configurations [3]. In order to model the mechanics associated with these polymers different stages of the shape fixation and recovery cycle and different phases of the material during this cycle need to be characterized. This includes developing a model for the amorphous phase and the subsequent semi-crystalline phases with different stress free states and melting of these phases. The model subsequently has been used to simulate results for a typical deformation cycle involving circular shear.

Modeling the Circular Shear in Light Activated Shape Memory Polymers With Three Networks

Shape memory polymers (SMP’s) are polymers that have the ability to retain a temporary shape, which can revert back to the original shape on exposure to specific triggers such as increase in temperature or exposure to light at specific wavelengths. A new type of shape memory polymer, light activated shape memory polymers (LASMP’s) have been developed in the past few years. In these polymers the temporary shapes are fixed by exposure to light at a specific wavelength. Exposure to light at this wavelength causes the photosensitive molecules, which are grafted on to the polymer chains, to form covalent bonds. These covalent bonds are responsible for the temporary shape and act as crosslinks. On exposure to light at a different wavelength these bonds are cleaved and the material can revert back to its original shape. A constitutive model of LASMP’s which based on the notion of multiple natural configurations has been developed (see Sodhi and Rao [1]). It has been applied to model the circular shear of light activated shape memory polymer with two networks. In this work we use this model to analyze the mechanical behavior of LASMP’s with three different networks undergoing a circular shear deformation cycle. This involves study of the behavior of the LASMP’s when two temporary configurations are formed by exposing the polymer to light at different time during the deformation process. In addition, we show that these materials are able to undergo complex cycles of deformation due to the flexibility with which these temporary configurations can be formed and removed by exposure to light.

Application of a Constitutive Modeling for Light Activated Shape Memory Polymer to Circular Shear

Shape memory polymers (SMP’s) are polymers that have the ability to retain a temporary shape, which can revert back to the original shape on exposure to specific triggers such as increase in temperature or exposure to light at specific wavelengths. A new type of shape memory polymer, light activated shape memory polymers (LASMP’s) have been developed in the past few years. In these polymers the temporary shapes are fixed by exposure to light at a specific wavelength. Exposure to light at this wavelength causes the photosensitive molecules, which are grafted on to the polymer chains, to form covalent bonds. These covalent bonds are responsible for the temporary shape and act as crosslinks. On exposure to light at a different wavelength these bonds are cleaved and the material can revert back to its original shape. A constitutive model of LASMP’s which based on the notion of multiple natural configurations has been developed (see Sodhi and Rao[1]). In this work we use this model to analyze the mechanical behavior of LASMP’s under a specific boundary value problem, namely, the problem of circular shear. We use this model problem to study the behavior of the LASMP’s when a temporary configuration is formed by exposing the polymer to light. In addition we show that these materials are able to undergo complex cycles of deformation due to the flexibility with which these temporary configurations can be formed and removed by exposure to light.

Modeling the Mechanics of Crystallizable Shape Memory Polymers With Two Crystallizing Phases for Crystallization Under Constant Strain

Shape Memory Polymers are a promising class of smart materials with applications ranging from biomedical devices to aerospace technology. SMPs have a capacity to retain complex temporary shapes involving large deformations and revert back to their original shape when triggered by external stimuli such as heat. Crystallizable SMPs are a subclass of SMPs where the transient shape is retained by formation of a crystalline phase and return to the original shape is due to melting of this crystalline phase [1]. Recently CSMPs with multiphase polymer networks containing two different crystallizable segments have been reported which have the capability to switch between three shapes when stimulated by changes in temperature [2,4]. These properties open up many new possibilities for applications. Our research is focused upon modeling the mechanics associated with these CSMPs. The model is developed using a framework based upon theory of multiple natural configurations [3]. The developed model is then used to simulate results for typical boundary value problems.

Light Activated Shape Memory Polymers: Some Inhomogeneous Deformation Examples

Shape memory polymers (SMP’s) belong to a large family of shape memory materials, which are defined by their capacity to store a deformed (temporary) shape and recover an original (parent) shape. SMP’s have the ability to change size and shape when activated through a suitable trigger. This trigger, which can be heating the polymer or exposing it to light of a specific frequency, is responsible for the new temporary shape. Return to the original shape can be achieved by a suitable reverse trigger. Light Activated Shape Memory Polymers (LASMP) are recently developed smart materials which are synthesized with special photosensitive molecules. These molecules when exposed to Ultraviolet (UV) light at specific wavelengths, form covalent crosslinks that are responsible for providing LASMP with their temporary shape. Light activation removes temperature constraints faced by thermoresponsive SMP for medical applications and also brings the added advantage of remote activation. Thus LASMP find use in a variety of applications ranging from MEMS devices to widespread usage for biomedical devices such as intravenous needles and stents. Furthermore, the aerospace industry has found use for these materials for applications ranging from easily deployable space structures to morphing wing aircraft. The authors have introduced a constitutive model to model the mechanics of these LASMP [1]. The modeling is done using a framework based on the theory of multiple natural configurations. A few homogenous and inhomogeneous examples were solved in [1], but with tacit understanding that the intensity of light and hence the extent of reaction is homogenous throughout the polymer sample. In this paper we use the developed model to solve the cases of inhomogeneous deformation with inhomogeneous exposure to light.

Modeling the Behavior of Crystallizable Shape Memory Polymers Subject to Inhomogeneous Deformations

The constitutive model for the mechanics of crystallizable shape memory polymers (CSMP) has been developed in the past [1, 2]. The model was developed using the theory of multiple natural configurations and has been successful in addressing a diverse class of problems. In this research work, the efficacy of the developed CSMP model is tested by applying it to the torsion of a cylinder, which is an inhomogeneous deformation. The crystallization of the cylinder is studied under two different conditions i.e. crystallization under constant shear and crystallization under constant moment.

Modeling and Simulation of Light Activated Shape Memory Polymers

This paper focuses on developing a model for light activated shape memory polymers (LASMP’s) undergoing deformation using the framework based on multiple natural configurations and simulating results for boundary value problems. LASMP’s are novel polymeric materials that are different in many ways from the first generation thermally controlled Shape Memory Polymers (SMP’s). Instead of using phase change to produce a mechanism, LASMP’s have photosensitive molecules grafted on their polymer chains. These photosensitive molecules, when exposed to light at certain wavelengths, form covalent bonds that act as crosslinks to give this class of SMP’s their temporary shape. By virtue of their different mechanism, LASMP’s provide a wide array of advantages such as remote activation and selective exposure, thus opening new doors as a potential for vast applications in the biomedical and aerospace industries [1].