Constitutive Model For Shape Memory Polymers Research Articles

Three-dimensional constitutive model for shape-memory polymers considering temperature-rate dependent behavior

The temperature-rate dependent thermomechanical behavior of shape-memory polymers (SMPs) is challenging to study, because the microstructure of SMPs cannot rearrange instantaneously to an equilibrium configuration in response to temperature changes. Herein, we report a temperature-rate dependent three-dimensional constitutive model for SMPs based on a two-phase model consisting of rubbery and glassy phases. To describe the effect of temperature rate on SMPs, the variation of the volume fraction of each phase affected by temperature was considered under different temperature-rate conditions. Additionally, the temperature-rate dependent thermal strain was incorporated into the two-phase model. The developed constitutive model was validated by simulating the shape-memory behavior of SMPs, and by comparing the simulation and experimental results under different temperature-rate conditions.

Numerical homogenization of coiled carbon nanotube reinforced shape memory polymer nanocomposites

Shape memory polymers (SMPs) are a group of smart materials that, by applying an external stimulation such as the temperature, retrieve their permanent shape from a temporary one. SMP nanocomposites have been developed to improve the mechanical, thermal, electrical, and magnetic properties of SMPs for potential applications in e.g. medical equipment, sensors, actuators, and drug delivery systems. In this research, SMP is reinforced with Coiled carbon nanotubes (CCNT) due to its geometric properties which let material tolerate higher strains and improve thermomechanical properties of SMP. In this paper, the effect of addition of CCNT on thermomechanical response of SMP under large deformations is numerically investigated. Employing a thermo-visco-hyperelastic constitutive model for SMP, a cubic representative volume element is realized using Monte Carlo algorithm. The effect of inclusion’s geometry (e.g. spring length or aspect ratio, pitch or number of coils of CCNT), volume fraction, as well as their distribution on the thermomechanical properties of SMP/CCNT composite in two stress- and shape recovery processes in different heating rates and pre-strains is studied using Finite Element technique. Results reveal that increasing the volume fraction up to 0.6%, leads to a 15% rise in the effective stress in the nanocomposite. Increasing the spring length of the CCNT, the strain recovery of the nanocomposite increases about 8%. It is shown that when the mechanical loading is parallel to the CCNTs orientation, the stress is about 25% larger than when the loading is perpendicular to the unidirectional CCNTs. But for the strain recovery, the orientation does not play an important role in the strain recovery.