Thermomechanical Behavior Of 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.

A modified phase‐based constitutive model for shape memory polymers

ABSTRACTConstitutive models used for predicting the thermomechanical behavior of shape memory polymers (SMPs) are critical for the development of SMP applications. Among the existing models, the phase transition concept attracts wide attention due to its good predictive capacity and great convenience. However, most of the present phase transition models for SMPs have limitations or deficiencies in considering the effect of temperature change rate on the thermomechanical behavior of SMPs. In this paper, based on the kinetics of phase transitions, we propose a constitutive model in which the temperature change rate is incorporated into the phase evolution function to consider the effect of the temperature change rate on the thermomechanical properties of SMPs. Then experimental data under different recovery conditions for two different types of SMP materials are used to validate the predictive capacity and versatility of the present model. The predicted results agree quite well with the experimental observations, which demonstrates that the present model is robust enough to predict the complex thermomechanical behavior for different SMPs. In addition, through experiments and model predictions, we find that the shape free recovery curves at different heating rates can be easily predicted by just moving a reference recovery curve along the horizontal direction by a distance whose value is calculated through the proposed equation. © 2018 Society of Chemical Industry

Experimental study of thermo-mechanical behavior of a thermosetting shape-memory polymer

The thermo-mechanical behavior of shape-memory polymers (SMPs) serves for the engineering applications of SMPs. Therefore the understanding of thermo-mechanical behavior of SMPs is of great importance. This paper investigates the influence of loading rate and loading level on the thermo-mechanical behavior of a thermosetting shape-memory polymer through experimental study. A series of cyclic tension tests and shape recovery tests at different loading conditions are performed to study the strain level and strain rate effect. The results of tension tests show that the thermosetting shape-memory polymer will behave as rubber material at temperature lower than the glass transition temperature (Tg) and it can obtain a large shape fix ratio at cyclic loading condition. The shape recovery tests exhibit that loading rate and loading level have little effect on the beginning and ending of shape recovery process of the thermosetting shape-memory polymer. Compared with the material which is deformed at temperature higher than Tg, the material deformed at temperature lower than Tg behaves a bigger recovery speed.

Numerical Simulations on Shape Memory Effect of Shape Memory Polymer

Shape memory polymer (SMP) is being used in many engineering fields due to its shape memory effect and the advantages of large recoverable strain, excellent manufacturability, light weight, low cost and bio-degradability. Therefore it is of practical interest to investigate its thermo-mechanical behaviors. In this paper, a numerical simulation method is supposed to simulate the thermo-mechanical behaviors of SMP using the finite element software of MSC Marc, which is good at simulating the thermo-mechanical behaviors of viscous elastic material. The comparisons between the numerical results and the experimental results by Tobushi et al. illustrate the supposed numerical simulation method well describes the thermo-mechanical behaviors of SMP during the thermo-mechanical processes realizing shape memory effect.

Thermomechanics of shape memory polymer nanocomposites

Shape memory polymers (SMPs) have the capacity to recover large strains when pre-deformed at an elevated temperature, cooled to a lower temperature, and reheated. The thermomechanical behavior of SMPs can be tailored by modifying the molecular structure of the polymer, or by using the polymer as a matrix for multiphase composites. Here we study the thermomechanics of a SMP polymer and its composites made by adding nano-scale SiC reinforcements. Our experimental study focuses on the thermomechanical behavior in three-point flexure. The results show that the SMP nanocomposites have a higher elastic modulus and are capable of generating higher recovery forces as compared to the SMP resin. When pre-deformed at a temperature well above the glass transition temperature, T g, the stress–strain response at the pre-deformation temperature governs the relationship between the recovery stress/strain and the corresponding constraining strain/stress. When pre-deformed at a temperature below T g, the recoverable stress/strain is not governed by the stress–strain response at the pre-deformation temperature. Rather, a peak recovery stress, which is less than the pre-deformation stress, appears at a temperature near T g. Ramifications of the results on future research efforts and emerging applications of SMPs and their composites are discussed.