A thermo-viscoelastic constitutive model addressing the cyclic shape memory effect for thermo-induced shape memory polymers

Abstract

The cyclic shape memory effect of thermo-induced shape memory polymers (TSMPs) is a typical thermo-mechanical process that can be affected by thermo-mechanical loading histories. During the deformation stage of the cyclic shape memory effect, polymer chains exhibit the initial dissociation of sub-entanglements, slipping and orientation with the increase in the deformation. The strain can be recovered with the internal rotation of the dihedral angle due to the enhancing motion of polymer chains during the reheating. Based on the rheological theory, a thermo-viscoelastic model is proposed to capture the cyclic shape memory effect of TSMPs. A temperature-dependent stress threshold value is introduced to reflect the slipping of polymer chains. In order to take into account how orientation affects the cyclic shape memory effect, a relationship between the strain and orientation is constructed and introduced into the evolution equations of elastic modulus, viscosity and irrecoverable strain. By comparing the experimental and simulated results at different loading levels and numbers of cycles, the proposed model is verified. The results show that the proposed model can reasonably predict the cyclic shape memory effect of TSMPs.

Insight into constitutive theories of 4D printed polymer materials: a review

“…Recently, Li et al [39] proposed a thermo-viscoelastic model to capture the initial dissociation of sub-entanglements, slipping, and orientation of polymer chains during the cyclic shape memory effect (CSME). For this purpose, the authors included a temperature-dependent stress threshold value and degree of orientation of the polymer chains in the constitutive model.…”

Experimental investigation on 4D printed intelligent assembly cushion with adjustable pre-tightening force

“…It is because of the material relaxation and its corresponding structural stress redistribution response. In the free recovery process after heating in figure 8(b), the deformation gradually recovers with some irrecoverable deformation due to the nonideal structure due to manufacturing deviation and large local deformation [15,33,34]. Figure 8(c) shows the recovery force at different constrained conditions, including free recovery condition, semi-constrained condition with a constrained displacement of 0.4 mm, and constrained condition.…”

“…The remaining energy is locked inside the material. If there is free recovery, the remained energy is released by transiting to elastic deformation energy, viscous deformation energy and shape memory energy since the deformation can be divided into elastic, viscous, shape memory and residual deformations, and so on [34,36,37]. If there is constrained recovery, the elastic energy, part of the remained energy, could be released, serving as the recovery force [38,39], but other viscous energy could be dissipated due to relaxation.…”

A simple phenomenological model for recovery behaviors of amorphous thermoset‐based shape memory polymers via a time‐varying viscosity

“…Castro et al 23 and Nguyen et al 24 considered multiple relaxation processes, rather than a single one in the study of Nguyen et al, 22 to enhance accuracy. With the efforts of numerous scholars, [20][21][22][23][24][25][26][27][28][29][30][31][32][33] theoretical models have gradually advanced in their ability to capture the complex thermomechanical behavior of SMPs. However, the pursuit of improving accuracy leads to a significantly increasing number of model parameters, regardless of which approach is employed.…”