A thermodynamics viscoelastic constitutive model for shape memory polymers

Abstract

In this study, a thermodynamics viscoelastic constitutive model was developed to describe behaviors of the typical thermo-mechanical cycle experimentations. In this model, the changes of thermodynamic and mechanics for SMPs in cooling/heating process were described clearly and the irreversible deformations were calculated. A new type of microstructure of SMPs was proposed and new definitions of phases: active phase and frozen phase were set forth in the present study. The new thermodynamics viscoelastic model is series by two parts: mechanical parts and thermal parts. A new transform equation for the transformation of frozen phase was proposed, and the transform delay time and cooling/heating rate were considered in this transform equation. A transform equation based on the transformation of frozen phase was proposed to describe the change of thermal expansion coefficient of SMPs. Finally, the typical thermo-mechanical cycle experimentation processes were calculated using the new thermodynamics viscoelastic constitutive model. Through the comparison between the calculated results and experimental results, the rationality and accuracy of the new thermodynamics viscoelastic constitutive model was finally verified.

Synthesis and properties of polylactide terpolymers P(LLA‐TMC‐GA) catalyzed by zirconium (IV) acetylacetonate

“…Shape memory polymers (SMPs) are stimuli‐responsive compounds that change their shape as a consequence of an external stimulus, such as temperature, light, electricity, magnetic, PH, etc. Usually SMPs show two phases, active phase and frozen phase …”

A comprehensive review on thermomechanical constitutive models for shape memory polymers

“…Pan et al (2018) based on the model provided by Liu et al (2006), and considering a rate-dependent T trans , developed a new constitutive model and calibrated the model for the polystyrene and an acrylate-based SMP (tBA/PEGDMA), for test results of Arrieta et al (2014b). In line with work of Wang et al (2009), Guo et al (2017) introduced another function for the frozen phase volume fraction. Then, employing a four-element model for the active phase and a three-element model for its frozen phase, they were able to model and calibrate the experimental results of Liu et al (2006) and Tobushi et al (1997) to predict the SMP strain recovery stage.…”

“…Total used thermally activated conventional SMP in the literature and its characteristics. Srinivasa (2011, 2013), Guo et al (2017), Li et al (2015, 2017a), Pan et al (2017, Saleeb et al (2017), , Srinivasa and Gosh (2008), Zeng et al (2018c), Mo (2014, 2016), Shi et al (2013), Tobushi et al (1997Tobushi et al ( , 2001, and Kafka (2008) Cross-linked ester-type PU…”

Mechanical Models, Structures, and Applications of Shape-Memory Polymers and Their Composites

“…However, it is unreasonable to assume that the frozen phase and the active phase are evenly distributed in the polymer based on the microstructures of particle-reinforced composites [46] and unidirectional fiber-reinforced polymer composites [65], and the phase transition between the two phases (end/start) at the same time. Therefore, Guo et al considered the microstructure of a semicrystalline SMP to propose a novel microstructure consisting of an active phase with a constant network and a frozen phase that can be switched between the free state and the frozen state [66]. A novel type of frozen phase transformation equation is shown in Table 2.…”