A constitutive theory for shape memory polymers. Part II

On modeling shape memory polymers as thermoelastic two-phase composite materials

“…The variant using the upper Hashin and Shtrikman bound leads to very similar curves. The global agreement between theory and experiment compares well with what could be obtained by Liu et al [14] and Chen and Lagoudas [17]. Like in these previous works, no hysteresis is produced when heating is applied immediately after cooling, keeping boundary conditions unchanged.…”

“…A good agreement with the three experimental strain recovery plots was also obtained by Liu et al [14] and by Chen and Lagoudas [17], but using additional data, since the α(T ) thermal expansion coefficient was fitted, with Chen and Lagoudas [17] furthermore using a fitted stress recovery curve. In the present approach, α(T ) is computed from the φ(T ) function for each composite model, as given by (6) Table 1 Optimized exponents m and n for the φ(T ) function (2) to fit the experimental strain recovery observed by Liu et al [14] after a compression of −9.1%.…”

“…One difference between theory and experiment is an opposite trend when heating begins: the experimental curves show an increasing stress, when the model predicts a decrease. The same difference with experiments was also found by Liu et al [14] and Chen and Lagoudas [17]. Actually, the model prediction corresponds to the slope at the lowest temperature being trivially equal to α g E g , since the material is glassy, with this result applying for both the upper and lower curves in Figure 4.…”

“…which is is in agreement with equation (22) of [17] but not with equation (30) of [14], where the L −1 g term is missing. This omission implies that there is a shape memory effect in the Liu et al [14] approach when both phases have the same moduli, whereas (11) leads to dε s = 0.…”

“…An encouraging agreement was found with experiments, which confirmed that a thermoelastic model is able to capture the basic stress and strain evolutions. Extensions of the model to finite strain were proposed by Diani et al [15] and by Chen and Lagoudas [16], who also provided a small-strain version (Chen and Lagoudas, [17]). The original small-strain model of Liu et al [14] has also been revisited by Wang et al [18], who proposed a first combination of the model with the theory of composite materials.…”