Phase evolution based thermomechanical crack closure mechanism of shape memory polymers

In this article, the thermomechanical fracture responses of shape memory polymers (SMPs) under two common stress free- strain recovery and fixed strain- stress recovery loading cycles are investigated. The shape memory properties of cracked SMPs for both single and mixed fracture modes are examined. The effect of phase transformation on the fracture parameters of the material is evaluated by the extended finite element method (XFEM). In addition, the fracture behavior is studied when the crack is created during the thermomechanical process. The results show that the initially cracked SMPs can fully preserve the shape memory property for both stress freestrain recovery and fixed strain- stress recovery cycles. Moreover, as a promising application, SMPs can be well employed in self-healing materials due to complete closure of the crack at the end of the shape recovery cycle. In cases where a crack is created in the midst of the fixed strain- stress recovery thermomechanical process, it is observed that the performance of the structure in providing desired reaction forces is reduced by increase of the crack length. Nevertheless, the presence of compressive forces in the initial steps of the force recovery cycle may potentially contribute to crack healing if additive healing agents are employed.

Automated summary

The article explores the thermomechanical fracture responses of shape memory polymers (SMPs) under stress free-strain recovery and fixed strain-stress recovery loading cycles, evaluating the effect of phase transformation on fracture parameters using the extended finite element method (XFEM). The study shows that SMPs with initially cracked SMPs can fully preserve shape memory properties and may be applied to self-healing materials. However, the presence of cracks in the fixed strain-stress recovery process can reduce the structure's ability to provide desired reaction forces, with potential for crack healing through compressive forces in the force recovery cycle.