Micromechanical Modeling of Two-Way Shape Memory Response of Semi-Crystalline Polymers Based on Equivalent Inclusion Method

Document Type : Research Paper

Authors

Department of Materials Science and Engineering, K. N. Toosi University and Technology, Tehran, Iran

Abstract

Two-way shape memory polymers (2W-SMPs) are a class of intelligent materials that demonstrate reversible form memory, rendering them suitable for a wide range of applications in response to external stimuli. During the phase transition in the shape memory cycle of semi-crystalline polymers, the 2W-SMPs are represented as a two-phase material, consisting of an amorphous matrix and the crystalline inclusions. This paper employs the Equivalent Inclusion Method (EIM), based on the Modified-Mori-Tanaka (MMT) approach, to determine the effective thermomechanical response of inclusions inside a heterogeneous matrix. Unlike existing phase transition models, the proposed model accounts for both phase interactions and the morphology (shape and size) of the inclusion phase throughout the thermomechanical cycle. The model was implemented using the UMAT user subroutine in ABAQUS to simulate the mechanical behavior of SMPs. Analysis of various inclusion shapes revealed that ellipsoidal shapes most accurately represent the morphology of the inclusion phase. In particular, a highly elongated ellipsoidal inclusion (a/c = 1/25) provided the best agreement with simulation results. A fivefold increase in the (a/c) aspect ratio of the crystalline inclusions resulted in approximately 10% increase in crystallization-induced strain, thereby improving consistency with shape memory experiments when the actual morphology was considered. The shape memory response of PCL under a stress of 250 kPa demonstrated a ~12.5% strain increase during cooling from 65 to -40 ̊C, with about 7% occurring near the crystallization point over a 40 ̊C interval. Incorporating phase interactions significantly enhanced the model's agreement with experimental results on shape recovery.

Keywords

References

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Iranian Journal of Materials Forming
Volume 12, Issue 3
2025
Pages 42-55

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