Anisotropic Mechanical Responses and Enhanced Recovery Force of Knitted Sandwich-Structured Shape Memory Polymer Composites
摘要
Knitted-fabric reinforced shape memory polymer composites (SMPCs) offer exceptional structural designability; however, the intricate coupling between their hierarchical architecture and synergistic thermo-mechanical performance remains insufficiently explored. In this study, a series of sandwich-structured SMPCs were fabricated using a rib-knitted fabric core and plain-woven face sheets, specifically investigating the effects of layer count, loop orientation (0°/90°), and core configurations on their mechanical and shape memory behaviors. The results reveal that the mechanical properties are dominated by the knitted architecture, where the 90° orientation exhibits significantly higher flexural strength than the 0° orientation due to the interlocking mechanism of loop pillars. While the introduction of fabric reinforcement slightly constrains the shape recovery ratio (Rr), it dramatically elevates the recovery force. Notably, the two-layers core SMPC in 90° direction achieves a peak recovery force of 15.6 N at 2% strain, representing a 6.0-fold increase over the neat shape memory epoxy polymer (SMEP). Furthermore, both shape recovery ratio and recovery force exhibited a non-monotonic parabolic trend with increasing bending strain, peaking at a critical threshold of 8%. This phenomenon is attributed to the energy-damage competition between increased elastic energy storage and irreversible structural degradation, such as loop over-stretching and interfacial debonding. Fractographic analysis confirms that failure is primarily driven by the mismatch in deformation capacity between the surface woven layers and the knitted core. This work provides a useful evidence for the synergistic optimization of load-bearing and actuation functions in next-generation intelligent sandwich-structured SMPCs.