In Situ Scanning Electron Microscopy Investigation of Flexural and Interlaminar Failure Mechanisms in Carbon Nanotube‐Reinforced Shape Memory Polymer Composites

The study examines carbon nanotube (CNT) reinforced shape memory polymer (SMP) composites designed to improve flexural performance and interlaminar fracture toughness. Two CNT architectures are compared: CNT “buckypaper” (BP) interleaves and dispersed CNTs, both incorporated into glass fiber SMP laminates. Mechanical testing is performed using a novel in situ scanning electron microscopy (SEM) platform to directly observe how damage starts and evolves during loading. Under flexural loading, baseline specimens show transverse tow splitting followed by catastrophic fiber kinking. With BP interleaves, catastrophic kink-band failure is suppressed, and damage is redirected into a distinct dual-shear-plane geometry due to CNT network-mediated constraint. Mode II fracture toughness testing shows a significant improvement in GIIc for BP interleaves compared with both baseline and dispersed CNT cases. In situ SEM indicates that delamination propagation follows sequential steps: initial BP interleave rupture, then crack propagation along the BP/fiber interface.