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

ABSTRACT Nanoscale reinforcements in polymer matrix composites offer improved performance through complex, multiscale failure mechanisms. This work investigates carbon nanotube (CNT) reinforced shape memory polymer (SMP) composites with the aim of enhancing flexural properties and interlaminar fracture toughness. Two architectures are considered: SMP‐impregnated buckypaper (BP) interleaves and dispersed CNTs, each incorporated into glass fiber SMP laminates. Mechanical testing using a novel in situ scanning electron microscopy (SEM) platform was conducted to evaluate mechanical performance, while directly observing damage initiation and evolution. Under flexural loading, baseline specimens exhibited progressive transverse tow splitting followed by catastrophic fiber kinking. BP interleaves suppressed catastrophic kink‐band failure through CNT network‐mediated constraint and redirection of compressive damage, resulting in a distinct dual‐shear‐plane geometry, while the dispersed CNTs produced distributed matrix reinforcement. Mode II fracture toughness testing demonstrated a significant improvement in G _IIc with BP interleaves relative to both baseline and dispersed CNT cases. In situ SEM revealed that delamination propagation was governed by sequential failure mechanisms: initial BP interleave rupture followed by crack propagation along the BP/fiber interface. These results outline the tradeoffs for both CNT reinforcement strategies, showing BP interleaving as superior for enhancing interfacial crack propagation resistance, and establish an in situ methodology for informed composite development.