Crack Deflection Mechanisms in Hierarchical Nano-Reinforced Composites

Abstract

Hierarchical nano-reinforced composites, inspired by natural materials like nacre and 
bone, exhibit superior fracture toughness through intricate crack deflection mechanisms. These 
structures incorporate nano-reinforcements such as carbon nanotubes (CNTs), graphene 
nanoplatelets (GNPs), and nanoparticles arranged in multi-scale architectures to manipulate crack 
paths, dissipate energy, and prevent catastrophic failure. This review synthesizes recent 
advancements in understanding crack deflection in such composites, drawing from experimental, 
computational, and theoretical studies. Key mechanisms include crack pinning, bridging, 
deflection at interfaces, and twisting in chiral hierarchies. For instance, CNT-reinforced carbon 
fiber epoxy composites promote multiple deflections via engineered microstructures, enhancing 
fracture toughness significantly. Computational optimizations reveal that nanotube positioning can 
amplify toughness through pinning and deflection. Natural layered composites demonstrate 
interfacial traps that arrest cracks. Findings indicate toughness improvements up to 10-fold, with 
applications in aerospace, biomedical, and structural engineering. Challenges like agglomeration 
and interfacial weaknesses are addressed through functionalization and hierarchical design. The 
paper highlights synergistic effects in hybrid systems and future directions for multiscale modeling 
to predict deflection behavior under dynamic loads.