Synergistic toughening of dissimilar Al/CFRP adhesive joints via ternary Co-Zn-Al layered double hydroxides nanoparticles: Fracture mechanics and cohesive zone modeling

The robust integration of Carbon Fiber Reinforced Polymers (CFRP) with aluminum is critical for advancing lightweight aerospace and automotive structures; however, the inherent brittleness of structural epoxies often compromises the damage tolerance of these dissimilar joints. This study addresses this challenge by investigating the fracture behavior of Al-Al and Al-CFRP joints reinforced with novel ternary Co-Zn-Al Layered Double Hydroxide (LDH) nanoparticles. Synthesized via co-precipitation and dispersed at varying concentrations ranging from 0.0 to 4.0 wt%, these nanofillers were tested under Mode I, Mode II, and mixed-mode loading conditions using Digital Image Correlation (DIC). Experimental results pinpointed a critical reinforcement threshold at 2.0 wt%, delivering a remarkable 278% enhancement in Mode II fracture energy. Scanning Electron Microscopy (SEM) analysis revealed a transition from brittle cleavage to rough, heterogeneous fracture surfaces, indicating operative mechanisms such as crack pinning and mechanical interlocking. Bridging experimental insights with predictive design, a Finite Element framework utilizing a bilinear Cohesive Zone Model (CZM) was developed and validated against DIC data. A subsequent parametric study elucidated the sensitivity of joint strength to overlap length and adherend stiffness.These findings demonstrate that Co-Zn-Al LDH nanoparticles significantly improve interfacial fracture toughness, offering a sophisticated pathway for designing durable, high-performance hybrid structures.