Experimental Investigation of Static Strength in CFRP and Aluminium Lugs Subjected to Uniaxial Tensile Loading

Abstract This study presents a comprehensive experimental investigation into the performance of lug structures made from Carbon Fibre Reinforced Polymers (CFRP) with three distinct lay-up configurations: Hard (L-C-H), Quasi-Isotropic (L-C-QI), and Soft (L-C-S). The behaviour of these CFRP lugs was compared against conventional metallic aluminium lugs (L-Al) to evaluate their load-bearing performance under uniaxial tensile loading. Among the CFRP configurations, the L-C-QI lay-up exhibited the highest load-bearing capacity, even surpassing that of L-Al. In contrast, the L-C-H lay-up demonstrated the lowest strength within the CFRP group. L-C-S exhibited matrix cracking near the bore hole, facilitating stress relief similar to ductile metals. The L-Al lugs underwent significant plastic deformation and ligament necking, leading to 136% higher energy absorption compared to the best-performing CFRP lug (L-C-QI). Additionally, the study found that as the Hooke’s stiffness of the lugs decreases, the angle between the failure surface and the loading direction increases, indicating a transition in failure mode from shear tear-out to net section tension. Significant delamination was observed on the bearing side of the lug bore hole in CFRP lugs, while aluminium lugs exhibited plasticity on the bearing surface and ligament necking. These findings offer insights into the static tensile behaviour and failure mechanisms of composite and metallic lug structures.