Impact of standard and unexpected bolt-hole-washer tolerances on the performance of pinned and torqued joints in CFRP composites

This study aimed to investigate the impact of some practical assembly errors on the performance of composite joints with M6 bolts in quasi-isotropic CFRP laminates with stacking sequence of [±45/0/90]2S, which are increasingly used in aerospace and automotive industries. The detailed experimental explanations of the behaviors of the bolted joints in CFRP composites with standard and unexpected joining parameters, exhibited a vital impact on the bearing and ultimate joint strength, stiffness, energy absorption, and failure mechanisms. The joining parameters include tightening torque (0-16Nm), bolt-hole clearance (0–240 μm), and washer-to-bolt hole clearance (0–500 μm) with different offset arrangements. The bolt axial force is monitored during the testing of double-lap bolted composite joints. The maximum performance of the bolted joints was observed at tightening torque of 12Nm, bolt-hole clearance up to 60 μm, washer-to-bolt hole neat-fit or with negative clearance arrangement. The first peak, 2 % offset, and ultimate strengths are increased, respectively, by 55.9 %, 56.4 % and 52.4 % compared to those of the pinned joints. The 2 % offset strength and stiffness of bolted joints with negative washer-to-bolt hole clearance arrangements is improved by 26.8 % and 57 % respectively compared to those having positive arrangements. Energy absorption increase almost linearly with bearing load with correlation coefficient of 0.982.