Study on bearing strength and failure mode of a carbon-epoxy composite laminate for designing bolted joint structures

A composite single-lap bolted joint was experimentally studied and its bearing behavior was predicted numerically. Prior to performing the experiment, an appropriate e/D ratio of the composite material was determined via double-lap bolted joint tests. Using the obtained e/D ratio, specimens were manufactured, and single-lap composite bolted joint tests were subsequently performed. Various joint tests were conducted with the number of bolt holes, pre-torque, and thickness as experimental variables. The preferred bearing failure mode was observed with the designed e/D ratio and bearing strength increased with increasing tightening torque. The bearing strength was significantly affected by the projected bearing area and exhibited a linearly proportional relation with the joint bearing area. The fracture mechanism was observed using optical microscopy, indicating fiber buckling, breakage, and delamination induced from the initial damage. An energy-based progressive failure analysis (PFA) was implemented to predict the composite bolted joints strengths. The adopted PFA accurately predicted the strength of the bolted joint in range of 12%.