Bearing stiffness of glass fibre-reinforced polyester: influence of coupon geometry and laminate properties

The bearing stress–strain response of glass fibre-reinforced polyester (GRP) laminates in a single-bolt double lap joint was investigated experimentally and numerically. Six GRP laminate types were tested according to the ASTM D5961 procedures for three coupon geometries. A 2-D finite element model that included material non-linearity, clearance and bolt–hole friction predicted the bearing stiffness very accurately. However, both numerical and experimental data disagreed with existing joint flexibility models developed for metals or carbon fibre-reinforced epoxy laminates with tight fitting bolts. Clearly, some adaptation of the joint flexibility formulae is needed when they are used for design of GRP structures with large bolt–hole clearance. On average, joints with a reduced width (w/D=2) were 26% more compliant than three times wider standard joints (w/D=6). Doubling the end distance had a smaller effect on the bearing stiffness. Laminates with more axial reinforcement had a clearly higher bearing stiffness for the small coupon width (w/D=2). For wider coupons (w/D=6), this trend became less apparent.