Bart Vangrimde

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.

Analysis of the bearing response test for polymer matrix composite laminates: bearing stiffness measurement and simulation

Abstract This paper is the first part of a project that aims to investigate the mechanical and fracture behaviour of bolted joints in general purpose glass fibre-reinforced polyesters (GRP). In the present study a procedure is set up to measure the bearing stiffness of a GRP laminate in a single-bolt double lap joint. With a three-dimensional finite element model it is shown that the bolt and fixture deformations affect the stiffness results. Hence the experimental displacement data were corrected before calculating the coupon bearing stiffness. The coupon bearing stiffness was also simulated by a two-dimensional finite element model. Provided that bolt–hole clearance, material non-linearity and bolt–hole friction are taken into account, good agreement is observed with experimental data. Bearing strain and bearing stiffness are based on the bearing deformation of the coupon, not on the hole elongation. This makes the stiffness data useful for design and allows an easy installation of the displacement measurement devices.