Experimental Strain Analysis of Combination Adhesives/Bolt Lap Joints Between Glass-Reinforced Plastic Laminates

摘要

An investigation was conducted of combination adhesive/bolt lap joints between glass-reinforced epoxy laminate panels bonded with a nylon-modified epoxy adhesive. Its purpose was to ascertain whether a combination of adhesives with mechanical fasteners would provide lap joints of significantly greater static strength than could be obtained by the use of either adhesives or mechanical fasteners separately. The strain distribution around a hole in an adhesive lap joint under tensile load was measured with electrical resistance strain gages bonded to the adherends. This distribution was compared to a similarly obtained strain distribution for a hole in a single panel of the same laminate. The two distributions were found to be almost identical, indicating that the presence of an adhesive does not reduce the stress concentration around a bolt hole and should not, therefore, be expected to strengthen bolted joints that tend to fail in tension across the weakened hole section. The fracture loads and modes of failure of an adhesive lap joint were compared with those of a similar adhesive lap joint 'reinforced' with bolts at the ends. This comparison revealed that the bolt holes were reducing excessively the critical area at the ends of the joint, where most of the resistance of the lap joint must be concentrated, and were actually reducing the strength of the joint. Such a result indicates that mechanical reinforcements requiring holes at the ends of an adhesive lap joint cannot be expected to increase the static strength of the joint. (Author)