Three-dimensional size effects in composite pin joints

Abstract

ABSTRACT--Mechanical fastening is commonly used in joining composite laminates. It is especially superior to adhesive bonding in joining thick composite laminates. The significant effects of composite thickness on the efficiency of pin joining have been reported in a previous study. The present study further investigated the three-dimensional (thickness as well as in-plane dimensions) size effects on pin joining. A glassfabric/phenolic composite material was used as the studied material while double-lap-single-pin joints were used as the experimental models. Based on four different thicknesses and seven different hole diameters, in total nine composite joint configurations were prepared. The nine configurations were organized into three groups with different H/D ratios (thickness versus hole diameter). Experimental results revealed that the load-displacement curves of the groups with H/D = 0.4 and 0.75 were brittle-type while those of the group with H/D = 1.5 were ductile-type. The microscopic damage modes of the joints with brittle-type curves were due to outward buckling for 8-ply cases and kink bands for 24-ply and 40-ply cases. The bearing strengths of the pin joints decreased monotonically in the group with H/D = 0.4 but increased then decreased in the groups with H/D = 0.75 and 1.5 as the joint size increased. It was found that both the material properties and the geometry parameters were responsible for the three-dimensional size effects.

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