Behavior of Pin-loaded Laminated Composites B. Okutan Baba Received: 31 August 2005 / Accepted: 10 April 2006 / Published online: 22 June 2006 # Society for Experimental Mechanics 2006 Abstract In this study, an investigation was carried out to determine the effects of joint geometry and fiber orientation on the failure strength and failure mode in a pinned joint laminated composite plate. Behavior of pin-loaded laminated composites with different stack- ing sequence and different dimensions has been observed experimentally. E/glass–epoxy composites were manufactured to fabricate the specimens. Me- chanical properties of the composites were character- ized under tension, compression and in-plane shear in static loading conditions. Laminated composites were loaded through pins. Single-hole pin-loaded specimens were tested for their tensile response and width-to- hole diameter (W/D) and edge distance-to-hole diam- eter (E/D) ratios evaluated. A series of experiments was performed with six different material configura- tions ([0/T45] s –[90/T45] s , [0/90/0] s –[90/0/90] s and [90/ 0] 2s –[T45] 2s ), in all, over 120 specimens. E/D ratios and W/D ratios of plates were changed from 1 to 5 and 2 to 5, respectively. Failure propagation and failure type were observed on the specimens. The influence of the joint geometry on the strength of the pin-loaded composites was assessed. When laminated composite plates were loaded to final failure, three basic failure modes consisting of net-tension, shear out and bearing failure were observed for the different geometric dimensions. All the connections tested showed that the fiber orientations have a definite influence on the position around hole circumference at which failure initiated. Net-tension failure occurred for specimens that had small width and large end distance. When the width was increased, the specimens which had small end distances failed in the shear-out modes. When the end distance was increased, bearing failure developed in addition to shear-out failure. The experimental results showed that the ultimate load capacities of E/glass– epoxy laminate plates with pin connection were increased by increasing W and E. However, increasing the E/D and W/D ratios beyond a critical value has an insignificant effect on the ultimate load capacity of the connection. Keywords Pin . Laminated composite . E/glass–epoxy . Failure modes . Joint geometry Introduction Owing to their low weight and high strength compared to metallic material, laminated composite materials offer more efficient structures for application in the automobile, construction and weight sensitive aero- nautical industries. Due to strength and safety require- ments, these applications require joining composites either to composites or to metals. It is rarely possible to produce a construction without joints due to limi- tations on material size, convenience in manufacture or transportation and the need for access. All con- nections or joints are potentially the weakest points in the structures so can determine its structural efficiency. Although leading to a weight penalty due to stress concentration created by drilling a hole in the lami- nate, mechanical fasteners are widely used because of their low cost, simplicity for assemble and facilitation of disassembly for repair. Joint efficiency has been a major concern in using laminated composite materials. Relative inefficiency and low joint strength have limited widespread appli- cation of composites. The knowledge of the failure strength would help in selecting the appropriate joint Experimental Mechanics (2006) 46: 589–600 DOI 10.1007/s11340-006-8735-z B. Okutan Baba (*) Canakkale Onsekiz Mart University, Canakkale, Turkey e-mail: obuket@comu.edu.tr SEM