Thickness effects on pinned joints for composites

Mechanical joints are commonly used for joining composite laminates, especially thick section composites. In most studies of mechanical joints, the interactions between pin diameter (D) and composite dimensions such as width (W) and distance from hole center to composite end (e), resulting in W/D and e/D ratios, are the primary parameters for joint evaluation since composite laminates are usually very thin. However, as composite thickness increases, the contact interaction between pin and composite alters. Subsequently, the composite joint stiffness and joint strength are affected. Since the contact interaction is strongly affected by pin diameter (D) and composite thickness (H), this study investigated mechanical joints with combinations of various composite thicknesses and pin diameters. Composite material made of woven glass fabric and phenolic matrix was investigated. Sixteen joint configurations based on four composite thicknesses and four pin diameters were examined. Both experiments and finite element analysis were conducted in this study. It was found that the: ratio of H-2/D-2 could be used to distinguish the two primary damage modes, i.e. pin bending and bearing failure. Results also showed that thick composites with small pins and thin composites with large pins had lower efficiencies for joint stiffness and joint strength than those having similar dimensions between pin diameter and composite thickness.