Analysis of composite laminates with multiple fasteners

Abstract

Fatigue- and fracture-related cracks are to be expected with the large number of fasteners present in aircraft structures. Therefore, contact stresses around the fastener holes and stress intensity factors associated with edge cracks are critical concerns in damage-tolerant designs. Mechanical joints consisting of many fasteners with a staggered pattern further complicate the already rather complex analysis for single-fastener joints. Load distribution among the fasteners significantly influences the failure load of multi-fastener joints. Most existing analyses are confined to single-fastener joints, and the data available for multi-fastener joints are rather limited. Very few experimental and/or analytical/numerical investigations of contact stresses for mechanical joints with staggered fasteners exist in the literature. Therefore, the accurate prediction of contact stresses (load distribution) and stress intensity factors associated with edge cracks is essential for the reliable design of such mechanical joints. This study concerns the development of an analytical methodology, based on the boundary collocation technique, to determine the contact stresses and stress intensity factors required for strength and life prediction of bolted joints with many fasteners. It provides an analytical capability for determining the contact stresses in mechanically fastened composite laminates while capturing the effects of finite geometry, presence of edge cracks, interaction among fasteners, material anisotropy, fastener flexibility, fastener-hole clearance, friction between the pin and the laminate, and by-pass loading. Also, it permits determination of the fastener load distribution, which significantly influences the failure load of a multi-fastener joint.