Asymptotic analysis of singular stress fields near contact boundaries in anisotropic elastic media

Asymptotic analyses have been used to investigate singular stress behavior in the neighborhood of material discontinuities in laminated plates with open and filled holes loaded in bearing. These analyses provide important insight into the stress fields in areas in which cracks and/or failure may initiate. Recent work also has shown that fracture in bolted composite joints may initiate near the outer edge of the bolt head or washer, particularly if the joint is preloaded. Material and geometric discontinuities exist in this region and singular stresses can be expected to exist here. However, investigation of the stresses in this area has not been reported in the literature.; In the present work, an asymptotic solution is combined with a far-field numerical solution to explore the features of the singular stresses that occur in composite bolted joints at the interface of the bolt head and the composite plate. Clamping loads are included in the analysis. An orthotropic graphite/epoxy material is considered for the plate. Aluminum, steel, and a thermoplastic bearing material are considered for the bolt head. Full contact (stick) and frictionless contact (slip) conditions are applied to the plate/bolt head interface. Results show that, compared to singularities at the ply interface of an open or pin-filled hole, relatively strong singularities exist at the interface of the bolt head and plate.