Analysis of the Net Tension Failure Mode in Composite Bolted Joints

Abstract

A failure analysis has been developed to predict the net tension strength of composite bolted joints. The analysis involved: 1) the development of a representative stress profile along the net tension failure plane and 2) the in corporation of this stress distribution into the appropriate failure criterion. A two-dimensional, plane stress finite element analysis employing quadrilateral elements with orthotropic material properties was used to determine the state of stress along the failure plane. The stress distribution along this plane was described by a polynomial expression and was generalized to apply to a wide range of geometries. The "point stress" failure criterion was applied to the generalized stress distribution equation resulting in the desired net tension strength prediction. Development of the failure criterion for a particular material system and laminate configuration involved empirically determining two notch sensitivity parameters, m and C. In this study, notch sensitivity parameters were determined for a [45/0/-45/0₂/-45/0/45/0₂/90] _s graphite/epoxy laminate. The strength predictions were verified using ex perimental net tension strength data.