Design, testing and analysis of bolted joints and connections

This chapter explores the design, testing and analysis of composite bolted joints and begins with a review of literature relating to joint mechanical behavior. The fundamental influence of joint geometry and stacking sequence on the joint response is discussed along with the significant effects of bolt-hole clearance, lateral constraint and loading velocity. The large number of studies featured in the literature review is an indication of the complexity involved in optimizing composite bolted joint design. In order to handle this complexity, accurate 3D FE modeling is considered an invaluable aid in the design of composite bolted joints and is a key focus of the chapter. The use of 3D FE modeling in the design of composite bolted joints is examined in the form of two case studies. The first case study outlines the prediction of bolt-hole clearance effects in single-bolt, protruding-head and countersunk joints, using linear elastic implicit FE models. The models are shown to accurately capture the delay in load take-up and reduced joint stiffness associated with bolt-hole clearance, while layer-by-layer stress distributions provide a detailed insight into the ply loading at the bolt hole. The nature of the ply loading in countersunk joints is shown to be very different to that of protruding-head joints and in all cases, ply stresses are shown to be highly dependent on the level of clearance. The second case study focuses on the prediction of bearing failure in a single-bolt countersunk joint, using a 3D explicit FE model. A physically based damage model is implemented in a VUMAT in order to predict bearing damage and includes Puck failure criteria, a nonlinear shear law and a crack band model to mitigate mesh sensitivity. The resulting progressive damage analysis is both predictive and robust, affirming the benefits of using explicit finite element analysis which are discussed earlier in the chapter.