Highly efficient numerical analysis of load distribution in composite bolted joints

In the design of composite aircraft structures, joint efficiency is a key area for realising the weight-saving potential of advanced composite materials. Cost-effective, efficient design practices are necessary for optimising the design of bolted composite joints. The current state-of-the-art involves detailed three-dimensional finite element analysis. Such models provide detailed information on load distributions in multi-bolt joints, joint deformation, stress and material damage progression. However, a major drawback with such threedimensional approaches is that computer power is not yet sufficient to model large-scale composite structures which contain potentially many hundreds of bolts. To overcome this issue, a highly efficient Global Bolted Joint Model (GBJM) is presented in this thesis. Two different methods are considered as potential candidates for the GBJMa discrete method and a mesh-independent method. In the discrete method, shell finite elements are used to model the composite laminates and the bolt is represented by a combination of beam elements and rigid contact surfaces. In the mesh-independent method, a user-defined finite element is used to model the bolt and joint foundation (i.e. composite material in the direct vicinity of the bolt-hole). The user-defined finite element is calibrated using analytical approaches and these are also developed and presented. Both GBJM approaches are validated against three-dimensional finite element models and, where possible, experimental results from both single-bolt and multi-bolt joint tests. It is shown that the mesh-independent approach is the best modelling strategy for both elastic and failure analysis of both single-bolt and multi-bolt joints, with time savings in excess of 99% achieved over three-dimensional finite element models. The method is subsequently used in a load distribution analysis of twenty-bolt joints, where each simulation ran in minutes. Employing analytical calibration methods, the GBJM can be used to represent a variety of joint configurations and loading scenarios and can hence be used in extensive parameter studies on aircraft structures. This method can potentially reduce conservatism in joint design practice, thus demonstrating its immediate industrial significance.