ECCM15 - 15 TH EUROPEAN CONFERENCE ON COMPOSITE MATERIALS, Venice, Italy, 24-28 June 2012 1 PULL-THROUGH FAILURE PREDICTION FOR COMPOSITE BOLTED JOINTS USING ONSET THEORY G. Pearce 1* , D. Kelly 1 1 School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Australia *g.pearce@unsw.edu.au Keywords: Composite Bolted Joints, Pull-through, Onset Theory Abstract This paper presents a failure analysis based on Onset Theory which has been implemented in the MSC.Marc finite element program and applied to predict the pull-through failure of bolted joints in unidirectional carbon fibre composite laminates. Failure prediction is coupled with a progressive failure analysis to predict the growth of matrix cracking and delamination. It has been shown that Onset Theory can reasonably predict the initiation of pull-through failure including all failure mechanisms although improved material data is for future studies. Failure progression was also well captured but was limited by the intrinsic difficulties of using simple damage mechanics to model discrete damage phenomena. 1 Introduction Composite laminates are highly susceptible to the localised failure induced by geometric discontinuities and concentrated loads, even more so than metallic structures. Consequently, bolted joints in composite structures play a critical role in overall structural performance. The importance of bolted joints has led many authors to investigate failure of bolted joints both experimentally and numerically. The majority of these studies have considered only in-plane failure modes, such as bearing, shear-out and net-tension. Transverse loading induced in fasteners is generally avoided because composite joints are very weak in this direction. Failures due to pull-through or pull-out loads are dominated by through-thickness laminate failure mechanisms such as transverse shear cracking and delamination. These mechanisms are controlled by the composite resin and as a result the critical failure loads are generally an order of magnitude lower than the in-plane failure modes [1, 2]. Despite this vulnerability, pull-through failure of composite joints has not been given much attention in the scientific literature because it has generally been considered that transverse joint loads can be minimised by smart joint design. Current design trends toward thin skinned post-buckling structures have invigorated interest in fastener pull-out. Under post-buckling conditions, bolted joints must carry significant tensile loads. It has also been shown that structures subjected to impact loads exhibit critical pull-through loads in fasteners [3]. To minimise the requirement for costly experimental test programs and accelerate the design phase for composite structures, it is critical that validated numerical models of composite joint pull-through failure are developed. This paper presents a full 3D modelling approach for