A study of fastener pull-through failure of composite laminates. Part 1: Experimental

Of the extensive number of investigations examining mechanically fastened composite joints, all but a few are limited to consideration of in-plane modes of failure. An experimental and numerical investigation of fastener pull-through failure of composite joints has therefore been undertaken. The experimental program included an investigation of the influence fastener head geometry, laminate thickness, stacking sequence and material system have upon the pull-through loading response. Circular specimens were transversely loaded to pre-determined displacements of the fastener, sections through the specimen taken and their failure mechanisms investigated with an optical microscope. Pull-through failure was found to be characterised by substantial internal damage similar to that observed for low-velocity impacted composite panels. Failure is not evident from inspection of the laminate surfaces. Damage is manifested in the form of a conically distributed network of matrix cracking and delaminations extending through-thethickness from the fastener head outer edge. directed away from the fastener hole. The internal/barely visible nature of failure represents a significant departure from that generally considered to distinguish fastener pull-through failure. The means by which to increase resistance to pull-through failure are discussed. This research constitutes work performed as part of the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) task on highly loaded joints. © 1999 Elsevier Science Ltd. All rights reserved.