Improvement of bearing strength of laminated composites by nanoclay and Z-pin reinforcement.

Abstract

The bearing behavior of bolted composite joints is significantly poorer than that of their metallic counterparts. The objective of the present study was to examine ways of improving the bearing performance of bolted joints in carbon fibre reinforced epoxy laminates. Two strategies were examined, namely stiffening of the matrix using nanofillers and through- thickness reinforcement of the laminates using z- pins. The development of a nanoparticle reinforced matrix resin, and its performance in a composite loaded in bearing, was the focus of the first part of the study. A commercial nanoclay, I30E from Nanocor, was chosen as the reinforcement since the nanoclay particles are modified with long alkyl chain amines which improves dispersion in the epoxy resin. The c onditions for preparing nanocomposites based on the nanoclay were examined for two epoxy resin systems , DGEBA and TGDDM. Significant improvements in the elastic modulus were obtained , with a 20% increase being recorded w ith 8.4 phr nanoclay content in the DGEBA resin and a 50% increase with 20 phr nanoclay content in the TGDDM system. Carbon fibre reinforced laminates w ere prepared from nanoclay reinforced TGGDM matrix resin, using a vacuum assisted prepregging process. The bearing strength and stiffness of the laminated composites was improved by 7% and 15% respectively but the strain to failure was reduced. The addition of nanoclay to the matrix resin was found to change the failure mode. Enhancement of the bearing performance of laminates by through-thickness reinforcement (z-pins) was examined as the second strategy trialed in this thesis. The bearing strength, stiffness and energy to failure of carbon fibre laminates was found to increase progressively with increasing volume content of z-pins , with increases of 10%, 10% and 16%, respectively , being achieved at a z-pin volume content of 4%. No significant change in strength, stiffness or failure energy was observed when the z-pin diameter was changed from 0.28 to 0.51 mm at the same volume content.