The Effect of Elevated Temperature on the Bond between High Modulus CFRP Sheet and Steel

The technique of strengthening steel structures with Carbon Fibre Reinforced Polymer (CFRP) has attracted growing attention in research field and in practice and its environmental durability is of high importance. This paper describes an investigation on the bond characteristics between high modulus CFRP sheet and steel plates under elevated temperature exposures. Tensile tests were carried out on CFRP/steel plate double strap joints at several environmental temperatures of 20°C, 40°C and 50°C, which represent the usually encountered conditions for civil infrastructure. High modulus (640 GPa) unidirectional carbon fibre sheets were applied in wet lay-up fabrication method. Some joints were formed by one layer of CFRP sheet and others by three layers of CFRP sheets. They were all tested to failure by tensile static load. The fracture surfaces of the failed specimens were studied using the scanning electron microscope (SEM) and the failure mechanism were discussed. The objective of the current experimental work is to determine the strain distribution along the bond length, ultimate strength, failure patterns and effective bond length under those thermal exposures. It was found that the ultimate load decreased significantly when the test temperature was above the glass transition temperature of the adhesive. Larger effective bond lengths were found for the joints tested at glass transition temperature. It is obvious that the short-term thermal exposure has little effect on their failure patterns. All the specimens failed by fibre breakage at the joint and cohesive failure accompanied some joints with very short bond length.