DIC based strain and damage analysis of large scale steel to composite adhesive joints subjected to tension and compression loading

This paper reports an experimental study of the mechanical response to tensile and compressive force of large scale steel to composite joints adhesively bonded with a thin layer of vinylester resin. In one specimen, the length of the reinforcing fibres in contact with the steel substrate has been reduced by saw cutting at both ends of the joint. This damaged specimen and four intact specimens were subjected to quasi-static tensile testing; six specimens were used for compression testing. The strain distribution at the composite surface and at the steel to hardwood connection of the specimen was monitored by digital image correlation (DIC). DIC allowed identifying the onset of damage in the tensile tested joints near the interface of the composite layer and the steel-hardwood connection. Both tensile and compression tested specimens failed due to significant peel strain concentration at the composite near the connection of steel and hardwood. The average strength of a specimen tested in compression was about 66% higher than the average strength of a specimen tested in tension. The strain concentration zone in the damaged specimen was away from the introduced saw cuts. As a result the damaged and intact tensile specimens showed the same failure strength and stiffness. All specimens failed by adhesive failure between the composite-hardwood interface.