Experimental and numerical analysis of strength and deformation of large-scale steel-composite adhesive joints subjected to fatigue followed by static loading

This work reports a study of the fatigue behaviour and quasi-static strength of full-scale adhesively bonded steel-composite joints. Three joints with an approximately 10-mm-thick layer of methyl methacrylate adhesive were manufactured in dockyard conditions. One specimen was tensile tested till failure, while two specimens were subjected to similar to 3.5 million fatigue cycles, followed by a residual tensile test supported with digital image correlation. The shear, longitudinal and peel strain values within the adhesive bondlines are significantly higher at the gripped sides due to the asymmetrical design of the steel brackets. All specimens showed a significantly higher shear strength than the design values defined by the shipbuilder. Fibre Bragg sensors monitored strains at steel and composite constituents and allowed to detect damage onset and evolution in tensile tested specimens. A finite element model of the joint was developed with material and interface properties based on dedicated small-scale experiments. The simulation results of strains during a static load test corresponded closely to the DIC measurements. All specimens failed near the composite-adhesive interface due to delamination of the composite panel.

Automated summary

This study investigates the fatigue behavior and static strength of full-scale adhesively bonded steel-composite joints. The experimental results show that the strain values in the adhesive bondlines are higher on the gripped sides due to the asymmetrical design of the steel brackets. All specimens exhibit significantly higher shear strength than the design values. Fibre Bragg sensors are able to detect damage onset in tensile tested specimens.