Effects of surface conditions on the adhesive strength of the novel composite epoxy/sol-gel material

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Sebha University
This paper reported an extensive study on the composite epoxy/sol-gel adhesive bonding of mild steels and the influences caused by the level of the surface roughness of the bonded substrates. Inorganic nanoparticles (NPs) were added as the reinforcement phase to a diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin that was modified by a hybrid sol-gel method. The mechanical performance was characterised by the shear test in order to evaluate the adhesive strength performance of the composite epoxy/sol-gel material on the surface of mild steel under different degrees of the surface roughness. The experimental results indicated that there is a decrease in the adhesive strength with the decreasing surface roughness. The surface of mild steels treated by the P120 abrasive paper (AP) revealed the highest average shear strength value of ~ 18±0.9 MPa amongst the examined samples. On contrast, abrading the substrate surface with the P600 AP gave the lowest average shear strength value of 10.5±0.7 MPa. The increase in the joint strength of the steel surface treated by the P120 AP compared with those of the P240, P400 and P600 AP treated samples is attributed to the availability of the extra interfacial bond area. The adhesive penetrated the pores, hardened, and then acted as the micro interlocking forces, leading to the increase in the real interfacial shear strength. In addition, the decrease in the value of the adhesive strength is due to a reduction of the mechanical interlocking. The scanning electron microscope (SEM) revealed that the specimens treated by the P120 AP have greater mechanical interlocking than that of the specimens treated by the P240 AP. Infinite Focus Microscope (IFM) results confirmed that a smoother surface gave a lower roughness profile, and thus decreased the interlock process.
composite epoxy/sol-gel, adhesive, surface roughness, lap shear strength.