The effect of knurling surface treatment on the strength of adhesively bonding between steel plate and carbon-phenolic composite

Due to the need of some industries for the direct bonding of metal and composite layers to each other and its special applications in the industry, this paper examines the solution for adhesive bonding between steel and carbon-phenolic composite. Since this composite layer does not inherently have a good adhesion to the steel surface, steel substrate surface preparation is inevitable in order to create a resistant bonding. In this research, for the preparation of steel surfaces, the knurling process with four types of knurl wheels with different geometries and pitches was used and then, by applying the adhesion tensile test, the strength of adhesive bonding of the composite layer to their surface was investigated. The results showed that in about 50% of all samples, the knurling operation was able to increase the adhesive bond strength compared to the sample with smooth metal surface. In Comparison of adhesive bond strength for two cross and straight knurl patterns, the tensile bond strength created by straight knurl shape was reported about 5 times greater than the cross knurl shape in the case of equal tensile and at pitch equal 0.6 mm. Also, the highest value for adhesive bond strength was reported in 12.62 MPa for preparated surface by using of straight knurl shape at pitch equal 0.6 mm which increased by 76% compared to machined smooth surface.