Experimental investigation on the multi-failure coupling strength mechanism of the hybrid Steel/GFRP adhesive joint

Abstract

The damage of a bi-material adhesive joint generally involves multiple failure modes, such as the fracture in the adhesive layer and the delamination on the different interfaces. The different combinations of these multiple failure modes generate various macro strengths of the adhesive joint, so the common strength criterion with an assumed single mode is normally limited to predict the damage. Therefore, it's necessary to present test and fracture strength identification methods for all possible failure modes in the adhesive joint. In this work, two kinds of materials – uniform thickness steel plates (UT) and orthogonal woven glass fibre reinforced plastics (GFRP) were used to prepare three types of single-lap shear specimens – UT/UT, GFRP/GFRP and UT/GFRP. With these specimens, firstly, the double-side gluing was found to have higher strength than that of the single-side gluing in both UT/UT and GFRP/GFRP specimens. Secondly, with different pre-crack positions, in total three kinds of failure modes in these adhesive joints have been activated and identified, which are the interface failure on the steel (strength: 21.0 MPa), the adhesive failure (strength: 16.0 MPa) and the interface failure on the GFRP (strength: 10.7 MPa). Finally, it is found that the macro shear strength of the hybrid UT/GFRP adhesive joint could be estimated by the sum of the independent shear strengths of each happened failure multiplied by their corresponding area percentages, which is the quantitative multi-failure coupling strength mechanism of the hybrid Steel/GFRP adhesive joint. This coupling mechanism would be applied for precisely predicting the strength of the bi-material adhesive joint.