Recently, considerable attention has been paid to the strength problem of the adhesive-bonded joint because of its wide usage to many mechanical structures, e. g., automobile, airplane and so on. But there exists some uneasiness for use of this type of joint, for no reasonable design standard has been established yet.
So, the authors planned and conducted a series of the experiments to research the effect of surface roughness of the adherend specimen on the adhesive strength under the torsional shear loading condition by using a thin wall cylindrical butt joint specimen, where an epoxy resin (Epikote 828) mixed with a hardner (TEPA) was used as an adhesive, structural steel (JIS. S45C) as an adherend and furthermore polysulfide (Thicol, LP-3) as a plasticizer.
The rigidity of the adhesive and the absorbed energy of the adhesive-bonded specimen in impact tests were varied to some extent by controlling the post curing temperature or by adding the plasticizer, and thus obtained three sorts of the adhesive-bonded specimens having different mechanical properties were used in this experiment.
From the results, it was observed that the surface roughness of the adherend specimen gave the influence on the shear strength in somewhat different manner depending on the mechanical properties of the adhesive used. To explain the strength behavior obtained in this study, discussions were tried based on fracture modes considered in connection with the adhesive/adherend interfacial feature of each adhesive-bonded butt joint specimen.