Single-lap-joint adhesively bonded metal specimen which is the national standard experimental method in use has an extremely non-uniform distribution of shear stresses along the joint

and tensile stress concentration of high values is produced on the steel substrate interfaces. Therefore the test result

which is not the real bonding shear strength between adhesive and steel substrates

can only be used as a test index for qualities of adhesives not the strength criterion for load is capacity evaluation. The combined bonding disc specimen is adopted for measuring bonding shear properties of adhesive on steel substrates

has a very uniform distribution of shear stresses in adhesive and along the bonding surfaces of steel substrates

of which the uniform coefficient is greater than 0.97. Furthermore

when adhesive joint is treated as an arc and steel substrates are chamfered at both ends of the joint

tensile stresses on the bonding surfaces can be reduced to less than 20 MPa which can hardly cause tensile failure. Thus

the results of combined bonding disc specimens can actually represent the real bonding shear strength or bonding shear-compression strength between adhesive and steel substrates

which can be used as strength criterion for load capacity evaluation of bonding members.