Adhesive tensile strengths of scarf and butt joints of steel plates. (Relation between adhesive layer thicknesses and adhesive strengths of joints)

For the study of fracture criteria, adhesive tensile strengths (σY) of scarf joints with a scarf angle of 30° and butt joints bonded by a brittle epoxy adhesive A and a ductile epoxy adhesive B have been measured at adhesive layer thicknesses (h) from 0.05 to 5.0mm, and three-dimensional elastic finite element analyses have been performed. σY of each joint decreased with an increasing value of h. A brittle fracture occurred on the scarf and butt joints bonded by adhesive A and the butt joints bonded by adhesive B. The fracture of scarf joints A and B satisfied a maximum principal stress criterion and the von Mises criterion, respectively. Gradients of σY-h curves for butt joints A and B were greater than those predicted from the results of stress analyses. The location of fracture initiation and fracture modes of adhesive layers observed with and optical microscope agreed with those expected from the results of experiments and stress analyses.