An Innovative Method to Determine Bonding Strength Envelope Based on Theory of Bi-Material Interface Mechanics

Bi-material interfaces exist in many advanced materials and structures. Measurement of interface bonding strength is more diffucult than measurement of strengths of homogeneous materials because of the presence of stress singularity at the interface corner, non uniform stress distribution along the interface and co-existence of normal and shear stress components. The order of the stress singularity depends on the interface geometry and material combination. Besides pure tensile and pure shear strength, a general biaxial normal-shear bonding strength criterion, for example, in the form of a strength envelope in normal-shear stress plane, is prefered to more realistically and adequately characterize the strength property of bi-material interface. This paper presents a new test method to determine the interface bonding strength envelope. The design of specimen geometry is based on an axi-symmetric asymptotic analysis on the stress field near the free edge of the bi-material interface, through which appropriate interface bonding angle is chosen to eliminate the stress singularity. As an example, the epoxy-aluminum interface strength envelope is determined by the new proposed method.