The Burdened Area as a Structural Indicator of Interface Bonding Strength

Abstract

In laminate structures, the interface debonding failures usually result from very complex fracture mechanisms which lead to different strengthening approaches. The bonding strength of two dissimilar bodies depends, to a great extent, on the bulk materials and the bonding structure in addition to the intrinsic interface adhesion. The structural effect on bonding strength will be emphasized in this investigation. The analysis will exhibit the relationship of materials, structures, and interface adhesion which is essential in understanding the failure mechanisms. This paper proposes that the burdened area on an interface is, according to experimental and analytical results, a structural indicator for bonding strength. Such a comprehensive parameter makes it easy to determine the complex contributions of so many structural parameters to the bonding strength. Although there are many microscopic observations of separated surfaces which support the concept of burdened area, a direct measurement of the burdened area is difficult in practice. Therefore an analytical or numerical evaluation is necessary. The solutions from the classical equation of elastic plate will be used to determine the distribution of interface stress as well as the size of burdened area. The bonding strength is considered as fracture toughness which is directly related with the burdened area. As a useful indicator for evaluating the bonding strength, the burdened area includes the effects of many structural parameters and mechanical properties, such as: elastic modulus, Poisson’s ratio, layer thickness, slanting angel, and corner radius. Burdened area is a property of structure because it is independent of the peeling loads, the material’s yielding strength and interface adhesion. As far as energy release rate is concerned, the boundary load is virtually distributed on the whole burdened area. The concept of burdened area will facilitate mechanical design of bonding strength and leads to a better understanding of various debonding failures.