The fracture energy of bimaterial interfaces

This article describes a framework applicable to the measurement and interpretation of the fracture energy of bimaterial interfaces. A major conclusion of this study is that the fracture energy, Γ_i, is not unique and usually exhibits values substantially larger than the thermodynamic “work of adhesion. ” The lack of uniqueness is related to mode mixity (shear/opening) effects experienced by interface cracks, as characterized by the phase angle of loading, ψ: typically, Γ_i, is found to increase as ψ increases. These trends are attributed to crack shielding caused by roughness of the interface fracture surface, to material nonlinearity,etc. The phase angle is, in turn, influenced by the choice of test specimen, resulting in values of Γ_i that differ between specimens in a manner attributed to the locus of Γ_i with ψ. Preliminary models that relate Γ_i to roughness, plasticity, segregation,etc., are described, leading to insights concerning microstructural aspects of “weaklrd and “strong” interfaces. This paper is based on a presentation made in the symposium “Interface Science and Engineering” presented during the 1988 World Materials Congress and the TMS Fall Meeting, Chicago, IL, September 26–29, 1988, under the auspices of the ASM-MSD Surfaces and Interfaces Committee and the TMS Electronic Device Materials Committee.