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, Γi, 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, Γi, 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 Γi that differ between specimens in a manner attributed to the locus of Γi with ψ. Preliminary models that relate Γi to roughness, plasticity, segregation, etc., are described, leading to insights concerning microstructural aspects of "weaklrd and "strong" interfaces. © 1990 The Metallurgical of Society of AIME.