Interfacial fracture energy Mode

The situation is more delicate when the two materials have different moduli. In this case, if the beams are of identical thickness the failure will no longer be purely mode I. In these circumstances the crack will deviate from the interface into the material with the lower deformation resistance, leading to additional energy dissipation. In these circumstances the measured values of the interfacial fracture energy will be larger than Gic- This problem can be overcome by using an asymmetrical test, in which the thicknesses of the two beams are unequal. At a particular ratio of thicknesses the measured fracture energy will be a minimum and this may be taken as the true value of G c. 

Yet, for systems A and C, the measured fracture energies remain low compared with the critical fracture energy of the bulk aluminum 10 J Moreover, we do not observe islands of passivation material on the A1 fracture surface and, inversely, we do not observe A1 on debonded surfaces of the passivation films. This suggests that the loss of interfacial adhesion is close to a brittle fracture process despite the influence of plasticity of the A1 substrate and crack blunting at the interface. This sort of brittle mode of interfacial failure, including plastic flow in a ductile material (the substrate), has been observed or discussed for a sapphire/Au interface. ... 

Similar to the Mode I fracture test, the energy release rate /jj can be experimentally determined as a function of the crack tip slip Sq and the global shear force gj. Once the experimental /n o curves are obtained according to Equation (8.13), the Mode 11 interfacial traction-separation law t = t(Sq) can be experimentally determined as foUows ... 

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