Interfacial fracture toughness Mode

Interfacial fracture toughness (Mode I) Capillary length (height)... 

Other examples of specimens that may be used to quantify interfacial fracture toughness as a function of mode mix include the blister test, the Brazil... 

Film Adhesion. The adhesion of an inorganic thin film to a surface depends on the deformation and fracture modes associated with the failure (4). The strength of the adhesion depends on the mechanical properties of the substrate surface, fracture toughness of the interfacial material, and the appHed stress. Adhesion failure can occur owiag to mechanical stressing, corrosion, or diffusion of interfacial species away from the interface. The failure can be exacerbated by residual stresses in the film, a low fracture toughness of the interfacial material, or the chemical and thermal environment or species in the substrate, such as gases, that can diffuse to the interface. 

In general, the use of FE signals accompanying the deformation and fracture of composites offer elucidation of failure mechanisms and details of the sequence of events leading upto catastrophic failure. The extent of interfacial failure and fiber pull-out are also potential parameters that can be determined. FE can assist in the interpretation of AE and also provide an independent probe of the micro-events occurring prior to failure. FE has been shown to be sensitive to the locus of fracture and efforts are underway to relate emission intensity to fracture mechanics parameters such as fracture toughness (Gjp). Considerable work still remains to fully utilize FE to study the early stages or fracture and failure modes in composites. 

The ratio of the mode I interlaminar fracture toughness in 77K-LNj to that in RT-air was 1.8 for ALF/epoxy laminates. This ratio was decreased to 1.2 to 1.3 for CF/epoxy laminates. Thus, the increase of the matrix toughness was directly translated into the increase of the interlaminar fracture toughness for ALF/epoxy laminates. The effect was smaller for CF/epoxy laminates. Fractographic observation indicated foe contribution of resin is larger for ALF/epoxy laminates. Dominant interfacial fracture concealed the effect of resin for CF/epoxy laminates. 

Calculation of the fracture toughness of the coating and the interfacial toughness can be undertaken in some cases where the deformation mechanisms can be identified and the type of failure produced is amenable to analysis. However, the analysis methods cannot be regarded as imiversal as the failure modes vary with materials and are often more complex than the models allow for. As the thickness of the coating is reduced the calculation of toughness is also made more difficult by the need to obtain accurate measurements of crack area and differences in the work of indentation which are beyond the resolution of current instrumentation. 

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