Characteristics of Crack Propagation at the Interface between Two Dissimilar Media.
Final rept. on phase 1,
NAVAL RESEARCH LAB WASHINGTON D C
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Studies were conducted on specimens of epoxy plates bonded to aluminum plates. The effect of surface roughness of the aluminum on fracture toughness was measured for four different surface finishes. It was found that increased surface roughness resulted in greater fracture toughness. This may be explained by the observation that the interfacial cracks replicated the surface features of the aluminum. Microscopic studies of the failure surfaces indicate that crack propagation occurs in the epoxy near the interface, and that a residue of epoxy remains bonded to the aluminum. The magnitude of the residual stresses due to casting and curing of the epoxy was determined by photoelastic techniques. Methods were developed for analyzing the birefringent pattern in the epoxy to determine the magnitude of the elastic residual stress and the frozen stress. It was found that residual stresses can contribute 15 to 20 of the strain required for crack initiation at the interface.
- Metallurgy and Metallography
- Solid State Physics