MATERIALS DEVELOPMENT AND MICROSTRUCTURAL CONTROL FOR IMPROVING FATIGUE FRACTURE PROPERTIES IN FILM MATERIALS

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(1) Using pure copper films, the two types of specimen that rolling direction was parallel and perpendicular to loading direction were prepared for a film fatigue testing. As a result, in the film loaded in the perpendicular direction to the rolling, slips and cracks were initiated at less number of cycles and lower stress amplitude, while a crack propagated slower because of the large crack closure. Also, there was a difference in crack observation on the specimen surface between the two types of specimen with the large aspect ratio of the grain stretched by rolling.(2) Commercially-pure iron films with the thickness of 100μ m were annealed at 873K, 1073K and 1173K after rolling, and the two types of specimen that rolling direction was parallel and perpendicular to loading direction were prepared for a film fatigue testing. The crystallographic analysis using EBSD system showed that the anisotropy of rolling texture remained after annealing, and there was a difference between the two … More types of specimen in crack observation. When compared at the same stress intensity factor range, ΔK_<est>K, evaluated from the crack opening displacement, fatigue cracks propagated faster in the film loaded to the perpendicular direction to the rolling. This was probably because the slip plane was different in accordance with the relationship between the rolling and crack propagation directions.(3) Commercial grade iron films were bonded to steel base plates by using epoxy resin or by diffusion. When using the epoxy resin, the compressive residual stress induced by a shrinkage deformation of the resin during the heat-curing and cooling process was larger in the 100 μm than the 50 μm thickness film, thus increasing the fatigue life in the 100 μm thickness film-bonded plates. On the other hand, under the same effective stress intensity factor range evaluated from crack opening displacements, ΔK_<est>, the fatigue crack propagation rate, da/dN, was almost the same for all the epoxy bonded specimens, but relatively larger in the resin-bonded than the diffusion-bonded film. This showed the lower fatigue crack propagation resistance of the film itself bonded by the epoxy resin layer. Less