3D Observation of Distorting Crack Growth in Three-Point Bending Specimen
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概要
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Fracture phenomena in industrial structures are initiated mostly at the surface or from internal cracks due to defects already existing in the material, and generally propagate in all directions, often having irregular shapes. In structures and machinery, inclusions in the material, corrosion, and fatigue from use and other reasons cause the inevitable occurrence of defects or cracks. There are not only material metallurgical defects but also the discontinuity of parts due to fastening, configuration design, lubrication, etc., in structures and machinery. In actual overloading accidents, not only crack opening load but also shear load affects the propagation phenomena of defects or the crack tip. Therefore, fracture behavior under mixed fracture mode is caused and these behaviors are not simple. In this study, we carried out a three-point bending experiment in mixed mode including mode I, and showed that the crack growth route varies in the fracture when the shape of the initial crack changes. It is important to establish a fracture route prediction theory for different shapes of initial cracks in order to minimize possible damage or prevent accidental failure, and to prevent the crack from propagating to the most important parts of the structure. From the results, the difference among the fracture routes was examined, showing that the extent and velocity of crack propagation, the stress intensity factor, and the energy release rate varied with the degree of initial crack of the specimen.