3% Si-Fe 片側切欠き平板の塑性変形および破壊
1975 年 24 巻 256 号 p. 53-59
詳細
1975 年 24 巻 256 号 p. 53-59
Single-edge-notched specimens of 3% Si-Fe polycrystals were stretched under pin-point loading. The feature of plastic defomation near the notch tip was observed by the etch pit method, and the distributions of strains in the loading direction (y-direction) and in the thickness direction (z-direction) were measured by a talysurf and a microscope. The characteristics of strain distribution in the near-tip field were clarified and the fracture criterion was discussed based on the observed strain distributions.
Main results are summarized as follows:
(1) The plastic deformation near the notch tip was confirmed to concentrate on two sets of mutually perpendicular planes inclining 45°to the loading axis and the specimen surface. This mode of deformation results in the necking of the surface and the corresponding crack tip opening displacement.
(2) The slopes of strain distribution curves in a log-log plot of the z-directional strain vs. distance ahead of the crack tip were -0.13 and -1.0 within and beyond the region of half thickness distance from the tip, respectively. The intensity of strain distribution was found to be proportional to the COD value. For the y-directional strain, the slopes were -0.71 and the strain intensity was proportional to the J integral.
(3) The empirical relation between the J integral and the gross displacement has the same tendency with the prediction of the linear elastic solution in small scale yielding and with that of the rigid plastic solution after general yielding.
(4) The critical value of the z-directional strain at the notch tip at the time of unstable fracture was found to be independent of the notch tip radius, but decreased with increasing crack length In fractographic observation of fracture surfaces, the larger extension of stable crack growth was detected for the smaller initial notch length.
