岩石の切削における破壊現象
1973 年 89 巻 1023 号 p. 291-295
詳細
1973 年 89 巻 1023 号 p. 291-295
In the present study were made microscopic observation on the chip formations inrock near and beyond the point of cutting.
The bit was stopped cutting and taken off from the cutting plane carefully, then the cutting plane was cemented over the wide range by Canada Balsam. This agglutinated rock sample was sliced to thin slab in parallel with cutting direction, and polished to make the thin section for microscopic observation. The thin section was successfull for us to observe the mode of rock fracture occuring in a vertical section of the cutting plane by a microscope of low magnification. Main results of observation for samples of marble, tuff and sandstone are as follows.
1) There are two different forms of fracture observed. One is the faulting and the other is the extention fracture.
2) The faulting occurs always first at the boundary between the crushed zone and the unbrocken rock with a constant angle of about 45° to direction of travel.
3) The extention fracture is brought about secondly at an angle ofabout 25° along with the propagation of cracks from the vicinity of the crushedzone to the surface.
4) These two forms of failure occur alternatively at every cut except for extremely small cut of depth. The region of faulting does not extend in relation to the increasing depth of cut, so that if depth of cut become larger, the faulting plane should be produced intersecting with the plane of extention fracture which has been caused previously.
