抄録
As it is well known, the Shinkansen has become one of the most important transportation in Japan from economical, industrial and ecological viewpoint. On the other hand, the surface defects in the Shinkansen track had been initiated on the railhead surface after 1980's. As far as the surface defects on the railhead, there are two kinds of defects called on "head check" and "dark spots" (shelling defects) in the Shinkansen's rail. In addition "White phase" exists on the surface of rail head. The authors have focused to the latter defects of the dark spots and considered that dark spots would be initiated from the surface layer. The occurrence of shelling is few in the dried tunnels. Conversely, most of the defects have been in the rails of high-speed than 150km/h and accelerated train section. For these reasons, it is considered that the moisture and tangential force to rail is responsible for the occurrence of shelling. However, the main factor of shelling occurrence is not proved yet. Moreover, the extremely thin layer known as "White phase" exists on the surface of the rail head. This "White phase" is penetrated by crack and the crack grows largely toward the wheel progress. Therefore, it is conceivable that this White phase would be one of the causes for starting point of the fatigue cracks known as shelling. The object of the study is to investigate the mechanism of contact rolling fatigue defect in view of shelling occurrence caused called by "White phase". The effects of tangent force and moisture exert on the occurrence of contact rolling fatigue defect are also investigated. The testing machine is the two-disks rolling-sliding machine. Each disk of the machine is possible to drive independently. The test specimen material is the representative rail steel that is given in the market. The contents that discussed in this paper are effects of (1) load (2) slip and (3) lubrication. Here, the drop of lubrication rate is set to 0.2cc/s with the fatigue limit of 1×(10)^7 cycles. The reason of selection of the oil for lubrication is to decrease the friction of the rail surface. The authors consider that we can control the wear of the rail by the oil and it will be possible to reproduce the damage easily. Furthermore, the dry condition with a small occurrence of damage isn't considered in this study. The authors have already clarified that the initiation of "Contact rolling defects" relates to Hertzian stress, lubrication, tangential force etc.
