Explore the vast range of titles available.

In this study, crack propagation in PPS thrust bearings under rolling contact fatigue (RCF) in water was observed, and relation between subsurface crack and internal shear stress parallel to the surface was investigated. It was found the cause of flaking was subsurface crack. They were evaluated in terms of contact stress and friction between their faces. It was discovered that subsurface cracks distributed around shear stress peak, and flaking failure was dominated by subsurface shear stress.

Additive manufacturing (AM) is a well-known method of 3D printers. The AM method forms components by laminating thin layers. Therefore, this method can make prototypes of parts and does not involve any tooling or human interference. However, the mechanical parts made by the AM method have unique problems. In particular, the effect of the strain rate on the mechanical property of Young’s modulus and Poisson’s ratio has not been studied in detail. Therefore, we investigated the effect of strain rates on 3D-printed ABS-like specimens in this study. In order to investigate the effect of tensile speed on 3D-printed ABS-like specimens, tensile tests were conducted at 0.2 mm/min, 2 mm/min, 60 mm/min, 800 mm/min, and 1000 mm/min. We obtained the experimental results that Young’s modulus increased with increasing tensile speed. Also, the specimen broke at multiple points in high-speed tensile tests. Poisson’s ratio values for all tensile speeds were almost constant around 0.38.

In order to investigate the effect of pre-crack lengths on strength of silicon nitride balls under cyclic pressure loads, growth behavior of 600~700μm pre-cracks were compared to those of 200μm~300μm and 400~500μm pre-cracks. Furthermore, the change in initial threshold limit of the maximum stress intensity factor was discussed. It was found that the increasing ratio of stress intensity factor during N=0 and N=1000 distinguished the failure and non-failure, and pre-crack length had strong effect on the threshold limits of the increasing ratio.

Additive manufacturing (AM) methods have become popular but the fracture mechanism of products made by AM is not well understood. In particular, the fracture of parts made by 3D printing needs more investigation. We have already investigated the effect of the lamination direction on the fractures in bearing specimens. In this study, we made some specimens by using a 3D printing method and performed some tensile tests. We investigated the effect of the lamination direction on the Young’s modulus of the specimens and tried to detect inner defect initiation using an acoustic emission (AE) sensor.

High-carbon high-strength JIS-SUJ2 bearing steel is one of the alloys used as rolling contact applications which need high wear resistance. This high hardness material is broken from non-metallic inclusions under fatigue stress. In this work, we developed a new observation method “fracture surface etching (FSE)” in order to observe the material microstructure on the fracture surface. We succeeded to draw clear grain boundaries on the fracture surfaces and closely observed the material microstructure around the crack origins by the FSE method. We concluded that the crack initiation area boundary is not formed by only the grain boundary, and the grain size around the Al2O3 inclusion on the fracture surface was similar to that of the flat surface which does not have inclusions before fatigue testing.

Low carbon steel is one of the most common steels used in industry because of its low cost. If more strength is required, it can be strengthened by induction heating which is also a low-cost method. In order to investigate the effect of induction heating on large diameter shafts, we performed rolling bending fatigue tests using 10 mm diameter specimens. We found that TRO cracks originating from the boundary between the soft and hard layers governed the fatigue fracture of the shafts.

3D printing methods are developing and they have become popular recently. 3D printing can easily make complex and seamless parts, however, there are questions about their strength. In particular, the strength of the places where the lamination layer joins is important. We performed rolling contact fatigue (RCF) tests in dry conditions using 3D-printed bearing race and observed the fracture behavior and cracks. We found that the main crack is related to the stress moving direction.

Martensitic high-carbon chromium bearing steel is used for rolling contact applications in various mechanical parts. Induction heating is one of heat treatment methods which take shorter time and lower energy compared with furnace heating. In the present work, we prepared induction-heated and furnace-tempered JIS SUJ2 bearing steel bar specimens. After rotating bending tests, we observed their fracture surfaces. It was found that the very large fisheye crack failures occurred and the crack size increased with increasing number of cycles to failure.

Bearing fails due to the flaking failure which is caused by the subsurface cracks. The observation of the subsurface cracks is not easy beacause the cracks propagate inside the material. In order to observe the whole subsurface cracks, we performed rolling contact fatigue (RCF) tests of carburized SCM415 until over 107 cycles with the single-ball RCF machine. After the RCF tests, we directly observed the subsurface cracks.

Heat treatment is very important factor for improving material strength. In our previous work, we combined a furnace heating and induction heating to develop a new method (furnace-induction heating, FIH). We observed the microstructure in JIS SUJ2 bearing steel and found that FIH process refined the prior austenite grains. In this work, we further investigated the relation between hardness distribution and retained austenite in furnace-induction heated JIS SUJ2 steel.