Papers by Author: Katsuyuki Kida

Abstract: The life of the PTFE thrust bearing under rolling contact fatigue (RCF) was investigated. The different conditions of axial loads and the rotating speeds under water were applied. The shapes of the bearing race before and after the tests were measured by a two-dimensional shape measurement sensor. The wear loss of PTFE bearing was rarely generated and the shape of the bearing changed slightly in the test. However, it was found that the lifetime of PTFE bearing depended on the temperature generated in the contact surface. In our testing machine condition, the bearing was collapsed over a load of 1600 N.

Abstract: Influence of load and rotation speed on life of PPS radial bearings under water lubricant condition was investigated. RCF tests were carried out at different loads and rotation speeds until 1.0×106 cycles. After testing, rolling contact surfaces were observed by using a laser confocal microscope. From the observation, it was concluded that the life of PPS radial bearings under water lubricant condition was dominated by cracks and flaking failures. The failure of PPS bearings was caused by the flaking failures. The cracks were observed prior to the flaking failures. The life when flaking failure occur depends on the load and the rotation speed.

Abstract: The polymer bearings have been widely used in recent years. In this study, ultra-high-molecular-weight-polyethylene (UHMWPE) is investigated. In order to investigate the relation between the lives, loads and rotation speeds, rolling contact fatigue tests were conducted. It was found that rotation speed related to the bearing life and wear loss.

Abstract: In our recent work, in order to realize joint element in lightweight and compact joints for tall humanoid robots, a new joint element was designed. It consists of a harmonic drive gearing device, a multi axis mechanism and a resin bush. The resin bush slides on a titanium crankshaft of the pole shape while the joint works. However, the bush was stuck, and stopped movement of the joint. In our present work, we observed the bush surfaces against two materials; the titanium and the 7075 aluminum alloy have been used. We could observe the differences between the titanium and the 7075 aluminum alloy by an optical microscope after the fatigue tests.

Abstract: Groove shape effect on wear behavior in PTFE radial bearings under rolling contact fatigue (RCF) was investigated. RCF tests in water-lubricated conditions were carried out at different loads and rotation speeds. The groove surfaces after testing were observed by using a laser confocal microscope and a two-dimensional shape measurement sensor. It was found that PTFE bearings under RCF generate wear debris, however no cracking or flaking failure could be observed. It is concluded that groove deformation depend on load rather than rotation speed. The biggest changes in groove profiles occurred when tested at loads close to 400N.

Abstract: Fatigue failure of machine components is caused by cyclic load. Non-destructive observation methods that can be related to stress are necessary to study the fatigue phenomena. In the present work, a three-dimensional scanning Hall probe microscope (SHPM) equipped with GaAs film sensors was used to observe the fundamental features of the magnetic fields in a tool steel specimen (SKS93, JIS B 4404: 2006, equivalent to AISI W4 tool steel) during tensile loading. The nature of the magnetic fields during tensile loadings of 430μstrain and 640μstrain was observed using the SHPM. It was found that the magnetic fields decrease due to the tensile loading.

Abstract: Rolling contact fatigue tests of 20mm-diameter 13Cr-2Ni-2Mo stainless steel bars was carried out using a newly developed single-ball system. The bars were quenched by induction heating method and after that tempered. Sectional observations of the subsurface cracks were made after the surface layer separations. Based on the observations, stress analysis was performed in order to investigate the relation between flaking failures and subsurface crack growth. From these calculations it was found that the shear stress propagated subsurface cracks and finally caused the flaking failures. Furthermore, eight specimens were fatigue tested and Weibull statics distribution of RCF life were calculated using Johnson's statistical method. It was found that the basic life (L10) of the bars under 5.3GPa Hertzian stress was 8.33×106 cycles.

Abstract: Martensitic high-carbon high-strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance is required. Refining the prior austenite grain size through repeated heating is a process commonly used to enhance the material’s strength. In this work, the microstructure of repeatedly quenched Ti, N-rich ultra-clean SAE 52100 steel was investigated. The material was melted by an electric furnace and formed by continuous casting and forging, and the crack origin on the fracture surface was investigated. It was found repeated furnace quenching effectively refined the martenstic structure.

Abstract: Fatigue failure of machine components occurs when cracks form in the stress concentration area and propagate under continued loading during component work. In order to understand the relation between the phenomena of stress concentration and crack propagation, non-destructive evaluation methods using in-situ measurements in the stress concentration areas are necessary. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was developed and the three dimensional magnetic fields were observed at room temperature in air. The effect of stress on the changes in the magnetic field in steel components is reported. A steel specimen (JIS SKS93) embedded in acrylic resin were strained at different loads and the magnetic field before and after straining were observed. The obtained magnetic images clearly corresponded with the shape of the steel plate. It was possible to measure the changes in the magnetic field of the steel sample after straining under tensile loading, by neutralizing the initial magnetic field of the specimens prior to testing.

Abstract: Radial ball bearings made of metal, ceramics and plastics are commonly used as important components in industrial machinery. Usage of high performance engineering plastic polymers is increasing progressively as a replacement for metal components due to the latest markets demands. Poly-ether-ether-ketone (PEEK) is a promising material for precision-machined custom bearings, products that are expected to suit special market needs. In the present study, PEEK radial ball bearings were manufactured by lathe machining under different parameters and their rolling contact fatigue (RCF) resistance under water lubricated conditions was investigated. We observed the surface of the bearings prior and after testing by laser confocal microscope. The wear loss was measured by weighing the bearings before and after test. Cracks and/or flaking failures were identified on the bearing surface after testing. From the RCF tests results, we found that, at water lubricated conditions, crack initiation occurred later in the material that was machined at slower feed rate while at dry condition, the feed rate had little influence on the wear loss and cracking. Wear loss in the case of bearings tested under water was much less severe than that of bearings tested at dry conditions.