Rolling contact fatigue (RCF) is the initiation and propagation of cracks through repeated rolling/sliding contact between two surfaces. Therefore, the application of fracture mechanics is essential. This failure mechanism has been found in roller bearing, gears and railway wheel/rail system. In this paper, the major past studies on RCF, mainly in wheel/rail systems, will be described with the overview of the fracture mechanics parameters that they deal with.

Subsurface-originated flaking caused by non-metallic inclusions is known as one of the failure modes occurring in rolling bearings. In steel materials, impurities unavoidable in manufacturing remain as inclusions. They act as a source of stress concentration and cyclic rolling contact can cause initiating cracks from the inclusions, resulting in flaking. This paper introduces the effectiveness of bonding the inclusions to the matrix as a mean for the improvement of bearing life. Hot isostatic pressing is used to bond the inclusions to the matrix. A method for evaluating flaking life using the stress intensity factor is also presented as a technique for upgrading conventional life prediction theory. It is shown that the stress intensity factor can be used to evaluate the life uniformly and accurately, even if the initial defect size and loading conditions are variously different.

Solid particles in lubricant have been known to have a detrimental effect on rolling bearing life. When a rolling bearing is used in lubricant which contains solid debris such as wear particles generated from gear machines, surface defects (dents) are formed on the raceway due to entrainment of debris particles into the contact between rolling element and the raceway. “Dent-initiated spalling”caused by rolling contact of dented raceway significantly reduces the bearing life, so it is necessary to improve the dent-initiated spalling life. Dent-initiated spalling is known to occur due to stress concentration at the edge of the dent, followed by microstructural fatigue. In this article, the material and heat treatment technology that suppress these effects and improve the dent-initiated spalling life is explained.

Micropitting which consists of spalls and cracks with the size of about 10µm is one of the failures of rolling bearings under boundary and mixed lubrication conditions. This article reviews studies on the mechanism of micropitting and estimation methods of micropitting lives.

Steel ball used for the deep groove ball bearing (hereafter steel ball) is an important mechanical component which supports the industries and our daily lives. The usage environment of steel ball has increasingly become multifaceted and severe with downsizing and souped-up on especially automotive and industrial machine applications. Since steel ball is under heavily-loaded environment, the improvement of steel ball reliability is one of the most important action assignments. In this commentary, the influence of heat treatment and residual stress formed by peening process on rolling fatigue life is described with the evaluation of various steel balls prepared by various heat treatment conditions (quenching & tempering temperatures), peening conditions, and manufacturing process.

To prevent global warming, spread of electric vehicles is progressing globally. In case of electric vehicles, it becomes impossible for car heating to use waste heat from engine operation, so heating function is also required for car air-conditioning system. Dual use of heating and cooling forces wider range of temperature and longer operation of compressor, which suggests severer lubrication condition. In the compressor of car air-conditioners, various bearings and materials are lubricated in a mixture of refrigeration oil and refrigerant. Longer fatigue life of bearing becomes further expected in such a severer condition. There are two major factors of fatigue life: base oil and additives in lubricants. In terms of the base oil, it is assumed that higher viscosity can form thicker oil film and obtain longer fatigue life. On the other hand, in terms of the additives such as anti-wear agents that react with metal surfaces, there are only a few examples of studies about fatigue life conducted under the mixture conditions of refrigeration oil and refrigerant. Still unknown about the effect of additives in refrigerant circumstance. In this study, the effect of phosphorous type anti-wear agents formulated in refrigeration oils was evaluated. It was found that phosphite esters in refrigeration oils contributes fatigue life extension in refrigerant circumstance.

Piston rings have been developed in response to an engine development. Piston ring packages have been demanded which is a low friction force, a low oil consumption and excellent at a durability. The work that a hydrodynamic friction is mainly is desirable, a design that is a low tension and a constant contact pressure is important. The treatment due to one ring to reduce an oil consumption is firstly important. In this paper, we mainly explain a hydrodynamic friction force focusing on the characteristic of a friction force in a piston ring and Oil Consumption.

The piston ring has been developed in response to the development of the engine. Piston ring constitution superior in low friction, lubricating oil consumption reduction, the durability has been demanded. For the low friction, the operation of the main constituent is ideal fluid lubrication. We described that the first ring was the operation in the state of Oil Starve in the first report. To balance with “Fluid lubrication operation of the main constituent”in “Lubricating oil consumption reduction”, the design method in consideration of the correspondence with one ring and piston ring axial behavior, the calculation of the gas flow between each land becomes important.

Short fatigue life of ball bearings is a serious problem in use for alternators. It has been decided that cracks in the bulk of near surfaces of balls and rings are formed through diffusion of hydrogen caused by decomposition of oils. However, it is unknown how the oils are decomposed to evolve hydrogen. On the other hand, triboplasma was discovered to be generated through discharging under oil lubrication. This suggests that the oils are decomposed by action of discharge plasma to evolve hydrogen. The purpose of present study is to investigate decomposition characteristics of oils by attack of the discharge plasma. Two kinds of hydrocarbon compounds; (1) aliphatic hydrocarbon compounds and (2) oxygen-containing aliphatic hydrocarbon compounds,were investigated. The results showed that there is a critical electrical resistivity between 1.1×10⁷Ω･m and 3.5×10⁷Ω･m,which separates all the compounds into two groups. The compounds having the values above this critical electrical resistivity,discharging takes place to evolve hydrogen. Whereas the compounds having the values below it, no discharging and no hydrogen evolution takes place. Thus, it is concluded that the compounds having electrical resistivity of below 1.1×10⁷Ω･m are hopeful candidate for developing oils having high anti-hydrogen-evolution properties.