Takefumi Otsu

Fatigue Characteristics of Nonferrous Bolts at Elevated Temperature

In order to investigate fatigue characteristics of nonferrous bolts at elevated temperature, fatigue tests of bolted joints which were tightened with three kinds of nonferrous bolts were been conducted at 100°C atmosphere. The test bolts were made of A5056 aluminum alloy and AZ31 and AZX912 magnesium alloy. Creep tests of the bolts at 100°C atmosphere were also conducted. The results showed that the fatigue limit of A5056 bolt was the highest of all regardless of the ambient temperature. The fatigue limits of AZ31 bolt and AZX912 bolt also were a half of the fatigue limit of A5056 bolt at both ambient temperature. Bolt clamping force losses due to creep deformation were observed for all bolts during fatigue tests at elevated temperature. Hence as additional tests, the creep tests which was controlled either the tensile force or the displacements respectively were conducted. As the results it was seen that the clamping force losses for all bolts were remarkably large although the each creep deformation was different for each bolt material. Therefore the results indicates that we have to pay attention to the clamping force reduction due to creep deformation if we use the nonferrous bolt in high temperature.

Effect of phosphorus film on frictional properties of molybdenum dithiocarbamate

This paper describes the effects of phosphorus film on the boundary lubrication performance of molybdenum compounds. To study this, ball-on-plate-type spinning friction test was conducted using molybdenum dithiocarbamate and acid phosphate ester as additives. To form surface phosphorus films, specimens were heated in acid phosphate ester for 1, 3, and 6 h, with the results showing that the formation of the phosphorus film depends on the heating time and on the increases in concentration of phosphorus with the heating time. It was also shown that the friction coefficient in the test with the lubricant containing molybdenum dithiocarbamate, depends inversely on the heating time, with specimens heated for 3 and 6 h having lower coefficients that the specimen heated for 1 h. Energy-dispersive X-ray analysis revealed that the chemical reaction films comprising phosphorus, oxygen, and sulfur formed on the friction surfaces after the test, with the concentrations of sulfur in the film increasing with increased concentrations of phosphorus. These results suggest that the thickness of the phosphorus film affected the amount of molybdenum disulfide formed on the surface. Moreover, as more molybdenum disulfide film formed, the friction coefficient decreased.

Effect of Slip on Permeation of Hydrogen into Steel in Cyclic Contact

The amount of hydrogen in the steel specimens obtained from a cyclic contact test was investigated in order to understand the process of permeation of hydrogen into the steel in rolling contact. Cyclic contact test with slip was conducted in a sealed chamber, in which cyclic stress, slip and surrounding gas were controlled. The amount of hydrogen in the steel after the test was analysed by secondary ion mass spectrometry. It was found that the amount of permeated hydrogen after the test performed in hydrogen gas was not greater than those after the tests in dry air and vacuum condition. It was also found that the oxide film and the hydroxide film were formed on the contact area after the test in hydrogen gas. These results suggested that the oxide film and the hydroxide film, formed in the process of cyclic contact with slip, prevented hydrogen from permeating into the steel.

Cavitation Phenomena in Pure-Sliding Grease EHL Films

Grease lubricants are widely used in many machine elements which work in elastohydrodynamic (EHD) lubrication regime. They have advantages over lubricating oils, but are prone to starvation, especially when operating at large speeds. At the same time the complex nature of lubricating grease is little understood and only little knowledge about its chemistry and physics is accessible, which makes the prediction of grease film behavior difficult. In the present paper the relation between lubricating grease composition and operating parameters on one hand and the cavitation length on the other, was evaluated.Copyright