Takeo Yoshioka

Diagnosis of Rolling Bearing by Measuring Time Interval of AE Generation

We have developed a new method for measuring time intervals of Acoustic Emission (AE) generation for diagnosis of a radial rolling bearing. The method makes the AE signal itself a trigger of the oscillation of the clock pulse and measures the time interval of AE generation by integration of the clock pulses. The measurement device consists of the threshold, clock, time interval measurement and memory circuit, and was applied to rolling contact fatigue experiments. It was confirmed by the experiments that the measured time intervals of AE generation on the inner raceway or the ball agreed with the value calculated based on the kinetics of the rolling bearing. Moreover, we could identify the elements in which a fatigue crack was propagating by the method before the spalling appeared. The identified elements agreed with the failed elements.

Monitoring of Ball Bearing Operation under Grease Lubrication Using a New Compound Diagnostic System Detecting Vibration and Acoustic Emission

Our new compound diagnostic system comprised of a compound sensor, a signal processor, and a personal computer installed signal processing software. The compound sensor made by an advanced sensor fusion technique was able to detect simultaneously the vibration acceleration and the acoustic emission by itself. The signal processor received a signal from the sensor and separated it into the vibration acceleration signal and the acoustic emission signal. The signal processor and the personal computer processed the acceleration signal and acoustic emission signal for diagnostic information. The rolling contact fatigue process of a ball bearing under grease lubrication was monitored using the compound system. The system outputs diagnostic information, for example, the means, the variance, the skewness, and the kurtosis of the vibration acceleration signal and the acoustic emission signal. In diagnosing the rolling contact fatigue failure, the root mean square (rms) value of the vibration acceleration was most effective, and the mean of the demodulated acoustic emission was second to the rms value of the acceleration in effectiveness. From the result of the evaluation, it became clear that the system was useful for diagnosing rolling contact bearings under grease lubrication.

Relationship between growth of rolling contact fatigue cracks and load distribution

The relationship between growth of rolling contact fatigue cracks and load distribution on an inner ring of the radial rolling bearing was investigated by a new acoustic emission (AE) source location method. The histograms of cumulative AE events at possible AE source positions located in rolling contact fatigue tests were compared with the location results given by a numerical simulation. In many tests, the location histograms were not symmetric and most of the peaks in the histogram were distributed behind the actual AE source position. These corresponded to the simulation where the effective area for propagation of the fatigue crack deviated to the entrance side for the rotational direction within the loading zone. From the comparison, it became clear that the fatigue crack had a tendency to propagate in a narrow area deviating to the entrance side in the early stage of its growth and the area spread to the exit side gradually with the growth process from the initiation of the fatigue crack to an appearance of spoiling. Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

A New Form of Rolling Contact Damage in Grease-Lubricated, Deep-Groove Ball Bearings

A new form of rolling contact damage was discovered in the fatigue tests of series 6206 deep groove ball bearings under pure radial load with grease lubrication. The appearance of the damage reveals a few cracks at right angles to the rolling direction of the ball, along with the formation of a dent about 20 μ m deep in the raceway surface. This is found to occur only on the stationary outer ring raceway and the ball surface and is distributed widely within the load zone. Furthermore, under the raceway surface several cracks propagating into the substrate at an angle of about 60-80 degrees relative to the raceway surface are observed not only under the damage site but also in other nearby locations. Only the cracks at the damage position open up to the surface. The grease used for the test contained a lithium complex thickener with mineral oil as the base oil with a kinematic viscosity of 141 mm2/s at 40°C. On the test bearings two pure radial load levels of 9.14 and 12.13 kN were applied. In order to prevent the occurrence of seizure at each load, the speed of the inner ring of the test bearing was maintained at 1800-2500 min− 1 and 600-800 min− 1, respectively, to keep the outer ring circumference temperature below 65°C. It is suggested that the damage is caused by metal-to-metal contacts due to lubricant starvation under grease lubrication and to a decrease in oil film thickness due to local increases in temperature.

A New Rolling Contact Damage of Deep Groove Ball Bearing Under Grease Lubrication

A new type of rolling contact damage was found out in the fatigue tests of the deep groove ball bearings #6206 under pure radial load and grease lubrication. In appearance, the damages had a few cracks at perpendicular to the ball revolution direction, sank about 20 μ m in the surface of rolling raceway, happened only in the raceway of stationary races and surface of balls, and distributed widely within loaded zone. And in the cross section there were a lot of cracks propagated at 60∼80 degrees to the rolling surface at not only damage position but also other parts. The cracks at the damage position just opened to the surface. It is supposed that the damages are caused by rolling contact fatigue and metal to metal contacts due to lubricant starvation under grease lubrication.Copyright

Elastohydrodynamic Lubrication Characteristics of Electrorheological Fluids

Abstract Electrorheological fluids (ER) are recently developed materials that undergo rapid reversible changes in viscosity when an external electric field is applied. These fluids may solve industrial tribology problems (e.g., the seizure caused by poor lubrication)-particularly those where control of tribological characteristics is desirable. Here, we studied the elastohydrodynamic lubrication (EHL) characteristics of ER fluids by using a ball-on-disk type tribo-testing machine to measure the thickness and shape of an EHL film, and by using a liquid crystal with low molecular weight as the lubricant between a steel disk and a glass disk. The minimum film thickness increased by a factor of approximately four when an electric field was applied across the lubrication area, and the increase was greater for higher rotational speeds of either the ball or disk. We confirmed this change in triboperformance by observing the shape of the EHL films. These results demonstrate the potential of using ER fluids to control the triboperformance of machine elements.