Alan Hase

Due to the continuing decrease in the proportion of young people in the population, it is likely to become more difficult to secure the researchers who will lead the next generation. To overcome this problem, it will be necessary to arouse the interest of children and young people in science and engineering. Tribology is the study and application of the principles of friction, lubrication, and wear, and is an interdisciplinary discipline spanning many fields; consequently, the study of tribology can encourage interdisciplinary learning. Furthermore, tribology is an important discipline of itself because it has a direct relationship to issues of energy and the environment. Teaching tribology to young people and helping them to understand it could arouse their interest in a variety of aspects of science and engineering. The key is how to introduce the various academic aspects of tribology, a complex and mysterious discipline, in an engaging manner. The author has energetically striven to promote introductory education to enlighten the next generation about tribology by using a novel educational method that incorporates a problem-solving game. This paper describes the effectiveness of this educational method, the content of the developed teaching materials, and the results in educational practice.

A method based on acoustic emission (AE) sensing in which two AE sensors are used to measure the tribological characteristics of two interacting friction materials simultaneously in real time was assessed for the in situ measurement and evaluation of the wear process of silver plating. AE sensors were attached to a silver-plated pin and a silver-plated plate, and the two AE signals were measured simultaneously on a pin-on-plate-type reciprocating sliding tester. The resulting changes in the AE signal could be classified into three phases. Surface observations and energy-dispersive X-ray spectroscopy analyses showed that the wear of the silver-plating layer progressed in Phase I, the nickel intermediate layer was exposed and wear of the nickel progressed in Phase II, and the contact electrical resistance increased and the copper substrate was exposed in Phase III. In summary, the wear process of a silver-plating layer, which cannot be identified from the changes in the frictional res...

Sulfur and phosphorus additives are used in lubricants as extreme-pressure and antiwear agents, which are typically used together to ensure reliability over a wide range of lubrication conditions. However, the working mechanism of the combined additive system has not been clearly defined due to difficulties obtaining information on the material surface where these additives work. This is because this surface is constantly being worn during testing. Therefore, in situ analysis applying an acoustic emission (AE) technique was proposed. AEs are elastic stress waves generated during the deformation and fracture of solids, which can be measured in real-time, providing information with respect to the magnitudes and types of damage. In this paper, an application of the AE helps to clarify how each additive acts on the surface in real-time. The working mechanism to understand improved reliability using both sulfur and phosphorous additives was investigated by the AE technique, along with conventional surface analysis methods. It is concluded that wear reducing properties were improved by the reaction of sulfur additives to remove the protruded parts, followed by the reaction of phosphorous additives to form a protective antiwear film.

We report a short note of preliminary and new experimental results that the generation of ammonia (i.e. nitrogen fixation) can occur on tribologically activated surfaces formed as a result of the frictional sliding of pure titanium when this is performed in a mixed gaseous environment of dinitrogen and dihydrogen at a total pressure of 6 × 10-4 Pa. Gaseous ammonia, synthesized at the tribologically activated surface on the actual area of contact and/or on fine debris of wear elements with a size of the order of ten or a few tens of nanometers, was detected by analyzing the partial pressures for each species between amu 1 and amu 50 present in the environmental gases during the sliding friction: this analysis was performed using a quadrupole mass spectrometer (QMS). This process, however, depends on the mode of wear, i.e. it is expected to occur only under mild conditions of wear.

In the elementary process of adhesive wear, wear elements, which are the elemental debris of wear particles, are generated at junctions of asperities, and subsequently grow into transfer particles between sliding surfaces through a mutual transfer and growth process. To elucidate the mechanism of adhesive wear and to establish a wear equation, it is necessary to investigate the characteristics of wear elements and transfer particles in more detail. In this study, changes in the numbers and shapes of wear elements for various metals were examined by means of scanning probe microscopy. In addition, the relationship between the numbers of wear elements and the adhesion forces, determined by friction force microscopy and force-curve measurements, was examined to evaluate the probability of generation of wear elements. The findings on the elementary processes of adhesive wear obtained from this study should be useful in establishing a future theory of wear.

The relationship between acoustic emission (AE) signals and wear phenomena in severe-mild wear transition is discussed on the basis of the results of observations of wear particles and worn surfaces of steel. Each wear mode, severe wear or mild wear, is reproduced for a different sliding velocity. The influence of relative humidity on mild wear is examined. We found a reduction in the true area of contact and the size of wear particles decreases the AE signal level in severe-mild wear transition. In the mild wear mode, an increase in the number of transfer particles lying between the sliding surfaces decreases the AE signal level. Further, a linear relationship is observed between the AE mean value and the specific wear rate, regardless of the wear mode. This is because the AE signals generated by the formation and removal of transfer particles mainly originate under conditions of repeated dry rubbing.

A method based on acoustic emission (AE) sensing in which two AE sensors are used to measure the tribological characteristics of two interacting friction materials simultaneously in real time was assessed for the in situ measurement and evaluation of the wear process of silver plating. AE sensors were attached to a silver-plated pin and a silver-plated plate, and the two AE signals were measured simultaneously on a pin-on-plate-type reciprocating sliding tester. The resulting changes in the AE signal could be classified into three phases. Surface observations and energy-dispersive X-ray spectroscopy analyses showed that the wear of the silver-plating layer progressed in Phase I, the nickel intermediate layer was exposed and wear of the nickel progressed in Phase II, and the contact electrical resistance increased and the copper substrate was exposed in Phase III. In summary, the wear process of a silver-plating layer, which cannot be identified from the changes in the frictional resistance or the contact electric resistance, can be detected from changes in the dual AE signals. Furthermore, changes in the wear state of both the pin and plate specimens can be identified from differences in the amplitudes of the AE signals and the timing of their detection.

As rolling bearings are widely used in various machines, there is a strong need to detect any problems as early as possible. Although vibration analysis is commonly used in the diagnosis of rolling bearings, it is possible that the failure of such bearings might be detected earlier by an acoustic emission (AE) technique. Methods for detecting potential fatigue damage in a thrust ball bearing by AE signal analysis and by vibration analysis were compared. For the AE signal analysis, the maximum amplitude and the frequency spectrum were used to detect and identify fatigue damage in the bearing. Features of AE signals detected when a defect was artificially formed on the raceway surface of a bearing by using a Vickers hardness tester were also examined. The AE technique detected initial cracks due to fatigue damage earlier than the vibration technique. Additionally, AE signals were always detected during bearing fatigue tests, but the AE signals detected during the running-in process, crack initiation, crack propagation, and flaking all contained different frequency components. Furthermore, the correlation map between the frequency spectra of AE signals and deformation and fracture phenomena (friction and wear modes) was updated by adding the new findings of this study.

During contact, deformation, and fracture of surface asperities between the friction surfaces of materials, acoustic emission (AE) waves are generated as the strain energy is released. By detecting the AE waves during friction using an AE sensor, the state of friction, wear, and lubrication between the friction surfaces can be measured and evaluated with high sensitivity. In this study, in order to establish a method for evaluating the writing performance of ballpoint pens by AE sensing, the measurement method was examined, and AE signal waveforms were analyzed. It was found that AE sensing can detect phenomena that do not appear as a change in frictional force during writing. In addition, frequency analysis of the AE signal waveforms revealed that differences in writing performance depending on the ink type of the ballpoint pen can be evaluated and interpreted.