Hozumi Goto

Effect of varying load on wear resistance of carbon steel under unlubricated conditions

Abstract Pin-on-disk type wear tests of mild steel in contact with itself were conducted under unlubricated conditions in moist air to investigate the effect of changes in load on the transition behavior between severe and mild wear. Machines in operation are usually subjected to varying loads. In this study, two contact load levels were used as a simple varying load condition. The load was changed in a step-wise manner between the low and high levels either once or twice during certain tests. Severe wear appears at the high load levels and mild wear at the low load levels in wear tests under constant loading. After oxidized, work-hardened wear surfaces have been formed under mild wear at the low load during the first stage, the wear mode changes to “quasi-mild wear” having a low rate at the high load in the final stage. The load range, where the low wear rate can be maintained under quasi-mild wear, extends to the higher load level after the change(s) in load. Once the quasi-mild wear surface has been generated, the wear mode can be maintained even at the high load for a very long sliding distance.

The influence of oxygen and water vapour on the friction and wear of an aluminium alloy under fretting conditions

Abstract An investigation was conducted to determine the effect of oxygen and water vapour on the friction and wear behaviour of an Al-Zn-Mg alloy under fretting conditions. Fretting wear experiments were carried out in wet air, dry air and in dry argon. In this case the peak-to-peak relative slip amplitude was varied from 20 to 260 μm to determine the critical slip amplitude of fretting wear in these environments. The experimental results indicated that the wear rates in dry air and in dry argon under macroslip conditions were almost the same and quite lower than the wear rate in wet air. This revealed that the effect of oxygen on fretting wear was not large but that water vapour accelerated the fretting wear of the aluminium alloy. The cyclically softened material due to overaging was observed below the contact surface during fretting in wet air. The mechanism involved rapid fretting wear in wet air which caused the removal of a heavily work-hardened layer as it was formed but the softened material below it was not removed.

Effects of ultrasonic vibration on the wear characteristics of a carbon steel: Analysis of the wear mechanism

Abstract To explain the fact that the wear rate of a carbon steel subjected to ultrasonic vibration decreases with an increase in the amplitude of vibration, a simple equation for the wear rate was derived using the theories of adhesive wear and analytical results of vibration. Analytical predictions were in good agreement with experimental results. One of the main factors affecting the wear behaviour under vibration is the contact time between specimens during 1 cycle of vibration. The amount of oxygen adsorbed on rubbing surfaces with repeated dynamic contact loading also affects the wear rate. The activation energy of oxygen adsorption with vibration is considered to be lower than that found in the process of ordinary wear without vibration. The variation in hardness of worn surfaces due to repeated friction passes has little effect on the wear rate with vibration.

Wear Behavior of Al-Si Alloy Impregnated Graphite Composite

Pin-on-disk type unidirectional sliding wear experiments for an Al-Si alloy impregnated graphite composite (pin) in contact with a bearing steel (disk) were conducted at various contact loads in wet and dry air to investigate the wear behaviors in detail. The pin-lifting phenomena of the composite as observed. The height was constant at lower loads and increased with load. The entrance of wear particles into the contacting surfaces brought about the pin lifting. Mixtures of graphite powder and wear particles adhered to the sliding surface of the bearing steel, resulting in the formation of wide, compacted surface films. The mean thickness of the films increased with load to a few micrometers. The composite exhibited better wear resistance than the matrices in wet air and the wear rate decreased especially at high loads. The wide, compacted films together with the pin-lifting phenomena prevent metal-to-metal contact, achieving a good anti-wear condition. On the other hand, the surface films that adhere in a scaled fashion in dry air have little wear reduction effect. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida October 11–13, 1999

Wear behaviour of a carbon steel subjected to an ultrasonic vibration effect superimposed on a static contact load

Abstract The effect of static contact load on the wear behaviour of a carbon steel subjected to ultrasonic vibration has been studied under unlubricated conditions using a pin-on-disk type of wear apparatus. A very large decrease in wear rate at a critical contact load was observed in the wear under vibration as well as in the ordinary wear, and a transition from a high wear to a low wear region appeared. The critical contact load increased with the amplitude of vibration. The worn surfaces of specimens became smooth and flat with decreasing static contact loads. Ripples due to vibration were observed with a scanning electron microscope. In the high wear region, the wear rate was almost proportional to the real contact area of the freshly sheared surface of asperities. In this case the area was corrected by the mean dynamic contact load and the contact time between specimens during one cycle of vibration.

Friction and Wear Properties of Aluminum-Silicon Alloy Impregnated Graphite Composite (ALGR-MMC) under Lubricated Sliding Conditions

In this work, friction and wear properties of aluminum-silicon alloy-impregnated graphite composite (ALGR-MMC) and its component matrices, graphite and aluminum-silicon alloy, in contact with bearing steel are investigated under lubricated sliding conditions. Pin-on-disk type wear experiments are conducted under “dry” sliding; i.e., in moist air with a relative humidity of 50% at 24°C; drop-feed lubrication; i.e., an oil drop with a certain volume selected in the range of 0.005–1 cm3 is deposited on the disk surface before commencing the wear tests; and immersion lubrication; i.e., the pin-on-disk contact is submerged in a 90-cm3 oil bath. Changes in friction and wear are continuously monitored. Tests revealed a reduction of the friction coefficient and wear rate for pins made in graphite with augmentation of the oil-drop volume. For aluminum-silicon alloy, breakdown of the oil film occurred below 0.03 cm3 volume of the drop, and since this was accompanied by a drastic rise of the friction and wear, damage of the counter surface was observed. Oppositely, a gradual decrease of the friction and wear with augmentation of the oil-drop volume was found for ALGR-MMC, without the breakdown of the oil film and/or damage of the counter surface. All tested materials reached the minimum friction and wear under immersion lubrication; however, graphite showed the worst and ALGR-MMC the best anti-friction properties. Since the friction coefficient and the wear rate of ALGR-MMC were much lower than those of the component matrices under all lubrication conditions, one concludes that the proposed composite material can be successfully used under both partially and fully lubricated sliding conditions.

Tribological Characteristics of Particle and Chopped Fiber-Reinforced Al-Si Alloy Matrix Composites

Reciprocating friction and wear tests of Al-Si alloy matrix composites in contact with bearing steel were conducted in air and lubricating oil to evaluate the friction and wear characteristics of the composites. In air, the coefficient of kinetic friction (μk) of the composites increases with load due to an increase in the real area of contact surfaces by metal-to-metal contact. In oil, the μk is constant above 50 N and drops with decreasing load. A parallel alumina fiber-reinforced composite to rubbing surface (PFRC) and a normal alumina fiber-reinforced composite (NFRC) exhibit good factional performance in air and oil. The frictional performance of a hollow silica particle-reinforced composite (SPRC) is the worst in air and oil because of the frictional resistance by fractured silica spheres and fragments. The wear rate (wL) of the composites in air increases with load and is much higher than that in oil. This indicates that the composites vs. the steel should not be operated under the unlubricated condition. The wL of the composites in oil also increases with load. The wL of the SPRC is as low as that of PFRC at low loads because there is still some load carrying ability of unexposed silica spheres right under the surface. It, however, increases at high loads by abrasive wear of the crushed and fractured silica fragments. Because of the better load carrying capacity of normal fibers, the NFRC exhibits better anti-wear properties than the PFRC in oil. This also indicates that the fiber orientation effect is a necessary but not sufficient factor in determining the overall behavior of the MMC vs. steel tribosystem, because the wear rate (wU) of the steel mating surface caused by the NFRC and PFRC exceeds that by the SPRC under abrasive wear conditions at high loads. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Friction and Wear Characteristics of Aluminum Alloy Impregnated Carbon Composite

Pin-on-disk unidirectional sliding friction and wear experiments for an aluminum alloy impregnated carbon composite in contact with a bearing steel were carried out at various levels of contact load in wet and dry air. The aluminum alloy impregnated carbon composite exhibits better friction and wear characteristics than the matrix materials, aluminum alloy and graphite in wet air. The coefficient of friction and wear rate decrease, especially at high loads in wet air. Graphite, together with metallic and oxidative wear particles, adheres to the disk sliding surface of the bearing steel, resulting in the formation of compacted, uniform surface films. The films prevent metal-to-metal contact, achieving a good sliding friction and wear condition.

Effect of water vapor in air on fretting wear of pure metals

Abstract Fretting wear experiments for several pure metals were conducted in air with various relative humidity levels using a hemisphere-on-flat type of fretting apparatus. The materials used were iron, aluminum, copper, silver, chromium, titanium and nickel. Each pure metal had a maximum wear volume at a specific humidity level ( RH max , which was independent of mechanical factors such as contact load, fretting amplitude and frequency in the range studied. The wear volume at RH max decreased with increasing shear strength of the pure metals at high hydrostatic pressures, indicating that adhesive wear was more predominant at RH max than abrasive or oxidative wear. The value of RH max decreased with increasing standard free energy of oxide formation for the pure metals. This demonstrated that RH max was strongly related to the surface chemistry of the pure metals.

Modeling and Simulation of a Screw-Worm Gear Mechanical Transmission to Achieve its Optimal Design under Imposed Constraints

This work deals with the modeling and simulation of a screw-worm gear mechanical transmission (worm gear screw jack), abbreviated WGSJ, to achieve its optimal design under imposed constraints. Optimal design is sought under two different conditions: to maximize the efficiency of WGSJ, for energy saving, and to minimize the overall size of WGSJ, for compact design. Several different models of buckling for the screwed shaft are taken into account by introducing a variable coefficient of fixity. Different strength theories of failure for the screwed shaft are taken into account, according to the type of material used, by introducing a variable weighting coefficient of the shear stress relative to the normal stress in evaluation of the equivalent stress. Variation of the mechanical transmissions efficiency and its overall size versus the coefficient of fixity and the shear stress weighting coefficient are presented and discussed.