【文章內(nèi)容簡介】 deterioration as a result of accelerated life test condit ions. Also for consistency o f results and parin g life test groups, it is good practice to utilize one standard test lubricant from a particular producer for the conduct of all general life tests. The statist ical nature of rolling contact fatigue requires many test samples to obtain a reasonable estimate of life. A bearing life test sequence thus needs a long time. A major job of the experimentalist is to ensure the consistency of th e applied test condit ions throughout the entire test period. T his process is not simple because subtle changes can occur during the test period. Such changes might be overlooked until their effects bee major. At that time it is often too late to salvage the collected data, and the test must be redone under better controls. For example, the stability of the additive packages in a test lubricant can be a source of changin g test condit ions. Some lubricants have been known to suffer addit ive depletion after an extended period of operation. The degradation of the addit ive package can alter the EHL condit ions in the rolling content, alterin g bearing life. Generally, the normal chemical tests used to evaluate lubricants do not determine the condit ions of the additive content. Therefore if a lubricant is used for endurance testing over a long time, a sample of t he fluid should be returned to the producer at regular intervals, say annually, for a detailed 河南科技大學(xué)外文 翻譯 9 evaluation of its condition. Adequate temperature controls must also be employed during the test. T he thickness of the EHL film is sensitive to the contact tempe rature. Most test machines are located in standard industrial environments where rather wide fluctuations in ambient temperature are experienced over a period of a year. In addit ion, the heat generation rates of individual bearings can vary as a result of the bined effects of normal manufacturing to lerances. Both of these conditions produce variations in operating temperature levels in a lot of bearings and affect the validity of the life data. A means must be provided to monitor and control the operatin g temperature level of each bearing to achieve a degree of consistency. A tolerance level of ? 3C is normally considere d adequate for the endurance test process. The deterioration of the condition of the mountin g hardware used with the bearings is another area requir ing constant monitoring. The heavy loads used for life testing require heavy interference fits between the bearing inner rin gs and shafts. Repeated mounting and dismounting of bearin gs can produce damage to the shaft surface, which in turn can alter the geometry of a mounted ring. T he shaft surface and the bore of the housing are also subject to deterioration from fretting corrosion. Frettin g corrosion results from the oxidation of the fine wear partic les generated by the vibratory abrasion of the surface, which is accelerated by the heavy endurance test loading. T his mechanism can also produce sign if icant variations in the geometry of the mounting surfaces, which can alter the internal bearing geometry. Such changes can have a major effect in reducing bearing test life. The detection of bearing failure is also a major consideration in a life test series. The fatigue theory considers failure as the init iation of the first crack in the bulk material. Obviously there is no way to detect this occurrence in practice. To be detectable the crack must propagate to the surface and produce a spall of sufficient magnitude to produce a marked effect on an operatin g parameter of the bearing: for example, noise, vibration, and/or temperat ure. 河南科技大學(xué)外文 翻譯 10 Techniques exit for detecting failures in application systems. The ability of these systems to detect early signs of failure varies with the plexity of the test system, the type of bearin g under evaluation, and other test condit ions. Currently no s ingle system exists that can consi