AGMA 92FTM8-1992 pdf free.The Role of Reliability for Bearings and Gears.
Within any vital operating equipment, the reliability of the components that make up the unit must be known if any sound predictions of life or stress capability r• to be made. Reliabilty of course is not an independent quality or factor of any component, whether it be bearing or gear. The interdependence of these three factors, life, stress (or load level) and reliability was demonstrated years ago by Waloddi Weibul]. (1) as illustrated in Fig. 1. The figure shows three interlinking plots in what Weibull called the complete fatigue diagram.
Section 1 on the figure is the typical S/N curve with S representing stress on a linear soale and N representing life in stress cycles on a log scale. The curves labeled P are the full range of probabilty that can theoretically occur from PO (100X reliability) to P1 (zero reliability). All testing or real life component operations fall within these extremes. For a given stress and expected or determined life, a probability or reliability value must exist. For bearings and gears one tends to consider only a few specific curves represented by section 1 of the diagram.
In sections 2 and 3 of Fig. 1, other representations of the stress-lit.— reliability relationship are illustrated. For this figure the spacing of the curves and the log or linear scales are arbitary. In actuality the underlying distributions or scales are determined by experi.nt. And when curves are drawn and eventually used in gear and bearing standards, they have been developed from tests. The S/N curves are based on fatigue tests and the reliability-life or reliability-stress relationships depend on related or additional testing, usually Hith multiple tests at each of several stress levels.
Reliability—Life for Bearings
The reliability—life relationship for bearings has been generated froa multiple tests run on all typos of rolling element bearings. Bearing life has been expressed as B-tO or L-lO for years and is L-lO in the latest bearing standards (2)(3)(4). L—lO is defined as basic rating life in millions of revolutions so that for a group of apparently identical rolling bearings, operating under the same conditions. 80 percent are expected to meet or exceed rating life and ten percent are expeoted to fail earlier. Thus, reliability in the broader sense is the percentage of an identical group that taill reach or exceed a specified life. For an individual bearing its reliability is the probability that it will reach or exceed the specified life.AGMA 92FTM8 pdf free download.