ISO 7905-3:1995 download.Plain bearings — Bearing fatigue — Part 3: Test on plain strips of a metallic multilayer bearing material.
1 Scope
This part of ISO 7905 specifies a method for the determination of the endurance limit in fatigue of plain strips of multilayer bearing materials. Additionally it provides the opportunity of studying the influence on the strips of hydraulic pressure and variable temperat u re
2 Test specimens
The test specimens shall be flat thin strips of rectangular cross-section to the dimensions shown in figure 1. To avoid fracture starting at the clamped portion, the edges shall be carefully chamfered by grinding and the test section shall be contured as shown in figure 1.
For a multdayer bearing material, the layer dimensions of the test specimen shall be representative of the manufacturing sequence and the test specimen shall be finished to the same surface texture. Care should be taken before and during the test not to damage the surface mechanically or by corrosion. The deficiency of this test method lies in the absence of possible residual stress associated with the bearing manufacturing process.
3 Test method
The test principle is illustrated in figure 2. The specimens shall be clamped at one end and loaded at the other end by force or displacement. The load shall fluctuate from tension to compression over the running surface. Additionally a tensile or compressive prestress may be applied in order to evaluate dependency upon mean stress. The test equipment is preferably located in a chamber containing a lubricant at fixed levels of temperature to ± 2 ‘C. Alternatively tests may be conducted in air at fixed levels of ternperature ± 2 ‘C.
Bending stress shall be measured by a strain gauge near the clamping point on the back of the bearing. The required bending stress at the damaged section may be evaluated by calculation, knowing the relative location of the strain gauge and first crack, and the thickness and Young’s modulus of the lining and steel backing.
NOTE 1 The stresses in plain layered strips under con
dition of bending may be evaluated theoretically.
The test frequency shall have a range of 50 to 80 Hertz. Crack detection shall be performed by dye penetrant method or by microscope. The amplitude shall be controlled by force (F) or displacement (s).
4 Evaluation and presentation of test results
The endurance limit stresses should be presented in the form of o-N curves at predetermined temperature (± 2 °C) against a detailed description of the bearing material. Normally ad-N curve testin is terminated for practical considerations at 50 x 10 stress cycles. The endurance limit stress may be quoted at a specified number of cycles e.g. 3 x 106, 10 x 108, 25 x 106 or 50 × 106. A specimen without failure during fatigue testing to a specified endurance should be identified in the report Due to the scatter of test resuits normally experienced and the statistical nature of the fatigue limit, it is recommended that the results be evaluated on the basis of a statistical method.
Another presentation of the endurance limit stress may be effected by means of the Haigh diagram which plots stress amplitude against mean stress Metallographic examination will provide detailed evidence of the damage mechanism, corrosive attack and diffusion resulting from thermal effects.