Effect of surface finish on fatigue strength

The components surfaces used in lubrication, friction and wear vary in their initial surface topography according to the particular use involved. In practice a real component from a machine or structure will generally have various surface finishes and different fatigue strengths. The usual stand by which various surface conditions are judged is the polished laboratory specimen. Irregular and rough surfaces generally exhibit interior fatigue properties. The present study represents a neat investigation which is carried out to correlate the various surface finish parameters with the endurance fatigue strength of a commercial aluminium alloy. The flow strain in both horizontal and vertical directions is monitored using two attached transducers during the testing of specimens grouped according to their surface finish features. Accordingly, the fatigue initiation life as interpreted from the generated flow curves is correlated with the surface finish parameters. Results indicate a great effect for all surface finish parameters. It leads to a significant correlation between the fatigue initiation life, final separation life and the fatigue endurance limit. Implementing the regression analysis leads to exponential correlations between the number of cycles for initiation of microcracks and applied cyclic stress, also between total life and alternating stress. Moreover, polynomial equations have been developed to relate the endurance stress to the various surface finish parameters.