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A brief description of the magnetic perturbation method is presented. Quantitative results, based on extensive experimental data, are reviewed that establish a strong correlation between magnetic signatures and inclusions and, also, fatigue crack development cycles on rod-type specimens fabricated from AISI 4340 steel. The dominant influence of “near surface” inclusions on fatigue crack development resulting in subsequent specimen fracture is established. Quantitative correlations between magnetic perturbation signatures and inclusions disclosed by metallurgical sectioning of ball bearing inner races are also presented. Endurance testing results on bearings, including several with magnetic signatures indicating inclusions, are reviewed. The significance of overall results is discussed.
inclusions, cracking (fracturing), bearings, fatigue (materials)
Vice president, Southwest Research Institute, San Antonio, Tex.