An Understanding of Fatigue Thresholds Through the Influence of Non‐metallic Inclusions in Steel

Abstract —In recent years the low fatigue growth rate regime has been the subject of extensive study revealing its complex and often seemingly inconsistent nature. The value of alternating stress intensity at threshold Δ K Th ) is sensitive to a range of variables which include mean stress, stress history, monotonie and cyclic yield strength, grain size and environment. A degree of coherency may be achieved by interpreting the data in terms of a crack closure mechanism which is a function of surface roughness. Experiments, in which the surface roughness (φ) has been altered by the introduction of non‐metallic inclusions, give insight into the significance of crack closure in this regime.