A review of Competing Modes fatigue behavior

Competing Failure Modes in fatigue refers to the occurrence of two distinct failure distributions in a homogenous data set. The disparate distributions have been attributed to failures occurring on the surface of test specimens and other failures from sub-surface to deeply imbedded sites. When such behavior occurs significant life differences between each group of up to a factor of 10 or more is observed. Conversely, under different testing conditions, principally temperature, failure from these distinct initiation sites yields results demonstrating little or marginal life differences. Competing Modes behavior has been reported in many steel, nickel, and titanium alloys. Given the extent of the occurrence of this behavior it seems reasonable that a new or at least modified perspective on fatigue behavior is in order. Discussion will be presented relative to the classical concept of the endurance limit and how a modified view is seemingly necessary. Additionally, discussion of how to manage the Competing Modes behavior from a fatigue curve design perspective will be presented.