Figure 2 Methods for each life phase (after Hoeppner-1971, 1986).
NOTE: Initiation as frequently used by the technical community is usually part of the nucleation (or formation), short crack growth, and stress dominated crack growth phase of life. One is never sure however how much of the life is taken up by the traditional use of the "initiation" concept. To avoid this we have used the term initiation herein only to refer to the beginning of a specific degradation process such as corrosion, fatigue, or initiation of crack propagation. As depicted in Figure 1 what often is referred to as "initiation" is life to a certain detectable crack size or damage size. This is a critical distinction in that use of "first" crack detection concepts, or related on condition evaluation terms, forces the designer to think about inspectability and detectability of specific forms of degradation. As well, it is imperative that the technical community develop an understanding of the nucleation and growth phases of degradation processes.
Review of Pitting Corrosion Fatigue Models, D.W. Hoeppner, V. Chandrasekaran, and A.M.H. Taylor, University of Utah and FASIDE International Inc.