Introduction

The phases of life of a structure may be classified as follows [1]:

• Nucleation or formation of damage by a specific, physical or corrosion damage process interacting with the fatigue process if appropriate. Corrosion and other processes may act alone to create the damage. a transition from the nucleation stage to the next phase must occur. Phase L₁
• Microstructurally dominated crack linkup and propagation ("short" or "small" crack regime). Phase L₂
• Crack propagation in the regime where either LEFM, EPFM, or FPFM may be applied both for analysis and material characterization (the "long" crack regime). Phase L₃
• Final instability. Phase L₄

Thus, the total life (L_T) of a structure is L_T = L₁+L₂+L₃+L₄. Figure 1 presents a depiction of the degradation process. The regions shown, e.g. 1, 2, 3, and 4, illustrate the portion of life, on the abscissa, and the corresponding growth in discontinuity size plotted schematically on the ordinate. This paper concentrates on the phases L₁ and L₂. That is, the corrosion process that results in the generation of a specific form of corrosion generating a specific form of discontinuity that is not necessarily a crack like discontinuity, and the development of short cracks and their propagation. The requirement of the community to come up with design methods to deal with corrosion or other degradation, fatigue, creep, and wear, is essential and some of the elements are depicted in Figure 2. This figure illustrates that most of the quantitative methods that have been developed used the concepts of mechanics of materials with an incorporation of fracture mechanics [2].

Review of Pitting Corrosion Fatigue Models, D.W. Hoeppner, V. Chandrasekaran, and A.M.H. Taylor, University of Utah and FASIDE International Inc.