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The synergistic combination of mechanical fatigue stresses and environmental agents acting together can be more detrimental than that of the summation of the contributions of each mechanism acting separately. Major attempts to understand the contribution of the different agents (microstructure, chemical composition of environment, temperature, loading conditions, etc.) have been reported in the literature. Nevertheless, current knowledge is insufficient to address life estimation with a sound physical basis from the initiation of localized corrosion (such as pitting) to the estimation of crack propagation. Major simplifications and assumptions have been required in the development of life prediction methodologies. This paper reviews recent effort made by the different interested parties, both in academia and industry, in the development of corrosion fatigue lifetime prediction procedures. The paper mainly focuses on methodologies proposed in the literature for O&G, nuclear, energy generation and aerospace applications, dealing with pitting corrosion-fatigue (CF) damage in aluminium alloys, carbon and stainless steels. The transition of a pit into a small crack and its growth is influenced by interaction of the pit stress/strain concentration and the local environmental conditions, making the modelling of this stages of the utmost complexity. A major trend in the models reviewed in this paper is to simplify the analysis by assuming the pit (a volumetric defect) as a sharp crack, decouple the CF problem and account for the mechanical and environmental contributions separately. These procedures heavily rely on fitting experimental data and exhibit low generality in terms of application to varying system conditions. There is a clear opportunity in this field to develop mechanistically based methodologies, considering the inherent dependence of the damage mechanism on the interaction of environmental, metallurgical and mechanical features, allowing more realistic lifetime estimates and defect tolerance arguments, where pit-to-crack transition and small crack initiation stages pose a significant challenge.

Under non-steady creep conditions, the stress and strain rate fields near the tip of a stationary crack can be described by the singular fields of Hutchinson, Rice and Rosengren for power-law creeping materials. Estimation formulae are presented for describing the amplitude of these fields under load and displacement controlled boundary conditions. For constant loading, the formulae reduce to the result of Riedel and Rice for short times after load application and to the steady state line integral C* for long times. At intermediate times, the estimate is validated by detailed finite-element computation. For displacement-controlled loading, the amplitude of the near-tip fields is shown to fall rapidly, consistent with finite-element analysis. The implications of the results for data collection and defect assessments are discussed in a companion paper. NOMENCLATURE A = area between contours B = constant in creep law of equation (2) B, = specimen thickness a, u =crack size, crack growth rate C ( a / w ) , C' = elastic compliance function, dC/d(a/w) C ( t ) = non-steady creep integral of equation (4) C* = steady state creep integral of equation ( 5 ) E, E' = Young's modulus, E/(l -v 2 ) e,, e,, = elastic strain, strain rate tensors h, = dimensionless function in equation (9) I, = dimensionless function of n in equations (7, 8) J = contour integral of equation (6) K = elastic stress intensity factor m ( a / w ) , m' = limit load ratio, dm/d(a/w) L, L , = characteristic lengths in equations (9, 11) n =creep stress index in equation (2) n, = unit normal r = distance from crack tip S, = deviatoric stress tensor ds = element of contour r t, to = time, normalising time P, Po, P, = applied load, normalising load, collapse load u,, u, = displacement, displacement rate tensors cS,,L',, = creep strain rate, creep strain rate tensors L ' ,~ = creep strain rate at stress uXf w = section width [ = contour around the crack tip x, y = Cartesian co-ordinates A, A = specimen load-line displacement, displacement rate L,, C, , = strain tensor, dimensionless function in equation (8) A,,, At, = creep, elastic components of A 0 = polar angle K = I in plane stress, K = 0.75 in plane strain 263 264 R. A. AINSWORTH and P. J. BUDDEN p = constant in equation (26), estimated in the Appendix v = Poisson's ratio u,,, 8,, = stress tensor, function in equation (7) uEl, CT$ = reference stress in equation (10). value for load Po uo = yield stress t = dimensionless time of equations (22) and (24) d, = exponent in crack growth law of equation (32)

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