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Ahstmet-The application of linear elastic fracture mechanics (LEFM) to the characterisation of fatigue crack growth has been reviewed. In Part I the present understanding of the factors influencing growth rate is summarised, and the current methods of fatigue crack growth rate data generation are considered in the light of this. In Part 11, documents are reviewed which provide advice on the prediction of fatigue crack growth and also those national standards in which fatigue crack growth considerations are implicit. NOMENCLATUREBecause of the nature of this review it is not possible to provide a precise nomenclature. Where possible, terminology consistent with the source document has been adopted. The following general terms occur most frequently: A, C, C,, =constants in the Paris equation u = crack length B = specimen thickness d = grain diameter du/dN = fatigue crack growth rate per cycle dq5/dA = rate of change in compliance with crack area E = Young's modulus E' = E for plane stress or E/(1 -v 2 ) for plane strain G = crack extension force per unit thickness J = Jcontour integral K = stress intensity factor Kal = parameters relating to the dependence of threshold on prior load history K.fb Kl K, = non-plane strain fracture toughness K,c = plane strain fracture toughness K = mean stress intensity factor N = number of loading cycles P = applied load K , , = maximum value of K during a loading cycle tn, n = exponents in the Paris equation PmX = maximum load during a cycle P,j, = minimum load during a cycle R = stress or load ratio (Pmn/Pmm) W = specimen width (or half width of a BSI CCT specimen) Y = stress intensity factor function Au = change in crack length AK = stress intensity factor range (K,,,,, -Lin) 'Author to whom correspondence should be addressed. U = AK,,/AK 45 F.F.E.M.S. I lil-D 46 R. J. ALLEN et al. AKeR= the range of K over which a crack is fully open on loading AKth = fatigue crack growth threshold A& = initial value of AK at the start of a test AP = load range (P,,, -P,,,) S = crack tip opening displacement (CTOD) v = poisson's ratio of = flow stress [ = (uTs + uys)/2] uTs = tensile strength uys = yield or 0.2% proof strength ux = stress in the x direction (see Fig. 1) uy = stress in the y direction (see Fig. 1) Units = MPa, m unless otherwise stated.

This paper presents a review of the application of LEFM to the characterisation of fatigue crack growth. This part covers national standards and other documents of comparable status that (a) offer explicit advice on the use of fatigue crack growth data, and (b) in which crack growth considerations are implicit. Documents falling into the first category were noted to have many features in common, differences occurring only in areas where the current understanding of the subject is far from complete (e.g. variable amplitude loading, long life, etc.). Documents implicitly addressing fatigue crack growth comprise three distinct groups: (i) those which aim to simplify fracture mechanics analyses for the user, (ii) those in which fracture mechanics has influenced design criteria, and (iii) those which aim to provide inspection and/or acceptance criteria. As with the "explicit documents", a degree of commonality was observed within each group of "implicit documents", the exception being the military aircraft specifications of the U.K. and the U.S.A.

Fatigue crack propagation tests have been carried out on three C-Mn structural steels at stress ratios between 0.67 and −4. Surface strain gage techniques have been used to determine crack-tip closure stress and an expression proposed to relate the proportion of the stress cycle for which the crack tip is actually open U to stress ratio. Satisfactory correlation of the crack propagation results for this range of stress ratios has been achieved by defining an effective stress intensity factor range as the proportion U of the total stress intensity range. In addition, reasonable correlation of the results was obtained on the basis of the tensile portion of the stress intensity factor range.