A Review of Fatigue Crack Growth Characterisation by Linear Elastic Fracture Mechanics (Lefm). Part I—principles and Methods of Data Generation

Abstract

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.

A reexamination of plasticity-induced crack closure in fatigue crack propagation

“…The technique for the determination of crack closure was later used by most researchers with little modifications for the crack opening displacement measurement and interpretation of crack closure or opening levels. A great number of technical papers related to crack closure have been published in the last three decades (Allen et al, 1988;McClung, 1999;Sehitoglu et al, 1996;Vasudeven et al, 1994). Noticeably, two volumes of ASTM Special Technical Publications, ASTM STP 982, and ASTM STP 1343, were specifically dedicated to the discussion of crack closure.…”

“…Noticing the overestimated crack closure effect, partial crack closure concept was developed by introducing a coefficient being less than unit as a multiplier to S op (Paris et al, 1999;Kujawski, 2002Kujawski, , 2003. On the other hand, Allen et al (1988) concluded that at a growth rate of the order of 10 À5 mm/ cycle and greater, closure did not occur except in the presence of shear lips. Vasudeven et al (1994) critically reviewed the published crack closure mechanisms for the near-threshold crack growth behavior and concluded that there can be no contribution from plasticity to crack closure.…”

An Approximate Method for Fatigue‐life Prediction of Framed Structures

“…The overall energy release rate can then be obtained from Eqs (14) and (6) as a combination, through constant coefficients, of the derivatives of functions zi(a) (i = 1,2 and eventually 3) once the slope of the stress diffusion lines, i.e. the function p(a), has been determined.…”

Fatigue crack growth of multiple interacting cracks: Analytical models and experimental validation

“…A simple and reliable tool that can be used for this kind of analysis is the Linear Elastic Fracture Mechanics . Many laws for fatigue crack propagation are available (e.g.…”