Fatigue crack growth in a diverse range of materials

Cyclic-fatigue crack growth in composite and adhesively-bonded structures: The FAA slow crack growth approach to certification and the problem of similitude

“…Figure 7 3, from [19], presents the da/dN versus ∆Κ curves for a AA2324-T359 aluminium alloy tested at values of R = -1, 0.3, 0.5 and 0.7. Figure 4, from [20], presents the da/dN versus ∆Κ curves for a AA7050-T7451 tested at values of R = 0.1 and 0.7. The common feature of each of these plots is that for a given CDF (i.e.…”

“…The Hartman-Schijve equation used in [1,8,11,20,24,25,32,36,[39][40][41][42][43][44] is basically an empirical equation that for metals takes the form:…”

“…and, as explained in [20,32,36], the values of A and ∆K thr are chosen to ensure that Equation (7) captures the entire crack growth history. This approach has the advantage that it can represent the growth of both long and small, naturally-occurring, cracks and can capture the variability seen in crack-growth histories as observed in both constant amplitude and operational flight-load spectra [24,32] as well as the coalescence of small cracks and their subsequent growth.…”

Microstructurally small fatigue crack growth rates in aluminium alloys for developing improved predictive models

“…These include: − assuming plasticity induced crack closure on the measured long crack data and adjusting the predicted growth for this [i.e. adjusted compliance ratio] [7]; − correlating crack growth to the crack tip opening displacement parameter [10]; − predicting formation of dislocations ahead of the crack front to correlate with crack growth [11]; − adjusting the effective threshold down [12]; − assuming exponential growth and a very low (or zero) growth threshold [13]; − determining a critical strain/distance threshold based on local notch/crack geometry [14,15]; and − using the average crack growth for spectra that contain repeating blocks of variable loading, [16]. The Threshold and Small Crack (TASC) research program at DST has used another approach: an innovative test and analysis technique to directly measure the crack growth rates of small cracks growing as the result of stress intensities just above the cyclic threshold region (∆K th ).…”

Fatigue threshold and crack growth rate of adhesively bonded joints as a function of load/displacement ratio

“…Therefore, it was concluded that the fatigue threshold was controlled by G max alone. Recently Jones et al [23,24] used a variant of the Hartman-Schijve equation to eliminate the effect of load ratio on mode I and mode II fatigue crack growth in a wide variety of polymer composites. However, in order to predict the crack growth rate at a specified range of the stress intensity factor, the method requires the measurement of the fatigue threshold for each load ratio of interest.…”