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The impact fatigue crack growth characteristics of a low carbon steel and an aluminium alloy were studied. An impact fatigue testing machine of the Hopkinson bar type was used in these experiments to conduct a series of crack growth tests under simple impact stresses.The following characteristics of impact fatigue crack growth behaviour were revealed: (1) crack growth rate is higher in impact fatigue than in non-impact fatigue; (2) crack opening ratio in impact fatigue takes a higher value than in non-impact fatigue; (3) crack tip plastic zone size is smaller in impact fatigue than in non-impact fatigue. NOMENCLATURE a = one-half of the total length of a central symmetrical crack C, m = constants in the relationship da/dN = C(AK)"' da/dN = fatigue crack growth rate AK = stress intensity factor range A o = applied stress range AKeR = effective stress intensity factor range defined as U A K N = number of stress cycles R = stress ratio defined as umm/u,,,,, S = average value of striation spacings U = crack opening ratio defined as (K,,,,, -K,,)/AK where Kop is the value of K needed to open a crack 1 = aspect ratio defined as 2a/W, where W is width of a specimen.

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