An investigation of the effects of artificial fatigue-crack closure on the subsequent growth of fatigue cracks, at constant range of stress-intensity factor, was carried out for the following closure materials: (i) electroplated nickel; (ii) electroless nickel; (iii) ethylcyanoacrylate (ECA) adhesive; (iv) low-melting point (LMP) solder. It was observed that (a) the wedge thickness and area of crack surface covered by the artificial-closure material and (b) the distance of the tip of the closure wedge from the crack tip (i.e. the penetration of the closure material towards the crack tip) were the main parameters controlling the reduction in the subsequent growth rate of the fatigue crack. The results suggest that if the crack thickness (opening) is completely filled with a dense wedge of artificial-closure material, the wedge becomes effectively rigid and the precise mechanical properties of the closure material will have only a secondary influence on subsequent fatigue-crack growth in comparison to (a) and (b) above. This follows from the fact that the closure material is effectively a very thin strip compressed between the rough (high friction) sides of a crack. A rigid-wedge and elastic-crack model was found to successfully predict the changes in fatigue-crack growth rate following artificial crack-closure and gave a lower bound to the measured growth rates. NOMENCLATURE a = Crack length B = Specimen thickness c = Distance from the wedge tip of the artifical-closure material to the crack tip C = Material constant in the Paris equation K, = Stress-intensity factor due to artifical-closure wedge Kc, = Stress-intensity factor due to natural crack-closure K,, = Maximum stress-intensity factor K , , = Minimum stress-intensity factor K, =Theoretical stress-intensity factor due to a rigid wedge m = Material exponent in the Paris equation R = Load ratio (K,JKmX) UTS = Ultimate tensile stress W = Specimen width Y = Uniaxial yield stress 2h = Mean crack opening or closure-wedge thickness AK = Stress-intensity factor range AKa = Effective stress-intensity factor range

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