An analysis is presented of factors causing fatigue crack resistance in metals exposed to liquid corrosive environments. A new approach involving invariant diagrams is proposed that takes simultaneous account of the stress-strain state and the electrochemical conditions at the tip of a crack. Variations in electrochemical conditions at the tip of a stationary crack and the relationship between the electrochemical conditions at the crack tip and the fatigue crack growth rate in aqueous corrosive environments are discussed with the aid of these diagrams.
NOMENCLATUREF = load M = bending moment a = crack length N = number of cycles v=crack growth rate u, = fatigue crack growth rate in corrosion environment K, =stress intensity factor for a Mode I crack K , , K,,, = initial level of Kl and maximum value of Ki AK = stress intensity factor range K,, = critical value of K, under plane strain conditions K, = critical value of Kl for a material of given thickness KlsCc = threshold value of K, under plane strain conditions in a corrosive environment t = time S = fracture surface C , , C, . . . C, = material constants A , , A , . . . A, = parameters defining physicochemical processes at a crack tip B , , B, . . . Bk = parameters characterising the state of the fracture surface pH, = hydrogen ion exponent of the environment pH, = value of pH at the crack tip pH, = value of pH within a crack at a distance x from the specimen surface pH,, = value of pH at the tip of a stationary crack under static loading pH,, = value of pH at the tip of a propagating crack under cyclic loading pHP, =value of pH,, at the moment a crack opens pH;< = value of pH,, at the moment a crack closes ApH,,. = variation of pH,, within a loading cycle + ; c = value of #J,, at the moment a crack opens $:< = value of at the moment a crack closes A+,, =variation of +,, within a loading cycle.
