Abstract
The fatigue crack growth in very large CCT specimens of Al alloy (A 5083-O) was measured in different environments, that is, in nitrogen gas, in laboratory air and in 3% NaCl solution. The crack growth rate was highest in 3% NaCl solution and lowest in nitrogen gas, and the relation between the crack growth rate and the stress intensity factor range was typical of corrosion fatigue.
From the observation of the environmental effect on the fatigue crack growth rate of the same material, it is considered that the reversed slip which contributes the recovery at the crack tip during unloading procedure is strongly dependent on testing environments; the reversed slip is hardly blocked in innert nitrogen gas, but the almost all of reversed slip is blocked in aggressive 3% NaCl solution.
From the above consideration, the relation between the crack growth rate, da/dN, and the stress intensity factor range, ΔK, with two material coefficients, C1, and C2, and one environmental coefficient, CR, having respective constant dimensions, can be written as
da/dN=C2ΔK2-CR(C2ΔK2+C1ΔK4)
=AΔK2+BΔK4, where A=C2(1-CR), B=C1×CR
It is expected that this equation is not only applicable to the experimental results of Al alloy A 5083-O, but also to other materials.
