Effects of Stress Rising Time and Stress Hold Time in a Loading Cycle on Corrosion Fatigue Crack Growth Behaviour in a Low Frequency Range

In order to clarify whether da/dN depends on cycle only, or on time only or on both cycle and time, crack growth behaviour, in a 3.5% NaCl solution, of low alloy Cr-Mo steel at a lower frequency range was experimentally studied, stress frequency f being controlled by stress rise time t_R and stress hold time t_H independently. From the results and the analysis, a new experimental formula was obtained for da/dN in non-linear terms of f, t_R and t_H. A stochastic process concept is proposed for the significance of the equation of this type. As a special case, a simple and convenient expression for da/dN and da/dt in corrosion fatigue (t_H=0s) was proposed in terms of frequency.