Abstract
The fatigue crack growth of steel in sea water is influenced by various factors, such as loading condition, environmental and metallurgical variables. In this report, the effects of waveform and frequency of cyclic loading on corrosion fatigue crack growth rate have been studied for a 660 MPa tensile strength steel in synthetic sea water. Used waveforms are triangular, trapezoidal, and positive-and negative-saw tooth, and frequencies ranged from 0.017 Hz to 0.83 Hz. The results show that da/dN at a certain ΔK is affected only by the rise time, Trise, in each load cycle. Furthermore, the relation between the crack growth rate per Trise, (da/dt)rise, and the increasing rate of K in Trise, (dK/dt)rise, is linear on log scales, and the coefficient is described as a function of ΔK. Consequently, the da/dN has been formulated with ΔK, Trise and (dK/ dt)rise as follows.
da/dN=∫Trise c1exp(-c2/(ΔK-c3))(dK/dt)c4 rise dt
This formulation uniformly describes the effects of both waveform and frequency. In addition, the formula can express even the effect of changing (dK/dt)rise in a cycle.
