Corrosion fatigue cracking stress ratio

Stress ratio. Rates of corrosion fatigue crack propagation generally are enhanced by increased stress ratio R, which is the ratio of the minimum stress to the maximum stress. 

Stress ratio is defined as the ratio of minimum stress to maximum stress. The rate of corrosion fatigue crack propagation is increased by an... 

Why is the rate of corrosion fatigue crack propagation increased by high stress ratios ... 

In common with many of the alloy-environment systems described so far, if the alloy is not susceptible to stress-corrosion cracking under constant stress or stress intensity, then little or no effect of environment on fatigue crack growth is observed. In these cases, frequency, R ratio and potential within the passive or cathodically protected ranges for titanium have no effect on growth rates. 

The corrosion fatigue behaviour of two pressure tank steels (Table 4) under pressurised water conditions was investigated [49]. As well, crack propagation velocities (Vr) were measured as a function of stress intensity, frequency (0.001-10.0 Hz) as well as the R ratio (0.16-0.72), namely in high purity water with 0.10 mg/1 CT, < 0.01 mg/1 O2 at pH 6-9 and at 288 °C. Crack propagation depends mainly on the... 

The situation is rather complex A higher load ratio results in a higher mean load, which causes an accelerated interaction between the environment and the crack tip. This would, however, vary from one material system to another. A uniaxial stress seriously shortens the corrosion fatigue life. The extension of corrosion fatigue relative to dry air increased from a factor of four at R (0.11 to 0.24) to as much as 20-30 fold at high... 

---