Effect of Waveform on Corrosion Fatigue Crack Growth

Abstract

Abstract-A study was made on the effects of stress rise time T,, maximum stress holding time T 2 , stress decreasing time T., and minimum stress holding time T4 of a cycle on fatigue crack growth for a low alloy carbon steel in 3% NaCl solution. Measurements of the effective stress intensity range ratio U and observations of crack tip response were performed to clarify the causes of waveform effects.The results were summarized as follows; T , had a strong accelerating effect due to corrosive dissolution of the fresh surfaces of the crack which were formed during T I . The crack growth rate was enhanced as TI increased and reached a constant value (about 3 times that in air) after TI = 10 s. The crack growth rate at low AK, however, decreased as T , increased more than T , = 1 s. T2, T., and T4 decreased the crack growth rate. The extent of decrease not only depended on the period of T2 (or T.,, T J , but also on AK and TI. A previously derived crack growth law which considered waveform and frequency effects, is also valid to a first approximation for the present results.

Corrosion fatigue testing: the combined effect of stress and high temperature corrosion

“…Slowing the frequency of the fatigue tests down can be achieved by increasing the duration of the entire selected waveform or selected periods of the waveform which include the stress or strain (depending on whether the fatigue test is performed in load or strain control) application time, the maximum stress/strain hold time, the stress/strain decreasing time and the minimum stress/strain hold. Fatigue tests, performed on a low carbon alloy steel in an aqueous solution of 3% NaCl at a temperature of 25°C, led to the conclusion that of all the periods of a waveform, lengthening the stress application period up to 10 seconds had the greatest environmental effect and was attributed to corrosive dissolution on fresh crack surfaces that were formed during that period of the waveform 10 . One premise to be examined is whether this observation applies to high temperature corrosion fatigue.…”