EFFECT OF RIPPLE LOAD ON THE STRESS-CORROSION CRACKING IN STRUCTURAL STEELS
The presence of small ripple loading can, under certain circumstances, significantly reduce time-to-failure and threshold stress intensity for stress-corrosion cracking (SCC) of steels. A predictive framework for such ripple-loading effects (RLE) is developed from concepts and descriptors used in SCC and corrosion fatigue characterisation. The proposed framework is capable of defining critical conditions required for the occurrence of RLE and predicting time-to-failure curves. The agreement between the predicted and laboratory data is excellent.
Effects of Stress Wave Forms on Low Cycle Corrosion Fatigue
by Kichiro ENDO and Kenjiro KOMAI (Faculty of Engineering, Kyoto University, Kyoto) Studies have been made of the influence of stress rate in trapezoidal strain waves on low cycle corrosion fatigue strength. The electrode potential of the specimens has been observed against the saturated calomel electrode during the cycles. The following facts have been made clear; (1) The corrosion fatigue strength is affected by the stress wave forms. The durability of the material gets cut short by the longer strain time in which the strain ranges from zero to maximum, owing to the fact that the corrosion potential of the specimens is retarded and does not follow up to the equilibrium state of stress. (2) The effect similar to the effect made on the strain time is found to be made on the stress rate. In the range of lower stress, however, the stress rate has less effect because the maximum duration of time of stress becomes more effective than the strain time. (3) When lower stresses are applied, the strain time has its effect on the period of pitting formation and of crack propagation, while the effect on the latter is much smaller than on the former under higher stress range. (Received Apr. 22, 1964)
VARIABILITY IN FATIGUE CRACK GROWTH RATE TESTING
To provide the data necessary to develop a recommended practice for fatigue crack growth rate testing, an extensive interlaboratory (round robin) program was conducted and the variability and bias associated with the current state of the art of fatigue crack growth rate testing was determined. Fatigue crack growth rate data (expressed in terms of linear elastic fracture mechanics parameters) were generated for a 190-ksi (1310-MPa) yield strength 10 Ni-8Co-1Mo steel at 15 different laboratories with several test specimen geometries. The results were evaluated statistically and on the basis of a graphical comparison, and the variability and bias associated with both the experimental and analytical aspects of crack growth rate testing were determined. In general, the overall interlaboratory variability was found to be approximately 3 to 1 (on crack growth rate at a given stress intensity range). The interalaboratory variability was typically 2 to 1. No significant geometry or data processing bias was encountered. The results of this study show that the primary source of variability associated with fatigue crack growth rate testing is the experimental procedure used to obtain the raw test data (crack length versus elapsed cycles). /Author/