Fatigue Crack Growth Behavior of a High-Strength Steel

Fatigue crack growth behavior of high-strength Ladish D6AC steel was examined under various conditions of frequency, environment, temperature, stress ratio, and stress intensity history. Materials with fracture toughness ranging from 50 to 100 ksi/sq. in., but with the same yield strength of 220 ksi...

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Bibliographic Details
Main Authors: Amateau,Maurice F, Kendall,Ernest G
Format: Report
Language:English
Subjects:
CRACK PROPAGATION
FATIGUE(MECHANICS)
FRACTURE(MECHANICS)
HIGH STRENGTH STEELS
Metallurgy and Metallography
STEEL
STEEL D6AC
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Summary:Fatigue crack growth behavior of high-strength Ladish D6AC steel was examined under various conditions of frequency, environment, temperature, stress ratio, and stress intensity history. Materials with fracture toughness ranging from 50 to 100 ksi/sq. in., but with the same yield strength of 220 ksi, were examined. Variations in fracture thoughness do not have a strong effect on crack growth rate at stress intensity levels within the log-linear portion of the crack growth curves. Different environments, such as dry air, laboratory air, and distilled water, were found to produce different fatigue crack growth behavior at 1 Hz but not at 10 Hz loading frequency. The lowest crack growth rate occurred in dry air, while the agressive environment of distilled water affected the crack growth rate more severly at lower stress intensity levels. The effects of temperature over the range from -40 to 175F are a uniform shift of the growth curve to low crack growth rates and a lowering of the stress intensity level for the onset of rapid fatigue crack propagation. Suppression of crack growth rate following high prior stress cycles is the most significant effect of stress history. This effect cannot be explained in terms of the relative plastic zone sizes alone. (Author)