Plane strain crack growth models for fatigue crack growth life predictions
- Babcock and Wilcox, Alliance, OH (United States). Research and Development Div.
- Mississippi State Univ., Mississippi State, MS (United States)
- Babcock and Wilcox, Barberton, OH (United States). Nuclear Equipment Div.
Experimental data and analytical models have shown that a growing fatigue crack produces a plastic wake. This, in turn, leads to residual compressive stresses acting over the crack faces during the unloading portion of the fatigue cycle. This crack closure effect results in an applied stress intensity factor during unloading which is greater than that associated with the K{sub min}, thus producing a crack-driving force which is less than {Delta}K = K{sub max} {minus} K{sub min}. Life predictions which do not account for this crack closure effect give inaccurate life estimates, especially for fully reversed loadings. This paper discusses the development of a crack closure expression for the 4-point bend specimen using numerical results obtained from a modified strip-yield model. Data from tests of eight 4-point bend specimens were used to estimate the specimen constraint factor (stress triaxiality effect). The constraint factor was then used in the estimation of the crack opening stresses for each of the bend tests. The numerically estimated crack opening stresses were used to develop an effective stress intensity factor range, {Delta}K{sub eff}. The resulting crack growth rate data when plotted versus {Delta}K{sub eff} resulted in a material fatigue crack growth rate property curve independent of test specimen type, stress level, and R-ratio. Fatigue crack growth rate data from center-cracked panels using Newman`s crack closure model, from compact specimens using Eason`s R-ratio expression, and from bend specimens using the model discussed in this paper are all shown to fall along the same straight line (on log-log paper) when plotted versus {Delta}K{sub eff}, even though crack closure differs for each specimen type.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 197592
- Journal Information:
- Journal of Pressure Vessel Technology, Vol. 118, Issue 1; Other Information: DN: Presented at Pressure Vessels and Piping Conference, Honolulu, HI (US), July 23--27, 1995; PBD: Feb 1996
- Country of Publication:
- United States
- Language:
- English
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