SEDL / STP / STP1292-EB / STP16135S

A Crack-Closure Model for the Fatigue Behavior of Notched Components

Hou, C-Y
Research assistant, University of Illinois, Urbana-Champaign, IL

Lawrence, FV
Professor, University of Illinois, Urbana-Champaign, IL

Pages: 20    Published: Jan 1996

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Abstract

Newman's Dugdale strip-yield model for crack closure was used to estimate the crack-closure behavior of cracks emanating from notches. The estimated effective stress-intensity ratio U(a) = ΔK^eff(a)/ΔK(a) obtained using Newman's model did not exhibit the frequently observed “dip” presumably caused by the notch plasticity. To incorporate the effects of notch plasticity into the Newman model, the plastic stretches caused by the notch were superposed on the plastic stretches caused by the crack tip. A finite element procedure was used to calculate the magnitude of the notch plastic stretches. It was found that the magnitude of the notch plastic stretches was much larger than that of the crack-tip plastic stretches and that the notch plastic stretches were the main source of the plastic wake when the crack tip was within the notch plastic zone. The validity of the proposed modification of Newman's Dugdale strip-yield model was verified by comparing the predicted results with the published experimental data for various notched components. The effects of the notch-plastic zone on U(a) were found to be significant for stress ratio R ⩾ 0 but to be unimportant for R ≤ - 1