Relations Between the Strain Energy Density Distribution and Elastic-Plastic Stress-Strain Fields Near Cracks and Notches and Fatigue Life Calculation

Abstract

Relations between the strain energy density distribution and the elastic-plastic strain-stress fields near notches have been analyzed. It was found that the strain energy density distribution in the plastic zone ahead of the crack or notch tip can be satisfactorily estimated on the basis of the theoretical elastic stress field. The strain energy density can be translated into the elastic-plastic strain and stress in the plastic zone if the nonlinear material stress-strain curve is known. Good agreement with finite element calculations has been achieved for cracks under plane strain conditions. It has also been shown that the equivalent strain energy approach can be useful for the notch-tip elastic-plastic strain calculation under both monotonic and cyclic loading. Very good agreement between the experimentally measured and calculated notch-tip strains has been obtained up to general yielding. The elastic-plastic notch-tip strain histories calculated on the basis of the equivalent strain energy density concept were used for fatigue life calculation of key-hole specimens tested under SAE transmission loading history. Significant improvement of fatigue life prediction has been achieved in comparison to the calculations based on Neuber's rule. Possible applications of the equivalent strain energy density concept for fatigue crack growth prediction are also discussed.