Stress Gradient at Notch Roots Using Volumetric Method

Abstract

The hot spot methods exhibit few defects to appraise flawless fatigue life prediction. The mentioned methods suffer from a real maximum stress location and magnitude, elaborated plastic zone features at notch tips or welded toes [G. Pluvinage, Fracture and Fatigue Emanating from stress concentrators, Dordrecht: Kluwer Academic Publishers, 2003.] and stress gradient [A. Buch, Analytical approach to size and notch effects in fatigue of material specimens, Material Science and Engineering, Vol. 15, 75–85, 1974.][A. Brandt, Calcul des pieces a la fatigue par la methode du gradient, Editor CETIM, 1980.]. According to the finite element elastic-plastic stress distribution along notch tips, the peak stress does not appear at notch head and it requires certain distance to attain maximum stress value. Moreover, the fatigue mechanism needs to be considered as a physical volume according to fatigue tests large scatters based on Weibull’s distribution method, specimen size and stress gradient dependence of experimental fatigue results [G. Pluvinage, Fracture and Fatigue Emanating from stress concentrators, Dordrecht: Kluwer Academic Publishers, 2003]. The stress gradients around notch tips are also significant according to the weight influence on extracted stresses along notch tips [G. Qylafku, Z. Azari, N. Kadi, M. Gjonaj, G. Pluvinage, Application of a new model proposal for fatigue life prediction on the notches and key-seats, International Journal of Fatigue,21, 753–760, 1999.][H. Adib, G. Pluvinage, Theoretical and numerical aspects of volumetric approach for fatigue life prediction in notched components, International Journal of Fatigue, 25(1), 67–76, 2003.]. In the present study, the role of relative stress gradient for fatigue life assessment using volumetric method is highlighted. The polynomial volumetric method point of view has been proposed which satisfies weight function conditions, removes numerical derivation errors, elucidates effective stress terms as subtraction of average stress and relative stress gradient based phrase.