Authors: Bruno Atzori, Paolo Lazzarin, Giovanni Meneghetti

Abstract: The paper presents a simplified version of the Notch Stress Intensity Factor (NSIF)
approach useful for fatigue strength assessments of welded joints. The evaluation of the NSIF from
a numerical analysis of the local stress field usually needs very refined meshes and then large
computational effort. A relationship is proposed here to estimate the Notch Stress Intensity Factor
from finite element analyses carried out by using a mesh pattern with a constant element size. The
main advantage of the presented relationship is that only the elastic peak stress numerically
evaluated at the V-notch tip is necessary to estimate the NSIF instead of the whole stress-distance
set of data (that is why the method has been called Peak Stress Method, i.e. PSM). An application of
the PSM to fatigue strength assessment of fillet welded joints made of structural steels and
aluminium alloys under tensile or bending loads is presented. In those joints, only mode I stress
distribution is singular at the weld toe due to the presence of a V-notch angle equal to 135 degrees.

17

Authors: Bruno Atzori, Paolo Lazzarin, Giovanni Meneghetti

Abstract: The paper presents a simplified version of the Notch Stress Intensity Factor (NSIF)
approach useful for fatigue strength assessments of welded joints. The evaluation of the NSIF from
a numerical analysis of the local stress field usually needs very refined meshes and then large
computational effort. A relationship is proposed here to estimate the Notch Stress Intensity Factor
from finite element analyses carried out by using a mesh pattern with a constant element size. The
main advantage of the presented relationship is that only the elastic peak stress numerically
evaluated at the V-notch tip is necessary to estimate the NSIF instead of the whole stress-distance
set of data (that is why the method has been called Peak Stress Method, i.e. PSM). An application of
the PSM to fatigue strength assessment of fillet welded joints made of structural steels and
aluminium alloys under tensile or bending loads is presented. In those joints, only mode I stress
distribution is singular at the weld toe due to the presence of a V-notch angle equal to 135 degrees.

253

Authors: You Tang Li, Ping Ma, Chang Feng Yan

Abstract: A model of notched shaft in which the crack, V-notch, U-notch and arc were described as notch uniformly, was put forward. The stress field near the notch tip of notched shaft was given using quadric coordinate system by selecting an appropriate displacement function at first, and then the stress field in Cartesian co-ordinates system was obtained. The 3-D model was set up and the local stress and strain near the tip of notch was calculated by using finite element software ANSYS, and the effect of notched parameters of shaft on stress was analysed. The results show that there is a small region, in which the effect of the tip radius and depth on the stresses is obviously. The effect of an open angle of notch on stress is very small. The smaller the ratios between the tip radius and depth of notch, the larger the stress concentrations near the tip of notch.

166

Authors: Ruslizam Daud, Ahmad Kamal Ariffin, Shahrum Abdullah, Al Emran Ismail

Abstract: This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

663

Authors: Radu Negru, Liviu Marsavina, Hannelore Filipescu, Cristiana Caplescu

Abstract: The aim of this paper is the application of two methods for notch fatigue life assessment, methods which are based on finite element analysis: the theory of critical distances and the volumetric method. Firstly, un-notched and notched specimens (for three different geometries) were tested in tension under constant-amplitude loading. The use of theory of critical distances (TCD) to predict the notch fatigue life involves the determination of the material characteristic length L based on experimental results obtained for the un-notched and one type of notched specimens. For the others notched geometries, based on linear-elastic finite element analysis, the fatigue strength is predicted using the TCD. In order to apply the volumetric method, elastic-plastic stress field around notches are considered and notch strength reduction factor are determined. Finally, the predictions of the two methods were compared with experimental fatigue data for notched specimens.

654