A notch stress intensity approach applied to fatigue life predictions of welded joints with different local toe geometry

Abstract

In the Notch Stress Intensity Factor (N-SIF) approach the weld toe region is modelled as a sharp V-shaped corner and local stress distributions in planar problems can be expressed in closed form on the basis of the relevant mode I and mode II N-SIFs. Initially thought of as parameters suitable for quantifying only the crack initiation life, N-SIFs were shown able to predict also the total fatigue life, at least when a large part of the life is spent as in the propagation of small cracks in the highly stressed region close to the notch tip. While the assumption of a welded toe radius equal to zero seems to be reasonable in many cases of practical interest, it is well known that some welding procedures are able to assure the presence of a mean value of the weld toe radius substantially different from zero. Under such conditions any N-SIF-based prediction is expected to underestimate the fatigue life. In order to investigate the degree of conservatism, a total of 128 fillet welded specimens are re-analysed in the present work by using an energy-based N-SIF approach. The local weld toe geometry, characterised by its angle and radius, has been measured with accuracy for the actual test series. The aim of the work is to determine if the N-SIF-based model is capable of taking into account the large variability of the toe angle, and to quantify the inaccuracy in the predictions due to the simplification of setting the toe radius equal to zero

Local strain energy density for the fatigue assessment of hot dip galvanized welded joints: some recent outcomes

“…Therefore it is possible to use a critical radius equal to 0.28 mm both for toe and root failures, as an engineering approximation [29]. It is useful to underline that R0 depends on the failure hypothesis considered: only the total strain energy density is here presented (Beltrami hypothesis), but one could also use the deviatoric strain energy density (von Mises hypothesis) ( [30]). The SED approach was applied to a large bulk of experimental data: a final synthesis based on 900 fatigue data is shown in Fig.…”

A Review of the Fatigue Strength of Load Carrying Shear Welded Joints

“…The radius r0 is a parameter of the characteristic material and shall be assumed to be independent of the load mode. For welded joints, the values of the radius r0 proved to be 0.28 mm for steel and 0.12 mm for aluminum (Livieri and Lazzarin, 2005;Lazzarin et al, 2003). A summary based on 900 experimental data obtained for the stainless steel construction has been accomplished, into a ∆W-N strip of the Scattering.…”

“…The connection between the life of the fatigue of Joints welded to the local tensions to finger from no welding or root, the main issue is the definition of geometric parameters of the weld bead, such as the radius of the finger of the foot and the form of the heel (Livieri and Lazzarin, 2005;Lazzarin et al, 2003). These parameters may vary not only for the different faces of the same design, but also within the same interdiction; moreover the radius of the tep may be considered to be equal to zero or tends toward zero (Atzori, 1985;Lazzarin and Tovo, 1998).…”

On the accuracy of nominal, structural, and local stress based approaches in designing aluminium welded joints against fatigue

“…As far as failures at the weld toes are concerned, the N-SIF approach estimates fatigue lifetime of welded components by modelling the weld seams as V-notches having opening angle equal to 135° and root radius equal zero [15][16][17][18]. The N-SIF approach can also be used to perform the fatigue assessment of welded joints in which cracks initiate at the weld roots, provided that a specific reference design curve is employed [16].…”