Fatigue strength of Al7075 notched plates based on the local SED averaged over a control volume

Abstract

When pointed V-notches weaken structural components, local stresses are singular and their intensities are expressed in terms of the notch stress intensity factors (NSIFs). These parameters have been widely used for fatigue assessments of welded structures under high cycle fatigue and sharp notches in plates made of brittle materials subjected to static loading. Fine meshes are required to capture the asymptotic stress distributions ahead of the notch tip and evaluate the relevant NSIFs. On the other hand, when the aim is to determine the local Strain Energy Density (SED) averaged in a control volume embracing the point of stress singularity, refined meshes are, not at all, necessary. The SED can be evaluated from nodal displacements and regular coarse meshes provide accurate values for the averaged local SED. In the present contribution, the link between the SED and the NSIFs is discussed by considering some typical welded joints and sharp V-notches. The procedure based on the SED has been also proofed to be useful for determining theoretical stress concentration factors of blunt notches and holes. In the second part of this work an application of the strain energy density to the fatigue assessment of Al7075 notched plates is presented. The experimental data are taken from the recent literature and refer to notched specimens subjected to different shot peening treatments aimed to increase the notch fatigue strength with respect to the parent material

Effects of stress ratio on high-cycle and very-high-cycle fatigue behavior of a Ti–6Al–4V alloy

“…It is noted that the fatigue strength and the fatigue life of materials are statistical and governed by defect distribution and specimen control volume [35][36][37], and the cleavage strength of each grain is not the same [38]. The probability density of grains for which cleavage occurs, f, follows the classical Gaussian distribution as the following equation: where σ max is the applied maximum stress, σ c,m is the mean value of the cleavage strength, and d is the related variance.…”

Fatigue strength of severely notched specimens made of Ti–6Al–4V under multiaxial loading

“…That pointwise criterion cannot be applied to sharp notches. With the aim to overcome this problem, a volume‐based SED approach originally proposed for sharp V‐notches and cracks has been extended to multiaxial fatigue loading as well as to quasi‐brittle failure for different materials (ceramics, graphite, polymethylmethacrylate and duraluminium) under static loadings. Radaj et al .…”

Rapid parametric analysis of SEN(T) specimens using algorithmic modelling: Evaluation of strain energy density and notch stress intensity factors

“…For sharp notches, failure can also be correlated with a characteristic fracture parameter (K N IC , J N IC ) [1]. In particular, the use of the NSIF has been widely applied to characterise the elastic stress field at sharp notches [2,3] and has found wide applicability in the fatigue assessment of welded joints [4][5][6][7].…”