Issue 37

G. Beretta et alii, Frattura ed Integrità Strutturale, 37 (2016) 228-233; DOI: 10.3221/IGF-ESIS.37.30 228 Focussed on Multiaxial Fatigue and Fracture Biaxial fatigue tests of notched specimens for AISI 304L stainless steel G. Beretta, V. Chaves , A. Navarro University of Sevilla. Departamento de Ingeniería Mecánica y Fabricación. Escuela Técnica Superior de Ingeniería. Universidad de Sevilla. Avda. Camino de los Descubrimientos, s/n. 41092, Sevilla. Spain. , , A BSTRACT . High cycle fatigue tests were conducted for stainless steel AISI 304L. The geometry was a thin walled tube with a passing through hole. The tests were axial, torsional and in-phase axial-torsional, all of them under load control with R = −1. The S-N curves were constructed following the ASTM E739 standard and the fatigues limits were calculated following the method of maximum likelihood proposed by Bettinelli. The crack direction along the surface was analysed, with especial attention to the crack initiation zones. The notch fatigue limits for different hole diameters were compared with the predictions done with a microstructural fracture mechanics model. K EYWORDS . Fatigue limit; Biaxial tests; Notch; Crack direction. I NTRODUCTION tress concentrations are the cause of fatigue failure in many industrial components. During the last few decades a great effort has been done by many researchers to understand the notch behaviour, either testing materials with notched geometries and/or proposing models to make predictions. Just focusing in the high cycle fatigue regime and the fatigue limit, many experimental works can be found in the literature: Gough tested V-notches in cylindrical specimens under combined stresses [1], Frost did tests on double V-notch flat plates made of mild steel [2], El Haddad et al. [3] and DuQuesnay et al. [4] did push-pull tests in plates with circular holes, Lukás et al. did push-pull tests of cylindrical specimens with circumferential semi-circular notches in 2.25Cr-1Mo steel and copper [5], Tanaka and Akinawa tested plates with elliptical notches [6], Meneghetti et al. tested double U-notch plates [7]. Susmel and Taylor conducted experiments using V- shaped notches loaded in tension at various angles of inclination [8] and Endo tested cylindrical specimens with a small surface hole, under axial, torsional and combined axial-torsional loading [9]. Many methods have been proposed to predict the fatigue limit of notches under multiaxial fatigue loading, as the square root of the defect area method proposed by Murakami and Endo to deal with defect-containing components [10], the Point Method of Taylor using the Susmel-Lazzarin critical plane criterion [8], the damage model extended to stress gradients proposed by Brighenti and Carpinteri [11], or the extension of the short crack growth model of Navarro and de los Rios [12] to specimens containing holes under in-phase biaxial loading [13]. However, despite all this work, it is a fact that the mechanisms of fatigue crack growth at notches are still not fully understood. In particular, it still remains unclear the direction of the crack during the initial growth of the crack, known as S