Issue 17

B. Atzori et alii, Frattura ed Integrità Strutturale, 17 (2011) 15-22 ; DOI: 10.3221/IGF-ESIS.17.02 15 Analysis of the fatigue strength under two load levels of a stainless steel based on energy dissipation B. Atzori, G. Meneghetti, M. Ricotta University of Padova, Department of Mechanical Engineering, 35131 Padova, Italy giovanni.meneghetti@unipd.it Published in Proceedings of 14 th International Conference on Experimental Mechanics ICEM14, Poitiers, France, 4-9 July, 2010 The European Physical Journal EPJ Web of Conferences volume 6-2010 ISBN: 978-2-7598-0565-5 R IASSUNTO . In questo lavoro è stato analizzato il comportamento a fatica di un acciaio inossidabile AISI 304L. Nella prima parte del lavoro sono presentati i risultati ottenuti da prove ad ampiezza di sollecitazione costante sintetizzati sia in ampiezza di tensione sia in termini di densità di energia dissipata dal materiale per ciclo, Q . Successivamente alcuni provini sono stati sollecitati ad un livello di carico superiore al limite di fatica per circa il 70% della presunta vita e poi ad un livello di tensione inferiore al limite di fatica ad ampiezza costante precedentemente determinato ed è stata confrontata l’energia dissipata nella seconda parte della prova con quella trovata in una prova ad ampiezza costante, allo stesso livello di tensione. Il confronto ha mostrato come per il materiale analizzato il parametro Q sia sensibile al danneggiamento precedentemente subito. A BSTRACT . In this paper the fatigue behaviour of a stainless steel AISI 304L is analysed. In the first part of the work the results obtained under constant amplitude fatigue are presented and synthesised in terms of both stress amplitude and energy released to the surroundings as heat by a unit volume of material per cycle, Q . Then some specimens have been fatigued in variable amplitude, two different load level tests: the first level was set higher while the second was lower than the constant amplitude fatigue limit. The Q values, evaluated during the second part of the fatigue test, have been compared with those calculated under constant amplitude fatigue at the same load level. The comparison allowed us to notice that the Q parameter is sensitive to the fatigue damage accumulated by the material during the first part of the fatigue test. K EYWORDS . AISI 304L; Dissipated energy; Fatigue; Stainless steel; Two load levels; Miner rule. I NTRODUCTION he evaluation of fatigue limit of materials based on the experimental measurements of thermal increments is an experimental procedure well documented in the literature [1-3]. Recently one of the Authors suggested to adopt the energy released to the surroundings as heat by a unit volume of material per cycle, Q , as a fatigue damage indicator [4]. In view of this, a particular strategy was conceived in order to derive the Q parameter from measurements of the material surface temperature. Parameter Q was able to correlate the fatigue strength of smooth and notched specimens made of stainless steel, fatigued under constant amplitude stress. To the authors’ knowledge, the material behaviour in terms of Q in the case of variable amplitude fatigue load was never investigated. In this paper two load level fatigue tests T