A multiscale approach of fatigue and shakedown for notched structures

GRACIELA BERTOLINO; ANDREI CONSTANTINESCU; M. FERJANI; PHILIPE TREIBER

Theoretical and Applied Fracture Mechanics

Elsevier

Lugar: Amsterdam; Año: 2007 vol. 48 p. 140 - 151

0167-8442

    The aim of this paper is to analyse the fatigue phenomena in the presence of stress gradients. It is well-known that mostfatigue criteria fail to predict the lifetime of components in the presence of high stress concentrations or stress gradients, asit is the case in the neighbourhood of cracks, holes notches and encountered for example in riveted or threaded structures.Proposed is a numerical approach in the framework of the high cycle fatigue domain in order to give a qualitative answer.The work starts from the numerical computation of macroscopic loading corresponding to some fatigue experiments onspecimens with an inclusion of metallic grains embedded in a macroscopic matrix. The computed fields are then analysed interms of the HCF (high cycle fatigue) criterion [1], which is based on the estimation of the shakedown limit at the grainscale. The infinite lifetime prediction is based on the assumption that fatigue occurs if at least one grain fails, i.e. reachesplastic shakedown. The predictions at mesoscopic and macroscopic scales are close if the macroscopic stress distribution ishomogeneous. However in the case of the stress gradient, lifetime predicted at the macroscopic scale is underestimatedwhen compared to the predictions made at the mesoscopic scale. Another result is that the gap between microscopicand macroscopic predictions obtained from these numerical computations can roughly be estimated by a diminution ofstress of the same order of magnitude as found in the experiments and phenomenological observations.