Issue 35

R.A. Cardoso et alii, Frattura ed Integrità Strutturale, 35 (2016) 405-413; DOI: 10.3221/IGF-ESIS.35.46 405 Focussed on Crack Paths Crack path simulation for cylindrical contact under fretting conditions R.A. Cardoso, J.A. Araújo, J.L.A. Ferreira, F.C. Castro University of Brasília, Brasil rapha_2213@hotmail.com A BSTRACT . In this work different strategies to estimate crack path for cylindrical contacts under fretting conditions are carried out. The main goal is to propose and to evaluate methodologies not only to estimate the direction of crack initiation but also the subsequent propagation in its earlier stages, where the stress field is multiaxial, non-proportional and decays very fast due to the proximity with the contact interface. Such complex conditions pose a substantial challenge to the modelling of crack path. The numerical simulations are provided by a 2D Finite Element Analysis taking into account interactions between the crack faces. The results show that, under fretting conditions, models based on the critical plane method are not effective to estimate the crack initiation orientation, while models based on a so called “critical direction” applied along a critical distance provide better results. Regarding the subsequent crack propagation orientation, it was possible to see that stress intensity factor based models where one considers an infinitesimal virtual crack emerging from an original pre- existent crack are powerful mechanisms of crack orientation estimation. K EYWORDS . Fretting fatigue; Crack propagation; Critical distances. I NTRODUCTION retting is the phenomenon that occur in mechanical couplings subjected to contact loads and small relative tangential displacement due to oscillatory loads. In association with remote fatigue loads, the process well known as fretting fatigue take place. Failure due to fretting fatigue usually is observed in engineering assemblies under vibration, such as riveted or bolted connections, dovetail joints in turbines and overhead conductors among, others. The fretting problem is characterized by a strong stress concentration in association with wear, which invariably leads to the nucleation of small cracks. Depending on the level of the stress gradient in such cracks they may arrest, since a threshold value at the crack tip be reached [1]. In order to conduct such analysis criteria able to precise the location, direction of initiation and the further crack path are essential. In these aspects many challenges must be faced, since the fretting problem is characterized for high levels of multiaxility and non-proportionality The aim of this work is to estimate the crack path under fretting conditions in cylindrical contacts assessing some already used methodologies and propose a new methodology to estimate the direction of crack propagation in their earlier stages. Experimental data from literature will be used to confront the theory. C RACK ORIENTATION MODELING s extensively shown in the literature, crack initiation and further propagation is usually characterized by two distinct stages, Fig. 1. The Stage I describes the earlier stage of propagation, commonly governed by Mode II while the Stage II is characterized by a Mode I dominated crack. However, according to [2], Stage I may be F A