Issue 33

F. Castro et alii, Frattura ed Integrità Strutturale, 33 (2015) 444-450; DOI: 10.3221/IGF-ESIS.33.49 444 Focussed on multiaxial fatigue Estimation of fretting fatigue life using a multiaxial stress-based critical distance methodology F. C. Castro, J. A. Araújo, M. S. T. Pires Department of Engineering Mechanics, University of Brasilia fabiocastro@unb.br L. Susmel Department of Civil and Structural Engineering, The University of Sheffield l.susmel@sheffield.ac.uk A BSTRACT . This work presents a methodology for life estimation of mechanical couplings subjected to fretting fatigue. In this approach, a stress-based multiaxial fatigue parameter is evaluated at a critical distance below the contact surface. The fatigue parameter is based on an improved formulation of the Modified Wöhler Curve Method, in which the shear stress amplitude is measured via the Maximum Rectangular Hull method. To apply the Theory of Critical Distances in the medium-cycle fatigue regime, the critical distance is assumed to depend on the number of cycles to failure. Available fretting fatigue data, conducted on a cylinder-plane contact configuration made of Al alloy 4% Cu, were used to assess the methodology. Most of the life estimates were within an error band given by a factor of 2. K EYWORDS . Fretting fatigue; Multiaxial fatigue; Life estimation; Theory of Critical Distances. I NTRODUCTION retting fatigue refers to the conjoint action of a small oscillatory motion between contacting bodies and a cyclic remote loading. The oscillatory motion often leads to surface damage phenomena that may speed up the formation of micro-cracks. Due to the remote loading, these cracks may propagate until catastrophic failure occurs. Many engineering assemblies are prone to fretting fatigue problems as, for instance, the blade/disk interfaces of gas turbine engines, wires of overhead conductors and riveted joints. Fretting fatigue usually displays high stress gradients that affect observed lives [1, 2]. Among the different formulations that account for the stress gradient in fretting, non-local approaches have received considerable attention in the literature [3]. The appeal of such approaches derives from their relative simplicity and from satisfactory correlations with experimental data [2, 4-7]. The Theory of Critical Distances (TCD) [8-10] has been one of the most used non-local approaches in the last ten years. In this approach, the size of the fatigue process zone is related to fatigue thresholds of cracked or sharply notched specimens. The success of the TCD in correlating fatigue thresholds of notched members has been widely reported in the literature (see [9, 10] and references therein). Due to the similarities between notch and fretting fatigue, an attempt to estimate fretting fatigue thresholds using the TCD has been carried out by Araújo et al. [6]. In that paper, the Modified F