REFERENCE: ICF100809OR IN SEARCH OF A PARAMETER FOR FRETTING FATIGUE A. L. Hutson2, T. Nicholas1, S. Olson2 and N. Ashbaugh2 1Air Force Research Laboratory, AFRL/MLLMN, Wright Patterson AFB, OH 45433, USA 2 University of Dayton Research Institute, Dayton, OH 45469-0128, USA ABSTRACT Fretting fatigue experiments were conducted to determine the fatigue limit stress at 107 cycles for Ti-6Al4V. A step-loading procedure was used to determine the fatigue limit stress that, in turn, was applied to the test geometry in numerical simulations using finite elements. Several fretting pad geometries and specimen thicknesses were used to obtain a range of normal and shear forces that produced the stress and displacement fields in the specimen. An evaluation was made of the conditions near the edge of contact where peak stresses occur to deduce parameters which lead to fretting fatigue failures at 107 cycles. However, no simple combination of stresses and slip displacements could be used to correlate all of the experimental data. A fracture mechanics methodology was also employed in order to determine the conditions for propagation or non-propagation of cracks that initiate in the edge of contact region. While no parameters were found which could uniquely predict the fretting fatigue failure, adjustment of the coefficient of friction based on computed slip displacements was shown to have a substantial effect on the stress and stress intensity factors. A correlation of friction coefficient with slip displacement is proposed as a possible method for consolidating data from fretting fatigue experiments conducted under different conditions. KEYWORDS fretting, fatigue, fracture mechanics, titanium INTRODUCTION Fretting fatigue is a type of damage occurring in the presence of contacts in which at least one of the components is subjected to bulk loading. It is normally associated with small magnitudes of relative slip, on the order of tens of microns, and little if any material removal and can lead to premature crack initiation and failure. Such damage has been indicated as the cause of many unanticipated disk and blade failures in turbine engines. Under laboratory conditions, the synergistic effects of various parameters make determination and modeling of the mechanical behavior of fretting fatigue extremely difficult. The stress state in the contact region involves very high peak stresses, steep stress gradients, multi-axial stresses and differing mean stresses. Further, there is controversy whether the problem is primarily one of crack initiation or a crack propagation
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