For the conditions modeled here, we hypothesized that initial slip conditions corresponding to µ=0.3 change over time to conditions of increasing µ, and thus increasing σx and corresponding K values. As shown above, higher tensile stresses and the resulting K values may be produced either by imposing a high clamping stress or by increasing µ. An equilibrium condition may exist for µ, which is dependent on the resultant relative displacement. If such a condition exists, an iterative method would be required to determine the final condition. COMMENTS & CONCLUSIONS Changes in µ over time for various fretting fatigue conditions vastly compound the problem of accurate life prediction for fretting fatigue, since it is very difficult to determine how µ will change over time. Further, such a change will be different for each combination of pad material, specimen material, applied loads, surface modification, and environment. Since fretting fatigue behavior is so profoundly influenced by µ which, in turn, may depend on relative displacements, additional research in how µ changes under fretting fatigue conditions is recommended. Within the constraints of the geometry and test configuration and loading conditions examined in this investigation and under the assumptions made in the analyses, particularly that of µ being 0.3, the following conclusions can be drawn. 1. High levels of slip may produce increases in µ, which might have to be revised to produce higher stresses and smaller displacements. 2. Stress and relative displacement (slip) fields are very sensitive to the value of µ chosen for analysis. 3. Under the assumption of a Mode I crack normal to the surface, if a crack nucleates, it will continue to propagate to failure. REFERENCES 1. Hutson, A.L., Nicholas, T., Olson, S.E., and Ashbaugh, N.E. Submitted to Int. J. Fatigue. 2. Fretting Fatigue: Current Technologies and Practices, ASTM STP 1367(1999). D.W. Hoeppner, V. Chandrasekaran, and C.B. Elliot (Eds). American Society for Testing and Materials, West Conshohocken, PA. 3. Hutson, A., Nicholas, T., and Goodman, R.(1999) Int. J. Fat. 21, 7, 663. 4. Hutson, A.L.(2000). MSc Thesis, University of Dayton, USA. 5. Fretting Fatigue, ESIS 18(1994). R.B. Waterhouse and T.C. Lindley (Eds). Mechanical Engineering Publications, London. 6. Standardization of Fretting Fatigue Test Methods and Equipment, ASTM STP 1159(1992). M. Helmi Attia, and R. B. Waterhouse (Eds). American Society for Testing and Materials, Philadelphia. 7. Peters, J.O. and Ritchie, R.O., Submitted to Int. J. Fat. 8. Moshier, M.A., Nicholas, T. and Hillberry, B.M., Submitted to Int. J. Fat. 9. Maxwell, D., and Nicholas, T.(1999). In: Fatigue and Fracture Mechanics: 29th Vol., ASTM STP 1321, pp. 626-641, T. L. Panotin and S. D. Sheppard (Eds), American Society for Testing and Materials, West Conshohocken, PA. 10. Ruiz, C., Boddington, P. H. B., and Chen, K. C.(1984) Experimental Mechanics 24, 208. 11. Thompson, S.R., Ruschau, J.J. and Nicholas, T. Submitted to Int. J. Fat. 12. John, R., Weight Function Analysis for a Single Edge Cracked Specimen, Unpublished work, Air Force Research Laboratory (AFRL/MLLN), Wright-Patterson AFB, OH. 13. Giannakopoulos, A.E., Lindley, T.C., Suresh, S., and Chenut, C. Submitted to Fat. Frac. Eng. Mat. Structures. 14. Szolwinski, M.P.. Matlik, S.F. and Farris, T.N.(1999). Int. J. Fat. 21, 671. 15. Farris, T.N., Harish, G., McVeigh, P.A., and Murthy, H.(2000). In: Proc of the 5th National Turbine Engine High Cycle Fatigue (HCF) Conference on CD, Session 13, Chandler, AZ.
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