Improvement of fatigue lifetime of mechanically surface treated materials in the low cycle fatigue regime

Improvement of fatigue lifetime of mechanically surface treated materials in the low cycle fatigue regime I. Altenberger, B. Scholtes Institutfar Werkstofftechnik, Universitat Gh Kassel, Monchebergstrafie 3, 34125 Kassel, Germany EMail: [email protected] Abstract Modern mechanical surface optimization processes go beyond mere empirical concepts. Especially surface characterization methods have significantly contributed to a more thorough understanding of fatigue mechanisms. Special focus is put on the relation between materials properties and microstructures created by near surface plastic deformations and their consequences on cyclic deformation, crack initiation and propagation during cyclic loading. Some typical examples are presented, demonstrating the beneficial effect of mechanical surface treatment on materials, subjected to high cyclic strain and stress. In this context, also the stability of microstructures and residual stresses in surface layers is discussed. 1 Introduction Shot peening and deep rolling are very effective and cheap mechanical surface finishing methods and often used for structural parts, e.g., in the automotive industry. Beneficial effects of mechanical surface treatments are mostly compressive residual stress profiles and strain hardening in near surface regions of components, yielding higher resistance against fatigue failure, corrosive environment or wear. Residual stresses, if remaining stable, are most important in the case of high strength materials. In the case of softer materials the improved fatigue behaviour is primarily a consequence of near surface strain hardening effects, whereas a partial or complete relaxation of residual stress may occur. Several examples exist demonstrating the effects of mechanical surface treatments on microstructure and cyclic behaviour of various engineering materials. However, most of the existing investigations on the fatigue behaviour Transactions on Engineering Sciences vol 25, © 1999 WIT Press, www.witpress.com, ISSN 1743-3533

Improvement of fatigue lifetime of mechanically surface treated materials in the low cycle fatigue regime

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