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Cyclic Slip Irreversibilities and the Evolution of Fatigue Damage

HAEL MUGHRABI

In this article, the physical origin of fatigue crack initiation in ductile metals is discussed from a historical perspective. The main focus is to assess those cyclic slip irreversibilities in a microstructural sense that occur not only at the surface but also in the bulk at the dislocation scale and to show how they contribute to surface fatigue damage. The evolution of early fatigue damage, as evidenced experimentally in the last decades, is reviewed. The phenomenon of cyclic strain localization in persistent slip bands (PSBs) and models of the formation of extrusions, intrusions, and microcracks are discussed in detail. The predictions of these models are compared with experimental evidence obtained on mono- and polycrystalline face-centered-cubic (fcc) metals. In addition, examples of the evolution of fatigue damage in selected fcc solid solution alloys and precipitation-hardened alloys and in body-centered-cubic (bcc) metals are analyzed. Where possible, the cyclic slip irreversibilities p, defined as the fraction of plastic shear strain that is microstructurally irreversible, have been estimated quantitatively. Broadly speaking, p has been found to vary over orders of magnitude (0 < p < 1), being almost negligible at low loading amplitudes (high fatigue lives) and substantial at larger loading amplitudes (low fatigue lives). DOI: 10.1007/s11661-009-9839-8
The Minerals, Metals & Materials Society and ASM International 2009

HAEL MUGHRABI, Professor Emeritus, is with the Department Werkstoffwissenschaften, Allgemeine Werkstoffeigenschaften, Universita¨t Erlangen Nu¨rnberg, 91058 Erlangen, Germany. Contact e-mail: [email protected] Hael Mughrabi obtained his primary school education in Germany and subsequently attended different British schools in Jerusalem, Palestine, and in Cairo, Egypt, where he graduated from secondary school at The English School in 1955. He is a German citizen. After a three-year apprenticeship as a mechanic and toolmaker at Bosch GmbH Company in Stuttgart, he entered the Engineering University of Stuttgart to study physics. During his studies, in his doctoral thesis work and in his subsequent occupation as a senior researcher at the Max-Planck-Institute of Metal Research in Stuttgart (1966–1983), he specialized in metal physics and performed mainly research in the fields of crystal defects, mechanical properties, and microstructural characterization. He held a Visiting Professorship at Cornell University in 1978–1979. After receiving offers from three universities, he joined the University of Erlangen–Nu¨rnberg in 1984 as a Professor of Materials Science and Engineering and Head of an Institute of General Materials Properties. In subsequent years, he held positions as Department Head METALLURGICAL AND MATERIALS TRANSACTIONS A

and Dean of the School of Engineering. Since 2002, Hael Mughrabi has been formally retired but is still active in various forms in research and in committee work. Hael Mughrabi