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Investigation of fatique crack growth rate of Al 5484 ultrafine grained alloy after ECAP process

Tomasz Brynk 1Marcin Rasiński 1Zbigniew Pakieła 1Lech Olejnik 2Krzysztof J. Kurzydlowski 1

1. Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland
2. Warsaw University of Technology, Faculty of Production Engineering, L.Narbutta, Warszawa 02-524, Poland


During the last decade equal-channel angular pressing (ECAP) has emerged as a widely-used fabrication route of ultrafine-grained (UFG) metals and alloys. Enhanced mechanical properties of UFG materials produced by severe plastic deformation, with a grain size smaller than 1μm, have been reported in a large number of publications. However, the higher strength does not imply higher resistance to fatigue both high- and low-cyclic. In fact, due to reduced plasticity of UFG materials higher fatique crack propagation rates are reported, particularly in low-amplitude range. The aim of this work was to investigate fatigue crack propagation in Al 5483 alloy subjected to ECAP treatment. Because of small dimensions of the coupons processed by ECAP, non standard, mini- samples were used in a crack propagation tests. Two test procedures were used to estimate stress intensity factor (K). The first one was based on optical measurements of crack length from images recorded during the test. The second method was based on Digital Image Correlation (DIC), which allowed to determine displacement field near the crack tip and, subsequently, to determine K value directly from the displacement data. The paper compares both methods of determining the K values. It also reports the relationship between the intensity of ECAP process (measured in terms of the number of ECAP passes) and fatigue crack propagation rate. In addition to fatigue resistance, the results of tensile tests carried out with mini-samples are presented. Applicability of such samples in the investigations of the mechanical properties of UFG materials is discussed.


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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium H, by Tomasz Brynk
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-21 15:31
Revised:   2009-06-07 00:48