Very high cycle fatigue of copper: Evolution, morphology and locations of surface slip markings

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. a b s t r a c tThe surfaces of commercially pure polycrystalline copper specimens subjected to interrupted 20 kHz fatigue tests in the very high cycle fatigue regime were investigated. The stress amplitude needed to form the early slip markings was found twice lower than the stress amplitude required to fracture which confirmed the results obtained by Stanzl-Tschegg et al. (2007). Three types of slip markings were classified according to their morphology and their location in the polycrystalline material. They are compared to slip markings observed during fatigue tests at frequencies lower than 100 Hz and numbers of cycles lower than 10 7 . For 20 kHz fatigue tests, stress amplitudes ranging from 45 MPa to 65 MPa produce straight and long early persistent slip markings located along twin boundaries. Stress amplitudes lower than 45 MPa produce clusters of fine early persistent slip markings mainly located at triple junctions.

Through thickness property variations in friction stir welded AA6061 joint fatigued in very high cycle fatigue regime

“…8b, Persistent slip bands could be observed locally in an area as plotted with dash line, from where the fatigue crack were initiated. The same fatigue crack initiation mechanisms in the VHCF regime, the development of persistent slip bands leading to the surface fatigue cracks, can also be observed in some single phase metals [11,[29][30][31][32]. Generally, the plastic deformation features for these materials were extensive on the specimen surface, but in this work the persistent slip bands seem to be limited in a very local small region distributed sporadically at the boundary between the TMAZ and HAZ due to the heterogeneities of microstructural and mechanical properties.…”

“…It has been reported that some ductile metals exhibit surface crack initiation sites [11][12][13], but the welded joints of these materials by fusion welding method usually had internal fatigue crack initiation sites induced by welding defects, which decreased the fatigue strength dramatically [9,14]. The fatigue crack initiation is extremely sensitive to the internal defects, but successful FSW welds generally contains no inherent defects or internal flaws.…”

Effect of Tempering Temperatures on Tensile Properties and Rotary Bending Fatigue Behaviors of 17Cr2Ni2MoVNb Steel

“…Thus, there was no obvious debris on the surface of the samples with tempering temperature of 620 • C. Fatigue consists of the cracks initiation zone, crack propagation zone, and the final fatigue zone. All the cracks are prone to initiate at or near the specimen surface because the cyclic plastic deformation at or near the surface acquires the maximum cyclic stress compared to that of internal regions [25]. Figure 10 displays the typical SEM micrographs of the ridges produced by the strong deformation at the samples surfaces.…”

Small-Scale Multiaxial Setup for Damage Detection Into the Very High Cycle Fatigue Regime

“…OFHC Cu (99.95 %) with a grain size of 30 μm was also studied by Phung et al [14] with fully reversed loading at 20 kHz. Phung et al used cylindrical and flat samples having gauge lengths of about 3 cm, with the cylindrical samples having diameters of 3 mm, and the flat samples a cross section of 3×2 mm.…”

“…One such experiment was carried out at 1 GHz and the authors argue that at such high frequencies the fatigue mechanisms are constrained and can differ from low frequency fatigue [3]. Nevertheless, it has been shown for pure copper that the lifetime in the VHCF regime is controlled by crack initiation as a consequence of irreversible plastic deformation at the surface, such as slip markings [10][11][12][13][14]. The slip markings can lead to the initiation of micro cracks, where one of them may undergo continued short crack growth, followed by fatal failure.…”