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PSB structure (adopted from [7]). Persistent slip-bands (PSBs) are associated with strain localisation due to fatigue in metals and cracking on the same plane. Transmission electron microscopy (TEM) and three-dimensional discrete dislocation dynamics (DDD [8]) simulation were used to reveal and understand dislocations type and arrangement/patterns to relate it to the sub-surface structure.
Lüders bands are a type of plastic bands, slip band or stretcher-strain mark which are formed due to localized bands of plastic deformation in metals experiencing tensile stresses, common to low-carbon steels and certain Al-Mg alloys. [1]
The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band, or dislocation. [1]
Fatigue has traditionally been associated with the failure of metal components which led to the term metal fatigue. In the nineteenth century, the sudden failing of metal railway axles was thought to be caused by the metal crystallising because of the brittle appearance of the fracture surface, but this has since been disproved. [ 1 ]
Fractures are initiated either by pitting or persistent slip bands. [3] Corrosion fatigue may be reduced by alloy additions, inhibition and cathodic protection, all of which reduce pitting. [ 4 ] Since corrosion-fatigue cracks initiate at a metal's surface, surface treatments like plating, cladding, nitriding and shot peening were found to ...
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Typically, slip bands induce surface steps (i.e. roughness due persistent slip bands during fatigue) and a stress concentration which can be a crack nucleation site. Slip bands extend until impinged by a boundary, and the generated stress from dislocation pile-up against that boundary will either stop or transmit the operating slip. [9] [10]
However, this approach completely fails to account for well-known intermittent deformation phenomena such as the spatial localization of dislocation flow into "slip bands" [8] (also known as Lüders band) and the temporal fluctuations in stress-strain curves (the Portevin–Le Chatelier effect first reported in the 1920s).