Cracks and extrusions caused by persistent slip bands

Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth

“…He also was able to show analytically that there is a stress singularity at the surface site where a PSB emerges, which favours crack initiation [48]. In its latest version, Brown's model of extrusion formation is very similar to the EGM model [13]. Figure 6 shows in a strongly simplified view the subsequent stages of the dislocation pattern in a PSB, as envisaged in the EGM model for 'low' temperatures at which point defects are immobile.…”

“…Typically, the local plastic shear strain amplitude in the PSBs is about 1%, compared with the much lower value of about 10 −4 in the matrix [40,41]. This behaviour is representative of FCC materials like copper or nickel and is studied best on single crystals [8][9][10][11][12][13][14][15][42][43][44]. PSBs develop only if well-defined thresholds of the plastic strain and the stress amplitude are exceeded.…”

“…At that stage, cyclic strain localization frequently sets in, leading to transcrystalline cracking at the surface (cf. [8][9][10][11][12][13][14][15]). In addition, intercrystalline fatigue damage can occur at grain boundaries.…”

“…The work on PSBs has fascinated many researchers and has led to a significantly improved understanding of the governing dislocation mechanisms of cyclic strain localization in FCC mono-and polycrystals (e.g. [10][11][12][13][14][15][40][41][42]). More details are found in a recent review of the literature by Antolovich & Armstrong [45].…”

“…These advances have been made possible by the tremendous progress achieved in the instrumentation of fatigue testing, in microscopic analysis of fatigue damage and in computational facilities. Details on these developments can be found in several monographs on metal fatigue [4][5][6][7] and in a number of reviews that appeared in the last few decades [8][9][10][11][12][13][14][15].…”