The significant size effect on nucleation and propagation of crack during tensile deformation of copper foil: Free surface roughening and crystallography study

Mesoscale Deformation-Induced Surface Phenomena in Loaded Polycrystals

“…Thus, in combination with geometrical irregularities, it can be the most powerful source of stress concentration. This agrees with the experimental and theoretical studies [5][6][7][8][9][10][11]17] showing that the specimen surface plays a key role in the appearance of stress concentrations and plastic strain nucleation. This conclusion is supported by the calculation results for the polycrystalline conglomerate consisting of 280 grains (Fig.…”

“…A scatter of local stresses and strains about their mean values is more pronounced in the surface layer than in the bulk of the material. This is the reason for first plastic deformation to nucleate on the surface as it is observed experimentally [5][6][7][8]. Let us analyze the frequency distributions of different stress and strain tensor components plotted in Fig.…”

“…The deformation-induced roughening is especially pronounced in polycrystalline metals where the surface out-of-plane displacements develop throughout all length scales from micro to macro [8][9][10][11]. A special role belongs to the mesoscale roughening, where the surface undulations occasionally take a form of ridges, ropes, wrinkles, checkered distributions of hills and hollows, etc.…”

“…are distributed uniformly over the specimen sections so that cracks have even chances to nucleate near the free surface or in the bulk. However, experimental studies (e.g., [5][6][7][8]) have reported that cracks under tensile or cyclic loadings primarily nucleated on the surface or within a thin subsurface layer. In order to describe this effect, we should go down from the macro to lower scales where the material is inhomogeneous.…”

“…Another prominent example of the microstructure-related surface phenomena is deformation-induced roughening, inevitably accompanying plastic deformation in polycrystalline metals and alloys. The specimen free surface becomes rough even in the conditions of uniaxial or biaxial tension where no external forces act perpendicular to the specimen surface to cause any out-of-plane surface displacements [8][9][10][11]. Again this behavior is failed to be predicted by macroscopic continuum mechanics but should be described in terms of micromechanics to take into account non-linear deformation modes attributed to the microstructural inhomogeneity.…”