On the interaction among stage I short crack, slip band and grain boundary: a FEM analysis

Abstract

A FEM model of a stage ! short crack in polycrystals was constructed based on the micromechanics and the physical process of its growth. The effective stress and effective plastic strain at the growing stage I short crack tip is slightly affected by the coplanar slip except in the vicinity of the grain boundary. Stage I growth is a mode transition process from pure shear to pure tensile, which is governed by the interaction among the crack, the slip at the crack tip and the approached grain boundary. The coplanar slip at the stage I crack tip enhances plastic CTSD and promotes the shear mode growth, nevertheless the grain boundary hindering the coplanar slip promotes the tensile mode growth. The apparent fast growth of stage I short cracks is accounted for by the enhanced CTSD resulting from the micro-plasticity in the coplanar PSB at the crack tip; and the minimum growth rate in the vicinity of a grain boundary is correlated with the expended CTSD and internal stress due to incompatible deformation at the boundary. The closure of stage I short crack in the first grain on the path is negligible, but dramatically increases as the crack deflects at the boundary entering into the second grain on its path.

Atomistic modelling of fatigue crack growth and dislocation structuring in FCC crystals

“…On the contrary, for larger DK values, the crack growth rates did not exhibit significant scatter, and the data tended to be positioned on a well-defined line on the da/dN versus DK plot. This suggests the existence of a Paris regime (Paris & Erdogan 1960) (Miller 1987a,b;Li 1990Li , 1994Potirniche et al 2004), inclusions and constituent particles (Fan et al 2001). The region on da/dN versus DK plot for microstructural cracks is above the one for nanocracks.…”

“…The interactions between cracks and grain boundaries are particularly important in determining fatigue resistance in materials (Paris & Erdogan 1960;Zurek et al 1982;Li 1990Li , 1994. In this section, we investigate the path changes of a fatigue nanocrack as it approaches a grain boundary and propagates into an adjacent grain, which is misoriented with respect to the first grain.…”

Simulating small crack growth behaviour using crystal plasticity theory and finite element analysis

“…They suggested an analytical relationship would be useful to relate the crack opening stresses to the relative position of the crack tip with respect to the grain boundary. One of the first efforts to model small crack growth and the interaction of a small crack with a grain boundary using finite element analysis (FEA) was that of Li, 19 who analysed stage I (mode II) small crack growth. He used classical isotropic plasticity theory and constrained the displacement of the nodes located on the plane of crystallographic slip to displace only in this crystallographic direction to simulate plastic slip.…”

Cyclic crystal plasticity analyses of stationary, microstructurally small surface cracks in ductile single phase polycrystals

“…According to Li 9 for small crystallographic cracks in Stage I growth predominately under single slip (minimal cross slip or multislip ahead of the crack tip), the growth process is dominated by the ΔCTSD( ≈ |Δδ p |) on the primary slip system. The contribution of secondary slip becomes more prominent as the tendency for multislip sets in, or as the crack encounters barriers that induce opening displacement.…”

“…Li's 6,9 work focused on the interaction of the crack tip with bi‐crystals of varying orientations, whereas Gall et al 4 . used planar double slip with varying crystal orientations in a single crystal to assess the CTOD and CTSD.…”