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Slip systems in zirconium alloys. 𝒃 and 𝒏 are the slip direction and plane, respectively, and 𝝎 is the rotation axis calculated in the present work, orthogonal to both the slip plane normal and slip direction. The crystal direction of the rotation axis vectors is labelled on the IPF colour key. [5]
Animation illustrating how stress on a Frank–Read source (center) can generate multiple dislocation lines in a crystal. The Frank–Read source is a mechanism based on dislocation multiplication in a slip plane under shear stress. [4] [5] Consider a straight dislocation in a crystal slip plane with its two ends, A and B, pinned.
The slip systems are described by the Schmid tensor, which is tensor product of the Burgers vector and the slip plane normal, and the Schmid tensor is used to obtain the resolved shear stress in each slip system. Each slip system can undergo different amounts of shearing, and obtaining these shear rates lies at the crux of crystal plasticity.
Notably, because independent slip systems are defined as slip planes on which dislocation migrations cannot be reproduced by any combination of dislocation migrations along other slip system’s planes, the number of geometrical slip systems for a given crystal system - which by definition can be constructed by slip system combinations - is ...
In crystalline metals, slip occurs in specific directions on crystallographic planes, and each combination of slip direction and slip plane will have its own Schmid factor. As an example, for a face-centered cubic (FCC) system the primary slip plane is {111} and primary slip directions exist within the <110> permutation families.
A screw dislocation can be visualized by cutting a crystal along a plane and slipping one half across the other by a lattice vector, the halves fitting back together without leaving a defect. If the cut only goes part way through the crystal, and then slipped, the boundary of the cut is a screw dislocation.
The plastic bending of a single crystal can be used to illustrate the concept of geometrically necessary dislocation, where the slip planes and crystal orientations are parallel to the direction of bending. The perfect (non-deformed) crystal has a length and thickness .
Smallman found that cross-slip happens under low stress for high SFE materials like aluminum (1964). This gives a metal extra ductility because with cross-slip it needs only three other active slip systems to undergo large strains. [12] [13] This is true even when the crystal is not ideally oriented.