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Dislocation velocity is largely dependent upon shear stress and temperature, and can often be fit using a power law function: [14] = where is a material constant, is the applied shear stress, is a constant that decreases with increasing temperature. Increased shear stress will increase the dislocation velocity, while increased temperature will ...
Also, multiscale nature of dislocation avalanche event gives dislocation velocity a large range. For example, single dislocations have been shown to move at speeds of ~10 ms −1 in pure Cu, but dislocation groups moved with ~10 −6 ms −1 in Cu-0.5%Al. The opposite is found for iron, where dislocation groups are found to move six orders of ...
The entire dislocation does not move at once – rather, the dislocation produces a pair of kinks, which then propagates in opposite directions down the length of the dislocation, eventually shifting the entire dislocation by a Burgers vector. The velocity of dislocations through kink propagation also clearly limited on the nucleation frequency ...
where is the diffusivity of the solute atom in the host material, is the atomic volume, is the velocity of the dislocation, is the diffusion flux density, and is the solute concentration. [5] The existence of the Cottrell atmosphere and the effects of viscous drag have been proven to be important in high temperature deformation at intermediate ...
Snap, [6] or jounce, [2] is the fourth derivative of the position vector with respect to time, or the rate of change of the jerk with respect to time. [4] Equivalently, it is the second derivative of acceleration or the third derivative of velocity, and is defined by any of the following equivalent expressions: = ȷ = = =.
where is the dislocation density, is the burgers vector, and ¯ is the average velocity of the dislocation. When the dislocation velocity is not too high (or the creep rate is not too high), the solute atom can follow the dislocations, and thus introduce "drag" on the dislocation motion.
The velocity at which the dislocations glide can be approximated by a power law of the form = = where m is the effective stress exponent, Q is the apparent activation energy for glide and B 0 is a constant.
When solute atoms are mobile and the dislocation velocity is not too high, the solute atoms and dislocation can move together where the solute atom decreases the motion of the dislocation. [ 6 ] The Portevin-Le Chatelier effect occurs in the specific case where solute drag creep is occurring and there is an applied stress, with a material ...