Twins, and plastic deformation: few papers

January 26, 2011

[1] Influence of constraints and twinning stress on magnetic field-induced strain of magnetic shape-memory alloys

Chmielus et al

Magnetic-field-induced strain of hard 14M and soft 10M martensitic samples of Ni-Mn-Ga single crystals was measured and optically observed in a rotating magnetic field in one-sided and two-sided constraint conditions. The soft sample showed smooth, continuous deformation of 0.6% when two-sided, and 2.7% when one-sided constrained. The hard sample produced no strain when two-sided, and discontinuous deformation of 1.8% when one-sided constrained. Thus, the constraints reduce, even block, twin boundary motion. This finding must be considered in experiment and applications.

[2] Repulsive force vs. source number: Competing mechanisms in the yield of twinned gold nanowires of finite length

Guo and Xia

Nanoscale twin boundaries play a significant role in the yield behavior of nanowires. They serve as both a source of dislocation nucleation and a generator of the repulsive force which acts against the nucleation of dislocations. In the present paper molecular dynamics (MD) simulations are performed to investigate the tensile deformation of twinned gold nanowires (NWs) of finite length. Emphasis is placed on competing mechanisms in the initial yield of nanowires: dislocation source number vs. repulsive force, both of which are controlled by the twin boundary spacing. The simulation results reveal that with decreasing twin boundary spacing there is a transition from softening to strengthening due to a change in the dominant mechanism of plastic deformation. An analytical model based on kinetic rate theory is also established to provide an insight into the competing mechanisms indicated by the simulation results.

[3] Plastic behavior of fcc metals over a wide range of strain: Macroscopic and microscopic descriptions and their relationship

Csanadi et al

The room temperature macroscopic and microscopic plastic behavior of four face-centered cubic metals (Al, Au, Cu and Ni) is investigated experimentally over a wide strain range, and theoretical modeling is used to simulate the established major micromechanisms describing the evolution of mobile and forest dislocations during plastic flow. It is shown that forest dislocations develop primarily due to interaction between mobile dislocations, while the contribution from forest–mobile interactions is only minor. The trapping of mobile dislocations and the annihilation of forest dislocations are both controlled by the same thermally activated dislocation motion. These observations permit a simplification of the theoretical model that leads to an analytical relationship for the evolution of the total dislocation density as a function of strain. From this analysis, correlations are drawn between the macroscopic parameters describing the stress–strain relationship and the fundamental characteristics of the microscopic processes.

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