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Mismatched Heteroepitaxial Growth and Strain Relaxation
Published in John E. Ayers, Heteroepitaxy of Semiconductors, 2018
A possible configuration for the spiral source in a heteroepitaxial layer was described by Beanland15 and is shown in Figure 5.16. It is assumed that a threading dislocation is anchored at a single point A, as shown in Figure 5.16a. With an applied stress, the dislocation may bow out above the pinning point, as in Figure 5.16b. The bowed section will continue to expand and may glide to the interface to relieve mismatch strain, as in Figure 5.16c. Further expansion of the bowed portion may lead to production of a half-loop if the bow reaches the surface and splits in two, as in Figure 5.16d. The original dislocation is then available to produce more dislocations by the same process.
Plastic flow Important regularities
Published in Lev Zuev, Autowave Plasticity, 2020
WWThe nature of the effect is usually associated [Bell, 1984; Khristal, 2001; Rizzi, Hähner, 2004] with strain-induced ageing caused by the formation of impurity atmospheres [Cottrell, 1958] on dislocations, which were detained during their movement by local barriers of different nature [Wirtman, 1987; Zbib, de la Rubia, 2002]. To continue the deformation, it is necessary to increase the effective stresses in order to ensure the separation of dislocations from the pinning points.
Analytic model for the line tension of a bowing dislocation segment
Published in Philosophical Magazine Letters, 2019
Benjamin A. Szajewski, Joshua C. Crone, Jaroslaw Knap
The onset of plasticity within crystalline materials is governed by nucleation and multiplication of dislocations. In common engineering materials, the microstructure is comprised of multiple grains, each of which is densely populated with dislocations among other crystalline defects [1,2]. The result is a complex network of defects with dislocation lines locally pinned along their lengths by forest dislocations [3,4], precipitates [5,6] and other obstacles [7], each acting to inhibit plastic flow. In response to an applied stress, the dislocations tend to bowout between pinning points, relieving strain energy. However, the extent of bowout is limited by line tension forces (Γ), which act to minimise the length of dislocation line. Above a threshold stress, which depends on Γ, dislocation multiplication occurs, and along with it plasticity. Consequently, quantitative analyses of Γ are crucial to enhancing our understanding of crystalline plasticity.