Glide bands

A complication is that the deformation field under an indenter is not homogeneous. It is characterized by local glide bands that form the rosette patterns mentioned earlier (Figure 2.2).This makes the process exceedingly difficult to accurately model using either analytic, or numerical computations. 

Figure 6.8 Schematic shear band in a grain surrounded by other grains. Strong concentrations of shear stress reside at each end of the glide band which has a length D (the grain diameter). The radii of curvature at the ends of the band are taken to be atomic diameters.

Glide bands are observed around hardness indentations in lysozyme so dislocations (with large displacements) are associated with its deformation. 

Muguruma, J. Higashi, A. (19636). Non-basal glide bands in ice crystals. Nature, Land. 198, 573. [196]... 

Typically around indents in single-crystal faces series of slip lines are visible as shown in Figure 3.1 and Figure 6.23. These are sketched on Figures 2.8 and 3.4. Such glide bands contain systems of loops lying in several... 

When the stress (compressive) rises to a value approaching G/10 near the Debye temperature, motion of gliding dislocations tends to be replaced by the formation of phase transformation dislocations. The crystal structure then transforms to a new one of greater density. This occurs when the compressive stress (the hardness number) equals the energy band gap density (gap/molecular volume). 

Figure 5.12 Glide activation energies from high temperature data vs. energy band gaps. Note that the data for the homopolar crystals (C, SiC, Si, and Ge) lie quite close to the correlation line, while the data for The heteropolar crystals show some scatter. The reason why GaP Is an exception is not known. Also, note that the slope of the correlation line is two. 

Raman spectral-band frequencies for poly (thietane) as a crystallized melt annealed at 62° satisfy the rules for a longitudinal acoustic-mode frequency for deducing thickness. The morphology and physical properties of isoprene thietane block copolymers have been studied. Potential energies have been calculated for helical- and glide-type conformations of poly (thietane), and the conformations of the homopolymer have been calculated. ... 

Figure 6.3 Plot of the glide activation energy against the band gap, E, for the Group 14 elements. Reprinted with permission from J.J. Gilman, Science, 261, 1436 (1993). 1993 American Association for the Advancement of Science.

If o < o < o, then the applied stresses lead to the formation of new glide layers and the shear band has the structure depicted in Fig. 6.16b. During this process, the glide-layer branching due to structure microinhomogeneities in the LRC may occur. However, the preferred orientation of the layers depends on the direction of the forces resulting from shear stresses. 

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