Crystal shearing

Figure 1.12. Principle of crystallographic shear (CS) in Re03 (a) formation of anion vacancies and (b) elimination of the vacancies by crystal shear and collapse, from corner-sharing octahedra to edge-sharing octahedra forming extended CS plane defects.

This view of the process of reduction of the oxides and the oxysalts of W and Mo has been supported by an electron microscopy study [34] and by electron spectroscopy [32, 35]. However, the actual mechanism by which vacancies arrange cooperatively in ordered manners to give rise to crystal shear is yet to be elucidated. 

Strong electronic (covalent or electrovalent) bonding is desirable within a crystal lamella, to provide structural strength and to ensure that when shear forces are applied to the crystal, shear takes place between lamellae, and not within them. Conversely, strong bonding between lamellae is undesirable, as it leads to high inter-lamellar shear resistance and high friction. Ideally, the inter-lamellar forces are limited to weak van der Waals forces, and the inter-lamellar space is often called the "van... 

Simulation studies of liquid crystal shear flow 349... 

SIMULATION STUDIES OF LIQUID CRYSTAL SHEAR FLOW... 

S. Sarman, Nonequilibrium Molecular Dynamics of Liquid Crystal Shear Flow, J. Chem. Phys. 103 (1995) 10378. 

We have already discussed confinement effects in the channel flow of colloidal glasses. Such effects are also seen in hard-sphere colloidal crystals sheared between parallel plates. Cohen et al. [103] found that when the plate separation was smaller than 11 particle diameters, commensurability effects became dominant, with the emergence of new crystalline orderings. In particular, the colloids organise into z-buckled" layers which show up in xy slices as one, two or three particle strips separated by fluid bands see Fig. 15. By comparing osmotic pressure and viscous stresses in the different particle configurations, tlie cross-over from buckled to non-buckled states could be accurately predicted. 

Much of this data has been or will be published elsewhere [5-10]. The data shows that the lattice and molecules of plastically deformed crystals experience significant and semi-permanent deformation. From this, insights are obtained that permit the development of an approximate deformed lattice potential for shocked or impacted crystals. Shear bands have been observed in shocked or impacted crystals. Some of shear bands show that molten material had been extruded from deep within the bands. These are possibly the source of the hot spots thought to be responsible for initiation during shock or impact. On the basis of these and other experimental observations it is concluded that energy dissipation and localization during plastic deformation is likely to be responsible for initiation of chemical reaction. 

The mechanical twins of the B structure appear by stressing the crystals shear, tension or extension. The first case is related to the simplest phenomenon where only one kind of twin layer is generated. In the other cases, generally two kinds of twin layers are generated at once, which makes the phenomenon rather complex. 

The transformation process of p phase can be accelerated under ciystals deformation and pressure [140], For example the partial transformation of P to y can be caused at room temperature through crushing of sample in hydraulic press. It accelerates probably nuclei formation of this phase as the result of crystals shearing. From the other side when the powdered sample of p phase is exposed to the hydrostatic pressure of 900 MPa no transformation is observed, becanse y has lower... 

Dynamic interfacial tension coefficient and its equilibrium value Side and interfacial energies of a polymeric crystal Shear stress... 

Reynolds, W.N. and Sharp, J.V. (1974) Crystal shear limit to carbon fiber strength. Carbon, 12 103-110. 

Silicate layers show an extreme anisotropic shape, strong interactions due to their polar-ionic character, and high stiffness compared to conventional polymers. These extraordinary properties resulted in extraordinary phase, orientation, and rheological behavior that is probably comparable discotic or sanidic liquid crystals. Shear rates, which are common in the standard or industrial... 

Relatively speaking the polymer field has not yet reached this stage, to some degree in fibers and films but even here there is much room for improvement. We have many tools to help us produce the optimtim structiire, and optimum properties pressure induced crystallization, shear induced orientation and crystallization, polymer blend composition to control melt rheology as well as the synthesis processes to produce the desired relationship between internal structure and application properties. This is the area of future research that deserves our attention. 

Consequently, the aggregation should take place slowly, but this was not observed during the course of the measurement. Before curve (d) (Fig. 8) was measured, the solution was subjected to shear stress through capillary flow. Here, the particles became oriented and aggregated through crystallization (shear-induced aggregation, i.e. crystallization). The trace of this curve (d) is similar to curve (a). 

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