Crystal plasticity

This calculation, which holds true for most metals, is generally applicable to TPs. However, the designer is to be familiar with the inherently nonlinear, anisotropic nature of most plastics, particularly the fiber-reinforced and liquid crystal plastics (Chapter 6). 

Electro-optic The liquid crystal plastics exhibit some of the properties of crystalline solids and still flow easily as liquids (Chapter 6). One group of these materials is based on low polymers with strong field interacting side chains. Using these materials, there has developed a field of electro-optic devices whose characteristics can be changed sharply by the application of an electric field. 

Vol. 8 Thermally Activated Mechanisms in Crystal Plasticity by D. Caillard and... 

Note 2 The term is used to describe orientationally disordered crystals, crystals with molecules in random conformations (i.e., conformationally disordered crystals), plastic crystals and liquid crystals. 

All the plastic phases listed in the table possess FCC structure crystal-plastic crystal transition temperature AS, entropy change at T, AS , entropy change at T , activation energy for molecular reorientation obtained from NMR spectroscopy. 

Attenuated total reflection (ATR) is the most common reflectance measurement modahty. ATR spectra cannot be compared to absorption spectra. While the same peaks are observed, their relative intensities differ considerably. The absorbances depend on the angle of incidence, not on sample thickness, since the radiation penetrates only a few micrometers into the sample. The major advantage of ATR spectroscopy is ease of use with a wide variety of solid samples. The spectra are readily obtainable with a minimum of preparation Samples are simply pressed against the dense ATR crystal. Plastics, rubbers, packaging materials, pastes, powders, solids, and dosage forms such as tablets can all be handled directly in a similar way. 

As early as 1829, the observation of grain boundaries was reported. But it was more than one hundred years later that the structure of dislocations in crystals was understood. Early ideas on strain-figures that move in elastic bodies date back to the turn of this century. Although the mathematical theory of dislocations in an elastic continuum was summarized by [V. Volterra (1907)], it did not really influence the theory of crystal plasticity. X-ray intensity measurements [C.G. Darwin (1914)] with single crystals indicated their mosaic structure (j.e., subgrain boundaries) formed by dislocation arrays. Prandtl, Masing, and Polanyi, and in particular [U. Dehlinger (1929)] came close to the modern concept of line imperfections, which can move in a crystal lattice and induce plastic deformation. 

Because all glasses are clearly solids, the names liquid crystal glass or plastic crystal glass are awkward. The terms LC-, PC- and CD-glass thus stand for glass obtained by quenching a liquid crystal, plastic crystal, or condis crystal, respectively. 

The thermotropic mesophases are well enough understood to propose a subdivision into six types. Depending on the type of disorder, they are called liquid crystals, plastic crystals or condis crystals (positional and if applicable conformational disorder, orientational disorder, and conformational disorder, respectively). For the corresponding glasses, which represent the frozen-in mesophases, the names LC-, PC-, and CD-glasses are proposed (Fig. 2). For macromolecules not only equilibrium... 

However, at lower constant loads the rate of crystal plastic deformation decreases and (at 80 °C) disentanglement becomes competitive leading to the development of isolated planar craze-like defects extending perpendicular to the tensile axis (Fig. 15). The ensuing concentration of stress will further localize most of the sample deformation in such creep crazes and lead to a macroscopic ductile-brittle transition—in this material observed at 20 MPa (Fig. 14 [67]). 

The long extensions of the -R groups are three-dimensionally arranged around the polymer back-bone chain, and the floppy chains prevent the formation of a lattice and therefore crystallization. Plasticization with materials ester-benzoates would further separate the molecules and provide more flexible hardened cement. 

M.F. Horstemeyer et al A multiscale analysis of fixed-end simple shear using molecular dynamics, crystal plasticity, and a macroscopic internal state variable theory. Modell. Sim. Mat. Sci. Eng. 11, 265-286 (2003)... 

Klyavin, O., Physics of crystal plasticity at helium temperature (in Russian), Nauka , Moscow, 1987. 

We have been particularly interested in the study of the plastic states of organic compounds,41 which are characterized by high values of AS of formation from the crystalline state, the AS of fusion (plastic-liquid transition) being much smaller. We find that the AH as well as the AS of the crystal-plastic transition generally decrease as the temperature range of stability of the plastic phase increases the AH and the AS of the plastic-liquid transition, on the other hand, increase as the temperature range of stability of the plastic phase increases.42 Neutron scattering, NMR spectroscopy, and several other techniques have been employed to study molecular reorientation in the plastic state.41 We... 

The main difference between a solid and a liquid is that the molecules in a solid are not mobile. Therefore, as Gibbs already noted, the work required to create new surface area depends on the way the new solid surface is formed [ 121. Plastic deformations are possible for solids too. An example is the cleavage of a crystal. Plastic deformations are described by the surface tension y also called superficial work, The surface tension may be defined as the reversible work at constant elastic strain, temperature, electric field, and chemical potential required to form a unit area of new surface. It is a scalar quantity. The surface tension is usually measured in adhesion and adsorption experiments. 

The mechanistic parallel of this equation to the well known equation in crystal plasticity involving dislocation motion has already been pointed out by Brown We now continue and examine in detail the nature of the three terms in Eq. (6). 

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