Deformation structural transformation

Non-destructive methods include holographic interferometry, resistance transducers, stress-sensitive covers, and other similar techniques. In practice, the following physical methods of non-destructive monitoring of residual stresses are commonly used X-ray diffraction, measurement of dielectric properties, and ultrasonic control. The main purpose of these methods is to monitor the structural transformations or distortions taking place as a result of residual stresses and local deformations. However, the application of methods such as X-ray diffraction to measure distortions in unit cel dimensions, ultrasonics to measure elastic wave propagation velocities, etc., all encounter numerous experimental problems. Therefore, in ordinary laboratory conditions only quantitative estimations of residual stresses can be obtained. 

The comparative optical photo with the same magnification gives the image of a polished surface without revealing structure elements. Structure transformation has been observed after deformational and thermal influences. Acoustomicroscope method of V(Z) - curves essentially increases possibility of obtaining information about investigated materials [3]. It allows to get the specific curves, for given materials, which are connected with elastic - mechanical constant ones. The example of such dependence for carbonaceous steel is demonstrated in Fig. 2. 

Above 50 bar, the video image clearly exhibits a high degree of deformation of the polymer. This structural transformation is reflected by the flattening of the solubility curve an increase in pressure does not lead to a corresponding rise in C02 solubility in the polymer. The deformation of the polymer at elevated pressures is irreversible even after depressurization. 

This peculiar superelastic behavior is owing to a stress-induced transformation from a high-strength crystalline phase to a very structurally similar, yet deformable, crystalline phase. On removing the stress, the deformed material transforms back to the initial... 

Yet another example of the geometry of deformation of interest to the present enterprise is that of structural transformation. As was evidenced in chap. 1 in our discussion of phase diagrams, material systems admit of a host of different structural competitors as various control parameters such as the temperature, the pressure and the composition are varied. Many of these transformations can be viewed from a kinematic perspective with the different structural states connected by a deformation pathway in the space of deformation gradients. In some instances, it is appropriate to consider the undeformed and transformed crystals as being linked by an affine transformation. A crystal is built up through the repetition... 

There are a number of different examples within which it is possible to describe the kinematics of structural transformation. Perhaps the simplest such example is that of the transformation between a cubic parent phase and a transformed phase of lower symmetry such as a tetragonal structure. We note that we will return to precisely such structural transformations in the context of martensitic microstructures in chap. 10. If we make the simplifying assumption that the transformed axes correspond with those of the parent phase, then the deformation mapping is of the form... 

Fig. 2.6. Illustration of the internal rearrangements that attend the structural transformation in Zr02 (adapted from Finnis et al. (1998)). Although the overall shape of the unit cell can be described in terms of an affine deformation characterized by a constant deformation gradient F, the individual internal atoms do not transform accordingly.

At the macroscopic scale, shear localization flow in the alloy develops during initial increments of deformation. Softening and globularization of structure in the macro shear band lead to realization of deformation at mesoscopic scale. In this case the mesoscopic scale deformation is determined by cooperative grain boundary sliding leading to superplastic flow. Superplastic flow results in deformation accumulation in the central area of the sample and impedes in structure transformation in periphery regions. 

The structural capsules start to be formed in films subjected to deformation in liquids until some tension threshold. Microcracks and microvoids appear and are filled with the inhibiting liquid under tensile stresses exceeding the polymer flow limit. Capillary channels connecting these voids with the process liquid and with each other start to merge or open in the course of structural transformations but do not disappear fully. The liquid may move over the network of the formed channels beyond the polymer matrix limits or concentrate in some voids able under certain conditions to enlarge the manifold. Thermal treatment of the deformed film intensifies the relaxation processes in the polymer matrix, the film shrinks in the tension direction and the capillaries between voids link up densely, thus insulating liquid particles from each other. If the film is treated in the extended state, a more complex mechanism of microcapsule formation is realized [4]. Cl liberation from microcapsules is related to their ability to break spontaneously under residual... 

Figure 10. Pressure-induced structural transformation obtained by MD simulations at room temperature, (a) A framework of comer-shared Si04 tetrahedra in a low-pressure phase (low-oristobalite), where silicon atoms are shown with circles. Oxygen atoms related with the structural transformation are numbered, (b) The framework structure deformed under pressure, (c) The framework structure after released pressure.

So, SiOz at 35 0 GPa transforms into the FezN type, then at 53 GPa to a structuie of the CaClz type, and after 68 GPa exists in the a-PbOz structure. GeOz converts into the CaCU type at 25 GPa, the a-PbOz type at 44 GPa and above 70-90 GPa adopts the FeSz type (the deformed structure CaFz) which is the densest phase of... 

ABSTRACT The paper provides the results of experimental study of structural transformation in clay on its deformation promoting changes in its physical and physico-mechanical properties. The processes on the contacts of structural elements are considered, as well as clay structure transformation upon ground consolidation, shear and swelling. It is pointed out that these structural changes should be taken into account when working out soil models for engineering calculations. 

Contacts in disperse rocks should be considered as defects in structure, which are subject to deformation. All specifics of deformation and strength properties in clay are controlled by the type of structural transformations and deformations developing on the contacts. The study of these processes elucidates the physical essence and regularities in the obtained experimental data. 

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