Syn-shearing deformation mechanisms of minerals in partially molten metapelites

We investigated an experimentally sheared (γ = 15, γ ̇ = 3 x 10-4s-1, 300 MPa, 750°C) quartz-muscovite aggregate to understand the deformation of parent and new crystals in partially molten rocks. The SEM and EBSD analyses along the longitudinal axial section of the cylindrical sample suggest that quartz and muscovite melted partially and later produced K-feldspar, ilmenite, biotite, mullite, and cordierite. Quartz grains became finer, and muscovite was almost entirely consumed in the process. With increasing , melt and crystal fractions decreased and increased, respectively. Amongst the new minerals, K-feldspar grains (highest area fraction and coarsest) nucleated first, whereas cordierite and mullite grains, finest and least in number, respectively, nucleated last. Fine grain size, weak CPOs, low intragranular deformation, and equant shapes suggest both initial and new minerals deformed dominantly by melt-assisted grain boundary sliding, which is further substantiated by higher misorientations between adjacent grains of quartz, K-feldspar, and ilmenite.

Effect of particle breakage on the shear strength of calcareous sands

The particle breakage of calcareous sands plays a key role in determining the particle shape and shear strength. This process has been analysed in the current study by employing the ring shear tests on calcareous sands sampled from the South China Sea. In this study, a set of parameters, e.g. roundness and aspect ratio, have been employed to quantify the geometrical properties of calcareous sands pre- and after the breakage. These two parameters have been found to correlate well with the vertical loading stress level, shear strain and shear strength. The particle breakage leads to the change of micro-structure during the shear test, as illustrated by the Scanning Electron Microscopy (SEM) images. It is found that during the shearing deformation, particle breakages can effectively reduce, while particle rearrangements can increase the shear strength of the calcareous sands.

The research for characters of detonated rupture disks used in rarefaction wave gun for test

In this paper, numerical and experimental analysis were carried out to study the characters of the detonated rupture disks used in rarefaction wave gun for test. The pressure bearing capacity and cutting blasting ability of the disks were studied in detail. The research results showed that the designed detonated rupture disks could withstand the maximum pressure of 140 MPa or more during launch process. The central detonating spoke had an annular cutting depth of about 1.3 mm. It was not the shearing deformation at the supporting edge but the excessive tensile deformation at the middle position that led to the failure. The disk was cut and destroyed as a whole satisfyingly, so the rationality and feasibility of the detonated rupture disks used in rarefaction wave gun for test were verified, which could provide a reference for the development of rarefaction wave artillery and similar low recoil weapons.

High-Temperature Equal-Channel Angular Pressing of a T6-Al-Cu-Li-Mg-Ag-Zr-Sc Alloy

Equal-channel angular pressing (ECAP) is known to induce significant grain refinement and formation of tangled dislocations within the grains. These are induced to evolve to form low-angle boundaries (i.e., cell boundaries) and eventually high-angle boundaries (i.e., grain boundaries). On the other hand, the precipitation sequence of age hardening aluminum alloys can be significantly affected by pre-straining and severe plastic deformation. Thus, ECAP is expected to influence the T6 response of aluminum alloys. In this study, a complex Al-Cu-Mg-Li-Ag-Zr-Sc alloy was subjected to ECAP following different straining paths. The alloy was ECAP at 460 K via route A, C, and by forward-backward route A (FB-route A) up to four passes. That is, ECAP was carried out imposing billet rotation between passes (route A), billet rotation by +90° between passes (route C), and billet rotation by +90° and inversion upside down between passes (FB-route A). The alloy was also aged at 460 K for different durations after ECAP. TEM microstructure inspections showed a marked influence of the different shearing deformations induced by ECAP on the alloy aging response. The precipitation kinetics of the different hardening secondary phases were affected by shearing deformation and tangled dislocations. In particular, the T1-Al2CuLi phase was the one that mostly showed a precipitation sequence speed up induced by the tangled dislocations formed during ECAP. The T1 phase was found to grow with aging time according to the Lifshitz-Slyozov-Wagner low-power regime.

Computer simulation of shearing deformation in polymer systems with polar groups

In this work, shear strain modeling in materials consisting of a thin polymer layer ([Formula: see text][Formula: see text]nm), adhesive bonded to a rigid substrate, considered not to be impacted by deformation, was performed. A discrete-continuum model of chains system with a given stiffness with polar groups is developed. The polymer chain was considered in the framework of the persistene model, and the polar groups were based on the lattice model on the tetragonal lattice. It was assumed that the main contribution to the energy of interchain interactions is due to the potential of the polar groups and was calculated using the Metropolis algorithm. The potential interactions between the nearest polar groups of chains included the energy of dipole–dipole interactions (Keesom energy) and the Lennard–Jones potential. It is taken into account that the possible orientations of the polar groups are determined by the average elongation of the chain. Calculations showed that the dependence of free energy on the interchain distance has two minima. The first minimum is characterized by the orientational ordering of the polar groups, the second — by their disordered state. The depth and position of the minima depend on temperature, bending stiffness of the chain, the modulus of the dipole moment of the polar groups and the depth of the potential well in the Lennard–Jones energy. A step-by-step simulation of shear strain in a polymer layer in an orientationally disordered state was carried out. The obtained stress–strain diagrams make it possible to estimate the value of the elastic limit and also to determine the stresses at the points of phase transitions from a disordered to an orientationally ordered state.

Characteristics of mechanical response and acoustic emission during granular shearing

<p>The shear behavior of granular materials has drawn considerable attention due to its great potential for various geophysical processes such as landslides and debris flows. Field and remote sensing observations reveal that the progressive maturation of these geophysical events may involve different styles of movement, such as stable creep, periodic slow sliding or accelerative sliding. Laboratory experiments also suggest that the mechanical conditions of granular materials may play a significant role in controlling diverse frictional behaviors, such as shear-rate weakening or strengthening. Furthermore, the granular frictional processes may involve abrupt perturbations of internal forces and release of strain energy. Such energy release events are manifested in the generation of high frequency (kHz-MHz) elastic waves, termed acoustic emissions (AEs), which deliver important information concerning the physical processes of granular shearing deformation.</p><p>A significant, though still inconclusive, body of research has been directed toward revealing possible mechanisms of AEs occurring on rock or among granular materials in shear. These studies attributed the generation of AEs to the formation of microcracks in intact rocks, the breaking of asperities between solid surfaces or the rearrangement of grain contacts. In this study, we performed laboratory tests on granular analogues composed of spherical glass beads in a ring shear configuration under conditions of room temperature and atmospheric humidity to examine whether the AE events are correlated with mechanical response. For measurements of elastic waves, a high-frequency AE transducer was installed near the shear plane. AE signals and mechanical data were synchronously sampled at the rate of 1 MHz using an additional recoding system.</p><p>The results show that (1) there is a strong correlation between the stress drop and the main acoustic burst; (2) the primary frequency bands are in the tens of kHz ranges for acoustic signals generated during granular shearing; (3) the onset of AE amplitudes precedes the impending global mechanical failures by several milliseconds.</p>

Efecto de la adición de materiales compuestos de estireno-butadieno/plumas de pollo en la modificación de asfaltos

Asphalt is an important material for road construction and other applications. That is why it is done the search for materials that in combination with the asphalt generate a product of better quality, lower environmental impacts and low costs, thus allowing to be reflected greater resistance of the asphalt to the extreme climatic conditions and traffic. To cover these different needs, asphalts with a better performance must be counted, having to modify their chemical, physical and rheological properties, in order to improve their behavior to the shearing, deformation, fatigue, ageing, elasticity, etc. In this work, studied the effect of adding composite materials with polymer of the type SBS lineal (Styrene-butadiene-styrene) and the feather of chicken, taking concentrations of 1, 3 and 5 PHR (parts per hundred of rubber) in ratios of 2, 4 and 6% in relation to the weight of asphalt. Techniques were applied to characterize such as dynamic viscosity, softening point, phase separation characterization, penetration index and fluorescent microscopy. As a result, using a polymer of the linear SBS type incorporating keratin from the chicken plume as reinforcement for the asphalt does not present interesting results for application areas such as where high fluidity is required.

Justification of the Rheological Model of Process of Plastic Material Injection by the Rollers

It is justified thatproblems related to the changes in structural and mechanical properties of plastic material and influence of structural elements of equipment and modes of implementation of the for-mation process on them are considered detail, taking into account empirical data, theoretical dependencies and results of physical experiments. It was established that during the mechanical influence of rollers with grooves on a structured dispersion plastic material in the node of injection of the molding machine, internal shear, and shearing deformation have a preponderant value. Accordingly, the productivity of machines is determined mainly by the structural parameters of the working bodies geometry, kinematics, and contact area. It is shown that increasing the pressure in the plastic material causes a decrease in its volume, but the relationship between pressure and volume has a nonlinear character. It has been established that regardless the variety of flour from which the plastic material was prepared for bagels, its moisture content and the duration of fermentation reduced viscosity of the effective plastic material along with the increase of the shear stress. The paper describes the refined rheological model of the Bingham body deformation, which develops instantaneously, and the velocity of the common elastic deformation in the dough is a simultaneous function of stresses and temperatures, which are close to exponential ones.