The research development of the structure in a-Fe Microcrystals with the Orientation deformed by compression with different values of the friction coefficient

The paper analyzes the change in the dislocation structure in a-Fe microcrystals with orientations <100> and <110> deformed by compression under conditions of limited flow with different values of the friction coefficient. The orientation stability of the microcrystal and texture is investigated when the compression axis deviates from the normal to the compression plane. Shooting and analysis of limited pole figures made it possible to establish that the operation of the OSS in the MC with the [100](001) orientation at different values of the friction coefficient at the sample-punch interface leads to a rotation of the latticework relatively to the MC axis. The specific conditions of plastic deformation under compression determined by the MC morphology prohibit displacement deyz., as the deformation is observed under conditions of limited flow. The operation of the OSS, consequently, leads to the MC partition with the [100] (001) orientation deformed by compression with the friction coefficient Kmax into parts and the rotation of the latticework around the growth axis. It is established the connection between the friction coefficient at the crystal-punch interface and the sliding geometry in a-Fe MCs deformed by compression under conditions of limited flow. The authors carried out the dimension of the friction ratio has a significant effect on the slip geometry and the dislocation structure formed in the MC of the [100] orientation deformed by compression along the (001) plane. Changes in the friction coefficient and the angle deviation of the compression axis from the normal to the compression plane in the MC with the [100] (001) orientation do not affect the slip geometry and the dislocation structure formed during plastic deformation.

Kinking facilitates grain nucleation and modifies crystallographic preferred orientations during high-stress ice deformation

Kinking can accommodate significant amounts of strain during crystal plastic deformation under relatively large stresses and may influence the mechanical properties of cold planetary cryosphere. To better understand the origins, mechanisms, and microstructural effects of kinking, we present detailed microstructural analyses of coarse-grained ice (~1300 µm) deformed under uniaxial compression at -30°C. Microstructural data are generated using cryogenic electron backscattered diffraction (cryo-EBSD). Deformed samples have bimodal grain size distributions, with thin and elongated (aspect ratio ≥ 4) kink domains that develop within, or at the tips of, remnant original grains (≥ 300 µm, aspect ratio < 4). Small, equiaxed subgrains also develop along margins of remnant grains. Moreover, many remnant grains are surrounded by fine-grained mantles of small, recrystallized grains (< 300 µm, aspect ratio < 4). Together, these observations indicate that grain nucleation is facilitated by both kinking and dynamic recrystallization (via subgrain rotation). Low- (< 10°) and high-angle (mostly > 10°, many > 20°) kink bands within remnant grains have misorientation axes that lie predominantly within the basal plane. Moreover, previous studies suggest the kinematics of kinking and subgrain rotation should be fundamentally the same. Therefore, progressive kinking and subgrain rotation should be crystallographically controlled, with rotation around fixed misorientation axes. Furthermore, the c-axes of most kink domains are oriented sub-perpendicular to the sample compression axis, indicating a tight correlation between kinking and the development of crystallographic preferred orientation. Kink band densities are the highest within remnant grains that have basal planes sub-parallel to the compression axis (i.e., c-axes perpendicular to the compression axis)—these data are inconsistent with models suggesting that, if kinking is the only strain-accommodating process, there should be higher kink band densities within grains that have basal planes oblique to the compression axis (for low kink-host misorientation angles, e.g., ≤ 20°, as in this study). One way to rationalize this inconsistency between kink models and experimental observations is that kinking and dynamic recrystallization are both active during deformation, but their relative activities depend on the crystallographic orientations of grains. For grains with basal planes sub-parallel to the compression axis, strain-induced GBM is inhibited, and large intragranular strain incompatibilities can be relaxed via kinking, when other processes such as subgrain rotation recrystallization are insufficient. For grains with basal planes oblique to the compression axis, strain-induced grain boundary migration (GBM) might be efficient enough to relax the strain incompatibility via selective growth of these grains, and kinking is therefore less important. For grains with basal planes sub-perpendicular to the compression axis, kink bands are seldom observed—for these grains, the minimum shear stress required for kinking exceeds the applied compressive stress, such that kinks cannot nucleate.

Tectonic stress in the structures of the Northern Priokhotie (Magadan region) according to geological data

Tectonic fracturing of the Mesozoic and Cenozoic structures was studied in the Northern Priokhotie (Magadan region). The cataclastic analysis method and the statistical method of fracture density analysis were used to reconstruct their state of stress. It is revealed that the folded structures of the Arman’-Viliga synclinorium are subjected to horizontal shearing; the axis of maximum compression is sublatitudinal (azimuth 67°, angle 12°); extension is submeridional (azimuth 161°, angle 19°). In the Uda-Murgal volcanic arc, horizontal extension with shear takes place; the compression axis is directed to NW (azimuth 259°, angle 29°), and the extension axis to NE (azimuth 152°, angle 26°). In the Okhotsk-Chukotka volcanogenic belt, volcanic structures are in the field of varying tectonic stresses, from predominant horizontal extension to horizontal shear. The Cenozoic intermontane depressions of the Miocene – Pliocene ages are subjected to horizontal shear; the compression axis is directed to NE (azimuth 214°, angle 29°), and the extension axis to NW (azimuth 121°, angle 4°). The results of the comparative analysis of the stress states in the above-mentioned areas reliably show that the diversity of the stress state types is statistically related to the structural positions of the studies sites. Such diversity cannot be explained by an influence of active faults, or by any consecutive superposition of deformations at different stages, despite the fact that the deformations have complicated the observed pattern of the stress states. We conclude that each subsequent geodynamic stage only introduced additional elements into the previous structure, but did not completely transform it.

Structure of fracture under the joint operation of two mechanisms of local destruction

Рассмотрены примеры сценариев хрупкого разрушения, в которых участвуют два механизма локального разрушения - развитие трещин нормального разрыва и компактирование, либо торошение, при сжатии. Работа является продолжением исследований структур разрушения в условиях сжатия [1]. Показано, что в модельной ситуации с цепочкой отверстий в пластине выбор механизма формирования локальных очагов разрушения или их совместного действия зависит от ориентации системы отверстий относительно оси сжатия. Другой пример относится к процессу разрушения ледяного покрова при его сжатии под действием течений и ветровой нагрузки. Рассмотрен вариант разрушения, в котором происходит взаимодействие двух видов разрушения - локализованное в виде трещиноподобного дефекта разрушение при сжатии (торошении) и формирование сопутствующих поперечных разрывов, разбивающих нагружаемый участок ледяного покрова на ряд полос вдоль напряжений сжатия. Examples of brittle fracture scenarios are considered, in which two mechanisms of local fracture participate - the development of normal fracture cracks and compaction, or hummocking, under compression. The work is a continuation of studies of fracture structures under compression [1]. It is shown that in a model situation with a chain of holes in a plate, the choice of the mechanism of formation of local fracture centers or their joint action depends on the orientation of the system of holes relative to the compression axis. Another example relates to the process of destruction of the ice cover when it is compressed under the influence of currents and wind load. The fracture variant is considered, in which two types of fracture interact: the fracture localized in the form of a crack-like defect during compression (hummocking) and the formation of accompanying transverse ruptures dividing the loaded ice sheet section into a series of bands along the compression stresses.

Applying seismic ring-fault models to real case scenarios

&lt;p&gt; Previous studies have found discrepancies concerning the seismic radiation between planar and curved faults; moment tensor (MT) interpretations, seismic moment estimation and waveforms change dramatically when the rupture is not planar. Therefore, assuming a point source on a planar fault for earthquakes in volcanic environments can be an oversimplification that needs to be addressed if we observe some seismological clues. First, we study waveforms for LP events at Etna. To explain these waveforms we propose a full-ring rupture with an inner net movement of magma, in in contrast to the planar fault approach that returns a pulsating rupture. Second, we study MT inversions for the biggest earthquakes during the 2014-2015 collapse of the Bardarbunga caldera, which show non-double couple solutions, with vertical compression axis. We calculate synthetic seismograms for partial-ring ruptures using an &amp;#8220;ideal&amp;#8221; seismic network, and one emulating the existing monitoring network at Bardarbunga. Observations using distal stations can return a better-constrained seismic moment, but they fail to characterise the dynamics involved. On the other hand, using proximal stations we obtain a reliable representation of the forces involved; however, the seismic moment is systematically overestimated due to the proximity to the curved source and the corresponding focussing effects. Finally, we correct the area of rupture due to fault shape to estimate the real cumulative seismic moment during the caldera collapse. The result shows a closer relationship between seismic and geodetic moment.&lt;/p&gt;

Spatial variation in the present-day stress field and tectonic regime of Northeast Tibet from moment tensor solutions of local earthquake data

SUMMARY Focal mechanism solutions and their predicted stress pattern can be used to investigate tectonic deformation in seismically active zones and contribute to understanding and constraining the kinematic patterns of the outward growth and uplift of the Tibetan Plateau. Herein, we determined the focal mechanisms of 398 earthquakes in Northeast Tibet recorded by the China National Seismic Network (CNSN) by using the cut-and-paste method. The results show that the earthquakes predominately exhibited thrust and strike-slip faulting mechanisms with very few normal events. We then combined the derived focal mechanisms with global centroid moment tensor (GCMT) catalogue solutions and previously published solutions to predict the regional distribution of the stress field through a damped linear inversion. The inversion results show that most of region is dominated by a thrust faulting regime. From the southern East Kunlun fault in the west to the northern Qilian Mountains along the Altyn Tagh fault (ATF), the maximum compression axis rotates slightly clockwise; farther to the south of the Haiyuan fault in the east, there is an evident clockwise rotation of the maximum compression axis, especially at the eastern end of the Haiyuan fault. In the Qilian Mountains, the axis of the compressive stress orientation approximately trends NE–SW, which does not markedly differ from the direction of India–Eurasia convergence, emphasizing the importance of the compressive stress in reflecting the remote effects of this continental collision. The overall spatial pattern of the principal stress axes is closely consistent with the GPS-derived horizontal surface velocity. A comparison of the stress and strain rate fields demonstrated that the orientations of the crustal stress axes and the surface strain axes were almost identical, which indicates that a diffuse model is more suitable for describing the tectonic characteristics of Northeast Tibet. Additionally, the compressive stress orientation rotated to ENE–WSW in the northern Qilian Mountains along the ATF and to ENE–WSW or E–W along the eastern part of the Haiyuan fault and its adjacent area to the south, highlighting the occurrence of strain partitioning along large left-lateral strike-slip faults or the lateral variation of crustal strength across these faults. Combining geodetic, geological and seismological results, we suggest that a hybrid model incorporating both the diffuse model associated with shortening and thickening of the upper crust and the asthenospheric flow model accounting for the low-velocity zone in the middle-lower crust may reflect the primary mode of crustal deformation in Northeast Tibet.

Анизотропия деформации памяти формы в монокристалле сплава Ni-=SUB=-49-=/SUB=-Fe-=SUB=-18-=/SUB=-Ga-=SUB=-27-=/SUB=-Co-=SUB=-6-=/SUB=-

Stress-strain behavior of a cubic-shaped Ni49Fe18Ga27Co6 shape memory single crystal uniaxially compressed in three directions perpendicular to its faces was studied. The crystallographic orientation of the sample was chosen so that the sample was deformed along two <110>А and one [001]А directions. A fundamentally different stress-strain behavior was observed for the deformations along <110>A and [001]A directions. At room temperature, irrespective of the magnitude of the phase strain, the crystal compressed in [001]A exhibited superelastic behavior i.e. the strain fully recovered after unloading. In contrast, deformation along <110>A directions to the strain levels above 4% induced a residual shape memory strain after the unloading. Strains measured along the directions perpendicular to the compression axis indicate an anomalous behavior of the Poisson's ratio.

Stress-induced detwinning and martensite transformation in an austenite Ni–Mn–Ga alloy with martensite cluster under uniaxial loading

Stress-induced martensitic detwinning and martensitic transformation during step-wise compression in an austenite Ni–Mn–Ga matrix with a martensite cluster under uniaxial loading have been investigated by electron backscatter diffraction, focusing on the crystallographic features of microstructure evolution. The results indicate that detwinning occurs on twins with a high Schmid factor for both intra-plate and inter-plate twins in the hierarchical structure, resulting in a nonmodulated (NM) martensite composed only of favourable variants with [001]NM orientation away from the compression axis. Moreover, the stress-induced martensitic transformation occurs at higher stress levels, undergoing a three-stage transformation from austenite to a twin variant pair and finally to a single variant with increasing compressive stress, and theoretical calculation shows that the corresponding crystallographic configuration is accommodated to the compression stress. The present research not only provides a comprehensive understanding of martensitic variant detwinning and martensitic transformation under compression stress, but also offers important guidelines for the mechanical training process of martensite.

Electrotechnical Model of Conductivity of Lead Telluride, Obtained by Method of Powder Pressing

The results of study of thermoelectric properties of lead telluride obtained by method of powder pressing arepresented. A modified electrical model for interpreting the empirical dependences σ (T) is proposed, according towhich the compressed sample is represented by a system of crystallites with intergranular boundaries whoseproperties differ along and across the compression axis.