Distinct Stages Of Deformation Research Articles

Graphyne nano-spirals under tension: Effects of base structures on superelasticity and fracture mechanisms

With advances in nanotechnology, two-dimensional nanostructures have shown great promise for a wide range of applications. Of particular interest is their spiral forms as essential components of nanoelectromechanical systems. In this paper, the mechanical behavior of the spirals made of different graphyne structures under tension is investigated using molecular dynamics simulation and the results are compared with graphene nano-spirals. Inspired from the conventional macroscale springs with various cross-sections that have different behaviors against the external axial loads, we comprehensively analyze the effects of various base structures on superelastic deformation capabilities and fracture mechanisms of the nano-spirals. In general, five distinct deformation stages corresponding to van der Waals nonbonding interaction and covalent bonding are observed in the force-strain diagrams. Moreover, the effects of inner and outer radii on the mechanical characteristics are examined. It is found that the stretchability of nano-spirals increases up to a maximum threshold as the outer radius increases, then decreases with its further increase. This decrease is seen more clearly in spirals made of graphene and γ-graphyne while α- and β-graphyne nano-spirals outperform in larger widths. Hence, we show that deliberate manipulation of the base structures can significantly extend the applicability of nano-spirals to larger widths.

Mechanical Aspects of Nonhomogeneous Deformation of Aluminum Single Crystals under Compression along [100] and [110] Directions

The deformation behavior of aluminum single crystals subjected to compression along the [100] and [110] directions is numerically examined in terms of crystal plasticity. A constitutive model taking into account slip geometry in face-centered cubic crystals is developed using experimental data for the single-crystal samples with lateral sides coplanar to certain crystal planes. Two sets of calculations are performed using ABAQUS/Explicit to examine the features of plastic strain evolution in perfectly plastic and strain-hardened crystals. Special attention is given to the discussion of mechanical aspects of crystal fragmentation. Several distinct deformation stages are revealed in the calculations. In the first stage, narrow solitary fronts of plastic deformation are alternately formed near the top or bottom surfaces and then propagate towards opposite ends to save the symmetry of the crystal shape. The strain rate within the fronts is an order of magnitude higher than the average strain rate. The first stage lasts longer in the strain-hardened crystals, eventually giving way to an intermediate stage of multiple slips in different crystal parts. Finally, the crystal shape becomes asymmetrical, but no pronounced macroscopic strain localization has been revealed at any deformation stage. The second stage in perfectly plastic crystals relates to abrupt strain localization within a through-thickness band-shaped region, accompanied by macroscale crystal fragmentation. Stress analysis has shown that pure compression took place only in the first deformation stage. Once the crystal shape has lost its symmetry, the compressive stress in some regions progressively decreases to zero and eventually turns tensile.

Implementation of an elastoplastic constitutive model to study the proppant embedment in coal under different pore fluid saturation conditions: A numerical and experimental study

Proppant embedment in coal is highly concerned in both research and practice due to the vulnerability of the softer surface nature in coal and its involvement in fracture treatment failures. The issue has been reported to further intensify under pore fluid conditions; however, to date very few studies have investigated this effect for coal propped fractures. Analysing proppant embedment in numerical models through standard material models is far from realistic for materials like coal because the distinct plastic deformation stages play an essential role in proppant embedment measurements. In this study, a Drucker Prager material model is implemented, which employs the shrinking of the failure criteria by the progress of plastic deformation to consider the strain-softening behaviour of coal. The numerical results show that the implemented material model can describe the distinct deformation stages experienced in coal materials. The simulation results for uniaxial compression tests, triaxial tests and proppant embedment tests agree well with their experimental counterparts. However, comparing the simulation and experimental results show that modification of the elastic modulus alone to incorporate surface changes experienced due to pore fluid saturations, which is the primary parameter considered in proppant embedment studies may provide an underestimation for proppant embedment measurements in coal.

In situ high-energy X-ray study of deformation mechanisms in additively manufactured 316L stainless steel

A key structural material planned to be used in the core of the Transformational Challenge Reactor is the additively manufactured 316L stainless steel (AM 316L SS). While the deformation of conventionally-manufactured 316 SS have been extensively studied, the deformation mechanism of AM 316L SS is less known. Here the room-temperature tensile behavior of AM 316L SS was studied in situ using high-energy X-ray diffraction and X-ray tomography. Diffraction yielded the lattice strains and the dislocation densities of the AM 316L SS, which were compared to those of a conventionally processed 316H SS. It was found that while the conventional 316H SS had three distinct deformation stages, namely stage II athermal hardening, stage III dynamic recovery, and stage IV, the AM 316L experienced only the stages III and IV after an initial transitional period. The plastic instability stresses (PIS), i.e. the true ultimate tensile strength, were nearly the same in both materials. The AM 316L had very low dislocation barrier strength throughout the plastic deformation, which, in combination with the invariant PIS, explained its high dislocation storage capability and the attractive combination of strength and ductility. Tomography revealed morphological changes of the built-in pores in the AM 316L during deformation and fracture, and it was concluded that large pores close to the surface might have significant roles in the necking stage.

Evolution of deformation mechanism and fluid flow in two pre-rift siliciclastic deposits (Pannonian Basin, Hungary)

Abstract Distinct stages of deformation and fluid flow-related diagenetic alterations are recorded in Lower Miocene sandstone and conglomerate of the Pannonian Basin, Central Europe. Multiple generations of structural elements (deformation bands, calcite dominoes and veins) as well as host rocks were investigated using petrographical, elemental and stable isotope geochemical methods together with fluid inclusion petrography and microthermometry. The integration of acquired structural and diagenetic data into a subsidence model constrains the spatial and temporal evolution of deformation mechanisms and diagenetic processes. The six investigated sites represent central and marginal areas during both the pre-rift and syn-rift phases of basin evolution. The elements of pre-rift phases were preserved at the eastern margin, where eogenetic calcite precipitated in the host rocks and in the early types of deformation bands. Their δ18OPDB isotope values from −4.3‰ to −1.9‰ paired with δ13CPDB isotope values from −3.8‰ to 1.8‰ refer to precipitation from connate marine and mixed marine and meteoric pore water. The syn-rift phases are represented by eogenetic calcite and start of shallow mesogenetic diagenetic alterations in marginal position as well as in the basin centre. The δ18OPDB and δ13CPDB isotope ratios in these calcites yielded values from −15.2‰ to −5.7‰ and from to −18.5‰ to -–1.6‰, respectively. The gradual depletion in heavy isotopes shows positive covariance as the deformation progressed in time. This trend is attributed to an increasing proportion of deeply circulating meteoric fluid. The sporadic fluid inclusion data confirm meteoric fluid contribution to certain carbonate cement phases. The distinguished calcite generations in pre-rift and syn-rift structural elements and host rocks were mainly related to the phases of intense subsidence that, together with the increased rift-related heat flow, warmed up the circulating fluids. The isotope values deviating from the general trend allow the recognition of local source of light carbon contribution to basin-wide fluid-flow evolution, and cannot be tied to the switch in tectonic settings from pre-rift compression to syn-rift extension.

Deformation of copper particles upon impact: A molecular dynamics study of cold spray

In this work, Molecular Dynamics simulations were performed to predict and provide detailed understanding of the deformation behavior of solid copper particles accelerated against a copper substrate. Simulations were carried out at an initial particle/substrate temperature of 300 K. The particles were assigned an initial velocity of 1000 m/s normal to the substrate surface, oriented in the [1 1 1] direction. The particles diameter was varied from 5 to 40 nm in order to assess changes in the deformation behavior due to size effects. For particles with diameters larger than 10 nm, the results showed well-defined patterns of dislocation activity associated with three distinct stages of deformation. The onset of plastic strain was localized at the flattened particles bottom, in the region of contact with the substrate, and characterized by the heterogeneous nucleation of Shockley partial dislocations. In the subsequent stage, a dense dislocation network was formed in the lower half of the particles, while the top of the particles remained undeformed. The plastic deformation of the top of the particles completed the process, resulting in the final flattened splat shape. High temperatures (above 1000 K) were observed at the particle-substrate interface, where fluid-like flow contributed to the formation of material jetting.

Microstructure and Compressive Properties of Al/Al<sub>2</sub>O<sub>3</sub> Syntactic Foams

Metal matrix syntactic foams with relativity low density (2.03 g/cm3) were prepared by stir casting method. The syntactic foam is comprised of alumina hollow spheres with a diameter range of 1.0-1.5 mm as reinforcement and ZL111 aluminum alloy as matrix. Calcium particles are used to increase the viscosity of the melt to ensure that low density hollow spheres are immersed in the melt. Microstructure characteristics and quasi-static compressive properties of syntactic foams were studied. The hollow spheres were uniformly distributed in the aluminum matrix, and the interface between them was in continuous contact. Compressive stress-strain curve exhibits three distinct stages of deformation: (i) the linear elastic stage; (ii) the plateau area; (iii) final densification stage. The compression strength and plateau stress are 85 MPa and 75 MPa, respectively. The main reasons for the sample failure are the collapse of hollow spheres and the formation of multiple shear bands.

Structure of Masuleh Shear Zone: Evidence for Early–Middle Jurassic Dextral Shear Along Paleo-Tethys Suture Zone in the Western Alborz, NW Iran

The Paleo-Tethys suture zone in northern Iran was formed when the Paleo-Tethys Ocean, (between Gonwana-derived Alborz Microcontinent and the Turan Plate), closed during the Eocimmerian orogeny and after they collided together in the Mid-Late Triassic. The NW-striking Boghrov-Dagh basement Fault Zone that lies in the vicinity of Masuleh village and the southern boundary of Gasht Metamorphic Complex is a part of the Eocimmerian suture zone in the Western Alborz. Along this part of the suture zone, tourmaline leucogranites intruded in metamorphic rocks. We recognize three distinct deformation stages (D1 to D3) in the study area especially in the Masuleh Shear Zone. D1 which was synchronous with formation of the main metamorphic minerals, such as sillimanite and staurolite under medium- to high-grade metamorphic conditions probably during the Hercynian event and a NE-directed shortening. The slaty cleavage in metamorphosed Upper Paleozoic rocks and crenulation cleavage and folds in the older rocks were produced due to D2 deformation during the Eocimmerian event under greenschist facies conditions. The Masuleh Shear Zone formed as a result of a ductile strike-slip shear during the Early-Middle Jurassic Mid-Cimmerian D3 event with a pure dextral to transtension shear sense at low to locally medium-grade conditions. All of the D3 structural features agree with a NNW-directed compression and an ENE-directed extension caused by overall dextral shear parallel to the Masuleh shear zone and the Boghrov-Dagh Fault Zone. Based on the available evidence, especially cross-cutting relationships between structural fabrics and rock units, emplacement of the Gasht-Masuleh leucogranites occurred after the D2 collisional event coeval to the possible slab break-off and before the D3 event, between Eocimmerian and Mid-Cimmerian movements.

The Combined Effect of Particle Size Distribution and Relative Density on the Large Strain Behavior of Sandy Soils

Sandy soils were investigated by means of a new ring shear device to understand the combined effect of particle size distribution and relative density on the soils’ deformation characteristics at large strains. The soils were sheared in undrained condition to at least 10 m to observe their responses before and after the attainment of steady state. Two main responses—purely contractive and partially contractive—were identified. Loose specimens were purely contractive and mobilized peak strength at small strains before undergoing rapid loss of shear resistance until steady state strength was achieved. On the contrary, dense soils exhibited partially contractive behavior by first contracting and then dilating as shearing progressed. Analyzed shear resistance-pore pressure relationships indicated that changes in relative density induced corresponding changes in dilation characteristics. The shear behavior of the soils at critical density demarcated the behavior of the loose from that of the dense soils. At densities below the critical, the specimens exhibited purely contractive behavior, and above the critical, the specimens’ behavior was defined by three distinct stages of deformation of phase transformation, peak and steady states. A comparison of the friction angle at phase transformation, steady state and critical state in all the soils revealed only little difference. At a given normal stress, the friction angle at phase transformation was equal to the friction angle at steady state in specimens at critical density. This study shows that the large strain behavior soils can offer valuable insight on the mechanism of rapid, long-travel slope movements that are often catastrophic.

Carbon nanotubes kirigami mechanical metamaterials.

Imparting elasticity and functionality to materials is one of the key objects of materials science research. Here, inspired by the art of kirigami, mechanical metamaterials comprising carbon nanotubes (CNTs) are hypothetically constructed. Using classical molecular dynamics (MD) simulations, a systematic study of the elastic limit, extensibility and yield stress of as-generated CNTs kirigami (CNT-k) is performed. Three designated kirigami patterns are employed to achieve high stretchability of CNTs. It is shown that CNT-k typically exhibits three distinct deformation stages, of which the first stage, which is referred to as geometric deformation, contributes quite a high proportion of the ductility. Various geometric parameters of CNT-k that influence the key mechanical properties of interest are respectively discussed. Three types of CNT-k with specifically identical geometric parameters exhibit distinct mechanical characteristics. This study provides an interesting example of interplay between the geometry, ductility, and mechanical characteristics of tubular materials.

New models to predict rock failure by linking the volume dilatant point with the peak stress point

The rock mass failure process can be divided into several distinct deformation stages: the compaction stage, elastic stage, stable failure stage, accelerated failure stage, and post-peak stage. Although each stage has been well studied, the relationship among the stages has not been established. Here, we establish two models which are the Strain model Q and Energy density model S by using the renormalization group theory and investigate the mechanical relationship between the volume dilatant point and peak stress point on the rock stress-strain curve. Our models show that the strain ratio (e f /e c ) and energy ratio (E f /E c ) at the volume dilatant point and peak stress point are solely functions of the shape parameter m. To verify our models, we further studied the failure process of rock specimens through several uniaxial compression experiments and found that the relationship between e f /e c or E f /E c and m shares a notably similar pattern to that from our theoretical model. However, the e f /e c and E f /E c values in our experiments are slightly smaller than those predicted by the models. In brief, we demonstrate that our models can be used to predict the failure process of the laboratory-scale hard brittle rock samples.

Experimental investigation of the conditions at which the collapse line coincides with the critical state line

The conditions at which the collapse line coincides with the critical state line were investigated by means of a new ring shear device. Natural and artificially constituted sands were tested in undrained conditions to evaluate their responses to variations in relative density. The collapse and critical state lines merged in specimens at the critical density in which the shear resistance and pore pressure briefly reached a condition of zero rate of change and remained momentarily constant and equal. At a given normal stress, the friction angle at the phase transformation was equal to the friction angle at the steady state in specimens at the critical density. At densities below the critical density, the specimens exhibited purely contractive behaviour; above the critical density, the specimens’ behaviour was defined by three distinct stages of deformation of phase transformation, peak and steady states. A comparison of the friction angle at the phase transformation, steady state and threshold state in all of the soils revealed only slight differences.

Mechanical Behavior of Spray-Coated Metallic Laminates

Thermal spray (TS) coatings have been extensively utilized for various surface modifications such as enhancing wear/erosion resistance and thermal protection. In the present study, a new function of TS material is explored by studying its load-carrying capability. Due to the inherent microstructures containing voids and interfaces, it has been presumed TS materials were not suitable to bear loads. However, the recent advances in TS technology to manufacture near fully dense TS coatings have expanded their potential applications. In the current experiments, TS nickel coatings are deposited onto metallic substrates, and their mechanical behaviors are closely examined. Based on the measured data, the estimated elastic modulus of TS Ni is about 130 GPa (35% less than bulk value), and the maximum tensile strength is about 500 MPa (comparable to bulk value). It was found that such a high value is attainable because the coating is deposited onto a substrate, enabling a load-transfer mechanism and preventing coating failure at a much lower stress level. Three distinct deformation stages are identified to describe this behavior. Such a clarification is critical for enabling TS process to restore structural parts as well as to additively manufacture load-bearing components.

Kinematic Analysis of Fault-Slip Data in the Central Range of Papua, Indonesia

DOI:10.17014/ijog.3.1.1-16Most of the Cenozoic tectonic evolution in New Guinea is a result of obliquely convergent motion that ledto an arc-continent collision between the Australian and Pacific Plates. The Gunung Bijih (Ertsberg) Mining District(GBMD) is located in the Central Range of Papua, in the western half of the island of New Guinea. This study presentsthe results of detailed structural mapping concentrated on analyzing fault-slip data along a 15-km traverse of theHeavy Equipment Access Trail (HEAT) and the Grasberg mine access road, providing new information concerning thedeformation in the GBMD and the Cenozoic structural evolution of the Central Range. Structural analysis indicatesthat two distinct stages of deformation have occurred since ~12 Ma. The first stage generated a series of en-echelonNW-trending (π-fold axis = 300°) folds and a few reverse faults. The second stage resulted in a significant left-lateralstrike-slip faulting sub-parallel to the regional strike of upturned bedding. Kinematic analysis reveals that the areasbetween the major strike-slip faults form structural domains that are remarkably uniform in character. The changein deformation styles from contractional to a strike-slip offset is explained as a result from a change in the relativeplate motion between the Pacific and Australian Plates at ~4 Ma. From ~4 - 2 Ma, transform motion along an ~ 270°trend caused a left-lateral strike-slip offset, and reactivated portions of pre-existing reverse faults. This action had aprofound effect on magma emplacement and hydrothermal activity.

铝合金正四面体点阵夹芯材料准静态压缩行为研究

本文通过冲压折叠法制造6061铝合金正四面体点阵夹芯芯体结构，采用钎焊连接面板及芯体，研究了相对密度为0.05正四面体点阵夹芯材料在T6、T7及退火三种不同热处理状态下的准静态压缩(初始应变速率为10−3 S−1)行为。研究结果表明：准静态压缩应力应变曲线均表现为三个明显的变形阶段，即线弹性阶段、较长的屈服阶段及致密化阶段，致密化应变为0.4；能量吸收主要发生在芯体剧烈的塑性变形阶段即较长的屈服阶段，吸能量T6态大于T7态，退火态最低；吸能效率由材料的塑性及强度共同决定，吸能效率T7总是大于T6，退火态开始最小，最后处于两者之间。 Tetrahedral lattice truss structures have been made by folding perforated 6061 aluminum alloy sheets. Simple air brazing was used to construct sandwich panels with cellular core; relative density was 0.05. The behavior of quasi-static compression (initial strain rate is 10−3 S−1) was studied in the present study, and three kinds of heart-treatment were investigated, which were T6, T7 and anneal. The results showed that: three distinct stages of deformation show in quasi-static compressive stress-strain curves, namely the linear elastic stage, the longer yield stage and the stage of densification, and densification strain is 0.4; energy absorption mainly occurs in the stage of longer yield, in which severe plastic deformations occur, and the energy absorption of T6 is higher than T7, while the anneal is the lowest; energy absorption efficiency is determined by the material plasticity and strength, and the energy absorption efficiency of T7 is greater than T6, while the annealed state is minimum at the beginning, and finally between T6 and T7.

Post-Laramide, Collapse-Related Fracturing and Associated Production; Wind River Basin, Wyoming

The mechanisms and timing of fracturing are important parameters to predicting intensely fractured trends with enhanced reservoir permeability and production potential. Fracture analyses were used to test hypotheses for the structural development of the Wind River Basin in Wyoming that include: 1) pre-Laramide regional compression; 2) Laramide ENE-WSW horizontal compression and left-slip faulting; and 3) multiple post-Laramide hypotheses: a) near-surface mechanisms; b) regional extension due to a variety of causes; and/or c) localized extensional reactivation and backsliding of thrust faults during release of compression and collapse of basin-bounding arches. Fracture data collected from Cambrian- to Eocene-aged formations throughout the basin included 1,900 joints and minor faults measured at 45 outcrop stations and 14,775 fractures compiled from 39 micro-resistivity image log interpretations. Inferred stress axes were calculated using eigenvector averaging and show two distinct stages of deformation: 1) Laramide ENE-WSW horizontal shortening followed by 2) post-Laramide extension consistent with modern stresses. Post-Laramide fractures in the basin parallel NW-SE striking joints observed across the Rocky Mountain foreland, except in the vicinity of E-W trending basin-bounding arch margins where these fractures closely parallel arch-bounding thrust faults. Fracture analyses are consistent with Laramide shortening followed by localized extension in proximity to both basin-bounding master thrusts and smaller productive structures in the basin. Seismic-based models show backsliding on these thrusts related to arch/anticline collapse. Recent wells at Frenchie Draw gas field have high initial production rates and probably intersected off-structure, intensely fractured trends along the margins of what appears to be a collapsed anticline.

Geochronological constraints on the Hartbees River Thrust and Augrabies Nappe: New insights into the assembly of the Mesoproterozoic Namaqua-Natal Province of Southern Africa

The region around Augrabies in the Namaqua sector provides insights into the processes that formed the Namaqua-Natal tectonic Province. Progressive ductile shear deformation during the long lasting Namaqua Orogeny was coeval with the global Grenvillian Orogeny. The Mesoproterozoic Namaqua-Natal Province is composed of severely deformed and metamorphosed rocks in terranes bounded by major thrust and shear zones. The interpreted research results deal with events around the Hartbees River Thrust, a suture zone where the granulite grade Grünau (Kakamas) terrane was overthrust onto the amphibolite grade Bladgrond (Bushmanland) terrane. The series of distinct deformation stages D1–D6 that have been identified during previous research in the western regions of the Namaqua sector, is also discernible in the study region around Augrabies. Microbeam geochronological techniques were used to date zircons from four samples of a granitic rock (the Karama’am Augen Gneiss) intrusive into the Hartbees River Thrust zone, and of a sample of granite (the Augrabies Granite) from the core of a large allochthonous sheath fold nappe in the Grünau terrane. The mean crystallisation age of the Karama’am intrusive is 1108±4Ma and of the Augrabies Granite 1168±6Ma. The sheath fold core of the latter granite is enclosed in the sheetlike Rooipad Granite (Riemvasmaak Granite) previously determined to be 1155±7Ma. Crustal residence times deduced from Lu–Hf isotopic compositions of zircon cores and xenocrysts, cluster around 1710Ma for the Augrabies Granite and about 200Ma older for the Karama’am Granite Gneiss (with the oldest date at 2069Ma). Collectively the available data enable reconstruction of the sequence of Namaqua Orogeny deformation stages: terrane assembly (D1) at ∼1195Ma with metamorphism at 1191±12Ma, pervasive folding and thrusting (D2) at 1168±6Ma, formation of major sheath and coaxial folds (D3) at 1155±7Ma, late open folds (D4) at 1090±16 and a late metamorphism (coeval with major shear zones D5–D6?) at 1018±11 to 1024±14Ma.

Geodynamic setting and emplacement of mylonitic granitoids within the North Golpayegan shear zone, Iran

The metamorphic complex of the North Golpayegan is part of the Sanandaj-Sirjan Zone. There are at least three distinct stages of deformation in this complex. Throughout the first stage, Paleozoic and Mesozoic sedimentary rocks have experienced regional metamorphism during Late Jurassic tectonic events related to the subduction of the Neo-Tethys oceanic lithosphere under the Iranian microcontinent. During the second deformation stage in the Late Cretaceous-Paleocene, the rocks have been mylonitized. The third stage of deformation in the region has led to folding and faulting superimposed on previous structures, and to exhumation of the metamorphic complex. This stage has determined the current morphology and N70E strike of the complex.

Yield behaviour associated with stacking faults in a high-temperature annealed ultra-low carbon high manganese steel

This paper investigated the tensile behaviour of high-temperature annealed ultra-low carbon high manganese steel with 42vol% delta-ferrite. The results show that the tensile stress-strain curve of plastic deformation exhibits three distinct stages of deformation: a yielding stage with a remarkably large elongation and a positive strain-hardening rate, a second stage in which the strain-hardening rate rapidly increases, and a third stage in which the strain-hardening rate slowly increase. The yield plateau is intrinsically associated with the increasing formation of strain-induced stacking faults. The stacking faults quickly form during yield deformation, and the yield elongation monotonically increases with the extent of the stacking faults. The localised strain concentration of delta-ferrite and the heterogeneous strain partitioning between harder delta-ferrite and softer austenite play important roles in the rapid formation of stacking faults during strain at the yield plateau, which is an important prerequisite for this yielding phenomenon. The results and analysis demonstrate that the rapid and then slow hardening deformation after the yield plateau result from strain-induced transformation and deformation twinning, respectively.

Sequence of distinct microyielding stages of the monocrystalline nickel-base superalloy CMSX-6 at high temperatures

Abstract The microyielding behaviour of the monocrystalline nickel-base superalloy CMSX-6 has been studied experimentally in tensile tests up to small strains at 900 °C, 1000 °C and 1100 °C and by transmission electron microscopy of the deformed specimens. Inspection of the microyielding stress-strain curve with highly resolved plastic strain showed four distinct stages of deformation at the lowest temperature (900 °C) but not at the two higher temperatures. By considering the superposition of the external stress with the original coherency stresses and with the deformation-induced internal stresses and by inspection of the electron micrographs, these deformation stages could be assigned to successive dislocation glide processes in the horizontal and vertical -channels and, finally, in the ′-particles.