Localization Of Shear Deformation Research Articles

In-situ rock shattering and strain localization along a seismogenic fault in dolostones (Monte Marine fault, Italian Central Apennines)

In-situ shattered rocks are often associated with seismogenic fault zones, but their mechanism of formation is still matter of debate, partly because of the limited number of field studies. Here we describe the characteristics of in-situ shattered rocks distribution along the NW-SE-striking seismogenic Monte Marine Fault (MMF) in the Italian Central Apennines. In the studied area, the MMF cuts through Mesozoic carbonates, is exhumed from <3 km depth and consists of two >5 km-long major hard-linked segments with normal kinematics. The linkage between the two fault segments occurs along a ∼2 km-long step-over zone with E-W trending faults and oblique-slip kinematics. To the northwest, fault-related shear deformation is localized in a ∼5 m-thick cataclastic fault core and off-fault deformation is dominated by in-situ shattered rocks up to ∼40 m-thick. Instead, in the step-over zone to the southeast, the in-situ shattered rocks are up to ∼500 m thick, particularly where MMF crosscuts older low-angle thrust faults.We integrated detailed field structural surveys with microstructural and grain size distribution analyses of the fault rocks to assess the mechanism of (1) formation of in-situ shattered rocks and, (2) progressive localization of shear deformation along the MMF. The obtained results, after the viability of several formation mechanisms (mechanical models) have been reviewed, support the hypothesis that the formation of in-situ shattered rocks was associated with the propagation of (multiple) seismic ruptures (mainshocks and aftershock sequences) within a mechanically heterogeneous fault zone. Heterogeneity is due to the occurrence of preexisting damage related to previous earthquakes, but also inherited from the older low-angle thrust faults. Therefore, we suggest that the origin of these shattered rocks is more compatible with seismic related processes than only with quasi-static fault growth models. On the other hand, the cataclastic fault core derived from the progressive accommodation of shear deformation within the in-situ shattered rock volumes during several seismic cycles. We conclude that the large volumes of in-situ shattered rocks are the result of seismic-related dissipative processes in a geometrically and mechanically heterogeneous fault zone. In this scenario, large volumes of in-situ shattered rocks are compliant low velocity zones which can influence the propagation of earthquake ruptures.

Anomalous strain rate dependence of ultra-low temperature strength and ductility of an electron beam additively manufactured near alpha titanium alloy

The strain rate (ε˙) dependence of ultra-low temperature strength and ductility was investigated systematically on a cryogenic near alpha titanium alloy Ti-3Al-3Mo-3Zr-0.2Y additively manufactured by electron beam selective melting (EBSM). As ε˙ increases under quasi-static tension at 77 and 20 K, ductility monotonically decreases when yield strength (YS) keeps ascending. As ε˙ increases from 5.6 × 10–4 s−1 once by one order of magnitude, elongation-to-fracture declines from 20.0 % to 16.5 % and 15.7 % at 20 K. However, unlike the regular monotone increase at 298 and 77 K, ultimate tensile strength (UTS) at 20 K rises to 1460 MPa first then drops to 1320 MPa. This study further examined how strain rate affects slipping, twinning and strain hardening behavior. The monotone increase in YS is primarily attributed to the increased CRSS for slips and the enhanced tendency of pyramidal 〈a〉 and 〈c + a〉 slipping and <101¯0 > 34° twinning at 20 K. On the other hand, the monotone decrease of ductility is essentially ascribed to the intensified deformation localization characterized by micro shear bands, multiple necking and single necking. More importantly, the mechanisms of abnormal UTS variation and disappearance of serration flow at 20 K are discussed in terms of strain hardening levels, degree of shear deformation localization and the interaction of slips and twins. This study provides deep insights into strain rate effect on cryogenic mechanical behavior of EBSM-built titanium alloy.

Deformation localization behavior research of AZ31 magnesium alloy under impact load

The dynamic mechanical properties of AZ31 magnesium alloys were analyzed under different strain rates by using a separated Hopkinson pressure bar system. The microstructure of the specimens was observed by optical microscopy. The results show that the dynamic yield strength of AZ31 magnesium alloy is insensitive to the strain rate. The compressive strength is increasing and shear deformation localization behavior is more obvious with the increase in the strain rate. Meanwhile, the temperature within the shear band is about 241 k and meets the twinning dynamic recrystallization temperature. Temperature rise promotes the grain refining effect.

In-Plane Shear Characterization of Unidirectional Fiber Reinforced Thermoplastic Tape Using the Bias Extension Method

Through an improved characterization methodology, this work contributes to better prediction quality in composite forming simulations for unidirectional thermoplastic composites. A better understanding of the forming behavior will aid in the adoption of these lightweight materials in aerospace applications. The bias extension method was implemented and applied to cross-ply laminates from unidirectional carbon fiber reinforced thermoplastic materials to characterize the in-plane shear deformation resistance of the molten material. Two commercially available materials were characterized at three rates and three temperatures. The shear deformation was measured directly on the specimen throughout the test using a video extensometer, avoiding the use of the pin-jointed net assumption to relate deformation to the clamp displacement. In addition, the distribution of shear deformation over the specimen surface was characterized after the test using image analysis. The observed deformation was similar to the typical deformation for woven materials, with some agreement to the pin-jointed net assumptions but also some identified deviations. Localization of shear deformation along the fiber direction of the outer ply was observed to occur at approximately 15° shear angle. The proposed bias extension method directly relates the measured force to the deformation on the specimen, ensuring the characterization of the correct deformation mechanism. This key benefit of the bias extension method solves a common issue found in other characterization methods for in-plane shear on the molten material.

Cutting deformation mechanism of SiCp/Al composites based on strain gradient theory

More and more experiments have shown that particle-reinforced metal matrix composites (PMMC) exhibit obvious size effects. The aclassic plasticity theory does not contain internal length scale and cannot explain this size effect. In this paper, based on the Taylor relationship, the concept of "geometrically necessary dislocations" and the mechanism of dislocation multiplication, slippage and extinguishing, a constitutive equation for SiCp/Al composites related to strain gradient is established. The established equation is imported into Abaqus for simulation by writing a user subroutine Vumat. Combining the simulation and experimental results, the effects of stress, temperature, cutting force, strain gradient effect and its dimensional effect on cutting deformation during machining SiCp/Al composites are analyzed from the perspectives of material micro-plasticity mechanics and material dislocation theory. The results show that the presence of SiC particles changes the microstructure of the matrix material, and induce a high strain gradient in the matrix. This high strain gradient makes the material more prone to shear deformation localization. In the cutting process, the defects and breakage of the SiC particles themselves will lead to the formation of micro-cracks. The growth of micro-cracks in the shearing area is an important factor in the generation of chips. By comparing the simulation results with the experimental results, the modified constitutive model is closer to the experimental results, indicating that the established theoretical model based on the strain gradient can better reflect the cutting process of particle-reinforced metal matrix composites.

Characterization of piercing damage in CFRP cross-ply laminates after punch shear machining via impact loading

In industrial processes, piercing and trimming are essential because composite structures are usually manufactured in a near-net shape to reduce machining operations. Punching and shear cutting using out-of-plane shear loading are expected to increase productivity. Nevertheless, little is known about the effects of such operations on polymer-matrix composites. This study presents on the characterization of piercing damage in typical carbon fiber reinforced plastic (CFRP) cross-ply laminates [0°2/90°2]s after punching using quasi-static (QS) and drop-weight impact (DWI) loadings. During QS punching, the upper and lower ply interfaces delaminate due to the high shear stress to cut fibers and gradual shear deformation in the middle ply; however, during DWI punching at a low impact velocity, delamination of the lower ply interface can be reduced due to the localization of shear deformation, as compared to that in QS punching. Finally, the damage accumulation process during DWI punching is discussed.

Influence of shear wave on the HCP nucleation in BCC iron under oblique shock conditions

The HCP nucleation in single crystal iron under oblique shock loading is investigated based on atomistic simulations. The stress profile and microstructure analysis reveal that the critical pressure of HCP nucleation is effectively reduced by applying the shear wave, and even the HCP nucleation can take place below the BCC-HCP equilibrium pressure. Under normal shock, the stress and energy distributions show some difference in the mixed phase, while the introduction of shear wave will change this difference as expected. The second HCP nucleation occurs under the specific strain constraint, which promotes the formation of HCP twins and results in shear deformation localization at the same time. Besides, the shear wave can either increase or reduce the potential barrier of the HCP nucleation, dependent on the shock intensity and shear direction, which indicates the over-pressure of HCP nucletion can be significantly reduced under some strong shear loading. The HCP nucleation stress threshold will first experience a linear change and undergo a significant reduction when the shear instability occurs.

Micro-Mechanisms of Shear Deformation Localization of Ti6Al4V Alloy under Shear-Compressive Loading Conditions.

Titanium Ti6Al4V alloy is a superior material that has extremely high strength, hardness and good anti-corrosion resistance. Dynamic shear-compression experiments were carried out on the alloy to investigate the micro-mechanisms of adiabatic shear banding (ASB) formation. The split Hopkinson pressure bar (SHPB) setup were used for the tests at high strain rates. It was found that the shear deformation localization (SDL) was considerably affected by the complex loading conditions. The micro-mechanisms for the ASB formation relied on different shear compressive proportion of loadings (SCLPs). Scanning electron microscope (SEM) observations showed that the ASB width was related with the SCLP and the fracture failure of alloy was induced by the nucleation and growth of microvoids. In transmission electron microscope (TEM) analysis, the microstructural changes of material within the ASB were characterized by dynamic recrystallization (DRX) and twining grain formation, dislocation migration, and stacking and grain refining processes. The results in this article demonstrates a complex image of microstructural evolution of alloy in the shear localization process.

Особенности массопереноса при ионной имплантации

Исследованы продукты реакции, полученные при ионной имплантации азота, кислорода и фосфора в вольфрамовую мишень. Выяснены условия создания новых соединений при высокодозной имплантации, приводящей к процессам быстрого массопереноса ионов в материал мишени. Установлено, что ионная имплантация азота в вольфрам приводит к возникновению фазы внедрения W2N с ГЦК-структурой; имплантация кислорода — к образованию фазы с плотноупакованной ГЦК-структурой, близкой по структуре и параметрам к W20; фосфора — к образованию фосфида вольфрама W2P с орторомбической структурой после дополнительного отжига при температурах, превышающих 800-900 0С. Сделана оценка локального давления потока ионов на поверхность мишени, которое приводит к локальному искривлению кристаллической решетки, благодаря чему возможен быстрый массоперенос имплантированных ионов в материале мишени.&#x0D; Образование фаз внедрения при ионной имплантации является результатом локализации сдвиговой деформации в условиях ускоренного массопереноса. В условиях высокодозной ионной имплантации формируются высоконеравновесные пересыщенные твердые растворы, а также высокодефектные структурно-неравновесные состояния с высокой кривизной кристаллической решетки.

MD simulation of stress-assisted nanometric cutting mechanism of 3C silicon carbide

Purpose This paper aims to reveal the mechanism for improving ductile machinability of 3C-silicon carbide (SiC) and associated cutting mechanism in stress-assisted nanometric cutting. Design/methodology/approach Molecular dynamics simulation of nano-cutting 3C-SiC is carried out in this paper. The following two scenarios are considered: normal nanometric cutting of 3C-SiC; and stress-assisted nanometric cutting of 3C-SiC for comparison. Chip formation, phase transformation, dislocation activities and shear strain during nanometric cutting are analyzed. Findings Negative rake angle can produce necessary hydrostatic stress to achieve ductile removal by the extrusion in ductile regime machining. In ductile-brittle transition, deformation mechanism of 3C-SiC is combination of plastic deformation dominated by dislocation activities and localization of shear deformation. When cutting depth is greater than 10 nm, material removal is mainly achieved by shear. Stress-assisted machining can lead to better quality of machined surface. However, there is a threshold for the applied stress to fully gain advantages offered by stress-assisted machining. Stress-assisted machining further enhances plastic deformation ability through the active dislocations’ movements. Originality/value This work describes a stress-assisted machining method for improving the surface quality, which could improve 3C-SiC ductile machining ability.

Effect of Texture on Mechanical Properties of AZX612 Magnesium Alloy Processed by Friction-Assisted Extrusion

Since magnesium alloys are lightweight, they are expected to be promising as structural materials, particularly in transportation. However, because a strong basal texture is prone to develop parallel to the sheet plane in wrought products, formability at room temperature is poor. In this study, to control the basal texture of AZX612 magnesium alloy and to improve its formability, a lateral extrusion method, namely, friction-assisted extrusion (FAE), was applied, and the microstructure, texture, and mechanical properties were investigated. The FAE process was carried out with the extrusion ratios ranging from 4 to 20 at temperatures of 300 and 350 ℃. The results showed that FAE changes the basal texture of the starting as-rolled material into that inclined by about 15° against the extrusion direction and raises the intensity of texture. The 0.2 % proof stress became significantly smaller than that of the as-rolled material in the extrusion direction but larger in the transverse direction, resulting in the larger anisotropy. This can be understood by the activity of basal slip. Elongation to failure was smaller under all extrusion conditions than in the as-rolled material, which was presumed to be caused by the localization of shear deformation.

Effects of work hardening rate on formation of nanocrystallized subsurface layer in Cu alloys

The effects of the work hardening rate on the formation of a nanocrystallized subsurface layer by sliding wear for pure Cu and Cu–Ge alloys are investigated. The nanocrystallized subsurface layer is called the wear-induced layer (WIL). The work hardening rates of the Cu–Ge alloys increase with Ge concentration. By sliding wear, the WIL is formed around a worn surface in all the specimens. The thickness of the WIL decreases with increasing Ge concentration. This means that a thinner WIL is formed in a specimen with a higher work hardening rate. The equivalent Hencky strain required to form the WIL is about 5 regardless of the work hardening rate of the specimen. In addition, a larger strain gradient is generated just below the WIL in the specimen with a higher work hardening rate. This decrease in the thickness of the WIL depending on the work hardening rate of the specimen can be explained by the localization of shear deformation around the worn surface.

Numerical Modeling of Failure Process of Soil Slopes

AbstractA finite-element analysis program was developed to analyze the progressive failure of a soil slope based on the progressive failure mechanism. The shear element was developed to comprehensively characterize the shear zone, which describes the soil shear deformation localization of progressive failure. The formulation of the shear element was derived using a format similar to that of the soil-structure interface element and incorporated into the traditional FEM to macroscopically simulate the deformation and failure processes of the slope. A series of algorithms, including the combination and transformation of the shear element and the entity element, were proposed to obtain the full solutions for the progressive failure of soil slopes. The simulation results using the developed program for the slip surface, failure process, and displacement distribution match the observations of centrifuge model tests well.

Multiscale Localization of Shear Deformation in Single Crystals of the Ni3Fe Alloy with Short-Range Atomic Order

Results of a quantitative study of multilevel, hierarchically organized localization of shear deformation attendant to compression of a Ni3Fe single crystal are presented. A statistical analysis of the results is performed and values of the characteristics of localization of shear deformation at selected scale-structure levels are obtained.

Effects of hydrogen on tensile properties and fracture surface morphologies of Type 316L stainless steel

The effects of hydrogen on the tensile properties and fracture surface morphologies of Type 316L stainless steel were investigated using virgin and prestrained specimens. Hydrogen gas exposure at 10 MPa and 250 °C for 192 h resulted in its uniform distribution in the specimens. Such internal hydrogen degraded the tensile ductility of the specimens. Cup–cone fracture occurred in the non-, Ar-, and H-exposed specimens. The fracture surfaces were covered with large and small dimples. The H-exposed specimens exhibited larger small-dimple areas than the non- and Ar-exposed ones. The diameter of the large dimples decreased with increasing small-dimple area. Three-dimensional analysis of the dimples showed that the small-dimple regions were void sheets produced by local shear strain. Hydrogen accelerated nucleation of voids and formation of the void sheets by enhancing localization of shear deformation, thereby reducing the average size of the dimples.

AE Regularity of Coal Failure Shear Deformation Localization under Triaxial Dynamical Loading

Based on MTS-815.02 servo-controlled rock mechanics and acoustic emission (AE) integrated test system, the strength, shear deformation localization and damage AE-energy-rate characteristics process of coal specimen from Weihuliang Coal Mine under tri-axial loading were analyzed. A new model of Weibull distribution on the AE higher energy-rate emergence interval under tri-axial loading had been established, the total probability of coal sample localization failure in an interval is proposed. Then, the forecasting analysis of the coal fracture failure can be studied. The results indicate that the Weibull distribution of the AE higher energy-rate emergence were similar to the experimental results that measured. It is very important to the identification and ration prediction of coal failure in the mining.

Frictional strength of fault gouge in Taiwan Chelungpu fault obtained from TCDP Hole B

Three fault zones (FZB1136, FZB1194 and FZB1243) are found in core samples in Hole B borehole penetrating through the Chelungpu fault, central Taiwan that activated at the 1999 Taiwan Chi-Chi earthquake. Each fault zone is composed of a black gouge zone (BGZ) and a gray gouge zone (GGZ) surrounded by a fault breccia zone (BZ) and/or fracture-damaged zone (FZ). We conducted tri-axial friction experiments on samples collected from subzones of the above three fault zones under the 1 km depth ambient condition with axial shortening rates of 0.1 to 10 µm/s to investigate frictional strength and its velocity dependence. We found that the coefficient of friction is 0.3 for the BGZ at FZB1136 (1136BGZ), which is lower than those at other fault zones. This result indicates that fault slip at the Chi-Chi earthquake occurred at the 1136BGZ. The estimated frictional strength profile across FZB1136 was that the frictional strength was the lowest (the coefficient of friction was 0.3) for the BGZ and increased up to 0.5 for undeformed host rock with increasing distance from the BGZ. Presence of the intermediate frictional strength zone consisting of the GGZ and the BZ suggests a development of off-fault damage zone where deformation occurred not only in the BGZ but also in the intermediate zone. This feature should be important to estimate total fracture energy released during earthquakes. We also suggest that coefficients of friction and the velocity dependences of the samples are closely related to localization of shear deformation and clay content, respectively.

An analysis of the dynamic shear failure resistance of structural metals

The localization of shear deformation and the eventual rupture inside shear bands are analyzed experimentally. The shear failure resistance of several structural metals is compared. The materials studied are HY-80, HY-100, HSLA-80, 4340VAR, and Ti-6Al-4V. The evaluation of failure progression focuses on the evolution of both the stress-carrying capacities and material microstructures. Experiments show that despite its significantly stronger rate sensitivity, Ti-6Al-4V is more susceptible to shear localization and rupture compared with the steels, as demonstrated by its relatively early and precipitous loss of stress-carrying capacity. This observation is supported by measurements of the shear band and rupture lengths in specimens deformed to various stages of failure development. Among the steels, the martensitic microstructure of HY-100 seems to be responsible for its higher susceptibility to localization. While all the steels studied show very similar dynamic constitutive responses, their significantly different shear failure behaviors suggest that macroscopic thermal-mechanical descriptions alone are not sufficient to account for the shear failure in the form of combined localization of strain and the eventual rupture through the shear bands. Consequently, microstructural damage mechanisms should also be considered. © 1998 Elsevier Science Ltd. All rights reserved.

On laser-induced reverse plugging effect

A new kind of failure induced by long pulsed laser, named as reverse plugging effect (RPE), was experimentally observed in thin foil of brass. The whole failure process can be divided into three stages, namely thermal reverse bulging, shear deformation localization and reverse perforation. In this paper, a description of experimental and theoretical study on this newly discovered phenomenon is presented in detail.

FLOW AND SEGREGATION BEHAVIOR OF A TWO-PHASE MODEL CONCRETE AROUND BIFURCATING PIPE LINES

The objective of this research is to investigate the deformation and segregation process of fresh concrete as two-phase material around bifurcations in a pipe line network Visualized tests with model concrete simulating fresh concrete under idealized two-dimensional condition were carried out. By Lagrangian and Eulerian evaluations of aggregate phase with the use of an image analysis, the deformation and segregation of model concrete around bifurcations was clarified, which was highly affected by boundary conditions and liquid viscosity. High viscous liquid phase was found to relax the mutual interaction between aggregate particles and to unify the localization of shear deformation of aggregate phase around the bifurcation point.