scholarly journals Ductile Shear Bands in a Naturally Deformed Quartzite

1982 ◽  
Vol 5 (1) ◽  
pp. 1-17 ◽  
Author(s):  
D. Gapais ◽  
S. H. White
Keyword(s):  
Shear Band ◽  
Large Strain ◽  
Shear Bands ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Band Structures ◽  
Transmission Electron ◽  
Dynamic Recrystallisation ◽  
Ductile Shear ◽  
Quartz Fabrics

Microscale shear bands are features that often occur oblique to the mylonitic foliation in mylonites. This paper is concerned with such structures within a quartz-mylonite. Geometrical features, microstructures and fabrics associated with shear bands are described. Both optical and transmission electron microscopy have been used. It was observed that the development of shear bands is closely related to (i) the onset of dynamic recrystallisation during deformation, (ii) a change of bulk deformation within the mylonites from relatively homogeneous to inhomogeneous and (iii) a marked softening of the mylonite. Across shear bands, dominant deformation mechanisms change from a dislocation creep type to grain boundary sliding. This induces strong modification of quartz lattice preferred orientations. The asymmetry of quartz fabrics due to shear should generally be favoured by the development of shear band structures. Our results indicate that the production of ductile shear band structures helps to accommodate large strain deformations at low temperatures. Results also indicate that grain and sub-grain sizes are not affected by variations in strain rate.

scholarly journals Evolution of Quartz and Calcite Microstructures Exhumed From Deep Brittle-Ductile Shear Zones in the Southern Alps of New Zealand

2021 ◽  
Author(s):  
◽  
Matthew P Hill
Keyword(s):  
New Zealand ◽  
Grain Boundary ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Differential Stress ◽  
Alpine Fault ◽  
Ductile Shearing ◽  
Boundary Sliding ◽  
Ductile Shear

<p><b>Arrays of brittle-ductile shears exposed in the Southern Alps of New Zealand, haveprovided a superb natural laboratory for insight into the microstructural evolution of lowercrustal shear zones during exhumation. Shears are exposed in the central section of theSouthern Alps at Sam Peak, Chancellor Ridge, and Baumann Glacier in a zone ~2 kmwide that is located 6–8 km structurally above the Alpine Fault. An array ofsystematically spaced shear zones that formed by embrittlement and faulting ofquartzofeldspathic schist took place at the same time as ductile shearing of quartzcarbonateveins embedded within the schist. This study has used field-based structuralmapping along with optical microscopy and universal stage measurements ofcrystallographic preferred orientations (CPO) to resolve the shear zone kinematics andrheology. On the basis of these data, the strain path can be reconstructed for the shearedveins during their progressive deformation. This began with their incidence as backshearsat the base of the Alpine Fault ramp and ended with their subsequent recrystallisation,uplift, and exhumation.</b></p> <p>The near-vertical shear planes have mean orientation of 221@89 NW ± 1o (n =780). They are inferred to have formed as backshears accommodating uplift of the PacificPlate as it was translated onto the oblique footwall ramp of the Alpine Fault during lateCenozoic oblique convergence. Detailed fault offset transect surveys across the shears atChancellor Ridge and Baumann Glacier reveal a mean spacing between the shear zones of25 ± 5 cm (n = 410). Quartz-carbonate marker veins are displaced in a dextral west-sideupshear sense. Fault offset geometry and a consistent arrangement of mineral fibrelineations that decorate fault surfaces, indicate that the mean displacement vector pitches35o SW in the shear plane (trend and plunge of: 262, 35 ± 7o). Ductilely deformed markerveins have been subject to a mean displacement of 9.9 ± 1.4 cm (n = 344) and a meanfinite ductile shear strain of 4.8 ± 0.3 (n = 219). A strain-rate for the ductile deformationof the veins is estimated at 3 x 10-11 sec-1 based on the observed finite ductile shear strain,an escalator kinematic model, and assumptions about the width of the deforming zone.</p> <p>Five deformation phases have affected the sheared veins during their transport upthe fault ramp: 1) initial brittle faulting and ductile shearing; 2) grain boundary sliding ofmylonitic quartz in response to a post-ramping differential stress drop; 3) recrystallisationand grain growth; 4) renewed late-stage dislocation creep; and 5) semibrittle deformationand exhumation. In the schist, the shears initiated as planar brittle faults at lower crustal depths of~21 km at a temperature of 450 ± 50oC. They developed in a zone of transiently highshear strain-rates near the base of the Alpine Fault ramp. Dislocation creep caused a CPOof quartz and calcite to develop in sheared veins. Using the flow law of Hirth et al. (2001)and the estimated strain-rate, a differential stress of ~165 MPa is inferred for ductiledeformation of the veins. Near-lithostatic (λ = 0.85) fluid pressures would have causedthe rocks to undergo brittle failure, a situation that is confirmed by a late component ofbrittle deformation that over prints the ductilely sheared veins. Syntectonic quartz-calciteveins infill the shear fractures, and these themselves have been sheared. The deformationof the veins was not a simple shear process but one with triclinic flow symmetry. This isinferred from discordance between the shear direction and the near-vertical principleextension direction that is revealed by the pattern and symmetry of quartz and calcite CPOfabrics.</p> <p>After the shears move away from the ramp-step, grain boundary sliding (GBS)accommodated by solid-state diffusion creep is inferred to have affected quartz veins.</p> <p>This deformation mechanism takes place because of 1) the small 8 μm grain size inheritedfrom Phase 1; 2) the presence of fluid in the shear zone; and 3) a stress drop to ~22 MPathat followed the initial up-ramping. Quartz CPO fabrics in the sheared veins areremarkably weak considering their large shear strains. GBS is inferred to have been achief deformation mechanism that caused the weakening of quartz CPO fabrics in thehighly sheared sections of deformed veins. Calcite has also affected the quartz fabricstrength as those veins containing >5% calcite have very weak quartz CPO fabrics. Incontrast to quartz, the CPO fabrics for the co-existing calcite remained strong andcontinued to develop by dislocation creep.</p> <p>The third phase of deformation, a process that may have contributed to subsequentweakening of quartz CPO fabrics, was recrystallisation and grain growth to 126 μm and anequigranular-polygonal grain shape fabric. This fabric was overprinted by late-stagedislocation creep microstructures in the fourth deformation phase in response increaseddifferential stress encountered by the rocks at lower temperatures in the upper crust. Thefinal phase of deformation to affect the sheared veins was semibrittle deformation atdifferential stresses of <189 MPa and temperatures of 200–280oC as the rocks passedthrough the steady-state brittle-ductile transition zone at depths of 8–10 km before beingexhumed at the surface.</p>

scholarly journals Evolution of Quartz and Calcite Microstructures Exhumed From Deep Brittle-Ductile Shear Zones in the Southern Alps of New Zealand

2021 ◽  
Author(s):  
◽  
Matthew P Hill
Keyword(s):  
New Zealand ◽  
Grain Boundary ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Differential Stress ◽  
Alpine Fault ◽  
Ductile Shearing ◽  
Boundary Sliding ◽  
Ductile Shear

<p><b>Arrays of brittle-ductile shears exposed in the Southern Alps of New Zealand, haveprovided a superb natural laboratory for insight into the microstructural evolution of lowercrustal shear zones during exhumation. Shears are exposed in the central section of theSouthern Alps at Sam Peak, Chancellor Ridge, and Baumann Glacier in a zone ~2 kmwide that is located 6–8 km structurally above the Alpine Fault. An array ofsystematically spaced shear zones that formed by embrittlement and faulting ofquartzofeldspathic schist took place at the same time as ductile shearing of quartzcarbonateveins embedded within the schist. This study has used field-based structuralmapping along with optical microscopy and universal stage measurements ofcrystallographic preferred orientations (CPO) to resolve the shear zone kinematics andrheology. On the basis of these data, the strain path can be reconstructed for the shearedveins during their progressive deformation. This began with their incidence as backshearsat the base of the Alpine Fault ramp and ended with their subsequent recrystallisation,uplift, and exhumation.</b></p> <p>The near-vertical shear planes have mean orientation of 221@89 NW ± 1o (n =780). They are inferred to have formed as backshears accommodating uplift of the PacificPlate as it was translated onto the oblique footwall ramp of the Alpine Fault during lateCenozoic oblique convergence. Detailed fault offset transect surveys across the shears atChancellor Ridge and Baumann Glacier reveal a mean spacing between the shear zones of25 ± 5 cm (n = 410). Quartz-carbonate marker veins are displaced in a dextral west-sideupshear sense. Fault offset geometry and a consistent arrangement of mineral fibrelineations that decorate fault surfaces, indicate that the mean displacement vector pitches35o SW in the shear plane (trend and plunge of: 262, 35 ± 7o). Ductilely deformed markerveins have been subject to a mean displacement of 9.9 ± 1.4 cm (n = 344) and a meanfinite ductile shear strain of 4.8 ± 0.3 (n = 219). A strain-rate for the ductile deformationof the veins is estimated at 3 x 10-11 sec-1 based on the observed finite ductile shear strain,an escalator kinematic model, and assumptions about the width of the deforming zone.</p> <p>Five deformation phases have affected the sheared veins during their transport upthe fault ramp: 1) initial brittle faulting and ductile shearing; 2) grain boundary sliding ofmylonitic quartz in response to a post-ramping differential stress drop; 3) recrystallisationand grain growth; 4) renewed late-stage dislocation creep; and 5) semibrittle deformationand exhumation. In the schist, the shears initiated as planar brittle faults at lower crustal depths of~21 km at a temperature of 450 ± 50oC. They developed in a zone of transiently highshear strain-rates near the base of the Alpine Fault ramp. Dislocation creep caused a CPOof quartz and calcite to develop in sheared veins. Using the flow law of Hirth et al. (2001)and the estimated strain-rate, a differential stress of ~165 MPa is inferred for ductiledeformation of the veins. Near-lithostatic (λ = 0.85) fluid pressures would have causedthe rocks to undergo brittle failure, a situation that is confirmed by a late component ofbrittle deformation that over prints the ductilely sheared veins. Syntectonic quartz-calciteveins infill the shear fractures, and these themselves have been sheared. The deformationof the veins was not a simple shear process but one with triclinic flow symmetry. This isinferred from discordance between the shear direction and the near-vertical principleextension direction that is revealed by the pattern and symmetry of quartz and calcite CPOfabrics.</p> <p>After the shears move away from the ramp-step, grain boundary sliding (GBS)accommodated by solid-state diffusion creep is inferred to have affected quartz veins.</p> <p>This deformation mechanism takes place because of 1) the small 8 μm grain size inheritedfrom Phase 1; 2) the presence of fluid in the shear zone; and 3) a stress drop to ~22 MPathat followed the initial up-ramping. Quartz CPO fabrics in the sheared veins areremarkably weak considering their large shear strains. GBS is inferred to have been achief deformation mechanism that caused the weakening of quartz CPO fabrics in thehighly sheared sections of deformed veins. Calcite has also affected the quartz fabricstrength as those veins containing >5% calcite have very weak quartz CPO fabrics. Incontrast to quartz, the CPO fabrics for the co-existing calcite remained strong andcontinued to develop by dislocation creep.</p> <p>The third phase of deformation, a process that may have contributed to subsequentweakening of quartz CPO fabrics, was recrystallisation and grain growth to 126 μm and anequigranular-polygonal grain shape fabric. This fabric was overprinted by late-stagedislocation creep microstructures in the fourth deformation phase in response increaseddifferential stress encountered by the rocks at lower temperatures in the upper crust. Thefinal phase of deformation to affect the sheared veins was semibrittle deformation atdifferential stresses of <189 MPa and temperatures of 200–280oC as the rocks passedthrough the steady-state brittle-ductile transition zone at depths of 8–10 km before beingexhumed at the surface.</p>

Nanoindentation investigation of the mechanical behaviors of nanoscale Ag/Cu multilayers

2007 ◽  
Vol 22 (12) ◽  
pp. 3423-3431 ◽  
Author(s):  
S.P. Wen ◽  
R.L. Zong ◽  
F. Zeng ◽  
Y. Gao ◽  
F. Pan
Keyword(s):  
Deformation Mechanism ◽  
Shear Bands ◽  
Grain Boundary Sliding ◽  
Indentation Creep ◽  
X Ray Diffraction ◽  
Petch Relationship ◽  
Size Dependent ◽  
Transmission Electron ◽  
20 Nm ◽  
Hardness Values

The microstructure, hardness, elastic modulus, and indentation creep of Ag/Cu multilayers prepared by magnetron sputtering were investigated by x-ray diffraction, transmission electron microscopy, and nanoindentation. The hardness values obey the Hall–Petch relationship as the periodicity decreases to 20 nm. For multilayers with periodicity smaller than 20 nm, the Hall–Petch relationship breaks down and the hardness values saturate at about 4.6 GPa; moreover, there are shear bands formed around their indents and strain bursts occurring during the load-holding process of indentation creep. These results imply that there is a transition of the deformation mechanism in the region where the periodicity is equal to 20 nm. This transition of the deformation mechanism can be ascribed to grain-size-dependent competition between the dislocations-mediated plasticity and grain-boundary sliding-mediated plasticity.

scholarly journals In Situ Generated Shear Bands in Metallic Glass Investigated by Atomic Force and Analytical Transmission Electron Microscopy

Metals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 111
Author(s):  
Harald Rösner ◽  
Christian Kübel ◽  
Stefan Ostendorp ◽  
Gerhard Wilde
Keyword(s):  
Shear Band ◽  
Metallic Glasses ◽  
Local Density ◽  
Shear Bands ◽  
Tensile Tests ◽  
Band Formation ◽  
Atomic Force ◽  
Transmission Electron ◽  
Shear Front

Plastic deformation of metallic glasses performed at temperatures well below the glass transition proceeds via the formation of shear bands. In this contribution, we investigated shear bands originating from in situ tensile tests of Al88Y7Fe5 melt-spun ribbons performed under a transmission electron microscope. The observed contrasts of the shear bands were found to be related to a thickness reduction rather than to density changes. This result should alert the community of the possibility of thickness changes occurring during in situ shear band formation that may affect interpretation of shear band properties such as the local density. The observation of a spearhead-like shear front suggests a propagation front mechanism for shear band initiation here.

scholarly journals Shear Bands in Materials Processing: Understanding the Mechanics of Flow Localization From Zener's Time to the Present

2020 ◽  
Vol 72 (6) ◽  
Author(s):  
Koushik Viswanathan ◽  
Shwetabh Yadav ◽  
Dinakar Sagapuram
Keyword(s):  
Shear Band ◽  
Large Strain ◽  
Shear Banding ◽  
Shear Bands ◽  
Ex Situ ◽  
Materials Processing ◽  
Complex Flow ◽  
Band Formation ◽  
Full Field ◽  
Material Systems

Abstract Shear banding is a material instability in large strain plastic deformation of solids, where otherwise homogeneous flow becomes localized in narrow micrometer-scale bands. Shear bands have broad implications for materials processing and failure under dynamic loading in a wide variety of material systems ranging from metals to rocks. This year marks 75 years since the publication of Zener and Hollomon's pioneering work on shear bands (Zener and Hollomon, J Appl. Phys., 15, 22–32, 1944), which is widely credited with drawing the attention of the mechanics community to shear bands and related localization phenomena. Since this landmark publication, there has been significant experimental and theoretical investigation into the onset of shear banding. Yet, given the extremely small length and time scales associated with band development, several challenges persist in studying the evolution of single bands, postinitiation. For instance, spatiotemporal development of strain fields in the vicinity of a band, crucial to understanding the transition from localized flow to fracture, has remained largely unexplored. Recent full-field displacement measurements, coupled with numerical modeling, have only begun to ameliorate this problem. This article summarizes our present understanding of plastic flow dynamics around single shear bands and the subsequent transition to fracture, with special emphasis on the postinstability stage. These topics are covered specifically from a materials processing perspective. We begin with a semihistorical look at some of Zener's early ideas on shear bands and discuss recent advances in experimental methods for mapping localized flow during band formation, including direct in situ imaging as well as ex situ/postmortem analyses. Classical theories and analytical frameworks are revisited in the light of recently published experimental data. We show that shear bands exhibit a wealth of complex flow characteristics that bear striking resemblance to viscous fluid flows and related boundary layer phenomena. Finally, new material systems and strategies for reproducing shear band formation at low speeds are discussed. It is hoped that these will help further our understanding of shear band dynamics, the subsequent transition to fracture, and lead to practical “control” strategies for suppressing shear band-driven failures in processing applications.

scholarly journals An Insight into Amorphous Shear Band in Magnetorheological Solid by Atomic Force Microscope

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4384
Author(s):  
Mohd Aidy Faizal Johari ◽  
Asmawan Mohd Sarman ◽  
Saiful Amri Mazlan ◽  
Ubaidillah U ◽  
Nur Azmah Nordin ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Shear Band ◽  
Shear Bands ◽  
Test Duration ◽  
Phase Imaging ◽  
Force Microscopy ◽  
Atomic Force ◽  
The Matrix ◽  
Relaxation Stress ◽  
Band Deformation

Micro mechanism consideration is critical for gaining a thorough understanding of amorphous shear band behavior in magnetorheological (MR) solids, particularly those with viscoelastic matrices. Heretofore, the characteristics of shear bands in terms of formation, physical evolution, and response to stress distribution at the localized region have gone largely unnoticed and unexplored. Notwithstanding these limitations, atomic force microscopy (AFM) has been used to explore the nature of shear band deformation in MR materials during stress relaxation. Stress relaxation at a constant low strain of 0.01% and an oscillatory shear of defined test duration played a major role in the creation of the shear band. In this analysis, the localized area of the study defined shear bands as varying in size and dominantly deformed in the matrix with no evidence of inhibition by embedded carbonyl iron particles (CIPs). The association between the shear band and the adjacent zone was further studied using in-phase imaging of AFM tapping mode and demonstrated the presence of localized affected zone around the shear band. Taken together, the results provide important insights into the proposed shear band deformation zone (SBDZ). This study sheds a contemporary light on the contentious issue of amorphous shear band deformation behavior and makes several contributions to the current literature.

scholarly journals Fracture in Bulk Amorphous Alloys

1998 ◽  
Vol 554 ◽  
Author(s):  
J. A. Horton ◽  
J. L. Wright ◽  
J. H. Schneibel
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Shear Bands ◽  
Bulk Amorphous Alloy ◽  
In Situ Tem ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Crack Tips ◽  
Temperature Fracture

AbstractThe fracture behavior of a Zr-based bulk amorphous alloy, Zr-10 Al-5 Ti-17.9 Cu-14.6Ni (at.%), was examined by transmission electron microscopy (TEM) and x-ray diffraction forany evidence of crystallization preceding crack propagation. No evidence for crystallizationwas found in shear bands in compression specimens or at the fracture surface in tensile specimens.In- situ TEM deformation experiments were performed to more closely examine actualcrack tip regions. During the in-situ deformation experiment, controlled crack growth occurredto the point where the specimen was approximately 20 μm thick at which point uncontrolledcrack growth occurred. No evidence of any crystallization was found at the crack tips or thecrack flanks. Subsequent scanning microscope examination showed that the uncontrolledcrack growth region exhibited ridges and veins that appeared to have resulted from melting. Performing the deformations, both bulk and in-situ TEM, at liquid nitrogen temperatures (LN2) resulted in an increase in the amount of controlled crack growth. The surface roughness of the bulk regions fractured at LN2 temperatures corresponded with the roughness of the crack propagation observed during the in-situ TEM experiment, suggesting that the smooth-appearing room temperature fracture surfaces may also be a result of localized melting.

Processing of Copper by Equal Channel Angular Pressing (ECAP) – Microstructure Investigations

2015 ◽  
Vol 641 ◽  
pp. 286-293
Author(s):  
Beata Leszczyńska-Madej ◽  
Maria W. Richert ◽  
Agnieszka Hotloś ◽  
Jacek Skiba
Keyword(s):  
Equal Channel Angular Pressing ◽  
Room Temperature ◽  
Subgrain Size ◽  
Pure Copper ◽  
Shear Bands ◽  
Angular Pressing ◽  
Ecap Process ◽  
Transmission Electron ◽  
Different Types ◽  
Diffraction Patterns

The present study attempts to apply Equal-Channel Angular Pressing (ECAP) to 99.99% pure copper. ECAP process was realized at room temperature for 4, 8 and 16 passes through route BC using a die having angle of 90°. The microstructure of the samples was investigated by means both light and transmission electron microscopy. Additionally the microhardness was measured and statistical analysis of the grains and subgrains was performed. Based on Kikuchi diffraction patterns misorientation was determined. There were some different types of bands in the microstructure after deformation. The shear bands, bands and in the submicron range the microshear bands and microbands are a characteristic feature of the microstructure of copper. Also characteristic was increasing of the number of bands with increasing of deformation and mutually crossing of the bands. The intersection of a bands and microbands leads to the formation of new grains with the large misorientation angle. The measured grain/subgrain size show, that the grain size is maintained at a similar level after each stage of deformation and is equal to d = 0.25 – 0.32 μm.

A Comparative Study on Superplasticity of Mg-Zn-Y-Zr Processed by ECAE and Hot Rolling

2007 ◽  
Vol 551-552 ◽  
pp. 203-208 ◽  
Author(s):  
Wei Neng Tang ◽  
Hong Yan ◽  
Rong Shi Chen ◽  
En Hou Han
Keyword(s):  
Hot Rolling ◽  
Superplastic Deformation ◽  
Rate Sensitivity ◽  
Sensitivity Coefficient ◽  
Grain Boundary Sliding ◽  
Diffusional Creep ◽  
Dislocation Creep ◽  
Fine Grained ◽  
Microstructure Observation ◽  
Elongation To Failure

Superplastic deformation (SPD) behaviors of two fine-grained materials produced by ECAE and hot rolling methods have been contrastively studied in this paper. It is found that the optimum superplastic condition in as-ECAEed material was at 350°C and 1.7×10-3s-1 with elongation to failure about 800%; while in as-rolled material, the largest elongation to failure about 1000% was obtained at 480°C and 5.02×10-4s-1. Microstructure observation showed that grain evolution and cavitation behavior were different in these two materials during superplastic deformation. The controlled mechanisms for superplasticity, i.e. grain boundary sliding (GBS), dislocation creep and diffusional creep, at different deformation conditions were discussed in terms of strain rate sensitivity coefficient, stress exponent and activity energy.

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