Ductile Zones Research Articles

Material Removal Mechanisms of Polycrystalline Silicon Carbide Ceramic Cut by a Diamond Wire Saw.

Polycrystalline silicon carbide (SiC) is a highly valuable material with crucial applications across various industries. Despite its benefits, processing this brittle material efficiently and with high quality presents significant challenges. A thorough understanding of the mechanisms involved in processing and removing SiC is essential for optimizing its production. In this study, we investigated the sawing characteristics and material removal mechanisms of polycrystalline silicon carbide (SiC) ceramic using a diamond wire saw. Experiments were conducted with high wire speeds of 30 m/s and a maximum feed rate of 2.0 mm/min. The coarseness value (Ra) increased slightly with the feed rate. Changes in the diamond wire during the grinding process and their effects on the grinding surface were analyzed using scanning electron microscopy (SEM), laser confocal microscopy, and focused ion beam (FIB)-transmission electron microscopy (TEM). The findings provide insights into the grinding mechanisms. The presence of ductile grinding zones and brittle fracture areas on the ground surface reveals that external forces induce dislocation and amorphization within the grain structure, which are key factors in material removal during grinding.

Ultrasonic Influence on Macrostructure and Mechanical Properties of Friction Stir Welded Joints of Al/Mg Sheets with 2 mm Thickness.

Friction stir welding (FSW) and ultrasonic vibration enhanced FSW (UVeFSW) experiments were conducted by using 6061-T6 Al alloy and AZ31B-H24 Mg alloy sheets of thickness 2 mm. The suitable process parameters windows were obtained for the butt joining of Al/Mg sheets. The effect of ultrasonic vibration on the macrostructure and mechanical properties of the dissimilar joints was studied. The results showed that the width of the weld nugget zone (WNZ) was enlarged to some extent and the hardness distribution in WNZ was more uniform in UVeFSW. In addition, the application of ultrasonic vibration effectively promoted the interpenetration degree of dissimilar materials in the WNZ so that the mechanical interlocking on the bonding interface of dissimilar Al/Mg materials was enhanced. The facture positions were changed from the bonding interface in FSW to the boundary between WNZ and the thermo-mechanical affected zone, and the ductile fracture zone was expanded. The highest ultimate tensile strength was 205 MPa at the process parameters set of 1200 rpm-50 mm/min in UVeFSW in this experiment. The average ultimate tensile strength of FSW/UVeFSW joints was 172.3 MPa and 184.4 MPa, respectively, and the average ultimate tensile strength was increased by 7.02% with the introduction of ultrasonic vibration.

The Early Mesozoic NE–SW Extensional Model and Exhumation Processes at the Southeastern Margin of the Central Asian Orogenic Belt: Insights from the Strain and Kinematic Vorticity Analysis of the Sonid Zuoqi Ductile Detachment Zone

AbstractThe Sonid Zuoqi ductile detachment zone is located at the southeastern margin of the Central Asian orogenic belt (CAOB), striking EW and dipping to the S. The major rock type of the Sonid Zuoqi ductile detachment zone is mylonite derived from granite. The sequence of mylonite features is: (1) S and C foliations of mylonite, and (2) extensional crenulation cleavage (ecc) or C and the kinematic vorticity (Wk) value changed from 0.70 to 0.95 and from 0.37 to 0.69, respectively; the strain type of the mylonites within the Sonid Zuoqi ductile detachment zone is compressional to planar strain. The strong deformation mylonite and Halatu plutons yielded a zircon U‐Pb age of 244 Ma and a zircon (U‐Th)/He age of 214 Ma, respectively. Based on the strain and kinematic vorticity analysis, together with the zircon U‐Pb and zircon (U‐Th)/He ages and the regional tectonic background, the study area experienced three stage evolution: tangential simple‐shear (244 Ma), simple‐shear‐dominated general shear represented by upper crustal extension (224 Ma) and pure–shear–dominated general shear represented by the Halatu pluton doming (214 Ma), which constrained the early Mesozoic NE–SW crustal extension at the southeastern margin of the CAOB. This NE–SW extension probably originated from the post‐orogenic extensional collapse of the CAOB, subsequent exhumation being controlled by the far afield effects of the closure of the Mongol–Okhotsk belt.

Tension anisotropy of rolled AA7075-T6 auminium alloy: Experiments, BP-Neural network modeling and orientation dependent failure mechanisms

This paper presents the investigations on anisotropic tension mechanical responses of AA7075-T6 based on experiments, classical strength theory, BP-neural network modeling and fracture morphology characterization. Results show that the tension strength anisotropy weakens with deformation degree. Compared to the traditional method, the machine learning model exhibits more flexible in solving the anisotropic plastic responses of AA7075-T6 auminium alloy sheet and provides more accurate predictions. Through analyzing the fracture surface of tension specimen at various orientations, the failure mechanism is sensitive to orientation. Specifically, the irregular distribution of dimples zones and cleavage steps can be observed at lower material orientation. As the orientation increases, the alternative occurrence of ductile and brittle features dominates the failure mechanism. The medium-size dimple caused by coalescence of small-size dimples represents a transition between ductile features zone and brittle characteristics region.

Critical cutting thickness model considering subsurface damage of zirconia grinding and friction–wear performance evaluation applied in simulated oral environment

Ductile mode removal is always a popular topic in zirconia ceramic cutting and grinding. The completely undamaged ductile mode grinding is extremely inefficient and difficult to control, which limits the clinical application of dental zirconia ceramics. Hence, considering the effect of subsurface damage, this paper redefines the ductile mode grinding removal of ceramic materials and establishes a critical cutting thickness model for zirconia ceramic grinding. Results show that the better the lubrication condition, the smaller the subsurface damage degree and the larger the removal range of ductile zone. To verify the model, grinding experiments of zirconia ceramic under different lubrication conditions are conducted. The results show that grinding under nanofluid minimum quantity lubrication obtains the lowest friction coefficient, which is reduced by 58.54 % and 18 % compared with dry grinding and minimum quantity lubrication (MQL), respectively. Under nanofluid minimum quantity lubrication (NMQL) condition, the critical cutting thickness is 2.27 µm, which is 160.92 % larger than that under dry grinding. The error between the theoretical model and the experimental results is 10.67 %, which verifies the correctness of the theoretical model. Furthermore, using the workpiece material obtained from grinding experiments, friction–wear experiments are conducted on dental zirconia ceramics under different loads in a simulated oral environment. The results show that zirconia ceramics obtained by NMQL grinding achieve better anti-friction and anti-wear performance than that of MQL. When the maximum cutting thickness of zirconia ceramics processed by NMQL grinding is 2.27 µm, the wear rate of the workpiece is 3.06 × 10−5 mm3/N·m, and at 2.6418 µm, the wear rate of the workpiece is 2.01 × 10−3 mm3/N·m. This paper aims to provide theoretical guidance and technical support for the ductile mode removal of hard, brittle materials.

The Seismic Performance of Self-Centering Ribbed Floor Flat-Beam Frame Joints

To achieve rapid post-earthquake repair of self-centering ribbed floor flat-beam frame structures, a ductile hybrid joint consisting of dog-bone-shaped, weakened, energy-dissipating steel bars connected to the upper and lower column sections through high-strength threads is proposed based on the damage control design concept. By moving the ductile energy-dissipating zone out to the locally weakened section of the energy-dissipating steel bars and the locally unbonded prestressed steel bars in the core area, the residual deformation was limited and the seismic performance improved. Based on the working principle of hybrid joints, low cycle loading tests were conducted on two joint specimens to analyze the influence of lateral prestress on the seismic performance of the hybrid joints. Numerical modeling methods were used to compare the position of the energy-dissipating steel bars in the composite layer and the friction performance of the joints. The research results indicated that the hybrid joint had stable load bearing, deformation, and energy dissipation capabilities, with damage being primarily concentrated in the energy-dissipating steel bars. Even at an inter-story displacement angle of 5.5%, the upper and lower column segments remained elastic. After unloading, the connection seam at the joint was closed, and the self-centering performance was good. When the inter-story displacement angle reached 5.5%, the lateral prestress increased from 150 kN to 250 kN, the ultimate bearing capacity of the joint increased by 16.3%, and the cumulative energy consumption increased by 30.0%. The influence of the friction coefficient of the joint surface on the structural performance was set at a threshold of 0.7. When it was less than the threshold, the ultimate bearing capacity and initial stiffness of the joint increased with the increase in the friction coefficient. After reaching the threshold, the increase in the ultimate bearing capacity of the joint slowed down, and the rate of stiffness degradation gradually accelerated. This joint showed excellent seismic performance and can thus achieve post-earthquake repair of structures.

Deformation‐induced graphitization and muscovite recrystallization in a ductile fault zone

AbstractA suite of slate samples collected along a 2 km transect crossing the Lishan fault in central Taiwan were evaluated to assess the role of ductile deformation in natural graphitization at lower greenschist facies metamorphic conditions. The process of natural aromatization, or graphitization, of an organic precursor is well established as a thermally driven process; however, experimental studies have shown that the energy provided by deformation can substantially reduce the activation energy required for graphitization. This study provides a natural example of deformation‐induced graphitization. A strain gradient approaching the Lishan fault was established by scanning electron microscope imaging and X‐ray diffraction analysis of phyllosilicates and quartz that showed an increase in the strength of slaty cleavage development via dissolution‐precipitation processes. Thermal conditions were constrained to be near isothermal using calcite‐dolomite geothermometry. Raman spectroscopic results from carbonaceous material, including D1‐full width‐at‐half‐maximum (FWHM), G‐FWHM, Raman band separation (RBS), and a lesser‐known vibrational mode B2g‐FWHM, showed robust linear trends across the same sampling transect. However, the G‐FWHM parameter showed a trend opposite of that expected from thermally driven graphitization. The Raman results are interpreted to reflect a strain‐driven reduction in graphite crystallite size (decrease in G‐FWHM) but improvement in structural ordering in individual coherent domains. A multiple linear regression with an R2 value of 0.92 predicts the graphite D1‐FWHM values from the XRD‐derived ratio of muscovite populations and muscovite microstrain, demonstrating the concomitant recrystallization of silicates and carbonaceous material across the strain gradient, despite the disparate processes accommodating the deformation. This study demonstrates the role of deformation in natural graphitization and provides a new perspective on the use of graphite as a geothermometer in strongly deformed greenschist facies rocks.

Fluid-Induced Metamorphism and Deformation at the Eastern Boundary of the Sveconorwegian Province

Abstract The Sveconorwegian orogen in Scandinavia and the Grenville orogen in Canada are both remnants of large and hot orogens that formed part of the supercontinent Rodinia around 1 billion years ago. Formerly deeply buried portions of crust in these orogens are exposed and offer insights into the tectonic dynamics of the basement within large orogens. The Eastern Segment of the Sveconorwegian Province hosts a ~ 30 000 km2 crustal portion that was buried to c. 40 km depth at a late stage of the orogeny, 980–960 Ma ago, and is bound towards the foreland in the east by a ~ 25 km wide zone of step anastomosing deformation, the Frontal wedge. This zone represents the outermost ductile deformation that developed within the crystalline basement in the orogen. We investigated a heterogeneously deformed and recrystallised syenodiorite with the aim to understand the character of the deformation-related metamorphism within the Frontal wedge. Field relations, microtextures, and mineral reactions show that the metamorphic recrystallisation was governed by hydrous fluid infiltration along the ductile deformation zones. Equilibrium was attained on a millimetre scale only and metamorphic recrystallisation was dependent on the introduction of hydrous fluid. The metamorphism reached high-pressure epidote-amphibolite-facies; geothermobarometric estimates suggest 540°C to 600°C and 9 to 12 kbar. Metamorphic zircon formed during the breakdown of Zr-bearing igneous phases, primarily baddeleyite. SIMS U–Pb analyses of igneous zircon and baddeleyite date the igneous crystallisation of the syenodiorite at 1230 ± 6 Ma. Metamorphic zircon grains are <20 μm and too small for precise dating, but yielded ages around 1 Ga. Collectively, the metamorphic data indicate that subvertical movements along steep planes within the Frontal wedge allowed for the regional-scale tectonic burial to ~40 km depth of the Eastern Segment to the west. Some of the same steep deformation structures were re-utilised as discrete movement planes during later exhumation.

Controls on mechanical properties of a carbonate mudstone: Insights from non-destructive techniques and geochemical data

This study quantifies geomechanical properties of carbonate mudrocks in the Arabian intra-shelf basin, focusing on different sedimentologic zones (proximal to distal). Core-based mechanical properties were obtained through unconfined conditions. Micro Rebound Testing (MRT) was conducted on 700′ ft of core at 0.5 ft intervals to capture high-resolution rock hardness (HLD), unconfined compressive strength (UCS), and static Young's Modulus (E). Additional tests validated log-based parameters, including impulse hammer, acoustic velocity testing for (E), P-wave and S-wave velocities (Vp and Vs), scratch testing, and XRF/XRD analyses for mineralogical and elemental variability impact on mechanical properties.Multivariate statistical analysis correlates mechanical properties with elemental data, showing direct proportionality to calcium percentage, (E), Vp, and Vs, while inversely correlated to aluminum, iron, sulfur, and total organic carbon (TOC), especially in distal zones. Porosity, as measured by neutron porosity log, is a significant control on mechanical properties, with higher porosity resulting in lower mechanical properties at any given calcium percentage. Variations in geomechanical properties within each zone are principally controlled by depositional environments, sediment supply, diagenesis, and a pycnocline dividing the water column into anoxic, dysoxic (or suboxic), and oxic conditions.Zone 1A and 4 exhibit high brittleness characterized by high Ca-calcite, HLD, (E), Vp, Vs., low terrigenous elements/minerals, and porosity. Zone 1B and 2A are moderately brittle, showing a slight decrease in brittleness and a slight increase in terrigenous elements/minerals, porosity, and organic matter, particularly in the distal zone (Zone 1B). Zone 2B, 3A, and 3B represent moderate to highly ductile zones with low levels of Ca-calcite, HLD, (E), Vp, Vs, and an increase in terrigenous elements/minerals, porosity, and TOC, especially in the distal zone (Zone 2B and 3B). This study highlights the value of high-resolution mechanical data from cores with applications for improved stress estimation and hydraulic fracture stimulation in unconventional reservoirs.

Machine Learning Approach to Predict the Illite Weight Percent of Unconventional Reservoirs from Well-Log Data: An Example from Montney Formation, NE British Columbia, Canada

Shale mineralogy is critical for the proper design and execution of hydraulic fracturing operations and for evaluating production potential. There has been relatively little research into using artificial intelligence for mineralogical prediction for the Montney Formation. This study aims to predict the Montney Formation illite wt.% using readily available conventional logs, where illite is one of the constituents of shale and can aid in analyzing the brittle and ductile zones within the shale formation. The wt.% of illite is often determined by examining core samples or cuttings using XRD or QEMSCAN; both techniques are time-consuming, costly, and cannot be performed without physical samples. Based on conventional log readings, this study uses artificial neural networks (ANNs) and principal component analysis (PCA) to construct an accurate prediction model for illite wt.%. The feed-forward neural network (FFNN) obtained good overall performance in illite wt.% prediction (R2 = 92%) utilizing the backpropagation algorithm and the B.R. technique for eight input parameters. The ANN model was tested by randomly selecting three wells from the same log dataset excluded from the core training and testing phases. Overall, R2 = 88.5% was found in the tests, which is encouraging. This work demonstrates the viability of employing the ANN in applications involving evaluating mineralogical components of a target source rock using traditional logs, especially when geochemical data are missing or inadequate.

Enhancing strength and ductility of Al-matrix composite via a dual-heterostructure strategy

Aluminum matrix composites (AMCs) often have low ductility, which has been a long-lasting issue in the last few decades. This problem arises largely from the non-deformability of reinforcement particles, which leads to premature failure of the matrix-particle interfaces. Here we propose a new microstructural design strategy for AMCs: distribute the reinforcement particles non-uniformly to form dual-heterostructured AMCs. The zones with high-density particles are recognized as the hard zones, which carry less plastic strain than the particle-free zones to prevent premature interfacial failure. A dual-heterostructured Al-matrix nanocomposite is fabricated, in which AlN nanoparticles are distributed in a dual-level hierarchy: first level heterogeneous nanoparticle distribution and second level heterogeneous zones with different grain sizes. The dual heterostructure produced a unique dual level hetero-deformation induced (HDI) strengthening and hardening to produce high strength and ductility. The dual level HDI strengthening effect has been revealed by the inflection points on the loading-unloading-reloading stress-strain curves. Furthermore, the evolution of local strain fields during the in-situ tensile deformation directly proved the occurrence of strain partitioning, in which the ductile particle free zones have carried a larger strain than the hard particle rich zones. Dispersive shear strain bands are observed for the first time in AMCs. These findings are expected to help design other metal matrix composites with superior mechanical properties.

The effect of strain on the crystallinity of carbonaceous matter: Application of Raman spectroscopy to deformation experiments

Raman spectroscopy, applied to the carbonaceous matter (CM) present in fault zones, is a potentially powerful tool to aid in the reconstruction of slip conditions, provided the respective effect of heating and strain can be disentangled. For this purpose, we have carried out static heating and deformation experiments on low-grade sediments containing disseminated CM particles and tracked the evolution of CM crystalline ordering (crystallinity) using Raman spectroscopy. Heating at high pressure (200 MPa), at varying temperatures (500 to 800 °C) and durations (3 to 1080 h) resulted in an increased crystallinity, which was observed by an increase in the intensity ratio of the Disordered Band over the Graphite Band (Intensity Ratio R1 parameter) of the Raman spectra. The experimental relationship between R1, T and duration was compiled into a law of evolution, which was then used to design the deformation experiments. Experiments were performed in a Paterson rig at 150 MPa or in a Griggs-type rig at 1 GPa. We observed two types of deformation microstructures: (1) purely brittle ones, such as breccia along slip planes and (2) ductile ones, such as foliated layers, resulting from grain reorientation and comminution along with dissolution precipitation. In all deformation microstructures, an increase in R1 is visible and interpreted to be the result of higher crystallinity of carbonaceous particles. Such increase is negligible in breccia, but is significant, up to 40%, in ductile deformation zones. The slow strain rates prevailing in ductile deformation prevented any local temperature increase, therefore the increase in crystallinity of the CM can be solely attributed to deformation. Thus, in natural fault zone, the increased crystallinity of CM reported in the literature and interpreted to be the result of frictional heating during earthquakes might rather be the result of strain localization without transient temperature increase.

Voluminous Paleoproterozoic plutonic belt of the Bacajá domain in Amazon Craton: Petrology, geotectonic setting and Pb–Pb zircon evaporation ages

To the north of the well-known Archean Carajás Metallogenetic Province, the Bacajá Domain abounds voluminous Rhyacian plutonic bodies predominate largely over remnants of Siderian and Neoarchean crust. The Rhyacian granitoids of the Bacajá Domain present a wide lithological variety and a geological evolution marked by syntectonic emplacement, which printed strongly elongated geometries to the bodies, according to a WNW regional orientation. The Rhyacian granitoids form three distinct units. The Bacajaí intrusive suite comprises 2112 ± 8 Ma metaquartz diorites, tonalites, granodiorites and monzogranites of calc-alkaline signature. Sm–Nd isotopic analyses of these rocks yielded a TDM age of 2310 Ma and an εNd value of +0.56. The Arapari intrusive suite is composed of quartz diorites, tonalites, granodiorites and monzogranites of calc-alkaline signature. A preliminary Pb–Pb zircon dating pointed an age of 2072 Ma to the Arapari intrusive suite. Nd isotopes yielded TDM ages varying from 2100 to 2170 Ma and positive εNd (+2.11 to +3.04). Both Bacajaí and Arapari intrusive suites have similar chemical signatures suggesting continental magmatic arc environment. The origin of Bacajaí and Arapari magmas could be explained by partial melting of mantle and crustal sources. The João Jorge intrusive suite encloses high-K calc-alkaline quartz diorites, monzogranites, syenogranites, alkali feldspar granites, shoshonitic alkali feldspar syenites and monzonites. The alkali feldspar syenites have Pb–Pb zircon age of 2076 Ma, TDM age of 2210 Ma and positive εNd value (+1.51). Spatial relationship between shoshonitic bodies and strike-slip shear zones or geological contacts seems to reflect the influence of crustal anisotropies on mantle-derived magmas ascending. Partial melting of metassomatized mantle after extraction of granite melts could explain the origin of syenites and monzonites. The three granitoid unities show rhythmic layering defined by alternation of quartz-feldspathic and ferromagnesian-enriched levels. Regionally penetrative steep-dipping magmatic foliation was formed in the presence of both crystals and melt, under conditions of increasing deformation and decreasing temperatures. The Bacajaí metagranitoids underwent locally thermal effects of hornblende hornfels facies caused by the later granitoid suites. These hornfelsed granitoids may present granoblastic textures, overgrown muscovite, reddish biotite and clinopyroxene. Late WNW strike-slip ductile zones and brittle faults crosscut some of the plutons, closing the ancient geological evolution of the Bacajá Domain.

Mechanism and Effect Factor of Toughening of High-Speed Train Wheels

The wheel of high-speed trains requires high strength and hardness while imposing high demands on plasticity and toughness, resulting from the needs of working conditions. The fracture toughness KQ, as an important indicator of dynamics, often varies in the wheel, which affects the overall performance of the wheel. This work performs tests and analyses on typical samples with large fracture differences in fracture toughness at the same position and uniformly distributed on the same wheel. The mechanism of fracture toughness fluctuation is investigated, and the factors affecting fracture toughness are identified. The test mainly focuses on macroperformance, microfracture morphology, inclusion category and shape influence, pearlite lamellar spacing, and pearlite block size. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and quantitative metallographic technology were employed to investigate the mechanism and influence factors on fracture toughness fluctuation. The analysis shows that the width of the ductile laceration zone is directly correlated with the toughness, and the toughness level is influenced by the cleavage size, pearlite lamellar spacing, and pearlite block uniformity.

Microstructure and low-temperature impact fracture behavior of QT400-18AL containing Ni

The effects of Ni content on the microstructures and low-temperature impact fracture behaviors of QT400-18AL ferritic ductile cast iron were systematically investigated by XRD, SEM, EBSD, and low-temperature impact test technique. The results demonstrate that the average diameter of graphite spheres and HAGBs increase with the increase of Ni content, whereas the nodule count, the crystal lattice constant and average grain size of the ferrite phase decrease. Additionally, the UTS, YS, and hardness of the QT400-18AL at room temperature increase with the increasing Ni content. The Ni-0.75 cast iron has the best room temperature mechanical properties with UTS of 391 MPa, YS of 253 MPa, and hardness of 140 HB. The average impact energy of the QT400-18AL decreases with the decrease in test temperatures and increase with the increase in Ni content at the same test temperatures. The fracture morphologies show that the ductile fracture zones increase with the increase in Ni content at the same impact temperature. Moreover, they decrease with the decreasing impact temperatures at the same Ni content, and the fracture types change from ductile fracture to ductile-brittle mixed fracture. The Ni-0.75 cast iron exerted satisfactory impact performance at −40 °C owing to the optimized combination of GBCD and dislocation density (KAM value), and its low-temperature impact energy was 12.64 J.

Interrelated pressure-temperature-time-paths of medium to high pressure metamorphic rocks in the Sierra Pie de Palo (W-Argentina): Evolution of a “hard” collisional wedge during an Ordovician microcontinent-arc collision

The Sierra Pie de Palo (W-Argentina) is part of an Ordovician collisional wedge between the Cuyania microcontinent and the Ordovician Famatinian arc along the west Gondwana protomargin. The flatly E-dipping collisional wedge formed by polyphase shearing. The lower plate consists of Neoproterozoic-Cambrian metasedimentary rocks and Mesoproterozoic mafic-ultramafic basement of eastern Cuyania. The Famatinian forearc represents the upper plate composed of Mesoproterozoic metasedimentary rocks intruded by Mesoproterozoic and Ordovician plutons and overlying Neoproterozoic metasedimentary rocks. Pseudosection modeling on 20 samples distributed over the entire wedge yields a range of recorded maximum PT conditions of 7–14 kbar/480–590 °C along metamorphic gradients of 10–20 °C/km. Clockwise PT-paths are common starting from a midcrustal level with gradients of 20–30 °C to maximum depth followed by thermal relaxation. Local anticlockwise PT-paths are observed (1) in high-grade basement klippen of the overriding Famatinian arc (8–10 kbar/700–765 °C) caused by late emplacement onto the nappe stack and (2) within late upper crustal ductile zones with normal shear sense.Isotopic ages of (re)crystallisation of metamorphic minerals and assemblages comprise: 429 ± 2 to 434 ± 7 Ma (Lu-Hf; garnet), 460 ± 6 Ma (UPb monazite in garnet), 404 ± 7 to 422 ± 8 Ma (Rb-Sr; white mica) and 403 ± 4 to 440 ± 8 Ma (40Ar/39Ar white mica). Including previous data, ages cluster around major peaks at 464 ± 1 Ma, 436 ± 3 Ma, 427 ± 3 Ma, 415 ± 2 Ma and 405 ± 1 Ma related to deformation during three orogenic stages: (1) subduction of the lower plate (eastern Cuyania) to the basis of the wedge at 470–455 Ma and later burial of the upper plate (Famatinian forearc) to similar depths at 440–415 Ma, a characteristic of a “hard” collision; (2) exhumation mainly by erosion and (3) late dissection of the wedge by upper crustal thrusts and some normal faulting at the top of the wedge during arrival of the colliding microcontinent Chilenia (405–360 Ma) at the new Devonian leading margin.

Microstructure evolution and strength-ductility improving mechanism change of heterogeneous CNT/2009Al composite after hot rolling

In this study, heterogeneous carbon nanotubes reinforced 2009Al (CNT/2009Al) composites composed of CNT-free ductile zones (DZs) and CNT-rich brittle zones were prepared by powder metallurgy, followed by hot extrusion and hot rolling. For the extruded heterogeneous composite (Hetero-C), its strength was increased by about 30 MPa with a more than 1/3 elongation increase, as compared with those of the uniform composite. After hot rolling, the two zones of the heterogeneous composite (R-Hetero-C) were much narrower than those of the Hetero-C, which was not beneficial to increase elongation. However, the texture analysis demonstrates that the Hetero-C had a< 111 > fiber texture, while the R-Hetero-C had strong plate textures including {011}< 111 > , {113}< 332 > and {215}< 342 > components. These plate textures with high Schmidt factor induced more matrix grains to participate in plastic deformation at relatively low stress, which could enhance the elongation but slightly reduce the strength. The synergy of these two different aspects led to the slightly reduced yield strength, similar ultimate tensile strength, and increased elongation for the rolled heterogeneous composite, as compared with those of the extruded heterogeneous composite.

Microstructure Evolution and Fracture Toughness Behaviour of Cryorolled LM6 Al Alloy

In the present work, the effect of cryo-rolling on the processed LM6 alloy samples has been studied. The solution treated (ST) sample of LM6 alloy has been processed through cryo-rolling with reduction of its thickness with values such as 30%, 40%, and 75%. One of the key material properties i.e., fracture toughness has been studied and equivalent energy fracture toughness ( ) is being evaluated according to the ASTM E 992 standard. The microstructure evolution after processing through cryorolling (CR) has been carried out with the help of optical microscopy and Scanning Electron Microscopy (SEM). Then, the calculated values of fracture toughness parameter i.e., equivalent energy fracture toughness ( is being correlated with the microstructure evolution after processing of LM6 alloy. It was found out that there is an improvement in equivalent energy fracture toughness ( ) as the reduction values increases. The 75% CR sample showed great increment of 67% as compared to ST alloy sample. The microstructure evolution also signifies the mix-mode fracture visualized through Scanning Electron Microscopy (SEM) and as the reduction values increase, the ductile fracture zone dominance increases on brittle fracture zone indicating there is improvement in fracture toughness of the ultra-fined grain LM6 alloy due to the grain refinement, dislocation strengthening and grain boundary strengthening.

Performance-based experimental study into quality zones of lightweight concrete using pumice aggregates

The quality and performance of concrete depends on the material used. Lightweight concrete is usually formed from aggregates with lightweight specific gravity, such as pumice. This study aims to identify the zone of quality and performance of concrete when partially replacing coarse aggregate (NA) with pumice coarse aggregate (PA). The performance parameters studied include unit weight, compressive strength, elastic modulus, tensile strength, and rupture modulus. Geochemical analysis and porosity of aggregate were carried out using SEM and X-RD. The percentage variation of pumice aggregate is 0 %PA, 25 %PA, 50 %PA, 75 %PA, and 100 %PA. Quality zones based on observations of the behaviour and mechanical properties of concrete are determined. The results show that concrete using PA consists of two quality zones, namely the brittle zone for concrete with PA above 50 % and the ductile zone for concrete with PA below 50%. Formulas to calculate the elastic modulus and the rupture modulus are proposed. Utilisation of pumice as lightweight concrete aggregate to get better lightweight concrete performance must be selective.

Experimental and numerical investigation of proppant embedment and conductivity reduction within a fracture in the Caney Shale, Southern Oklahoma, USA

The current worldwide energy supply is insufficient to meet the rising demand. As a result, the energy prices are expected to keep soaring despite the recent increases in a variety of renewable energy resources. Although not renewable, shale oil and gas — “unconventional” hydrocarbon resources are relatively clean forms of energy resources, which still hold a vast share of the energy market. For many oil and gas companies, meeting profitable production goals from shale reservoirs is sometimes challenging, due to the loss of fracture conductivity and premature declines in the production. In this paper we investigate the stress-dependent changes in the hydraulic conductivity of proppant-filled fractures and mechanical fracture–proppant interactions in Caney Shale, a calcareous, organic-rich mudrock, through laboratory experiments and numerical modeling. American Petroleum Institute (API) fracture conductivity tests were conducted using 2% KCl on five locations within the Caney Shale that consisted of selecting three brittle (reservoir) zones and two ductile zones. Confining pressures ranged from 1,000 psi to 12,000 psi at 210 °F. Conductivity, permeability as well as embedment were measured during the test. Also, an additional, laboratory in-situ visualization test was conducted to examine the detailed proppant-shale matrix interaction under elevated stress (3,920 psi effective stress) and temperature (252 °F), with a synthetic reservoir fluid. Our experimental results have confirmed that improved fracture conductivity is attributed to proppant size, and that the increase in porosity of the proppant pack, closure pressure changes and the reduction in fracture conductivity are a function of many factors such as fracture closure stress.