Structure Of Transition Zone Research Articles

Surface gradient heterogeneity induced tensile plasticity in a Zr-based bulk metallic glass through ultrasonic impact treatment

The excellent mechanical properties of bulk metallic glasses (BMGs) ensure them as a potential engineering material, however, the brittle nature; especially nil tensile plasticity restricts their engineering applications. Ductile phase precipitation is confirmed as an effective way to improve the BMG's plasticity; nevertheless, it is at the expense of BMG's strength due to the low strength of ductile phases. In this paper, ultrasonic impact treatment (UIT) was applied to Zr63.78Cu14.72Ni8Co2Al10Nb1.5 bulk metallic glasses and obvious tensile yield platforms, i.e., tensile plasticity, were obtained, regardless of zero tensile plasticity for the as-cast one. The samples after 4 or 8 runs UIT show a 1.1-1.2% plastic deformation. UIT ensures the BMGs more stable with more endothermic enthalpy in glass transition zone and separated structure with hard and soft regions. A surface gradient heterogeneity caused by UIT is responsible for a favorable shearing path and apparent tensile plasticity.

Analysis on the Strength of Cement Mortar Mixed with Construction Waste Brick Powder

The pile‐up of massive construction waste causes serious challenges to environment and engineering practice. In order to promote the reuse rate of construction waste bricks, the effects of the content and fineness of construction waste brick powder and of brick powder‐silica flour mixture on the strengths of cement mortar were experimentally investigated. Based on the test results, the significance of the particle characteristics of brick powder on mortar strength was analyzed by grey entropy method. The experimental results show that the early strength of cement mortar decreases due to the addition of brick powder; the reduction is, however, not significant when the content of brick powder is less than 10%; the 28 d strength of cement mortar increases with a proper content of brick powder. The grey entropy analysis indicates that the particle characteristics have strong influence on the activity of brick powder and mortar strength; the strength is significantly dependent on specific surface area and the fraction of particles smaller than 20 μm. Fine brick powder and silica flour can improve the macroscopic strengths of cement mortar by affecting the type and quantity of hydration products and the structure of interfacial transition zone between cement paste and sand.

Mantle Transition Zone Structure Beneath Myanmar and Its Geodynamic Implications

AbstractLinking the India‐Tibet collision to the north and the Andaman oceanic subduction to the south, Myanmar occupies a crucial position in the India‐Eurasia convergence system. Various seismological studies have indicated that the Indian plate is obliquely subducted along the Burma arc. However, the depth extent and continuity of the subducted slab remain enigmatic. With seismic recordings collected from 114 recently deployed seismic stations, we map the topographies of the mantle transition zone (MTZ) boundaries, that is, the 410‐ and 660‐km discontinuities, beneath Myanmar using receiver functions. Regional 3‐D velocity models were adopted to account for the lateral velocity heterogeneity. The 410‐km discontinuity is uplifted by over 15 km within 95°E‐97°E and 21°N‐24°N beneath Myanmar. This feature correlates well with the east‐dipping high‐velocity anomaly in the tomographic models, with a velocity increase of 0.9%–1.2% at the 410‐km discontinuity depth, suggesting that the subducted slab has reached the MTZ. The uplift of the 410‐km discontinuity terminates to the south at ∼21°N, indicating a distinct change in slab geometry. Our results also reveal a depressed 660‐km discontinuity, which is spatially offset to the southwest of the uplifted 410‐km discontinuity. We propose that the offset between the 410‐km discontinuity uplift and the 660‐km discontinuity depression could indicate a slab break‐off and tearing beneath Myanmar, which was triggered by the northward motion of the Indian plate during the eastward subduction. We further speculate that the slab tear could mark the transition from oceanic to continental plate subduction.

Multifault complex rupture and afterslip associated with the 2018 Mw 6.4 Hualien earthquake in northeastern Taiwan

SUMMARYWe investigate the coseismic and post-seismic deformation due to the 6 February 2018 Mw 6.4 Hualien earthquake to gain improved insights into the fault geometries and complex regional tectonics in this structural transition zone. We generate coseismic deformation fields using ascending and descending Sentinel-1A/B InSAR data and GPS data. Analysis of the aftershocks and InSAR measurements reveal complex multifault rupture during this event. We compare two fault model joint inversions of SAR, GPS and teleseismic body waves data to illuminate the involved seismogenic faults, coseismic slip distributions and rupture processes. Our preferred fault model suggests that both well-known active faults, the dominantly left-lateral Milun and Lingding faults, and previously unrecognized oblique-reverse west-dipping and north-dipping detachment faults, ruptured during this event. The maximum slip of ∼1.6 m occurred on the Milun fault at a depth of ∼2–5 km. We compute post-seismic displacement time series using the persistent scatterer method. The post-seismic range-change fields reveal large surface displacements mainly in the near-field of the Milun fault. Kinematic inversions constrained by cumulative InSAR displacements along two tracks indicate that the afterslip occurred on the Milun and Lingding faults and the west-dipping fault just to the east. The maximum cumulative afterslip of 0.4–0.6 m occurred along the Milun fault within ∼7 months of the main shock. The main shock-induced static Coulomb stress changes may have played an important role in driving the afterslip adjacent to coseismic high-slip zones on the Milun, Lingding and west-dipping faults.

Kinetid in larval cells of Spongillida (Porifera: Demospongiae): tracing the ancestral traits

The kinetid (flagellar/ciliary apparatus) of eukaryotic cells is an important source of phylogenetic information. It was found to be a prospective morphological phylogenetic marker in sponges, since its arrangement in choanocytes is congruent with the topology of the phylogenetic trees. However, investigation of the kinetid of sponge larval cells remains fragmentary. Here, we report the results of an ultrastructural study on the larval kinetids of the freshwater sponges Eunapius fragilis and Lubomirskia baikalensis (Demospongiae: Spongillida). Their kinetids were found to comprise a kinetosome associated with an accessory centriole and linked to the nucleus by a simple fibrillar root. The kinetosome bears a transverse cytoskeleton: filamentous train and microtubules which radiate from a microtubule organising centre (MTOC) shaped as a large hollow foot. In the short transition zone, between the central axonemal microtubules and kinetosome, a transverse plate with an axosome (central thickening) occurs. We have reviewed the kinetids of different sponge larvae to reconstruct the ancestral state of these traits. Thus, we suggest that spongillids retain the plesiomorphic characteristics of roots and an accessory centriole. But they possess the peculiarities of the transition zone, transverse cytoskeleton and MTOC structure.

Evolution of mechanical properties and permeability of concrete during steam curing process

Steam curing involves a complex moisture-thermal coupling process, which greatly affects the performance evolution of cement-based materials. The effects of mineral admixtures and curing ages on the hydration process, mechanical properties and permeability of concrete during the steam curing process had been studied, and the pore structure, micromorphology and interfacial transition zone (ITZ) were also determined by multi-scale image processing and scanning electron microscopy. The results show that the concrete performances are significant changed during the steam curing process, which can be divided into three stages. In the early stage, hydration products are less, the porosity is larger, and the ITZ is weaker. With the increase of the curing temperature and age, the hydration products are continuously deposited, the microstructure is denser, the mechanical properties are enhanced, and the permeability is decreased significantly. As a result, an empirical model is developed to describe the relationship between effective pore structure (multi-scale pores structure and ITZ) and gas permeability.

Characteristics, genetic mechanism and oil & gas exploration significance of high-quality sandstone reservoirs deeper than 7000 m: A case study of the Bashijiqike Formation of Lower Cretaceous in the Kuqa Depression, NW China

Ultra-deep clastic reservoirs generally have poor physical properties and low single-well productivity, but Well BZ9, which is newly drilled in the Kuqa Depression of Tarim Basin, NW China, encounters a thick high-quality reservoir in the Bashijiqike Formation of Lower Cretaceous deeper than 7600 m and produces a high-yield industrial gas flow. In order to reveal the characteristics and genesis of the Bashijiqike Formation reservoir and reduce the exploration risk of ultra-deep oil and gas layers, we discussed its characteristics, genetic mechanism and oil & gas exploration significance based on cores, well logging and experimental analysis, combined with regional temperature–pressure conditions and burial evolution history. The following research results were obtained. First, the rock types of ultra-deep reservoir of the Bashijiqike Formation in this area are medium- and fine-grained feldspathic litharenite and lithic arkose with point-line contact between grains, and its reservoir space is dominated by primary intergranular pores. At present, it is still at its middle diagenetic stage. Second, different from other ultra-deep fractured low-porosity sandstone reservoirs, this set of ultra-deep reservoir is a pore-type reservoir with porosity of 4–13%, permeability of 0.1–50.0 mD and better porosity and permeability correlation. Third, during the sedimentation of the Bashijiqike Formation, thick sand bodies of delta front were widely developed, medium- and fine-grained sandstones accounted for more than 85% and grains had strong compressive capacity. After that, this reservoir experienced long-term shallow burial during the early–medium stage and rapid deep burial during the late stage, and the burial compaction effect was weaker. During the late stage, a canopy structure was formed from the overlying Paleogene thick gypsum salt bed due to thrust and compression, and it further suppressed vertical compaction. In the meantime, the study area was far from the orogenic belt and the structural transition zone, so the lateral compressive stress was weak. Therefore, the primary intergranular pores were preserved in large quantities. It is concluded that coarse lithology, weak compaction and low tectonic stress are the key factors to the development of this ultra-deep high-quality reservoir. In addition, the development of large-scale effective reservoirs deeper than 7000 m provides favorable material conditions for the high-abundance enrichment of natural gas and the reserves of trillion cubic meters in the Kuqa Depression, and the oil and gas exploration potential is huge.

Stabilization of austenitic structure in transition zone of “austenitic stainless steel/NiCr alloy” joint fabricated by wire-feed electron beam melting

The gradient material “stainless steel/NiCr alloy” has been designed using the additive manufacturing method – double wire-feed electron-beam melting. The effect of gradual addition of Ni-based alloy on phase transformation and microstructure in additively-fabricated “stainless steel/NiCr alloy” joint has been revealed. Despite the abrupt change in wire composition during the fabrication of the joint, the wide transition zone is formed between two parts of the additively-manufactured billet: γ-austenitic matrix and dendritic δ-ferrite in steel part gradually passing into Fe-based austenite, then into Ni-based austenite, and, finally, into γ-(Ni,Cr) austenite with cellular-shape dendrites in NiCr part. The steel-based transition zone of the as-built joint possesses pure austenitic structure stabilized by nickel in comparison with two-phase dendritic microstructure typical for additively-manufactured CrNi stainless steel. The increased microhardness (2.3–2.4 GPa) corresponds to stable austenitic steel structure of the joint.

Seismic Evidence for a Hot Mantle Transition Zone Beneath the Indian Ocean Geoid Low

AbstractThe Indian Ocean Geoid Low (IOGL) is the most prominent geoid anomaly (−106 m) on the globe, whose origin remains elusive. In the present study, we investigate the mantle transition zone (MTZ) structure beneath the region using P receiver functions (PRFs), to examine its role in the genesis of this feature. Results from 3‐D time to depth migration of PRFs reveal a thin MTZ primarily due to an elevation of the 660 km discontinuity. This is suggestive of anomalously hot temperatures in the mid mantle beneath the IOGL region, possibly sourced from the African Large Low Shear Velocity Province (LLSVP). The combined effect of the hot (low‐density) material in the MTZ proposed in this study and the (high‐density) cold slab graves atop the core‐mantle boundary inferred from previous studies can possibly explain this geoid low.

Improving the Mechanical and Durability Performance of No-Cement Self-Compacting Concrete by Fly Ash

The eco-binder with optimized fractions of ternary solid waste materials of ground granulated blast furnace slag (GBFS/slag), class F fly ash (FFA), and circulating fluidized bed combustion (CFBC) fly ash was successfully used to manufacture no-cement self-compacting/self-consolidating concrete (NC-SCC). In the current study, the enhancement of mechanical and durability properties of NC-SCC with FFA was evaluated using the experimental testing of compressive strength, water absorption, sorptivity, dynamic elastic properties, and ultrasonic pulse velocity. Experimental results showed that addition of FFA at 30 wt% as partial replacement of slag was considered as the optimum value to produce the NC-SCC with the highest mechanical properties including compressive strength, dynamic moduli, and superior durability properties due to the lowest water absorption and volume of permeable voids computed from the test on initial and secondary rate of capillary absorption. Microstructural performance detected by using scanning electron microscopy (SEM) obviously supported that the structure of interfacial transition zone between binder and aggregate of the NC-SCC with optimized FFA addition seemed to be strengthened by the extra hydration products contributed to the FFA particles.

Detailed structure of mantle transition zone beneath southeastern China and its implications for thinning of the continental lithosphere

This paper presents a new study on 3-D structure, temperature and water content estimation of the mantle transition zone (MTZ) by P-wave receiver functions common conversion point (CCP) method on broadband array with 267 temporary stations and 203 permanent stations in southeastern China. The results show different structural characteristics of the MTZ to the north and south of the 29°N line. In the northern part, the 660-km discontinuity is generally deeper than globe models, and there are two independent local depressions with characteristics of high velocity, low temperature, and water shortage. We interpret them as two previous subducting plates stagnated in MTZ, possibly related to two separate subduction events at different times. While in the southern part, the 410-km discontinuity is locally depressed, resulting in thinning of the MTZ. Particularly, in the Cathaysian Block south of the 29°N line, based on the MTZ structure and the estimation of temperature and water content, we conside dehydration of the MTZ as one of the important mechanisms of lithospheric thinning through interaction with the asthenosphere. We then propose a dynamic model that combines paleo-Pacific flat-slab subduction and upper mantle convection to explain the lithospheric extension and thinning, magmatic rock distribution, weak seismic activity and basin-and-range geomorphology. This model differs from that north of the 29°N line in the North China Block.

Micromechanical Properties of Concrete under Freezing-Thawing Condition

The researches on micromechanical properties of concrete subjected to freeze-thaw cycles are few. Under freeze-thaw action, the changes of micromechanical structure and mechanical properties of mortar and interfacial transition zone (ITZ) were characterized by nanoscratch. The volume fraction of micropores increases almost linearly, up to approximate 45%. Moreover, the scratch hardness of different micro-phases in mortar and ITZ decreases gradually with the increase of freeze-thaw cycles, which can be attributed to the increase of micropores. In addition, the thickness of the ITZ gradually increases to 60 um under 1500 F-T cycles, which is consistent with the results using SEM.

Mechanical and transport properties of recycled aggregate concrete modified with limestone powder

In this work, the mechanical and transport properties of recycled aggregate concrete (RAC) modified with limestone powder were studied. The results indicate that replacing 10 wt% cement with limestone substantially improves the compressive strength of RAC. A better resistance to chloride and water ingress can also be achieved owing to the decreased pore connectivity. The initial sorptivity is found to increase linearly with increasing permeable voids content. Mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analyses demonstrate that adding limestone leads to a refinement of pore structure and densification of both bulk paste and interfacial transition zone, respectively. X-ray diffraction (XRD) patterns suggest that incorporation of limestone prevents the transformation from ettringite (AFt) to monosulfate (AFm), thus increasing the total volume of hydration products. Thermogravimetry and differential scanning calorimetry (TG/DSC) analyses confirm an improved hydration process in RAC containing limestone, explaining for the enhanced mechanical and transport properties.

Prominent thermal anomalies in the mantle transition zone beneath the Transantarctic Mountains

Abstract The Transantarctic Mountains (TAMs), Antarctica, exhibit anomalous uplift and volcanism and have been associated with regions of thermally perturbed upper mantle that may or may not be connected to lower mantle processes. To determine if the anomalous upper mantle beneath the TAMs connects to the lower mantle, we interrogate the mantle transition zone (MTZ) structure under the TAMs and adjacent parts of East Antarctica using 12,500+ detections of P-to-S conversions from the 410 and 660 km discontinuities. Our results show distinct zones of thinner-than-global-average MTZ (∼205–225 km, ∼10%–18% thinner) beneath the central TAMs and southern Victoria Land, revealing throughgoing convective thermal anomalies (i.e., mantle plumes) that connect prominent upper and lower mantle low-velocity regions. This suggests that the thermally perturbed upper mantle beneath the TAMs and Ross Island may have a lower mantle origin, which could influence patterns of volcanism and TAMs uplift.

Effect of shrinkage reducing admixture on creep of recycled aggregate concrete

It is widely accepted that recycled concrete aggregates originated from construction and demolition wastes are promising materials to contribute to the conservation and rational use of natural resources as well as the protection of the environment. In this work, a comprehensive experimental investigation has been carried out in order to assess the effect of shrinkage reducing admixture (SRA) on the mechanical properties and creep of concrete manufactured with recycled coarse aggregates from the different parent concrete with compressive strengths of 30 MPa and 80 MPa, respectively. Meanwhile, mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) have been performed to determine the variation of internal microstructure. The results indicate that the quality of recycled aggregates has important effect on the properties of concrete. The addition of SRA furtherly reduces the early mechanical properties of recycled aggregate concrete, and however, improves the later mechanical and creep properties. Compared with the reference concrete manufactured with natural coarse aggregates, concrete manufactured with SRA and recycled coarse aggregates with high quality exhibits the later higher compressive strength and elastic modulus as well as lower creep, which is largely due to the later more compact microstructure such as interfacial transition zone and pore structure.

The structure of the upper mantle transition zone beneath Northeast China associated with mantle plume migration

The structure of the upper mantle transition zone beneath Northeast China associated with mantle plume migration

The structure of the upper mantle transition zone beneath Northeast China associated with mantle plume migration

The structure of the upper mantle transition zone beneath Northeast China associated with mantle plume migration

SHS Joining of Ta with NiAl: Structure of Transition Zone

SHS Joining of Ta with NiAl: Structure of Transition Zone

Gradient transition zone structure in “steel–copper” sample produced by double wire-feed electron beam additive manufacturing

This paper describes the results of an investigation into a microstructure formation on a wire-feed electron beam additive manufactured “steel–copper” bimetallic sample. The peculiarities of a gradient zone structure with a smooth change of components’ concentration are revealed. The heterogeneity of copper and steel distribution in the gradient zone is provided by copper solidification and precipitation mechanisms. Both solidification of coarse copper inclusions in the interdendrite areas or along the dendrite boundaries and precipitation of fine Cu-based particles at the cooling stage from the solid solution of Cu in γ-Fe are the main factors of structure formation during the double wire gradient zone deposition. The presence of such fine copper precipitates from the supersaturated solid solution was revealed by means of transmission electron microscopy. The shape of copper particles in the gradient zone varies from spherical to oblong and irregular. The shape of steel particles and/or grains is mainly determined by the peculiarities of the crystallization zone and is characterized by the primary crystallization of γ-iron dendrites from the liquid melt. A physical scheme describing a variation in phase composition and microstructure in gradient zone of the bimetallic specimen was proposed.

Multi-scale study on mechanical property and strength prediction of aeolian sand concrete

The aim of this work is to promote the utilization of aeolian sand for concrete production. The workability and mechanical property of aeolian sand concrete (ASC) is studied. The effect mechanisms of aeolian sand on the mechanical property of concrete are revealed from multiple scales. For the macro scale, use the pressure tester to test the compressive strength. For the mesoscopic, use the scanning electron microscope (SEM) to observe the structure of the interface transition zone (ITZ) and the nuclear magnetic resonance (NMR) to test the pore structure. Meanwhile, the distribution of chemical bonds is analyzed by the Fourier transform infrared (FT-IR) spectrometer and the microstructure of hydration products are characterized by the SEM for the microscopic. The results show that using parts of aeolian sand can improve the working and mechanical property of concrete. The physical influence mechanism is that it perfects the gradation of the aggregate and increases the density of concrete, reduces the effect of aggregate size and micro-region bleeding, improves the structure of ITZ and pores. For the chemical, it may accelerate the hydration reaction speed of cement and change the microstructure of hydration products. Finally, a strength prediction model of ASC is established based on the published and tested data, which agrees well with the tested result.