Intense Shear Research Articles

Microstructure and electrochemical study of equal channel angular pressed Al-Zn alloys

This research focuses on the effect of severe plastic deformation (SPD) on microstructure and properties of Al and Al-Zn (in 1, 2, 3, 4, 5 wt%) anodes of Al-air battery. The Al-Zn alloys with a diameter of 12.5 mm and 62.5 mm long were pressed in an ECAP die (press angle $=90°, XP=20°), using route Bc with 2, 4, 6, 8 passes at room temperature. Microstructural characterization was carried out using scanning electron microscope (SEM). The cast samples were solutionized at 450 °C for 1 hr after pressing. Grain size of the as-ECAP samples decreased with an increase of ECAP passes. The smaller grain size resulted in strengthening of Al-Zn. An decrease in grain size was due to significant change in the microstructure from an intensive shear stress after ECAP. Polarization test in a 3.5wt% NaCl solution were used to study electrochemical behaviours of the as-cast and ECAP Al-Zn alloys. The conclusion from the research will be used as a platform to develop Al anodes for Al-air battery in the future.

The effect of low frequency ultrasonic treatment on the release of extracellular organic matter of Microcystis aeruginosa

The effect of low frequency ultrasonic treatment on the growth of cyanobacteria and the behavior of extracellular organic matter (EOM) were investigated in this study. The growth of cyanobacteria can be controlled effectively by low frequency ultrasonic treatment, and the inhibitory effect of ultrasound on the photosynthetic ability of cells was more significant than on the cells density (the minimum values of cells density and chlorophyll-a was obtained at day 3 and day 1 respectively). Significant rupture of cells was observed when irradiated by a higher intensity ultrasound (ultrasonic dosage ≥ 1.5 J/mL). Tyrosine-like components were mainly distributed in the soluble EOM and loosely bound EOM fractions; both of the tryptophan-like components and polyaromatic humic-like components were distributed in the soluble EOM, loosely bound EOM, and tightly bound EOM fractions; and polycarboxylate humic-like components were mainly distributed in soluble EOM fraction. Given that the production of hydroxyl radicals was measured, negligible due to the limit of ultrasonic treatment duration (≤1 min). On the other hand, intensive shock waves and shear forces of collapsing acoustic cavitation bubbles were considered as the main reason for the rupture of cells and the changes of the behavior of EOM. A higher intensity ultrasonic treatment resulted in a greater release of EOM, including bound EOM (ultrasonic dosage ≥ 0.1 J/mL), and intracellular organic matter (ultrasonic dosage ≥ 1.5 J/mL). Moreover, the determination of protein and polysaccharide suggested that the bonding of polysaccharides to cells surface is stronger than that of proteins to cells surface, and a portion of the polysaccharides in other fractions was transferred to the tightly bound state during the first serval days after ultrasonic treatment.

Identification of Microfluidization Processing Conditions for Quality Retention of Sugarcane Juice Using Genetic Algorithm

Microfluidization is a novel non-thermal technology which encompasses high-velocity impact, intense shear, and occasionally cavitation on liquid-liquid or solid-liquid systems. In this work, sugarcane (Saccharum officinarum L.) juice was microfluidized at three different pressures (100, 120, 140 MPa) with two different passes (1 and 2). The effect of microfluidization on the total soluble solids (TSS), total phenolic content (TPC), free radical scavenging activity (FRSA), total flavonoid content (TFC), chlorophyll, color, polyphenol oxidase (PPO) activity and microbiological quality was evaluated. Both TSS and PPO showed a gradual decrease (p < 0.05) with the increase in pressure and passes indicating particle breakdown and enzyme inactivation, respectively. At 120 MPa, the TPC, TFC, and FRSA of the juice increased whereas a reduction in values was observed at pressure levels of 100 MPa and 140 MPa. No visual discoloration was observed in the microfluidized sample as compared with the control sample. The chlorophyll content of the treated juice increased significantly with pressure (p < 0.05). Sensory attributes showed no difference between fresh and processed sample. Treatment condition of 124 MPa/2 passes was found most effective in maintaining the quality of sugarcane juice based on a genetic algorithm–based optimization technique. Microbiological and sensory analysis suggested a shelf life of 6 days for microfluidized sugarcane juice over a < 2-day shelf life for control at a storage temperature of 4 °C.

Unique Banded Cylindrites of Polyoxymethylene/Poly(butylene succinate) Blends Induced by Interfacial Shear

Unique banded cylindrites of polyoxymethylene/poly(butylene succinate) blends were induced by the intense interfacial shear, which was applied by pulling a single glass fiber (GF) with non-nucleation ability. The crystalline morphology and structure of banded cylindrites were quantitively correlated with the shear rates to provide revealing insights in shear-induced nucleation and lamellar assembly. Densely packed row-nuclei emerged on the surface of pulled GF and the nucleation density increased dramatically with the shear rate. The subsequent lamellar extension and twisting were restricted perpendicularly to the GF axis, resulting in the formation of banded cylindrites. As the shear rate increased, the band spacing showed a linear decrease and the eccentricity of elliptical bands showed a linear increase. It was attributed to the augment of unbalanced surface stress caused by steric hindrance of serried nuclei. While the growth rate of banded cylindrites remained constant regardless of the shear rate, s...

Early Palaeoproterozoic structural reconstitution of a suite of rocks from the Mahadevi Layered Complex, Tamil Nadu, India

The Palghat‐Cauvery Shear Zone (PCSZ) of the Granulite Terrane of South India is perceived to be a late Neoproterozoic transcontinental shear zone that develops extensive mylonite and sheath folds. The Mahadevi Layered Complex (MLC), the area of present study, is situated in the eastern part of the PCSZ. The studied area exposes vast expanse of felsic orthogneisses with large enclaves of mafic granulite interlayered with meta‐BIF. Our study records two distinct deformational events (D1–2) that produced E‐W closing regional folds with gently curved fold axis. The curved fold axes results in the regional dome‐and‐basin structure. Kinematic markers suggest that a weak shear couple was accompanied with the D2 deformation. Preponderance of the granoblastic fabric in the rocks, restriction of mylonites only in local conjugate shear zones, and the structures produced during D1–2 deformations are at variance with the view that (a) existence of a sheath fold as previously reported from the area and (b) the PCSZ marks the zone of intense shear deformation. Preliminary petrological information from the studied area shows that D1–2 deformational events were accompanied by high‐pressure granulite‐facies metamorphism that was followed by a steeply decompressive retrograde P‐T path. The U–Pb zircon ages from the felsic orthogneiss fixes the date of emplacement of its magmatic protolith and the regional high‐pressure metamorphism at ≥2,530 and ca. 2,479 Ma, respectively. Integrating all the information it is suggested that the evolution of the MLC occurred in a continent‐continent/arc collisional setting at the dawn of the Proterozoic Eon. This study does not support the existence of a “mega sheath fold” in the MLC as has been published in the recent literature.

A novel rotation generator of hydrodynamic cavitation for the fibrillation of long conifer fibers in paper production.

Refining of cellulose pulp is a critical step in obtaining high quality paper characteristics, however, this process is slow and costly especially for refining longer conifer fibers which are the preferred source for high quality paper production and give the paper its strength. In this study, we have applied a novel rotation generator of hydrodynamic cavitation for refining conifer rich pulp samples. Our results show that the device is capable of generating intense shear forces and multiple zones of developed cavitation and is successful in increasing the drainage rate of high consistency pulp (3%). The paper produced by means of the obtained pulp has higher quality because of its higher tensile index (50.5 kN m kg-1) and burst index (3 kPa m2 g-1). These physical parameters were sufficient for newsprint paper and other paper/board quality manufacture. In addition, this laboratory scale rotation generator proved to be economically efficient in comparison to the routinely employed laboratory beaters. To our knowledge, this is the first example of using hydrodynamic cavitation for the refinement of softwood fiber pulp of standard industrial consistencies (3%).

Effects of conform continuous extrusion and heat treatment on the microstructure and mechanical properties of Al–13Si–7.5Cu–1Mg alloy

The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated. The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy, respectively. The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing. After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494°C for 1.5 h and aging at 180°C for 4 h, its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa. Its wear resistance was also enhanced. The factors leading to the enhanced strength, hardness, and wear resistance of the alloy were discussed in detail.

From plastic flow to brittle fracture: Role of microscopic friction in amorphous solids.

Plasticity in soft amorphous materials typically involves collective deformation patterns that emerge on intense shearing. The microscopic basis of amorphous plasticity has been commonly established through the notion of "Eshelby"-type events, localized abrupt rearrangements that induce flow in the surrounding material via nonlocal elastic-type interactions. This universal mechanism in flowing disordered solids has been proposed despite their diversity in terms of scales, microscopic constituents, or interactions. Using a numerical particle-based study, we argue that the presence of frictional interactions in granular solids alters the dynamics of flow by nucleating micro shear cracks that continually coalesce to build up system-spanning fracturelike formations on approach to failure. The plastic-to-brittle failure transition is controlled by the degree of frictional resistance which is in essence similar to the role of heterogeneities that separate the abrupt and smooth yielding regimes in glassy structures.

Aggregation of stable colloidal dispersion under short high-shear microfluidic conditions

We have designed and carried out intense shear-driven aggregation of charge-stabilized polystyrene nanoparticles (NPs) to big fractal clusters, in a single and a double Z-shape microchannels (SZ-MC and DZ-MC). Both the MCs have the same cross-section, but the length of DZ-MC is double of SZ-MC. It is found that when the NP dispersion repeatedly passes through each of the two MCs, the conversion of the NPs to big clusters can only reach a plateau value that is far smaller than full conversion. The plateau conversion at a given mean velocity (shear rate) is larger for the DZ-MC than for the SZ-MC, i.e., it increases as the MC length (or the residence time of one pass) increases. This surprising phenomenon can be explained upon considering that, as the conversion increases, the average NP separation distance increases, i.e., the time for the specific shear-driven bi-particle aggregation to occur increases. When the aggregation time becomes larger than the NP residence time in a MC, the NP dispersion passing through the MC does not lead to aggregation. The situation does not change if we let the NP dispersion repeatedly pass through the MC many times (i.e., by increasing the cumulative residence time), because if the residence time of one pass is not enough for the NPs to overcome the interaction energy barrier, when they come out from the MC, the intense shear force disappears and the NPs return to their original interaction state.

Unified modelling of adiabatic shear banding and subsequent micro-voiding driven dynamic failure of viscoplastic solids

Adiabatic shear bands (ASBs) are intense shear localisation zones resulting from thermomechanical instability in dynamically loaded, high strength structural materials. In the wake of the ASB, Micro-voids (MVs) have been observed which coalesce and ultimately rupture the material. ASBs thus favour premature MV induced damage and further material failure. In the present work, the coupled effects of ASB+MV on the representative volume element (RVE) are reproduced in a unified model within irreversible thermodynamics framework considering a large scale postulate. The influence of the softening mechanisms such as thermal softening and/or DRX induced softening on the ASB onset is accounted for. The model is numerically implemented as a user material subroutine into the engineering finite element (FE) computation code LS-DYNA and its feasibility and performances are assessed on both RVE and structural scales. The dynamic shear compression loading of a hat shaped structure is simulated for that purpose. The respective contributions of ASB and MV on the progressive material deterioration can be clearly identified.

Phase-field study of crack nucleation and propagation in elastic–perfectly plastic bodies

Crack initiation and propagation in elastic–perfectly plastic bodies is studied in a phase-field or variational gradient damage formulation. A rate-independent formulation that naturally couples elasticity, perfect plasticity and fracture is presented, and used to study crack initiation in notched specimens and crack propagation using a surfing boundary condition. Both plane strain and plane stress are addressed. It is shown that in plane strain, a plastic zone blunts the notch or crack tip which in turn inhibits crack nucleation and propagation. Sufficient load causes the crack to nucleate or unpin, but the crack does so with a finite jump. Therefore the propagation is intermittent or jerky leaving behind a rough surface. In plane stress, failure proceeds with an intense shear zone ahead of the notch or crack tip and the fracture process is not complete.

Microstructural characteristics of magnesium alloy sheets subjected to high-speed rolling and their rolling temperature dependence

Microstructural and textural variations of an AZ31 Mg alloy during its high-speed rolling (HSR) and their dependence on the rolling temperature are investigated by performing HSR at temperatures of 300°C, 350°C, and 400°C at a rolling speed of 470m/min with 80% reduction in a single pass. Shear band formation is observed in all the high-speed-rolled (HSRed) materials; however, with increasing rolling temperature, the density and intensity of the shear bands decrease considerably because of an increase in deformation homogeneity. With increasing rolling temperature, the area fraction of dynamically recrystallized (DRXed) grains gradually increases owing to the promoted twinning-induced recrystallization behavior. With an increase in the rolling temperature from 300°C to 350°C, the average grain size of the HSRed materials decreases owing to the reduced area fraction of coarse unDRXed grains; however, at 400°C, the average grain size increases owing to the increased DRXed grain size. With decreasing rolling temperature, the basal texture of the HSRed materials tilts from the normal direction toward the rolling direction, owing to the intensive shear deformation at lower temperatures. The texture intensity also increases with decreasing rolling temperature because of an increase in the area fraction of the unDRXed region, which has a considerably strong texture.

Crystalline structure and remarkably enhanced tensile property of β-isotactic polypropylene via overflow microinjection molding

In this work, the β-nucleating agent (β-NA) filled isotactic polypropylene (iPP) parts were prepared via an overflow microinjection molding (OMM). All OMM parts show an obvious skin-core structure. With increasing the β-NA content, the shear layers with highly oriented shish-kebab structure are progressively thickened, resulting in an effective improvement in tensile strength. Specifically, a maximum tensile strength of 69.8 MPa is observed in the OMM sample with 0.2 wt% of β-NA. Moreover, the elongation at break gradually increases with increasing β-NA content, which is ascribed to the increase of β-crystal content. This study gives more insights into the microstructures of β-nucleated iPP microparts processed under intense shear flow, which could open a promising door to optimize the properties of microparts.

Mesoscopic, magnetic and petrofabric study of the High Himalayan gneisses and leucogranite along oblique and frontal ramps of the Vaikrita Thrust in Satluj and Bhagirathi valleys: Thrust locking and superposed folding

Field, microstructural and anisotropy of magnetic susceptibility (AMS) studies were performed along the oblique thrust ramp of the Satluj river valley and frontal thrust ramp of the Bhagirathi river valley. The presence of asymmetric and sheath folds indicates intense shearing near the thrust. The simple shear gradually decreases with an increase in distance from the thrust and pure shear with upright folds becomes prominent. The AMS studies suggest slightly higher pure shear in the frontal ramp region as compared to the oblique ramp region where oblique slip was predominant. The sense of shear criteria and orientation of superposed folds indicate locking of the thrust. Normal faults are the youngest structure.

Sulfadiazine degradation using hybrid AOP of heterogeneous Fenton/persulfate system coupled with hydrodynamic cavitation

Sulfadiazine (SDZ) is a prominent antibiotic pollutant that appears in wastewater discharges from domestic, agricultural and pharmaceutical sectors. In this paper, we have reported studies in SDZ degradation using a novel hybrid AOP that coupled hydrodynamic cavitation with heterogeneous Fenton and persulfate. Two solid Fenton catalysts (α-Fe2O3 and Fe3O4) in the form of nanoparticles were synthesized. The composition of reaction mixture was optimized using statistical techniques. Effect of four operating parameters, viz. (1) SDZ initial concentration, (2) inlet pressure of cavitating flow, (3) pH and (4) type of heterogeneous Fenton catalyst (at optimum loading), on SDZ degradation was studied. A kinetic model for SDZ degradation was proposed based on homogeneous Fenton/persulfate system, and experimental degradation profiles were analyzed vis-à-vis simulated profiles. The highest degradation of SDZ (81%) was obtained for SDZ initial concn. = 20 ppm, pH = 4, inlet pressure = 10 atm, Na2S2O8 = 348.5 mg/L, H2O2 = 0.95 mL/L and α-Fe2O3 catalyst (181.8 mg/L). Kinetic model analysis showed best match between experimental and simulated profiles for [Fe2+]/[H2O2] initial ratio = 4. This indicated efficient catalytic activity of α-Fe2O3 nanoparticles – close to that of homogeneous catalyst. This is a consequence of high rate of mass transfer at surface of α-Fe2O3 particles due to intense turbulence and shear generated in cavitating flow in hydrodynamic cavitation reactor.

Bendability enhancement of an age-hardenable aluminum alloy: Part I — relationship between microstructure, plastic deformation and fracture

In this study, the bendability of two 1 mm thick sheets of monolithic AA6016 and composite AA6016X alloys is investigated using a series of wrap-bend tests, with emphasis on understanding the relationship between microstructure, the nature of plastic deformation and fracture behavior. The composite AA6016X alloy consists of a central core of AA6016 sandwiched between 100 μm thick clad layers of AA8xxx series aluminum alloy, processed using thermomechanical roll-bonding. It is shown that the bendability of monolithic AA6016 alloy is limited due to the formation of severe surface undulations and surface cracking, which is associated with the heterogenous nature of slip that concentrates into 5°–15° misoriented coarse slip bands of very high dislocation content in the order of 1014/m2, and intense shear bands originating from surface low cusps in the form of mutually orthogonal transgranular bands. The micro-cracks initiate at the surface and propagate along these intensely sheared regions, primarily consisting of grains with near S texture component. Grain boundary decohesion occurs along boundaries that are highly misoriented with misorientations ranging from 40° up to as high as 60°, further assisting crack propagation. The composite AA6016X alloy exhibits unlimited bendability with no signs of fracture even after a maximum bend angle of 180°. The extremely high bending strains in AA6016X are accommodated in a homogeneous manner through a grain subdivision process within the AA8xxx clad layers, promoting the formation of deformation induced high angle boundaries. This homogeneous accommodation of strain within the clad layers reduces surface roughness and further enhances the bendability of the alloy.

Bendability enhancement of an age-hardenable aluminum alloy: Part II — multiscale numerical modeling of shear banding and fracture

In this study, the sequence of microstructural events leading to failure and the relationship between crystallographic texture, shear band development, micro-crack initiation and propagation during wrap-bending of monolithic AA6016 and composite AA6016X sheet alloys are studied using crystal plasticity based finite element methods (CPFEM). The numerically predicted results for texture evolution, shear bands development and fracture behavior after wrap bending show good agreement to the corresponding experimental observations. It is shown that failure during bending of AA6016 is controlled by the development of intense shear bands that emanate from surface low cusps along the outer tensile edge and provide a minimum energy path for micro-cracks to propagate, promoting a predominant transgranular failure. Upon intersection with another shear band, the advancing crack tip alternate from a less critical localization condition to a more critical one, as it requires lesser energy for the creation of new fracture surfaces while sustaining the imposed plastic deformation. Grains with Cube or near Cube texture are rather resistant to shear banding and crack propagation whereas the contrary is true for grains with near S and near Goss orientations. It is also shown that the ductile clad layers within the composite AA6016X alloy act as an efficient barrier against the development and propagation of shear bands within the less ductile inner core, thereby significantly enhancing the bendability of the alloy. Through a systematic study, it is further shown that the bendability of AA6016 alloy can be improved significantly through proper engineering of the microstructure.

Mineral phase equilibria and zircon geochronology constrain multiple metamorphic events of high‐pressure pelitic granulites in south‐easternTibetan Plateau

The Ailao Shan (ALS) metamorphic belt separates the Indochina Block to the west from the South China Block and is an important region for understanding the history of evolution of the Palaeo‐Tethys in relation to the collision of the Indian and Eurasian plates and the formation of the Tibetan Plateau. The multiple metamorphic events andP–T–tpaths of the ALS belt remain debated. Here, we present the results of an integrated study of the petrography, mineral chemistry, phase equilibria modelling, and zircon U–Pb geochronology of high‐grade metasedimentary rocks from this belt. Abundant metamorphic zircon grains with mineral inclusions of Sil/Ky + Bt + Pl + Qz ± Mnz record two metamorphic events, the first one during the Triassic (227–220 Ma), although intense shearing overlapped during the Cenozoic and mineral assemblages of this thermal event were not preserved. The second metamorphic event occurred during the Palaeogene (49 –23 Ma) and involved three stages: (a) a peak high‐pressure (HP) granulite‐facies metamorphism (M1) with a mineral assemblage of Ky + Grt1 + Bt1 + Pl + Qz ± Kfs; (b) a postpeak near‐isothermal decompression (M2) characterized by Sil1–2 + Grt2 + Bt1 + Pl + Qz + Kfs + Ilm and the decompression reactions of Grt + Ky + Qz = 3An and Ky = Sil; and (c) a late decompressional cooling (M3) with a mineral assemblage of Sil3 + Grt3 + Bt2 + Pl + Qz + Mnz ± Kfs, followed by a series of hydration reactions. The metamorphic evolution occurred along a clockwiseP–T–tpath with peakP–Tconditions of 13.5–14.0 kbar and 810–820°C. Our new data, combined with those from previous studies, reveal that the Diancang Shan–Ailao Shan Complex Belt is not a single suture that represents the closure of the Palaeo‐Tethyan Ocean during the Triassic, but that it also represents a typical continent–continent collisional orogenic belt that formed during the Eocene–Oligocene prior to the strong left‐lateral, ductile deformation along the Ailao Shan–Red River shear zone.

Perturbation threshold and hysteresis associated with the transition to turbulence in sudden expansion pipe flow

The complex flow resulting from the laminar-turbulent transition in a sudden expansion pipe flow, with expansion ratio of 1:2, subjected to an inlet parabolic velocity profile and a vortex perturbation, is investigated by means of direct numerical simulations. It is shown that the threshold amplitude for disordered motion is described by a power law scaling, with -3 exponent, as a function of the subcritical Reynolds number. The instability originates from a region of intense shear rate, which results on the flow symmetry breakdown. Above the threshold, several unsteady states are identified using space-time diagrams of the centreline axial velocity fluctuation and their energy. In addition, the simulations show a small hysteresis transition mode due to the reestablishment of the recirculation region in the subcritical range of Reynolds numbers, which depends on: (i) The initial and final quasi-steady states, (ii) the observation time and (iii) the number of intermediate steps taken when increasing and decreasing the Reynolds number.

Low‐Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

AbstractLaboratory measurements of seismic moduli and attenuation in antigorite serpentinite at a confining pressure of 200 MPa and temperatures up to 550 °C provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced oscillations at small strain amplitudes and seismic frequencies (millihertz to hertz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa/K. Increasing temperature above 500 °C results in more intensive shear attenuation ( ) and associated modulus dispersion, with increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite ( at 550 °C and 0.01 Hz) than in olivine ( below 800 °C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.