Showing papers on "Slip (materials science) published in 2020"

Hall and ion slip effects on unsteady MHD free convective rotating flow through a saturated porous medium over an exponential accelerated plate

Abstract: In this paper, we have investigated the Hall and ion slip effects on the unsteady magnetohydrodynamic (MHD) free convective rotating flow over an exponentially accelerated inclined plate entrenched in a saturated porous medium with the effect of angle of inclination, variable temperature and concentration. The flow induced by the presence of heat source/sink and destructive reaction. The Laplace transform technique has been used to solve the governing equations. The effects of the non-dimensional parameters on the governing flow velocity, temperature and concentration are examined with graphical profiles. Also for engineering interest the shear stress, Nusselt number and Sherwood number are obtained analytically and discussed computationally with reference to foremost flow parameters. It is reported that the presence of magnetic field prevents the flow reversal. Angle of inclination sustains a retarding effect on velocity distribution. The present study has an immediate application in understanding the drag experienced at the heated and inclined surfaces in a seepage flow.

Ultrasoft slip-mediated bending in few-layer graphene.

Abstract: Continuum scaling laws often break down when materials approach atomic length scales, reflecting changes in their underlying physics and the opportunities to access unconventional properties. These continuum limits are evident in two-dimensional materials, where there is no consensus on their bending stiffnesses or how they scale with thickness. Through combined computational and electron microscopy experiments, we measure the bending stiffness of graphene, obtaining 1.2–1.7 eV for a monolayer. Moreover, we find that the bending stiffness of few-layer graphene decreases sharply as a function of bending angle, tuning by almost 400% for trilayer graphene. This softening results from shear, slip and the onset of superlubricity between the atomic layers and corresponds with a gradual change in scaling power from cubic to linear. Our results provide a unified model for bending in two-dimensional materials and show that their multilayers can be orders of magnitude softer than previously thought, among the most flexible electronic materials currently known. The bending stiffness of few-layer graphene is shown to decrease significantly with the bending angle due to shear and slip between the atomic layers, which culminate in superlubric behaviour as the bending angle further increases.

Slow slip source characterized by lithological and geometric heterogeneity

Abstract: Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust.

Bioconvection in the Rheology of Magnetized Couple Stress Nanofluid Featuring Activation Energy and Wu's Slip

Abstract: Abstract In order to meet the current challenges in the fabrication of nanobiomaterials and enhancement of thermal extrusion systems, current theoretical continuation is targeted at the rheology of couple stress nanofluid by exploiting activation energy, porous media, thermal radiation, gyrotactic micro-organisms, and convective Nield boundary conditions. The heat and mass performances of nanofluid are captured with an evaluation of the famous Buongiorno model, which enables us to determine the attractive features of Brownian motion and thermophoretic diffusion. The couple stress fluid is beneficial to examine multiple kinds of physical problems because this fluid model has the capability to describe the rheology of various complex fluids, e. g., fluids having long-chain molecules as a polymeric suspension, liquid crystals, lubricants, and human and animal blood. Simultaneous behavior of the magnetic field and porosity are studied with thermal radiation effects. The distribution of velocity has been conducted by using second-order velocity slip (Wu’s slip) and activation energy features. For the dimensionless purpose, the similarity variable has been initiated, and the modeled equations are renovated sufficiently. A famous shooting method is used to determine the numerical solutions, and accurate results have been obtained. A variety of critical flow parameters is graphically illustrated with physical significance.

A Numerical Exploration of Modified Second-Grade Nanofluid with Motile Microorganisms, Thermal Radiation, and Wu’s Slip

Abstract: This study is carried out to scrutinize the gyrotactic bioconvection effects on modified second-grade nanofluid with motile microorganisms and Wu’s slip (second-order slip) features. The activation energy and thermal radiation are also incorporated. The suspended nanoparticles in a host fluid are practically utilized in numerous technological and industrial products such as metallic strips, energy enhancement, production processes, automobile engines, laptops, and accessories. Nanoparticles with high thermal characteristics and low volume fraction may improve the thermal performance of the base fluid. By employing the appropriate self-similar transformations, the governing set of partial differential equations (PDEs) are reduced into the ordinary differential equations (ODEs). A zero mass flux boundary condition is proposed for nanoparticle diffusion. Then, the transmuted set of ODEs is solved numerically with the help of the well-known shooting technique. The numerical and graphical illustrations are developed by using a collocation finite difference scheme and three-stage Lobatto III as the built-in function of the bvp4c solver via MATLAB. Behaviors of the different proficient physical parameters on the velocity field, temperature distribution, volumetric nanoparticles concentration profile, and the density of motile microorganism field are deliberated numerically as well as graphically.

Significance of bioconvection in chemical reactive flow of magnetized Carreau–Yasuda nanofluid with thermal radiation and second-order slip

Abstract: Several non-Newtonian fluids are of practical interest, and it is fascinating to examine the rheology of such fluids with various flow features. In this study, the flow of Carreau–Yasuda nanofluid has been analyzed in the presence of gyrotactic microorganisms. The impressive features of nanofluid are displayed by abiding the thermophoresis and Brownian motion aspects. The second-order velocity slip effects are decomposed in the mathematical simulations. Further, the governing flow problem governed the impact of thermal radiation, chemical reaction and convective Nield boundary conditions. Although some attempts are available in the literature which examines the rheological features of Carreau–Yasuda nanofluid, whereas the analysis for bioconvection of flow of this non-Newtonian fluid model in the presence of second-order slip features is not proposed yet. Further, it has been noticed that many investigators used first-order or partial slip effects associated with their flow problems. The flow problem becomes more realistic due to the interaction of second-order slip constrains and subsequently develops a more stable boundary layer. The governing equations for the formulated flow problem are partial differential equations. Standard dimensionless quantities are recommended to alter the flow equations in dimensionless forms. The solution of the locally similar problem has been computed numerically via shooting technique. All the computations are performed by using bvp4c with the help of MATLAB software. Following the iterative procedure, the solution is accurate up to convincing accuracy of $$ 10^{ - 4} . $$ The step size for the present simulation is taken as $$ \Delta \eta = 1 \times 10^{ - 4} . $$ The results are also verified by comparing with already reported numerical computation and found a convincible accuracy. The implication of each parameter is executed for velocity, temperature, concentration and microorganisms’ distributions. Moreover, the substantial quantities, namely skin friction coefficient, motile density number, local Nusselt number, and local Sherwood number numerically evaluated and are overviewed for various parameters. The study reveals that velocity distribution decays with the presence of first-order slip parameter and Rayleigh number, while an enhanced velocity profile has been noted for variation of Weissenberg number. An improved nanoparticle temperature and concentration distributions have been found with the utilization of the second-order slip factor and combine parameter. It is further observed that the density of motile microorganisms declined with Peclet number and bioconvection Lewis number. In recent days, a growing interest has been developed from scientists toward the significance of nanoparticles because of their diverse engineering, industrial and commercial applications. The proposed observations can be useful in extrusion systems applications, biomolecules, biomimetic systems, energy production improvement and enhancement of manufacturing processes.

Strain rate dependency of dislocation plasticity

Abstract: Dislocation slip is a general deformation mode and governs the strength of metals. Via discrete dislocation dynamics and molecular dynamics simulations, we investigate the strain rate and dislocation density dependence of the strength of bulk copper single crystals using 192 simulations spanning over 10 orders of magnitude in strain rate and 9 orders of magnitude in dislocation density. Based on these large set of simulations and theoretical analysis, a new analytical relationship between material strength, dislocation density, strain rate and dislocation mobility is proposed, which is in excellent agreement with the current simulations as well as with experimental data. The results show that the material strength is a non-monotonic function of dislocation density and displays two universal regimes (first decreasing, then increasing) as the dislocation density increases. The first regime is a result of strain rate hardening, while the second regime is dominated by the classical Taylor forest hardening. Accordingly, the strength displays universally, as a function of strain rate, a rate-independent regime at low strain rates (governed by forest hardening) followed by a rate hardening regime at high strain rates (governed by strain rate hardening). All the results can be captured by a single scaling function. Finally, the fluctuations of dislocation flow are analyzed in terms of the strain rate dependent distribution of dislocation segment velocities. It is found that the fluctuations are governed by another universal scaling function and diverge in the rate independent limit, indicating a critical behavior. The current analysis provides a comprehensive understanding on how collective dislocation motions are governed by the competition between the internal elastic interactions of dislocations, and the stress required to drive dislocation fluxes at a given externally imposed strain rate.

Tensile properties and microstructural features of 304L austenitic stainless steel produced by wire-and-arc additive manufacturing

Abstract: Additive manufacturing (AM) has gained great importance in the recent development to produce metallic structural elements for civil engineering applications. However, research effort has been focused mainly on powder-based processes, while there is still limited knowledge concerning the structural response of wire-and-arc additive manufactured (WAAM) metallic elements, and very few experimental data concerning their mechanical properties. This paper presents the first results of a wide experimental campaign aimed at assessing the mechanical properties of WAAM plates produced using a commercial ER308LSi stainless steel welding wire. The aim is to evaluate the effect of the orientation in the tensile behavior of planar elements considering specimens extracted along three different directions with respect to the deposition layer: transversal direction (T), longitudinal direction (L), and diagonal direction (D). Compositional, microstructural, and fractographic analyses were carried out to relate the specific microstructural features induced by WAAM to the mechanical properties. The results show that the chemical composition of the plates meets the requirements of UNS-S-30403 for an AISI 304L austenitic stainless steel. The as-built samples were substantially defect-free and characterized by a very fine microstructure of γ and δ phases The fineness of the microstructure and the negligible defect content led to values of tensile strength and elongation to failure in line with the traditionally manufactured stainless steel elements. Anisotropy in the tensile properties between T, L, and D specimens was observed, and the highest elastic and plastic properties were measured in D specimens. This result is related to the crystallographic and mechanical fibering induced by the additive process, that led also, in case of D samples, to the highest density of cell boundaries, obstacles to the dislocation slip, located at 45° with respect to the loading direction, where plastic deformation preferentially occurs.

Complex Rupture of an Immature Fault Zone: A Simultaneous Kinematic Model of the 2019 Ridgecrest, CA Earthquakes

Abstract: The July 4, 2019 Mw6.4 and subsequent July 6, 2019 Mw7.1 Ridgecrest Sequence earthquakes ruptured orthogonal fault planes in the Little Lake Fault Zone, a low slip rate (1 mm/yr) dextral fault zone in the area linking the Eastern California Shear Zone and Walker Lane. This region accommodates nearly one fourth of plate boundary motion and has been proposed to be an incipient transform fault system that could eventually become the main tectonic boundary, replacing the San Andreas. We investigate the rupture process of these events using a novel simultaneous kinematic slip method with joint inversion of high-rate GNSS, strong motion, GNSS static offset, and InSAR data. We model the Coulomb stress change to evaluate how the first mainshock may have affected the second. Our findings suggest complex interactions between several fault structures, including dynamic and static triggering, and provide important context for regional seismic source characterization and hazard models.

Study of Two-Phase Newtonian Nanofluid Flow Hybrid with Hafnium Particles under the Effects of Slip

Abstract: This paper investigates the role of slip in a two-phase flow of Newtonian fluid. The nano-size Hafnium particles are used in the base fluid. The fluid under consideration is studied for two cases namely (i) fluid phase (ii) phase of particles. Both cases are examined for three types of geometries. The governing equations are simplified in nondimensional form for each phase along with boundary conditions. The resulting equations have been analytically solved to get exact solutions for both fluid and particle phases. Different features of significant physical factors are discussed graphically. The flow patterns have been examined through streamlines.

Thermal conductivity variation and heat generation effects on magneto-hybrid nanofluid flow in a porous medium with slip condition

Abstract: The application of hybrid nanoparticles rather than nanoparticles is one of the greatest critical tasks for enhancing heat transfer. Therefore, the purpose of this article is to analyze the flow an...

3-D magnetohydrodynamic AA7072-AA7075/methanol hybrid nanofluid flow above an uneven thickness surface with slip effect

Abstract: A 3-D magnetohydrodynamic flow of hybrid nanofluid across a stretched plane of non-uniform thickness with slip effects is studied. We pondered aluminum alloys of AA7072 and AA7072 + AA7075 in methanol liquid. The aluminum alloys amalgamated in this study are uniquely manufactured materials, possessing enhanced heat transfer features. AA7072 alloy is a composite mixture of Aluminum & Zinc in the ratio 98 & 1 respectively with added metals Silicon, ferrous and Copper. Equally, AA7075 is a mixture of Aluminum, Zinc, Magnesium, and Copper in the ratio of ~90, ~6, ~3 and ~1 respectively with added metals Silicon ferrous and Magnesium. Numerical solutions are attained using R-K based shooting scheme. Role of physical factors on the flow phenomenon are analyzed and reflected by plots and numerical interpretations. Results ascertain that heat transfer rate of the hybrid nanoliquid is considerably large as matched by the nanofluid. The impact of Lorentz force is less on hybrid nanofluid when equated with nanofluid. Also, the wall thickness parameter tends to improve the Nusselt number of both the solutions.

Modeling of Cattaneo-Christov double diffusions (CCDD) in Williamson nanomaterial slip flow subject to porous medium

Abstract: Here magnetohydrodynamics (MHD) nanomaterial slip flow of Williamson fluid is addressed. The flow is discussed over a porous medium and generated via nonlinear stretching phenomenon. The behavior of heat and mass transport are discussed subject to Cattaneo-Christov double diffusions (CCDD). Mathematical modeling for both CCDD is performed under the basic concept of Fourier's and Fick's laws. The energy equation for the consider flow problem is developed using Brownian motion, dissipation and thermophoretic diffusion. Relevant transformations variables are utilized to convert the partial differential equations into ordinary ones. Flow parameters are discussed on the velocity, temperature and concentration through built-in-Shooting method. Skin friction is computed and discussed through bar chart versus Weissenberg number and slip parameter. It is concluded that the skin friction coefficient is decreased for higher values of Weissenberg number and slip parameter. Furthermore, velocity field decays against Weissenberg number, slip parameter and porosity parameter.

Mechanical and hydrological effects of seamount subduction on megathrust stress and slip

Abstract: Subduction of rough seafloor and seamounts is thought to impact a broad range of geodynamic processes, including megathrust slip behaviour, forearc fluid flow and long-term structural evolution in the overriding plate. Although there are many conceptual models describing the effects of seamount subduction, our quantitative and mechanistic understanding of the underlying deformation and fluid processes remains incomplete. Here we investigate the interplay between sediment consolidation, faulting and the evolution of stress and pore fluid pressure in response to seamount subduction, using a numerical model that couples mechanical and hydrological processes and is constrained by laboratory and field observations. Our results show that subducting topography drives marked spatial variations in tectonic loading, sediment consolidation and megathrust stress state. Downdip of a subducting seamount on its leading flank, enhanced compression and drainage lead to large fault-normal stress and overconsolidated wall rocks. A stress shadow in the seamount’s wake leads to anomalously high sediment porosity. These variations help explain observed patterns of megathrust slip, with earthquakes and microseismicity favoured at the downdip edge of seamounts and aseismic or slow slip in the updip stress shadow. Changing stresses and pore fluid pressures during subduction of seamounts, as simulated with a numerical model that couples mechanical and hydrological processes, help explain observed patterns of megathrust slip.

Fault valving and pore pressure evolution in simulations of earthquake sequences and aseismic slip.

Abstract: Fault-zone fluids control effective normal stress and fault strength. While most earthquake models assume a fixed pore fluid pressure distribution, geologists have documented fault valving behavior, that is, cyclic changes in pressure and unsteady fluid migration along faults. Here we quantify fault valving through 2-D antiplane shear simulations of earthquake sequences on a strike-slip fault with rate-and-state friction, upward Darcy flow along a permeable fault zone, and permeability evolution. Fluid overpressure develops during the interseismic period, when healing/sealing reduces fault permeability, and is released after earthquakes enhance permeability. Coupling between fluid flow, permeability and pressure evolution, and slip produces fluid-driven aseismic slip near the base of the seismogenic zone and earthquake swarms within the seismogenic zone, as ascending fluids pressurize and weaken the fault. This model might explain observations of late interseismic fault unlocking, slow slip and creep transients, swarm seismicity, and rapid pressure/stress transmission in induced seismicity sequences.

A slip law for glaciers on deformable beds

Abstract: Slip of marine-terminating ice streams over beds of deformable till is responsible for most of the contribution of the West Antarctic Ice Sheet to sea level rise. Flow models of the ice sheet and till-bedded glaciers elsewhere require a law that relates slip resistance, slip velocity, and water pressure at the bed. We present results of experiments in which pressurized ice at its melting temperature is slid over a water-saturated till bed. Steady-state slip resistance increases with slip velocity owing to sliding of ice across the bed, but above a threshold velocity, till shears at its rate-independent Coulomb strength. These results motivate a generalized slip law for glacier-flow models that combines processes of hard-bedded sliding and bed deformation.

Slow Slip Events in New Zealand

Abstract: Continuously operating global positioning system sites in the North Island of New Zealand have revealed a diverse range of slow motion earthquakes on the Hikurangi subduction zone. These slow slip ...