Multiple Slip Research Articles

Multiple Slip Effects on MHD Unsteady Flow Heat and Mass Transfer Impinging on Permeable Stretching Sheet with Radiation

This paper reports multiple slip effects on MHD unsteady flow heat and mass transfer over a stretching sheet with Soret effect; suction/injection and thermal radiation are numerically analyzed. We consider a time-dependent applied magnetic field and stretching sheet which moves with nonuniform velocity. Suitable similarity variables are used to transform governing partial differential equations into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved numerically by applying an implicit finite difference method with quasi-linearization technique. The influences of the various parameters on the velocity temperature and concentration profiles as well as on the skin friction coefficient and Sherwood and Nusselt numbers are discussed by the aid of graphs and tables.

Fabrics and water contents of peridotites in the Neotethyan Luobusa ophiolite, southern Tibet: implications for mantle recycling in supra-subduction zones

The preservation of ultra-high-pressure and super-reducing phases in the Neotethyan Luobusa ophiolite in Tibet suggests their deep origin near the mantle transition zone. Dunite and harzburgite core samples from the Luobusa Scientific Drilling Project show supra-subduction zone geochemical signatures and equilibration temperatures of c. 950–1080°C. Olivine shows A-, B-, C- and E-type fabrics, and combinations of A- and E-type or B- and E-type fabrics. Transmission electron microscopy observations show straight dislocations and the activation of multiple slip systems [100](010), [001](010), [001](100) and [100](001) in olivine. The mean water content in olivine, orthopyroxene (Opx) and clinopyroxene (Cpx) from 24 peridotite samples was 16 ± 5, 90 ± 21 and 492 ± 64 ppm, respectively, which is different from the water content of hydrated peridotites above the mantle wedge. The trace element compositions of Cpx exclude significant metasomatism after melt extraction. The high hydrogen partition coefficient between Cpx and Opx ( D H Cpx/Opx = 5.56 ± 0.96) implies equilibrium at high pressures and rapid exhumation. Based on deformation experiments, the B- and C-type fabrics could be formed in a subduction zone at depths >200 km, whereas the A- and E-type fabrics were produced in the shallow mantle. In a process triggered by slab rollback, the Luobusa peridotites may have been rapidly exhumed within a subduction channel and mixed with the lithospheric mantle of the forearc. Supplementary material: Major oxide contents in Opx, Cpx and spinel, trace element concentration in Cpx, micrographs and TEM images of peridotite are available at https://doi.org/10.6084/m9.figshare.c.4307828 Thematic collection: This article is part of the ‘Tethyan ophiolites and Tethyan seaways collection’ available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways

Comparing the Through-Thickness Gradient of the Deformed and Recrystallized Microstructure in Tantalum with Unidirectional and Clock Rolling.

Controlling the microstructure homogeneity is crucial in achieving high quality tantalum (Ta) sputtering targets used in integrated circuit fabrication. Unluckily, traditional rolling easily generates a microstructure gradient along the thickness direction in Ta sheets. The deformation and recrystallization behavior of unidirectional and clock rolled Ta with an 87% strain were therefore systematically compared to investigate whether the change of strain-pass can effectively ameliorate the microstructure gradient along the thickness. Electron backscatter diffraction was used to analyze the misorientation characteristics of the deformed grains. A strong microstructure gradient exists in the unidirectional rolled (UR) sheets. Many microshear bands and well-defined microbands occurred in {111} deformed grains in the UR sheets, especially in the center region, while the grain fragmentation with {111} and {100} orientation in the clock rolled (CR) sheets was more homogenous along the thickness. The kernel average misorientation (KAM) and grain reference orientation deviation-hyper (GROD-Hyper) further confirmed these differences. X-ray line profile analysis (XLPA) indicated that the stored energy distribution was more inhomogeneous in the UR sheets. Schmid factor analysis suggested that the strain path changes due to clock rolling promoted the activation of multiple slip systems in {111} oriented grains. Upon static annealing, homogeneous nucleation combined with a slower grain growth rate resulted in finer and more uniform grain size for the CR sheet. In contrast, a strong recrystallization microstructure-gradient along the thickness formed in the UR sheets, which is attributed to the fact that the higher stored energy and more preferential nucleation sites led to faster recrystallization in the center region, as compared with the surface region. Thus, clock rolling can effectively improve the homogeneity of the through-thickness recrystallization microstructure of Ta sheets.

Characteristic Tectonic Tremor Activity Observed Over Multiple Slow Slip Cycles in the Mexican Subduction Zone

AbstractWe develop a single‐station tremor spectrum template detection method that we applied to continuous seismic data recorded by the Mexican National Seismological Service broadband stations. This allows for an unprecedented long‐term analysis of tectonic tremor in Mexico over multiple slow slip events (SSEs). We only detect tremor that are within previously discovered tremor regions, thereby extending the catalog in time but not space. The resulting catalog demonstrates the strong correlation of bursts of tremor activity and aseismic slip over multiple slow slip cycles. The M ~ 7 long‐term SSEs in the states of Guerrero and Oaxaca are associated with the longest sequences of tremor bursts. Each of these tremor bursts are made up of a series of smaller bursts. In between the large M7 SSEs, there are shorter‐duration, isolated tremor bursts. In Guerrero, these shorter bursts were found to accompany M ~ 6 short‐term SSEs. The occurrence of these short‐duration tremor bursts in Oaxaca demonstrates that small short‐term SSEs occur in both major slow slip regions in Mexico. The discrete range of tremor burst sizes and rates suggests that slow slip events in the Mexican subduction zone are organized into characteristic moment and moment rates. The catalog also reveals other aseismic transients, such as postseismic slip in Oaxaca after the 16 February 2018 Mw 7.2 Pinotepa Nacional earthquake. We highlight that such long‐term catalogs are a useful tool together with geodetic observations to monitor slow slip activity that potentially plays a role in the subduction megathrust cycle.

Upper‐Bound Finite Element Adaptive Analysis of Plane Strain Heading in Soil with a Soft Upper Layer and Hard Lower Layer

This paper investigates the stability of a rectangular tunnel face affected by surcharge loading in soil with a soft upper layer and hard lower layer using upper‐bound finite element methods with a plastic‐dissipation‐based mesh adaptive strategy (UBFEM‐PDMA). Seven different positions for the soil interface are selected to study this problem. The upper bounds on the ultimate surcharge loads σs are presented in terms of dimensionless stability charts. The σs increases with tunnel depth, and it increases when the position of the soil interface moves up along the tunnel face. The failure mechanism primarily involves a wedge‐shaped zone around the tunnel face and two slip lines originating from the top and bottom of the tunnel face, and it is mainly influenced by three factors, i.e., the position of the soil interface, the soil properties, and the tunnel depth. In contrast to the failure mechanism for uniform soil, multiple slip lines exist in the tunnel face in soil with a soft upper layer and hard lower layer. The results compare reasonably well with those in the literature and those from the numerical method.

Development of Deformation Bands During Cyclic Deformation of Multiple Slip Oriented Copper Single Crystals with multiple slip orientation

Development of Deformation Bands During Cyclic Deformation of Multiple Slip Oriented Copper Single Crystals with multiple slip orientation

Similarity of fast and slow earthquakes illuminated by machine learning

Tectonic faults fail in a spectrum of modes, ranging from earthquakes to slow slip events. The physics of fast earthquakes are well described by stick–slip friction and elastodynamic rupture; however, slow earthquakes are poorly understood. Key questions remain about how ruptures propagate quasi-dynamically, whether they obey different scaling laws from ordinary earthquakes and whether a single fault can host multiple slip modes. We report on laboratory earthquakes and show that both slow and fast slip modes are preceded by a cascade of micro-failure events that radiate elastic energy in a manner that foretells catastrophic failure. Using machine learning, we find that acoustic emissions generated during shear of quartz fault gouge under normal stress of 1–10 MPa predict the timing and duration of laboratory earthquakes. Laboratory slow earthquakes reach peak slip velocities of the order of 1 × 10−4 m s−1 and do not radiate high-frequency elastic energy, consistent with tectonic slow slip. Acoustic signals generated in the early stages of impending fast laboratory earthquakes are systematically larger than those for slow slip events. Here, we show that a broad range of stick–slip and creep–slip modes of failure can be predicted and share common mechanisms, which suggests that catastrophic earthquake failure may be preceded by an organized, potentially forecastable, set of processes. Both fast and slow earthquakes are preceded by micro-failure events that radiate energy. According to machine learning, these events can foretell catastrophic failure in laboratory experiment earthquakes.

Multiple slip effects on mixed convection of Oldroyd-B fluid towards a stretchy surface with radiation and chemical reaction using Cattaneo-Christov heat flux

The steady two-dimensional MHD mixed convection flow and heat transfer characteristics of an Oldroyd-B fluid over a linear stretchy sheet is considered. The flow caused by a linear stretchy sheet with effects of velocity, temperature and concentration slips. The thermal radiation, internal heat generation effects are included in the study. The resulting governing PDEs rebuild into ODE model by applying a suitable similarity transformation and then are solved by homotopy analysis method. The effects of the various constants on the velocity, temperature and concentration fields are discussed. It is found that the velocity, temperature and concentration fields decrease when increasing the corresponding slip constants.

Area failure probability method for slope system failure risk assessment

Quantitative risk assessment of slope failure provides valuable information for slope reinforcement design and risk mitigation. Most of previous studies assessed the slope failure risk based on the critical slip surface with the minimum factor of safety. In general, the critical slip surface is unknown prior to the slope stability analysis and can vary with the underground soil profile. It was, however, observed in slope stability analyses that a slope may, simultaneously, fail along multiple slip surfaces. How to effectively incorporate multiple failure slip surfaces (MFSS) into slope failure risk assessment remains an open question. This paper develops a new method that provides an overview of the failure probability of soil masses at different locations on a slope, which is referred to as the area failure probability chart (AFPC) in this paper. Based on the AFPC, a general slope failure risk assessment framework is proposed to incorporate MFSS into slope failure risk assessment. The proposed approach is illustrated through a slope example. It is found that AFPC shows results of slope reliability analysis in a straightforward and visible way, which enhances the risk perception and communication for geotechnical practitioners, and ignoring MFSS leads to underestimation of slope failure risk.

Effect of Temperature on Small-Scale Deformation of Individual FCC and BCC Phases of Al0.7CoCrFeNi High Entropy Alloy

High Entropy Alloys (HEAs) represent an important class of structural materials because of their high strength, ductility, and thermal stability due to the solid solution nature of the multi-component metallic system. Understanding the mechanical response of isolated phases (FCC and BCC) of a dual-phase HEA is integral to understanding mechanical properties of these special alloys in bulk. We investigate the compressive response of single crystalline cylinders with diameters between 400 nm and 2 µm excised from individual grains within FCC and BCC phases of Al0.7CoCrFeNi HEA at 295 K, 143 K and 40 K. Micro-compression experiments were conducted in an in-situ SEM equipped with a custom-constructed cryogenic setup; FCC samples had a [324] crystallographic orientation, and those extracted from the BCC phase had a [001] orientation. We observed a smaller is stronger size effect in the yield strength as a function of pillar diameter, D, of both alloy phases for all temperatures, τ_y ∝D^m with a power law exponent, m, decreasing from -0.68 at 295K to -0.47 at 143K to -0.38 at 40K for FCC phase, and remaining constant at ~-0.33 for all temperatures for the BCC phase. We also observed reduced work hardening rates and more extensive strain bursts during deformation at lower temperatures in all samples. All deformed FCC samples contained multiple parallel slip offsets for all pillar sizes and temperatures; compressed BCC pillars had wavy slip traces, which are evidence of multiple intersecting slip systems. Transmission Electron Microscopy (TEM) microstructural analysis of the compressed FCC samples reveals parallel slip lines and distorted slip planes, while compressed BCC samples contained entangled dislocation networks, as well as several twinned regions in samples deformed at 40 K. Molecular dynamics (MD) simulations of representative FCC and BCC HEA compressions reveal that deformation in FCC HEAs is dominated by nucleation and propagation of partial dislocations along parallel slip planes but by partial dislocation/twinning in the BCC HEA at all temperatures. Simulations also predict a decrease in stacking fault energy with increased alloying. For example, a reduction in the stable stacking fault energy of the FCC HEA up to 55% with respect to pure constituents is observed. This reduction in stable stacking fault energy may drive the observed deformation mechanisms. We also discuss theories of low-temperature strengthening in HEAs, compare them to our experimental data and assess how they manifest in the observed temperature-dependent size effect.

A High Resolution Digital Image Correlation Study under Multiaxial Loading

In this study, a miniaturized cruciform-shaped sample geometry which allows reaching high plastic strain under equibiaxial loading with reduced thickness at the test section is presented. The thinning method results in excellent surface quality that can be used for electron backscatter diffraction (EBSD) and high-resolution digital image correlation (HRDIC) investigations. The new cruciform geometry is used to study the slip activity in metastable austenitic stainless steel 304 during uniaxial and equibiaxial deformation using HRDIC. The results are discussed with respect to the Schmid law and the effect of multiple slip activity on the nucleation of martensitic transformations.

The effect of pre-twinning on the mechanical behavior of free-end torsion for an extruded AZ31 magnesium alloy

In this paper, the effect of pre-twinning on the mechanical behavior of free-end torsion (FET) for an extruded AZ31 Mg alloy was investigated via pre-compression along extruded direction with 1.5%, 3.5%, 5.5% and 6.5% plastic strain levels. After pre-compression, torsion was performed at room temperature. The yield strength was enhanced remarkably during FET test after 3.5% pre-compression. However, the change of yield strength is small during FET with pre-compression (PRC) greater than 3.5%. Refinement hardening induced by twinning contributes to the enhancement of yield strength for PRC 3.5 specimen. With pre-strain increasing, the change of yield strength is ascribed to dislocation hardening. The stage II and stage III of strain hardening were observed during pure torsion and FET test after 1.5% pre-compression. In contrast, the stage II is suppressed and the stage III only occurs during FETs after 3.5%, 5.5% and 6.5%. The pre-twinning favor the activation of prismatic slip under torsion, which enhances multiple slip and dynamic recovery. The transition of deformation mechanisms from basal slip to multiple slip leads to the change of strain hardening during FET after different pre-strain levels.

Deformation behaviour of Al–Cu–Li alloy containing T1 precipitates

ABSTRACTIn the present work, a systematic investigation of crystallographic texture evolution and strain hardening behaviour was undertaken to comprehend the deformation behaviour in the presence of T1 (Al2CuLi) precipitates. Characteristic texture components symbolising multiple slip condition such as Copper and S were observed upon rolling which is in contrast with other Al alloys containing shearable precipitates. Strain hardening ability was also observed to be remarkably high in the presence of T1 precipitates. The texture and strain hardening results are compared with another age hardenable Al alloy (Al–Mg–Si alloy) containing shearable precipitates to clearly bring out the difference in the nature of T1 precipitates.

Heat conduction and mass transfer in a MHD nanofluid flow subject to generalized Fourier and Fick’s law

Heat and mass transmission in Casson nanofluid flow induced by a linearly placed stretching sheet due to Cattaneo-Christov double diffusion convection with the company of thermal radiation scrutinized here. Multiple slip boundary conditions have been accounted here. Leading equations of the course have been normalized via similarity approach and unraveled resulting equations numerically by using RK-4 shooting procedure. Here dual characteristic of velocity field has been perceived for the parameters, velocity slip and Casson fluid. After numerical designs, influence of emergent flow parameters on flow specific are made appropriately via graphs and charts and explained the consequences with proper reasoning.

Superplasticity in Gold Nanowires through the Operation of Multiple Slip Systems

AbstractDislocation activity in metallic nanowires often causes shear localization and premature necking, resulting in an early fracture. Here, in situ nanomechanical testing reveals a strong orientation‐dependent dislocation‐mediated superplastic deformation in gold (Au) nanowires, with more than 100% uniform elongation achieved before the fracture of [111]‐oriented nanowires. Such superplastic deformability of [111]‐oriented Au nanowires originates from the close coordination of homogeneously activated dislocation events on the three equivalent slip planes, which effectively eliminates the dislocation‐induced deformation localization in Au nanowires with other orientations. This work sheds new light on the dislocation plasticity in metallic nanostructures, and is of technological importance for designing metallic nanostructures and nanodevices with high reliability.

Modeling the temperature and high strain rate sensitivity in BCC iron: Atomistically informed multiscale dislocation dynamics simulations

Multiscale discrete dislocation plasticity (MDDP) simulations are carried out to investigate the mechanical response and microstructure evolution of single crystal BCC iron subjected to high strain rate compression over a wide range of temperature. The simulations are conducted at temperatures ranging between 300 K and 900 K and strain rate ranging between 102 to107 s−1. Atomistically informed generalized mobility law was incorporated in MDDP to account for the effects of temperature and strain rate on dislocation mobility, lattice friction and elastic constants.MDDP based constitutive equations interrelating temperature and strain rate with the flow stress at high strain rate shock-less and shock conditions are proposed. The simulation results of the temperature and strain rate dependent yield strength and Hugoniot elastic limit are in good agreement with reported experimental results. Detailed investigations of the dislocation microstructure evolution show the formation of extended screw dislocation lines at temperatures below 340 K due to the large value of the lattice friction of the pure screw segments. Moreover, small sessile loops of radius in the order of few nanometers are formed. The formation of these sessile loops is facilitated by the easiness of multiple cross slip on available slip planes.

3D flow of Carreau polymer fluid over variable thickness sheet in a suspension of microorganisms with Cattaneo-Christov heat flux

Numerical study of three dimensional Carreau liquid flow with heat and mass transport features over a variable thickness sheet filled with microorganisms is analyzed. We considered the non-uniform heat sink or source and multiple slip effects. The governing non-linear partially differential expressions are developed into ordinary differential systems by using variable transformations. These expressions are solved numerically by using Runge-Kutta fourth order method connected with shooting methodology. A Parametric study is implemented to demonstrate the effects of Hartmann number, Prandtl number, Weissenberg number, Peclet number, chemical reaction and heat sink/source parameters on liquid velocity, temperature and concentration profiles. The quantities of physical interest are described within the boundary layer. From this analysis, we found that the magnetic parameter decrease the local Sherwood and local Nusselt numbers for both and cases. The constraint of chemical reaction enhances the mass transfer rate and decelerates the density of motile mass transfer rate. The space dependent and temperature dependent heat source/sink suppress the local Nusselt number.

Dislocation based plasticity in the case of nanoindentation

Understanding plasticity initiation and evolution in nanoindentation tests is a fundamental issue. In this study, a continuum model is developed to analytically predict the force-depth curve by coupling the classical Hertzian solution for elastic field and the evolution of dislocation density. By considering multiple slip systems, the present model predicts the “pop-in” event well. Large-scale molecular dynamics simulations are performed to evaluate the mechanical behavior of bcc Fe under nanoindentation of a spherical indenter and to verify the continuum model. The comparison between molecular dynamics simulations and model predictions shows that the initiation and evolution of dislocation networks is strongly dependent on the loading orientation, which is associated with different deformation patterns. Applying the transition state theory, we investigate the slip-twinning transition as a function of loading rate, which supports the basic hypothesis in the continuum model that the activation of shear loop requires lower energy compared with twin nucleation, although twins can nucleate temporally and annihilate into shear loops finally. The present model provides a general framework to evaluate and rationalize the “pop-in” behavior of any materials with elastoplastic response.

Ductile deformation mechanism in semiconductor \u03b1-Ag2S

Inorganic semiconductor α-Ag2S exhibits a metal-like ductile behavior at room temperature, but the origin of this high ductility has not been fully explored yet. Based on density function theory simulations on the intrinsic mechanical properties of α-Ag2S, its underlying ductile mechanism is attributed to the following three factors: (i) the low ideal shear strength and multiple slip pathways under pressure, (ii) easy movement of Ag–S octagon framework without breaking Ag−S bonds, and (iii) a metallic Ag−Ag bond forms which suppresses the Ag–S frameworks from slipping and holds them together. The easy slip pathways (or easy rearrangement of atoms without breaking bonds) in α-Ag2S provide insight into the understanding of the plastic deformation mechanism of ductile semiconductor materials, which is beneficial for devising and developing flexible semiconductor materials and electronic devices.

Effects of multiple slip on MHD combined convective flow of viscoelastic nanofluid over a stretchy sheet with heat absorption

We explore the impact of MHD combined convective flow of viscoelastic nanofluid over a stretchy sheet with heat absorption & multiple slip conditions. The similarity variables are employed to convert the PDE’s into dimensionless ODE’s and they are solved using homotopy analysis method (HAM). The impact of governing parameters on the velocity, temperature & nanoparticle concentration are analyzed with the help of tables and graphs.