Showing papers on "Slip (materials science) published in 2018"

Magnetically-driven phase transformation strengthening in high entropy alloys

Abstract: CrCoNi alloy exhibits a remarkable combination of strength and plastic deformation, even superior to the CrMnFeCoNi high-entropy alloy. We connect the magnetic and mechanical properties of CrCoNi, via a magnetically tunable phase transformation. While both alloys crystallize as single-phase face-centered-cubic (fcc) solid solutions, we find a distinctly lower-energy phase in CrCoNi alloy with a hexagonal close-packed (hcp) structure. Comparing the magnetic configurations of CrCoNi with those of other equiatomic ternary derivatives of CrMnFeCoNi confirms that magnetically frustrated Mn eliminates the fcc-hcp energy difference. This highlights the unique combination of chemistry and magnetic properties in CrCoNi, leading to a fcc-hcp phase transformation that occurs only in this alloy, and is triggered by dislocation slip and interaction with internal boundaries. This phase transformation sets CrCoNi apart from the parent quinary, and its other equiatomic ternary derivatives, and provides a new way for increasing strength without compromising plastic deformation.

Deformation behaviors and cyclic strength assessment of AZ31B magnesium alloy based on steady ratcheting effect

Abstract: In this paper, deformation behaviors and microstructure evolution of a hot-rolled AZ31B magnesium alloy under cyclic loadings are investigated. The relationship between plastic deformation and microstructure evolution and the crack formation mechanisms are discussed. Under a high cyclic stress (90–140 MPa), steady ratcheting effect occurred in the material and the development of ratcheting strain went through three stages: 1) Stage I - initial rapid increase stage; 2) Stage II - steady stage; and 3) Stage III - final abrupt increase stage. Under a low cyclic stress (≤ 90 MPa), inconspicuous ratcheting effect was found in the material, indicating a light damage in the material. When the cyclic stress is below 30 MPa, no ratcheting effect is found and only elastic deformation occurs in the material. The formation of cracks in Stages I & II is mainly due to the activation of the basal slip system. The mean geometrically necessary dislocations (GND) are calculated to analyze the relationship between the basal slip and the ratcheting effect during the cyclic loading. Finally, a new approach is proposed to estimate the AZ31B magnesium alloy’s cyclic strength (at 107 cycles) according to the cyclic stress at which steady ratcheting effect starts to occur in the material.

Rotating flow of Ag-CuO/H 2 O hybrid nanofluid with radiation and partial slip boundary effects.

Abstract: The main object of the present paper is to examine and compare the improvement of flow and heat transfer characteristics between a rotating nanofluid and a newly discovered hybrid nanofluid in the presence of velocity slip and thermal slip. The influence of thermal radiation is also included in the present study. The system after applying the similarity transformations is solved numerically by using the bvp-4c scheme. Additionally, numerical calculations for the coefficient of skin friction and local Nusselt number are introduced and perused for germane parameters. The comparison between water, nanofluid and hybrid nanofluid on velocity and temperature is also visualized. It is observed that the velocity and temperature distributions are decreasing functions of the slip parameter. Temperature is boosted by thermal radiation and rotation. It is found that the heat transfer rate of the hybrid nanofluid is higher as compared to the traditional nanofluid.

Tactile Sensors for Friction Estimation and Incipient Slip Detection—Toward Dexterous Robotic Manipulation: A Review

Abstract: Humans can handle and manipulate objects with ease; however, human dexterity has yet to be matched by artificial systems. Receptors in our fingers and hands provide essential tactile information to the motor control system during dexterous manipulation such that the grip force is scaled to the tangential forces according to the coefficient of friction. Likewise, tactile sensing will become essential for robotic and prosthetic gripping performance as applications move toward unstructured environments. However, most existing research ignores the need to sense the frictional properties of the sensor–object interface, which (along with contact forces and torques) is essential for finding the minimum grip force required to securely grasp an object. Here, we review this problem by surveying the field of tactile sensing from the perspective that sensors should: 1) detect gross slip (to adjust the grip force); 2) detect incipient slip (dependent on the frictional properties of the sensor–object interface and the geometries and mechanics of the sensor and the object) as an indication of grip security; or 3) measure friction on contact with an object and/or following a gross or incipient slip event while manipulating an object. Recommendations are made to help focus future sensor design efforts toward a generalizable and practical solution to sense, and hence control grip security. Specifically, we propose that the sensor mechanics should encourage incipient slip, by allowing parts of the sensor to slip while other parts remain stuck, and that instrumentation should measure displacement and deformation to complement conventional force, pressure, and vibration tactile sensing.

Fate of Large-Scale Structure in Modified Gravity After GW170817 and GRB170817A.

Abstract: The coincident detection of gravitational waves (GW) and a gamma-ray burst from a merger of neutron stars has placed an extremely stringent bound on the speed of GWs. We showed previously that the presence of gravitational slip (η) in cosmology is intimately tied to modifications of GW propagation. This new constraint implies that the only remaining viable source of gravitational slip is a conformal coupling to gravity in scalar-tensor theories, while viable vector-tensor theories cannot now generate gravitational slip at all. We discuss structure formation in the remaining viable models, demonstrating that (i) the dark-matter growth rate must now be at least as fast as in general relativity (GR), with the possible exception of that beyond the Horndeski model, and (ii) if there is any scale dependence at all in the slip parameter, it is such that it takes the GR value at large scales. We show a consistency relation that must be violated if gravity is modified.

Deformation Behavior of Ultra-Strong and Ductile Mg-Gd-Y-Zn-Zr Alloy with Bimodal Microstructure

Abstract: An ultra-strong and ductile Mg-8.2Gd-3.8Y-1Zn-0.4Zr (wt pct) alloy was developed by using hot extrusion to modify the microstructure via forced-air cooling and an artificial aging treatment. A superior strength–ductility balance was obtained that had a tensile yield strength of 466 MPa and an elongation to failure of 14.5 pct. The local strain evolution during the in situ testing of the ultra-strong and ductile alloy was quantitatively analyzed with high-resolution electron backscattered diffraction and digital image correlation. The fracture behavior during the tensile test was characterized by synchrotron X-ray tomography along with SEM and STEM observations. The alloy showed a bimodal microstructure, consisting of dynamically recrystallized (DRXed) grains with random orientations and elongated hot-worked grains with $$ \left\langle { 10{\bar{\text{1}}}0} \right\rangle $$ parallel to the extrusion direction. The DRXed grains were deformed by the basal 〈a〉 slip and the hot-worked grains were deformed by the prismatic 〈a〉 slip dominantly. The strain evolution analysis indicated that the multilayered structure relaxed the strain localization via strain transfer from the DRXed to the hot-worked regions, which led to the high ductility of the alloy. Precipitation of the γ′ on basal planes and the β′ phases on the prismatic planes of the α-Mg generated closed volumes, which enhanced the strength by pinning dislocations effectively, and contributed to the high ductility by impeding the propagation of micro-cracks inside the grains. The deformation incompatibility between the hot-worked grains and the arched block-shaped long-period stacking ordered (LPSO) phases induced the crack initiation and propagation, which fractured the alloy.

Evolution of real contact area under shear and the value of static friction of soft materials.

Abstract: The frictional properties of a rough contact interface are controlled by its area of real contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the real contact area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. Here, through direct measurements on various contacts involving elastomers or human fingertips, we show that the real contact area also decreases under shear, with reductions as large as 30%, starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the area-reduction rate of individual contacts obeys a scaling law valid from micrometer-sized junctions in rough contacts to millimeter-sized smooth sphere/plane contacts. For the class of soft materials used here, our results should motivate first-order improvements of current contact mechanics models and prompt reinterpretation of the rate-and-state parameters.

Simultaneous investigations the effects of non-Newtonian nanofluid flow in different volume fractions of solid nanoparticles with slip and no-slip boundary conditions

Abstract: In this study, the laminar and forced flow of non-Newtonian nanofluid in a two-dimensional microtube has been numerically simulated. The non-Newtonian, pseudo-plastic fluid is included of a solution with 0.5% wt fraction of CMC in Water as the base fluid. In this research, in order to increase the heat transfer rate, the mentioned non-Newtonian fluid has been combined with volume fractions of 1 and 1.5% of CuO nanoparticle and has been created the non-Newtonian cooling nanofluid. In this investigation, the effect of slip velocity boundary condition on the wall of microtube has been considered. In order to have an accurate estimation of dynamic viscosity of non-Newtonian nanofluid, the power-law model, for numerical simulation has been used. This research has been investigated in Reynolds numbers of 100, 500, 1500 and 2000. The results indicate that, the increase of volume fraction of solid nanoparticles and slip velocity coefficient, cause the increase of heat transfer. By enhancing the slip velocity coefficient, better mixing accomplishes which causes the reduction of temperature gradients among the fluid layers close to the surface. In Reynolds numbers of 1500 and 2000, comparing to Reynolds numbers of 100 and 500, Nusselt number, on the microtube wall increases significantly.

The study of non-Newtonian nanofluid with hall and ion slip effects on peristaltically induced motion in a non-uniform channel

Abstract: In this study, we considered the unsteady peristaltic motion of a non-Newtonian nanofluid under the influence of a magnetic field and Hall currents. The simultaneous effects of ion slip and chemical reaction were also taken into consideration. The flow problem was suggested on the basis of the continuity, thermal energy, linear momentum, and nanoparticle concentration, which were further reduced with the help of Ohm's law. Mathematical modelling was executed using the lubrication approach. The resulting highly nonlinear partial differential equations were solved semi-analytically using the homotopy perturbation technique. The impacts of all the pertinent parameters were investigated mathematically and graphically. Numerical calculations have been used to calculate the expressions for the pressure increase and friction forces along the whole length of the channel. The results depict that for a relatively large value of the Brownian parameter, the chemical reaction has a dual behaviour on the concentration profile. Moreover, there is a critical point of the magnetic parameter at which the behaviours of the pressure increase and friction forces are reversed for progressive values of the power law index. The present investigation provides a theoretical model that estimates the impact of a wide range of parameters on the characteristics of blood-like fluid flows.

Review: Modes and Processes of Severe Plastic Deformation (SPD).

Abstract: In this review, severe plastic deformation (SPD) is considered as a materials processing technology. The deformation mode is the principal characteristic differentiating SPD techniques from common forming operations. For large plastic strains, deformation mode depends on the distribution of strain rates between continuum slip lines and can be varied from pure shear to simple shear. A scalar, invariant, and dimensionless coefficient of deformation mode is introduced as a normalized speed of rigid rotation. On this basis, simple shear provides the optimal mode for structure modification and grain refinement, whereas pure shear is “ideal” for forming operations. Special experiments and SPD practice confirm this conclusion. Various techniques of SPD are classified and described in accordance with simple shear realization or approximation. It is shown that correct analyses of the processing mechanics and technological parameters are essential for the comparison of SPD techniques and the development of effective industrial technologies.

Comparative investigation of five nanoparticles in flow of viscous fluid with Joule heating and slip due to rotating disk

Abstract: Present article addresses the comparative study for flow of five water based nanofluids. Flow in presence of Joule heating is generated by rotating disk with variable thickness. Nanofluids are suspension of Silver ( A g ), Copper ( C u ), Copper oxide ( C u O ), Aluminum oxide or Alumina ( A l 2 O 3 ), Titanium oxide or titania ( T i O 2 ) and water. Boundary layer approximation is applied to partial differential equations. Using Von Karman transformations the partial differential equations are converted to ordinary differential equations. Convergent series solutions are obtained. Graphical results are presented to examine the behaviors of axial, radial and tangential velocities, temperature, skin friction and Nusselt number. It is observed that radial, axial and tangential velocities decay for slip parameters. Axial velocity decays for larger nanoparticle volume fraction. Effect of nanofluids on velocities dominant than base material. Temperature rises for larger Eckert number and temperature of silver water nanofluid is more because of its higher thermal conductivity. Surface drag force reduces for higher slip parameters. Transfer of heat is more for larger disk thickness index.

On the Relationship Between Fault Permeability Increases, Induced Stress Perturbation, and the Growth of Aseismic Slip During Fluid Injection

Abstract: Fluid injections into the deep subsurface can, at times, generate earthquakes, but often, they only produce aseismic deformations. Here we analyze the influence of fault hydromechanical properties on the growth of injection‐induced aseismic slip. Using hydromechanical modeling, we show how permeability enhancement in addition to the background stress and frictional weakening has an important effect on the pressure diffusion and slip growth during injection. We find that the more pronounced the fault permeability enhancement, the stronger is the growth of the aseismic slip zone. The effect of enhanced permeability is more pronounced when the fault is initially close to failure. Our results show that aseismic slip grows beyond the pressurized zone when the fault permeability increases, while slip remains behind the pressurized zone when permeability does not vary from its initial preslip value. Thus, fault permeability increases should be considered as complementary mechanism to current models of fluid‐induced aseismic slip.

Shallow very-low-frequency earthquakes accompany slow slip events in the Nankai subduction zone.

Abstract: Recent studies of slow earthquakes along plate boundaries have shown that tectonic tremor, low-frequency earthquakes, very-low-frequency events (VLFEs), and slow-slip events (SSEs) often accompany each other and appear to share common source faults. However, the source processes of slow events occurring in the shallow part of plate boundaries are not well known because seismic observations have been limited to land-based stations, which offer poor resolution beneath offshore plate boundaries. Here we use data obtained from seafloor observation networks in the Nankai trough, southwest of Japan, to investigate shallow VLFEs in detail. Coincident with the VLFE activity, signals indicative of shallow SSEs were detected by geodetic observations at seafloor borehole observatories in the same region. We find that the shallow VLFEs and SSEs share common source regions and almost identical time histories of moment release. We conclude that these slow events arise from the same fault slip and that VLFEs represent relatively high-frequency fluctuations of slip during SSEs.

Investigation into the effects of slip boundary condition on nanofluid flow in a double-layer microchannel

Abstract: In this research, the laminar flow and heat transfer of kerosene/MWCNT nanofluid in a novel design of a double-layer microchannel under the influence of oscillating heat flux and slip boundary condition have been studied. This research has been investigated in the dimensionless lengths of (λ 1) 1/3, 2/3 and 3/3 and dimensionless slip velocity coefficients ranging from 0.001 to 0.1. The suspension of nanoparticles in kerosene as the base fluid has been studied in Reynolds numbers of 1–100 and volume fractions of 0–8%. The results indicate that, by using novel design of double-layer microchannel in λ 1 = 1/3, the maximum rate of performance evaluation criterion is obtained and by increasing the slip velocity coefficient, the amount of PEC becomes significant. Among the studied cases, in all Reynolds numbers and volume fractions, the dimensionless length of 1/3 has the maximum amount of friction coefficient. Also, by enhancing the volume fraction of nanoparticles, slip velocity coefficient, Reynolds number and significant reduction in thermal resistance of solid wall, Nusselt number enhances.

Slip Detection With a Biomimetic Tactile Sensor

Abstract: Slip detection helps to prevent robotic hands from dropping grasped objects and would thus enable complex object manipulation. Here we present a method of detecting slip with a biomimetic optical tactile sensor-the TacTip-that operates by measuring the positions of internal pins embedded in its compliant skin. We investigate whether local pin movement is a strong signal of slip. Accurate and robust discrimination between static and slipping objects is obtained with a support vector machine (accuracy 99.88%). We then demonstrate performance on a task in which a slipping object must be caught. For fast reaction times, a modified TacTip is made for high-speed data collection. Performance of the slip detection method is then validated under several test conditions, including varying the speed at which slip onset occurs and using novel shaped objects. The proposed methods should apply to tactile sensors that can detect the local velocities of surface movement. The sensor and slip detection methods are also well-suited for integration onto robotic hands for deploying slip control under manipulation.

An Explanation of Episodic Tremor and Slow Slip Constrained by Crack-Seal Veins and Viscous Shear in Subduction Mélange

Abstract: Episodic tremor and slow slip (ETS) occurs in the transition zone between the locked seismogenic zone and the deeper, stably sliding zone. Actual mechanisms of ETS are enigmatic, caused by lack of geological observations and limited spatial resolution of geophysical information from the ETS source. We report that quartz‐filled, crack‐seal shear and extension veins in subduction melange record repeated low‐angle thrust‐sense frictional sliding and tensile fracturing at near‐lithostatic fluid pressures. Crack‐seal veins were coeval with viscous shear zones that accommodated deformation by pressure solution creep. The minimum time interval between thrusting events, determined from a kinetic model of quartz precipitation in shear veins, was less than a few years. This short recurrence time of low‐angle brittle thrusting at near‐lithostatic fluid overpressures within viscous shear zones may be explained by frequent release of accumulated strain by ETS.

Complex fault geometry and rupture dynamics of the Mw 6.5, 2016, October 30th central Italy earthquake

Abstract: We study the October 30th 2016 Norcia earthquake (MW 6.5) to retrieve the rupture history by jointly inverting seismograms and coseismic GPS displacements obtained by dense local networks. The adopted fault geometry consists of a main normal fault striking N155°and dipping 47° belonging to the Mt. Vettore-Mt. Bove fault system (VBFS) and a secondary fault plane striking N210° and dipping 36° to the NW. The coseismic rupture initiated on the VBFS and propagated with similar rupture velocity on both fault planes. Up-dip from the nucleation point, two main slip patches have been imaged on these fault segments, both characterized by similar peak-slip values (~3 m) and rupture times (~3 s). After the breakage of the two main slip patches, coseismic rupture further propagated southeastward along the VBFS, rupturing again the same fault portion that slipped during the August 24th earthquake. The retrieved coseismic slip distribution is consistent with the observed surface breakages and the deformation pattern inferred from InSAR measurements. Our results show that three different fault systems were activated during the October 30th earthquake. The composite rupture model inferred in this study provides evidences that also a deep portion of the NNE-trending section of the Olevano-Antrodoco-Sibillini (OAS) thrust broke co-seismically, implying the kinematic inversion of a thrust ramp. The obtained rupture history indicates that, in this sector of the Apennines, compressional structures inherited from past tectonics can alternatively segment boundaries of NW-trending active normal faults or break co-seismically during moderate-to-large magnitude earthquakes.

No slip gravity

Abstract: A subclass of the Horndeski modified gravity theory we call No Slip Gravity has particularly interesting properties: 1) a speed of gravitational wave propagation equal to the speed of light, 2) equality between the effective gravitational coupling strengths to matter and light, Gmatter and Glight, hence no slip between the metric potentials, yet difference from Newton's constant, and 3) suppressed growth to give better agreement with galaxy clustering observations. We explore the characteristics and implications of this theory, and project observational constraints. We also give a simple expression for the ratio of the gravitational wave standard siren distance to the photon standard candle distance, in this theory and others, and enable a direct comparison of modified gravity in structure growth and in gravitational waves, an important crosscheck.

On stagnation point flow of a micro polar nanofluid past a circular cylinder with velocity and thermal slip

Abstract: The concerned problem is dedicated to study stagnation point flow of MHD micropolar nanomaterial fluid over a circular cylinder having sinusoidal radius variation. Velocity jump slip phenomenon with porous medium is also taken into account. To be more specific, the physical situation of micropolar fluid in the presence of both weak and strong concentration is mathematically modeled in terms of differential equations. Here, three nanoparticles namely Titania ( TiO 2 ) , Copper ( Cu ) and Alumina ( Al 2 O 3 ) compared with water as base fluids are incorporated for analysis. The resulting non-linear system has been solved by Runge-Kutta-Fehlberg scheme. Numerical solutions for velocities and temperature profiles are settled for alumina–water nanofluid and deliberated through graphs and numerical tables. It is seen that the skin friction coefficients and the rate of heat transfer are maximum for copper–water nanofluid related to the alumina–water and titania–water nanofluids. Also, the precision of the present findings is certified by equating them with the previously published work.

Fast and Slow Slip Events Emerge Due to Fault Geometrical Complexity

Abstract: Active faults release elastic strain energy via a whole continuum of modes of slip, ranging from devastating earthquakes to slow slip events (SSEs) and persistent creep. Understanding the mechanisms controlling the occurrence of rapid, dynamic slip radiating seismic waves (i.e., earthquakes) or slow, silent slip (i.e., SSEs) is a fundamental point in the estimation of seismic hazard along subduction zones. Using the numerical implementation of a simple rate-weakening fault model, we show that the simplest of fault geometrical complexities with uniform rate-weakening friction properties give rise to both SSEs and fast earthquakes without appealing to complex rheologies or mechanisms. We argue that the spontaneous occurrence, the characteristics and the scaling relationship of SSEs and earthquakes emerge from geometrical complexities. The geometry of active faults should be considered as a complementary mechanism to current numerical models of SSEs and fast earthquakes.