Showing papers on "Slip line field published in 2005"

Earthquake slip weakening and asperities explained by thermal pressurization

Abstract: An earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion. This slip weakening occurs over a critical distance, D(c). Understanding the controls on D(c) in nature is severely limited, however, because the physical mechanism of weakening is unconstrained. Conventional friction experiments, typically conducted at slow slip rates and small displacements, have obtained D(c) values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes. Here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the Median Tectonic Line fault zone, Japan. We show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid is the slip-weakening mechanism. Our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity.

Apparent slip and viscoplasticity of concentrated suspensions

Abstract: The apparent slip flows of incompressible and viscoplastic (Herschel–Bulkley) fluids in plane Couette, capillary, and rectangular slit dies under fully developed, isothermal, and creeping flow conditions were analyzed assuming that the apparent slip layer consists solely of the binder and its thickness is independent of the flow rate. Both the drag-induced (plane Couette) and pressure-induced (capillary and slit) flows generate the same dependencies of the wall-slip velocity on the wall shear stress. Navier’s slip coefficient, which relates the wall-slip velocity to the shear stress, is similar for all three flows and is a function of the thickness of the apparent slip layer and the shear viscosity of the binder. The assumed apparent slip mechanism provides methodologies for the determination of the slip velocity values that are consistent with the traditional Mooney method and furthermore allows the determination of the true shear rate of the suspension at the wall and the yield stress. The analysis of t...

Fusion by earthquake fault friction: Stick or slip?

Abstract: Field observations of pseudotachylites, and experimental studies of high-speed friction indicate that melting on a slipping interface may sig- nificantly affect the magnitude of shear stresses resisting slip. We investigate the effects of rock melting on the dynamic friction using theoretical models of shear heating that couple heat transfer, thermodynamics of phase transitions, and fluid mechanics. Results of laboratory experiments conducted at high (order of m/s) slip velocities but low (order of MPa) normal stresses suggest that the onset of frictional melting may give rise to substantial increases in the effective fault strength, presumably due to viscous effects. However, extrapolation of the modeling results to in situ conditions suggests that the efficiency of viscous braking is significantly reduced under high normal and shear stresses. When transient increases in the dynamic fault strength due to fusion are not sufficient to inhibit slip, decreases in the effective melt viscosity due to shear heating and melting of clasts drastically decrease the dynamic friction, resulting in a nearly complete stress drop ("thermal runaway"). The amount of energy dissipation associated with the formation of pseudo- tachylites is governed by the temperature dependence of melt viscosity, and the average clast size in the fault gouge prior to melting. Clasts from a coarse- grained gouge have lower chances of survival in a pseudotachylite due to a higher likelihood of non-equilibrium overheating. The maximum temperature and energy dissipation attainable on the fault surface are ultimately limited by either the rock solidus (via viscous braking, and slip arrest), or liquidus (via thermal runaway, and vanishing resistance to sliding). Our modeling results indicate that the thermally-activated fault strengthening and rupture arrest are unlikely to occur in most mafic protoliths, but might be relevant for quartz-rich rocks, especially at shallow (< 5-7 km) depths where the driving shear stress is relatively low.

Numerical Analysis of a Journal Bearing With a Heterogeneous Slip/No-Slip Surface

Abstract: The no-slip boundary condition is part of the foundation of the traditional lubrication theory. It states that fluid adjacent to a solid boundary has zero velocity relative to the solid surface. For most practical applications, the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for certain engineered surfaces the no-slip boundary condition is not valid. Measured velocity profiles show that slip occurs at the interface. In the present study, the effect of an engineered slip/no-slip surface on journal bearing performance is examined. A heterogeneous pattern, in which slip occurs in certain regions and is absent in others, is applied to the bearing surface. Fluid slip is assumed to occur according to the Navier relation. Analysis is performed numerically using a mass conserving algorithm for the solution of the Reynolds equation. Load carrying capacity, side leakage rate, and friction force are evaluated. In addition, results are presented in the form of Raimondi and Boyd graphs. It is found that the judicious application of slip to a journal bearing’s surface can lead to improved bearing performance.

The wrinkle‐like slip pulse is not important in earthquake dynamics

Abstract: [1] A particular solution for slip on an interface between different elastic materials, the wrinkle-like slip pulse, propagates in only one direction with reduced normal compressive stress. More general solutions, and natural earthquakes, need not share those properties. In a 3D dynamic model with a drop in friction and heterogeneous initial stress, the wrinkle-like slip pulse is only a small part of the solution. Rupture propagation is determined primarily by the potential stress drop, not by the wrinkle-like slip pulse. A 2D calculation with much finer resolution shows that energy loss to friction might not be significantly reduced in the wrinkle-like slip pulse.

Breakdown of the Schmid Law in BCC Molybdenum Related to the Effect of Shear Stress Perpendicular to the Slip Direction

Abstract: The breakdown of the Schmid law in bcc metals has been known for a long time. The asymmetry of shearing in the slip direction 〈111〉 in the positive and negative sense, respectively, commonly identified with the twinning-antitwinning asymmetry, is undoubtedly one of the reasons. However, effect of stress components other than the shear stress in the slip direction may be important. In this paper we investigate by atomistic modeling the effect of shear stresses perpendicular to the Burgers vector on the glide of a/2〈111〉 screw dislocations. We show that these shear stresses can significantly elevate or reduce the critical resolved shear stress (CRSS) in the direction of the Burgers vector needed for the dislocation motion, i.e. the Peierls stress. This occurs owing to the changes of the core induced by these stresses. This effect may be the reason why slip systems with smaller Schmid factors may be preferred over that with the largest Schmid factor.

Evaluation of the stability of anchor-reinforced slopes

Abstract: The conventional methods of slices are commonly used for the analysis of slope stability. When anchor loads are involved, they are often treated as point loads, which may lead to abrupt changes in ...

On the boundary slip of fluid flow

Abstract: This paper presents a stress controlled boundary slip model and predicts the fluid-solid interface slip in a system of parallel sliding plates or a sphere approaching a smooth plane. The numerical simulation results are in striking agreement with the existing experimental observations. This model assumes that there is a limiting shear stress. No slip occurs if the surface shear stress is smaller than the limiting shear stress, and slip occurs when the surface shear stress equals it. It is found that boundary slip dramatically decreases the hydrodynamic pressure if the two squeezed surfaces have the same slip property. Finally, the hydrodynamic force reaches a saturation status and almost does not decrease any more. Compared with the no-slip solution, hydrodynamic force is found to decrease by over two orders in the case of boundary slip. When the squeezed surfaces have different slip properties, however, the hydrodynamic pressure is mainly controlled by the surface having a smaller surface limiting shear stress, and reduces more slowly compared with the case of two surfaces having the same slip property. Even when one of the surfaces has a zero surface limiting shear stress, a considerable hydrodynamic force still exists.

Investigation into relative slip during fretting fatigue under partial slip contact condition

Abstract: A finite element analysis based methodology was developed to compute local relative slip on contact surface from the measured global relative slip away from contact surface. A set of springs was included in finite element model to simulate fretting fatigue test system. Compliance of springs was calibrated by comparing experimental and computed global relative slips. This methodology was then used to investigate local relative slip during fretting fatigue in cylinder-on-flat contact configuration under partial slip contact condition for unpeened and shot-peened titanium alloy, Ti–6Al–4V. Relative slip on contact surface is significantly smaller (about one order) than the measured global relative slip by using a conventional extensometer near the contact surface. Effects of coefficient of friction, rigidity of fretting fatigue system and applied stress to specimen on the global and local relative slips were characterized. Coefficient of friction and contact load have considerable effect on local relative slip, and practically no effect on global relative slip. Gross slip condition can develop at some locations on contact surface in spite of overall partial slip condition. Increase in rigidity of fretting fatigue system increases local relative slip but decreases global relative slip. Finally, fatigue life diagrams based on relative slip on contact surface are established for both unpeened and shot-peened titanium alloy. These show the same characteristics as of the conventional S–N diagram where fatigue life decreases with increase of relative slip.

Reactions of slip dislocations with twin boundary in Fe-Si bicrystals

Abstract: Specimens for in situ TEM straining were prepared from Fe-5.5 at.%Si Σ 3 bicrystals with {112} grain boundary plane. They were strained under three different directions of the stress at the boundary with respect to the orientation of the grains. Transfer of slip across the boundary was analysed. In one case, the transfer of slip was realized by a transformation of the slip dislocation in one grain into the slip dislocation in the other grain. Low energy dislocation was created in the GB in accordance with general transfer criteria. In the second case, the incoming and outgoing slip systems were in direct contraction to the general transfer criteria. In the third case, oriented for common slip system in both grains, the trapped incoming slip dislocations dissociated into twinning dislocations which created twins on the other side of the boundary.

Rheology of shear thickening suspensions and the effects of wall slip in torsional flow

Abstract: The rheological characterisation of concentrated shear thickening materials suspensions is challenging, as complicated and occasionally discontinuous rheograms are produced. Wall slip is often apparent and when combined with a shear thickening fluid the usual means of calculating rim shear stress in torsional flow is inaccurate due to a more complex flow field. As the flow is no longer “controlled”, a rheological model must be assumed and the wall boundary conditions are redefined to allow for slip. A technique is described where, by examining the angular velocity response in very low torque experiments, it is possible to indirectly measure the wall slip velocity. The suspension is then tested at higher applied torques and different rheometer gaps. The results are integrated numerically to produce shear stress and shear rate values. This enables the measurement of true suspension bulk flow properties and wall slip velocity, with simple rheological models describing the observed complex rheograms.

Temperature jump and slip velocity calculations from an anisotropic scattering kernel

Abstract: This article deals with the problem of temperature jump and slip velocity at the wall in gas/surface interaction. A consistent modelling of an impermeable surface involving an anisotropic scattering kernel developed in previous works is used to establish boundary conditions in unstructured molecule gas flows. Thus, a temperature jump relation is derived in which the gas viscous effects at the wall and the mean velocity gradients appear. Likewise, a slip velocity relation is obtained in which both the slip coefficient and the thermal creep coefficient depend on the wall-to-gas temperature ratio. Moreover, both the temperature jump and the slip velocity relations involve not only one accommodation coefficient as usual, but also the gas/surface information through the various (notably normal and tangential) accommodation coefficients of the momentum components.

Three‐dimensional finite element modeling of stress interaction: An application to Landers and Hector Mine fault systems

Abstract: [1] We model the coseismic and postseismic stress changes and the surface deformation caused by earthquake dislocations through a three-dimensional (3-D) finite element numerical procedure applied to the 1992 Landers and the 1999 Hector Mine earthquakes. Our goal is to investigate the stress interaction between these complex nonplanar fault systems. The modeling strategy proposed in this study allows the calculation of elastic deformation and Coulomb stress changes either by imposing the slip distribution as a boundary condition along assigned faults or by retrieving the slip pattern on preexisting faults imposing the regional stress field. We study how different initial stress conditions (including the depth dependence of isotropic components of the regional stress), different values of Coulomb friction coefficient, and the 1-D rigidity layering can affect the slip pattern on assumed faults and the resulting Coulomb stress changes. We propose here an original approach to simultaneously model slip distribution, surface deformation, and stress perturbations consistently with the rheological parameters of the lithosphere and its state of stress.

The statistical origin of bulk mechanical properties and slip behavior in fcc metals

Abstract: A dislocations-based model is presented for predicting the flow stress of a pre-deformed metal single crystal. The model is based upon a combination of basic dislocation physics, the distribution of dislocation segment lengths in cell walls and percolation theory. With only the magnitude of the Burgers vector and the elastic shear modulus as inputs, and with no adjustable parameters, the model correctly predicts the formation of slip lines and slip bands, the linear behavior of the stress–strain curve in stage II hardening, the Voce behavior in stage III and the magnitude of the flow stress for deformed Al single crystals.

Determination of stress state in chip formation zone by central slip-line field

Abstract: Stress state of chip formation zone is one of the main problems in metal cutting mechanics. In two-dimensional case this process is usually considered as consistent shears of work material along one of several shear surfaces, separating chip from workpiece. These shear planes are assumed to be trajectories of maximum shear stress forming corresponding slip-line field. This paper suggests a new approach to the constriction of slip-line field, which implies uniform compression in chip formation zone. Based on the given model it has been found that imaginary shear line in orthogonal cutting is close to the trajectory of maximum normal stress and the problem about its determination has been considered as well. It has been shown that there is a second central slip-line field inside chip, which corresponds well to experimental data about stress distribution on tool rake face and tool-chip contact length. The suggested model would be useful in understanding mechanistic problems in machining.

Effects of slip condition on the characteristic of flow in ice melting process

Abstract: In this paper a laminar flow of water on an ice layer subjected to a slip condition is considered numerically. The paper describes a parametric mathematical model to simulate the coupled heat and mass transfer events occurring in moving boundary problems associated with a quasi steady state steady flow process. The discretization technique of the elliptic governing differential equations of mass, momentum and energy is based on the control volume finite difference approach and enthalpy method. the results illustrate , the distribution of heat transfer coefficient, ice melting thickness, slip velocity at solid moving boundary and boundary layer thickness for some values of slip velocity coefficient , Cu

Fusion by earthquake fault friction: Stick or slip? - eScholarship

Abstract: [1] Field observations of pseudotachylites and experimental studies of high-speed friction indicate that melting on a slipping interface may significantly affect the magnitude of shear stresses resisting slip. We investigate the effects of rock melting on the dynamic friction using theoretical models of shear heating that couple heat transfer, thermodynamics of phase transitions, and fluid mechanics. Results of laboratory experiments conducted at high ( order of m/s) slip velocities but low ( order of MPa) normal stresses suggest that the onset of frictional melting may give rise to substantial increases in the effective fault strength, presumably due to viscous effects. However, extrapolation of the modeling results to in situ conditions suggests that the efficiency of viscous braking is significantly reduced under high normal and shear stresses. When transient increases in the dynamic fault strength due to fusion are not sufficient to inhibit slip, decreases in the effective melt viscosity due to shear heating and melting of clasts drastically decrease the dynamic friction, resulting in a nearly complete stress drop ( thermal runaway''). The amount of energy dissipation associated with the formation of pseudotachylites is governed by the temperature dependence of melt viscosity and the average clast size in the fault gouge prior to melting. Clasts from a coarse-grained gouge have lower chances of survival in a pseudotachylite due to a higher likelihood of nonequilibrium overheating. The maximum temperature and energy dissipation attainable on the fault surface are ultimately limited by either the rock solidus ( via viscous braking, and slip arrest) or liquidus ( via thermal runaway and vanishing resistance to sliding). Our modeling results indicate that the thermally activated fault strengthening and rupture arrest are unlikely to occur in most mafic protoliths but might be relevant for quartz-rich rocks, especially at shallow (< 5 - 7 km) depths where the driving shear stress is relatively low.

Determination of slip surface in slope based on theory of slip line field

Abstract: A method to search for the slip surface in slope through finite element result based on the theory of slip line is improved;and the influence of the flow rule on the slope stability is studied based on this method In this method,the elastic area and plastic zone can be distinguished and the different flow rules can be considered The methods to protract the orientation field of slip line and trace the slip line from any point in export portion are brought out The slip line of which the safety factor is least,is the critical slip surface The examples have shown the reliability of the method The study indicates that the flow rule has small influence on the stability of the slope without restriction;however,the critical slip surface may be different If there are loads on the top of the slope, especially the loads are crucialt,he flow rule can influence both the safety factor and the slip surface remarkably If the associated flow rule is adopted,the stability of the slope may be overestimated