Showing papers on "Slip (materials science) published in 1986"

The dynamics of the spreading of liquids on a solid surface. Part 1. Viscous flow

Abstract: An investigation is made into the dynamics involved in the movement of the contact line when one liquid displaces an immiscible second liquid where both are in contact with a smooth solid surface. In order to remove the stress singularity at the contact line, it has been postulated that slip between the liquid and the solid or some other mechanism must occur very close to the contact line. The general procedure for solution is described for a general model for such slip and also for a general geometry of the system. Using matched asymptotic expansions, it is shown that for small capillary number and for small values of the length over which slip occurs, there are either 2 or 3 regions of expansion necessary depending on the limiting process being considered. For the very important situation where 3 regions occur, solutions are obtained from which it is observed that in general there is a maximum value of the capillary number for which the solutions exist. The results obtained are compared with existing theories and experiments.

Crustal Earthquake Instability in Relation to the Depth Variation of Frictional Slip Properties

Abstract: Recent stability studies using constitutive relations of the type found by Dieterich, Ruina, and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes. The class of friction laws discussed has the property that the sliding stress depends on normal stress, temperature, slip rate, and slip history. For sliding at a fixed slip rate V and fixed environment (e.g., normal stress, temperature, etc.) the shear strength τ evolves toward a steady state value τss(V). Stability analysis show that for dτss(V)/dV 0 (velocity strengthening) implies stable steady state sliding, at least for a broad class of constitutive laws more fully described in the paper. Experiments by Dieterich and by Tullis and Weeks on Westerly granite with mature sliding surfaces indicate that dτss(V)/dV is negative at room temperature, whereas higher-temperature experiments by Stesky show that dτss(V)/dV becomes positive above approximately 300°C. Therefore, in the case of the earth, where temperature increases with depth, the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth, from a regime with dτss(V)/dV 0. This is not inconsistent with, but rather refines, the suggestion by Sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow. Further, our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth. The depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone. Following Mavko, a two-dimensional quasi-static strike-slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the Lachenbruch-Sass depth variation of temperature for the San Andreas fault. The resulting predictions of such features as the confinement of crustal earthquakes to shallow depths, the development of locked patches, the recurrence time for the seismic cycle, the seismic stress drop and displacement, etc., are generally in agreement with the observed characteristics of large-scale strike-slip earthquakes along the San Andreas fault. Calculations based on the laboratory data predict, for example, that stick-slip nucleates around 5–7 km, that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13–15 km depths, that rapid postseismic creep occurs over another 3–4 km depth, and that at greater depths, steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above. The most uncertain parameter is the slip weakening distance L for evolution of fault surface state; we illustrate how features of the predicted earthquake cycles vary with L over the range for which calculations are feasible.

Effect of Cyclic Deformation on the Pseudoelasticity Characteristics of Ti-Ni Alloys

Abstract: Change in the pseudoelasticity characteristics of Ti-Ni alloys during tension cycling was investigated. The critical stress for inducing martensites and the hysteresis of a stress-strain curve decreased with increasing number of cyclic loading, while the permanent elongation increased. The degree of the change in these values showed a strong dependence on the maximum applied stress during stress-induced martensitic transformation. However, no change was induced by cyclic elastic deformation even though high stress was applied. It was also found that the stabilization of the pseudoelasticity characteristics during cyclic loading was established using special thermomechanical treatments which are effective to raise the critical stress for slip. Based on these results it is concluded that the cause for the effect of cyclic deformation is the generation of dislocations in the martensitic phase.

Wall Slip in Viscous Fluids and Influence of Materials of Construction

Abstract: The question of slip and the influence of materials of construction on the observed extrudate irregularities are examined for high viscosity molten polyethylenes. Capillary rheometer studies were conducted for several linear (LLDPE and HDPE) and branched (HP‐LDPE) polyethylenes, Viton A, and Barex‐210. Extensive blown film fabrication studies were conducted for narrow MWD UNIPOL process LLDPE resins. The results indicate that the assumption of “no‐slip at the rigid boundary” is generally not valid for polyethylenes above a critical shear stress of approximately 0.1–0.14 MPa, when either surface or gross irregularities are present in the extrudate. Loss of extrudate gloss at the critical shear stress defines the onset of melt fracture. Within the range of variables examined, the critical stress is relatively insensitive to molecular characteristics (molecular weight, MWD, and chain branching), melt temperature, and the detailed design of the capillary. Contrary to capillary rheometer observations, blown fi...

Dominant c slip in naturally deformed quartz: Implications for dramatic plastic softening at high temperature

Abstract: A combined microstructural, X-ray texture goniometry and transmission electron microscopy study has been undertaken to document rare examples of c direction of slip in naturally deformed quartz. The presence of optically visible basal (0001) subgrain boundaries and strong concentrations of c axes parallel to the inferred shearing direction (close to the stretching lineation) are considered characteristic of c slip. Dominant c slip appears to be limited to high-temperature (>650 °C) and possibly hydrous conditions. The possibility of plastic softening associated with the relatively easy glide on this system is discussed.

Brecciation processes in fault zones: Inferences from earthquake rupturing

Abstract: Surface-rupture patterns and aftershock distributions accompanying moderate to large shallow earthquakes reveal a residual brittle infrastructure for established crustal fault zones, the complexity of which is likely to be largely scale-invariant. In relation to such an infrastructure, continued displacement along a particular master fault may involve three dominant mechanical processes of rock brecciation: (a)attrition brecciation, from progressive frictional wear along principal slip surfaces during both seismic and aseismic sliding, (b)distributed crush brecciation, involving microfracturing over broad regions when slip on the principal slip surfaces is impeded by antidilational jogs or other obstructions, and (c)implosion brecciation, associated with the sudden creation of void space and fluid-pressure differentials at dilational fault jogs during earthquake rupture propagation. These last, high-dilation breccias are particularly favorable sites for hydrothermal mineral deposition, forming transitory low-pressure channels for the rapid passage of hydrothermal fluids. Long-lived fault zones often contain an intermingling of breccias derived from all three processes.

The dynamics of the spreading of liquids on a solid surface. Part 2. Surfactants

Abstract: A theoretical study is made of the effect of the presence of a surfactant on the dynamics involved in the movement of the contact line when one liquid displaces an immiscible second liquid where both are in contact with a smooth solid surface. The general procedure of solution is described for a general model for slip between solid and liquid near the contact line and also for a general macroscopic geometry. For small capillary number and for small values of the length over which slip occurs, it is shown, using singular perturbation analysis, that either 2 or 3 regions of expansion are necessary depending on the type of limiting process being considered. Solutions are obtained for both situations but for the more important three-region expansion case (where there can be large dynamic effects), a detailed discussion is given of the manner in which the observable macroscopic contact angle is shown to depend on the contact line velocity and on surfactant concentration. The conditions of validity for the theory are also discussed.

Fault dimensions, displacements and growth

Abstract: Maximum total displacement (D) is plotted against fault or thrust width(W) for 65 faults, thrusts, and groups of faults from a variety of geological environments. Displacements range from 0.4 m to 40 km and widths from 150 m to 630 km, and there is a near linear relationship betweenD andW 2. The required compatibility strains (e s) in rocks adjacent to these faults increases linearly withW and with $$\sqrt D $$ and ranges frome s=2×10−4 toe s=3×10−1. These are permanent ductile strains, which compare with values ofe s=2×10−5 for the elastic strains imposed during single slip earthquake events, which are characterised by a linear relationship between slip (u) andW. The data are consisten with a simple growth model for faults and thrusts, in which the slip in successive events increases by increments of constant size, and which predicts a relationship between displacement and width of the formD=cW 2. Incorporation of constant ductile strain rate into the model shows that the repreat time for slip events remains constant throughout the life of a fault, while the displacement rate increases with time. An internally consistent model withe s=2×10−5, giving repeat times of 160 years and instantaneous displacement rates of 0.02 cm/yr, 0.2 cm/yr, and 2.0 cm/yr when total displacement is 1 m, 100 m, and 10 km, and slip increasing by 0.5 mm with each event, gives a good approximation of the data. The model is also applicable to stable sliding, the slip rate varying with ductile strain rate and withW 2.

Scaling differences between large interplate and intraplate earthquakes

Abstract: A study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes, in which M sub o varies as L sup 2 or u = alpha L where L is rupture length and u is slip. In contrast to interplate earthquakes, for which alpha approximately equals 1 x .00001, for the intraplate events alpha approximately equals 6 x .0001, which implies that these earthquakes have stress-drops about 6 times higher than interplate events. This result is independent of focal mechanism type. This implies that intraplate faults have a higher frictional strength than plate boundaries, and hence, that faults are velocity or slip weakening in their behavior. This factor may be important in producing the concentrated deformation that creates and maintains plate boundaries.

Strain Hardening of Hadfield Manganese Steel

Abstract: The plastic flow behavior of Hadfield manganese steel in uniaxial tension and compression is shown to be greatly influenced by transformation plasticity phenomena. Changes in the stress-strain (σ−e) curves with temperature correlate with the observed extent of deformation twinning, consistent with a softening effect of twinning as a deformation mechanism and a hardening effect of the twinned microstructure. The combined effects give upward curvature to the σ−e curve over extensive ranges of plastic strain. A higher strain hardening in compression compared with tension appears to be consistent with the observed texture development. The composition dependence of stacking fault energy computed using a thermodynamic model suggests that the Hadfield composition is optimum for a maximum rate of deformation twinning. Comparisons of the Hadfield steel with a Co-33Ni alloy exhibiting similar twinning kinetics, and an Fe-21Ni-lC alloy deforming by slip indicate no unusual strain hardening at low strains where deformation is controlled by slip, but an unusual amount of structural hardening associated with the twin formation in the Hadfield steel. A possible mechanism of anomalous twin hardening is discussed in terms of modified twinning behavior (pseudotwinning) in nonrandom solid solutions.

Terrane motion by strike-slip faulting of forearc slivers

Abstract: Forearc slivers, bounded by a trench and an active strike-slip fault, occur in about 50% of modern subduction zones. Analysis of earthquake slip vectors indicates that modern sliver terranes typically migrate at rates of 1–2 cm/yr. Tertiary transport of some forearc slivers by 1000 km or more is therefore expected as a consequence of normal subduction. Active arc-parallel strike-slip faulting occurs whenever interplate coupling is strong and convergence is somewhat oblique; strike-slip rate increases with greater convergence obliquity.

A block model of distributed deformation by faulting

Abstract: It is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation. We propose a simple two-dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone. One surprizing feature of this model is that the component of strike-slip motion on the faults within the deforming zone is in the opposite sense to the strike-slip component across the zone as a whole. Thus slip vectors within the zone are not the same as that between the bounding rigid plates: in contrast to deformation at oceanic plate boundaries. Examples of active fault geometries similar to those of our model can be seen in Greece, Iran and the western USA.

Long-range internal stresses and asymmetric X-ray line-broadening in tensile-deformed [001]-orientated copper single crystals

Abstract: Copper single crystals oriented for multiple slip with [001] axes have been deformed in tension and investigated by X-ray line-broadening measurements using {002} Bragg reflections. The intensity distributions of the broadened line profiles of the deformed crystals exhibit an asymmetry whose ‘sign’ depends on the particular reflection used. It is shown that the asymmetric line profiles are due to the superposition of two mutually displaced symmetrically broadened line profiles. These two sub-profiles can be ascribed to the material located in the cell walls and in the cell interiors of the dislocation cell structure, respectively. The mutual displacements of the sub-profiles are evaluated quantitatively in terms of deformation-induced long-range internal stresses, which aid the applied stress in the cell walls and oppose it in the cell interiors. It is shown by a simple model that the long-range internal stresses are a necessary consequence of the plastic strain mismatch between the soft cell int...

Dynamic motion of a single degree of freedom system following a rate and state dependent friction law

Abstract: Sequences of dynamic instabilities are analyzed for a single degree of freedom elastic system which slides along a surface having frictional resistance depending on slip rate and slip rate history, in the manner of Dieterich, Ruina and others. The system is represented as a rigid block in contact with a fixed surface and having a spring attached to it whose opposite end is forced to move at a uniform slow speed. The resulting "stick-slip" motions are well understood in the classical case for which there is an abrupt drop from "static" to "sliding" frictional resistance. We analyze them here on the basis of more accurate frictional constitutive models. The problem has two time scales, an inertial scale set by the natural oscillation period T of the analogous frictionless system as T/2:rr and a state relaxation scale L/V occurring in evolution, over a characteristic slip distance L, of frictional stress u towards a "steady state" value uss(v) associated with slip speed V. We show that u _ uss(v) during motions for which acceleration a satisfies aL/V 2 > T/2n during much of the essentially quasi-static "stick" part of the cycle when there is a sufficiently small imposed velocity at the load point. Thus the physically irrelevant time scale (L/V during inertial controlled motion, T/2n during quasi-static motion) is much shorter than the relevant scale, which is troublesome from a numerical point of view as it is the shorter time scale which constrains allowable step size. We propose efficient numerical procedures to deal with such response, in which the full equations with inertia and state relaxation are solved only in a transition regime when both time scales are significant. We show results for several friction laws, all having history dependence based on a single evolving state variable and all having properties that &/V > 0 for instantaneous changes in V, that u evolves towards uss(v) as exp (--6/L) with ongoing slip 6 when V- const, and that duSS(V)/dV < 0 except possibly at high V. During the dynamic instabilities we find that motion continues at a nearly steady state condition, u _ 'rss(v), until dynamic overshoot becomes so significant that "arrest" begins. In the arrest stage, V drops rapidly to very much lower values (never zero in our models) under nearly fixed state conditions, and then the long quasi-static "stick" phase of the motion begins again.

Nature and dissociation of the dislocations in TiAl deformed at room temperature

Abstract: TiAl polycrystalline specimens, having the L10 structure, have been deformed at room temperature and examined by transmission electron microscopy. The observations revealed a new type of slip superdislocations a/2〈112〉 gliding in the (111) planes, in addition to the a〈101〉 and a/2〈110〉 dislocations previously described in L10 compounds. Dissociation configurations of the superdislocations a/2〈112〉 and a〈101〉 have been observed: they explain the numerous extrinsic faulted dipoles limited by 1/6〈112〉 partials which are commonly observed in the deformed samples. In particular, the superdislocations dissociate only discontinuously on small segments (about 50 nm) along the dislocation line. It is argued that the superdislocations are pinned by jogs, and the rearrangement of the core structure around the jog leads to a faulted loop surrounded by a sessile 1/6〈112〉 partial. Faulted dipoles arise from the trailing of these loops. Extrinsic faults are usually rarely observed since they require the slip of...

Rupture history of the 1984 morgan hill, california, earthquake from the inversion of strong motion records

Abstract: Near-source strong motion velocity records and teleseismic short-period P waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 Morgan Hill earthquake. Both forward modeling and constrained, least-squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0.2 to 2.0 Hz. These data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine-tenths of the local S-wave velocity. The majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions, each with an extent of about 5 km with their centers separated by about 12 km. However, each of the sources has detailed structure of its own, and a simple two-point-source model is not an accurate representation of the Morgan Hill earthquake. The second source occurs about 4.5 sec after the first and is approximately 3 times larger. The maximum dislocation on the fault plane is about 1 m. The total moment of the earthquake is estimated to be 2.1 × 10^(25) dyne-cm. The Morgan Hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike-slip faults.

Seismic evidence for conjugate slip and block rotation within the San Andreas Fault System, southern California

Abstract: The pattern of seismicity in southern California indicates that much of the activity is presently occurring on secondary structures, several of which are oriented nearly orthogonal to the strikes of the major through-going faults. Slip along these secondary transverse features is predominantly left-lateral and is consistent with the reactivation of conjugate faults by the current regional stress field. Near the intersection of the San Jacinto and San Andreas faults, however, these active left-lateral faults appear to define a set of small crustal blocks, which in conjunction with both normal and reverse faulting earthquakes, suggests contemporary clockwise rotation as a result of regional right-lateral shear. Other left-lateral faults representing additional rotating block systems are identified in adjacent areas from geologic and seismologic data. Many of these structures predate the modern San Andreas system and may control the pattern of strain accumulation in southern California. Geodetic and paleomagnetic evidence confirm that block rotation by strike-slip faulting is nearly ubiquitous, particularly in areas where shear is distributed, and that it accommodates both short-term elastic and long-term nonelastic strain. A rotating block model accounts for a number of structural styles characteristic of strike-slip deformation in California, including: variable slip rates and alternating transtensional and transpressional features observed along strike of major wrench faults; domains of evenly-spaced antithetic faults that terminate against major fault boundaries; continued development of bends in faults with large lateral displacements; anomalous focal mechanisms; and differential uplift in areas otherwise expected to experience extension and subsidence. Since block rotation requires a detachment surface at depth to permit rotational movement, low-angle structures like detachments, of either local or regional extent, may be involved in the contemporary strike-slip deformation of southern California. A block nature of the crust also implies that not only will strains be inhomogeneous and likely concentrated along edge-bounding faults, but that local stress orientations will largely be responding to local kinematic constraints of block rotation and fault interaction. This behavior, coupled with the presence of possible regional detachments, accounts for some of the precursory changes observed at considerable distances prior to large earthquakes and the triggering of seismicity or slip on nearby faults or around adjacent block edges. Although fault displacements along secondary structures associated with block rotations remain small, they may still influence the nucleation and the characteristic rupture length of large earthquakes. A more complete description of what these structures are, and how they interact, may prove critical to any fundamental understanding of the earthquake process and any realistic assessment of the regional seismic hazard.

Fatigue crack growth and fracture toughness behavior of an Al-Li-Cu alloy

Abstract: Slip behavior, fracture toughness, and fatigue thresholds of a high purity Al-Li-Cu alloy with Zr as a dispersoid forming element have been studied as a function of aging time. The fracture toughness variation with aging time has been related to the changes in slip planarity,i.e., slip band spacing and width. Although the current alloy exhibits planar slip for all aging conditions examined, the crack initiation toughness,Klc, compares favorably with those of 2XXX and 7XXX aluminum alloys. Near threshold fatigue crack growth results in air and vacuum suggest that irregularities in the crack profile and the fracture surfaces and slip reversibility are some of the major contributing factors to the crack growth resistance of this alloy.

Mechanics of shear rupture applied to earthquake zones

Abstract: The mechanics of shear slippage and rupture in rock masses are reviewed. The essential ideas in fracture mechanics are summarized emphasizing the interpretation and relation among the fracture parameters in shear cracks. The slip-weakening model is described. The general formulation of the problem of nonuniform slip distribution in a continuum is covered.