Showing papers on "Slip (materials science) published in 1973"

Body wave spectra from propagating shear cracks.

Abstract: An earthquake source model studied in this paper predicts a higher value of P wave corner frequency than S wave corner frequency; the ratio of P to S wave corner frequency is about 1.3 on the average. This result owes mainly to the slip characteristics on the fault, that is, the center of the fault slips for a longer time than the edges and consequently a greater relative displacement takes place near the center. Relationships of source dimension with the corner frequencies for P and S waves are derived to estimate the source dimension of earthquakes from teleseismic body wave spectra. The far-field spectra from the present model of equidimensional rupture propagation demonstrate the spectral decay of ω-2 at high frequencies. The seismic efficiency is found to be independent of the size of source dimension and expressed as a function of initial stress, stress drop, and rupture velocity. Being interpreted in terms of this model, the ratio of frictional stress to final stress can be estimated from observations of rupture velocity.

Admissible Speeds for Plane-Strain Self-Similar Shear Cracks with Friction but Lacking Cohesion

Abstract: Summary Dynamic shear cracks with friction have recently been studied as models for shallow-focus earthquakes both in the laboratory and analytically. There is some evidence from laboratory experiments that zones of slip may spread with velocities greater than the S-wave speed but so far theoretical models with rupture velocities faster than the S-wave speed have not been considered. In particular the shearing version of Broberg’s self-similar crack propagating at the Rayleigh speed has been suggested as the solution for cracks lacking cohesion. The present paper shows that this RayIeigh-speed crack may be valid if limiting static friction is sufficiently high, but otherwise the crack may run at the P-wave velocity. The mathematical method used is to show that a self-similar motion is likely and then to eliminate all possible crack speeds except those in a range of speeds between the Rayleigh speed vR and the S-wave speed us, or, if the static friction is weak, the P-wave speed is found to be the only admissible speed. It is worth noting that for propagation speeds between the Rayleigh and shear speeds there is also a weil-known non-physical solution analytically identical to Broberg’s solution but having a stress singularity of the wrong sign. The solutions proposed in this paper do not have any stress infinities at all. Analogous solutions apply to tensile cracks but the physics in that situation is not clear. In the final section some conclusions are drawn concerning frictional sliding in a fully three-dimensional situation.

Deformation mechanisms in oriented high-density polyethylene

Abstract: The deformation of samples of oriented high-density polyethylene has been analysed in terms of three principal deformation mechanisms,fibrillar slip, lamella slip andchain slip. From a study of small- and wide-angle X-ray diffraction patterns it is possible to deduce which mechanism or mechanisms are operating in particular cases. Material prepared in three different ways has been examined and it appears that in all three cases the primary mechanism for plastic deformation is [001] chain slip.

Frictional heating of the descending lithosphere

Abstract: Linear chains of active volcanoes are usually associated with oceanic trenches. It is postulated that the active volcanoes lie above the point on the slip zone between the descending lithosphere and the overlying mantle where partial melting of the descending oceanic crust takes place. By assuming that the frictional stress on the slip zone is either constant or proportional to depth, the thermal structure of the descending lithosphere is determined. The alternative theories are used to determine the shear stresses and friction coefficients for various trench-volcano systems. Values for the shear stress and friction coefficient have standard deviations of 10 and 24%, respectively. We conclude that the shear stress on a slip zone is probably weakly dependent on depth with a value near 1.35kb. Our results are compared with previous calculations.

Thrust line criterion in embankment stability analysis

Abstract: A METHOD OF ANALYSING THE STABILITY OF EMBANKMENTS IS DESCRIBED WHICH ACCOUNTS FOR THE INTER-SLICE FORCES AND SATISFIES FORCE AND MOMENT EQUILIBRIUM CONDITIONS. THE METHOD IS APPLICABLE TO ANY SHAPE OF SLIP SURFACE WITH OR WITHOUT A TENSION CRACK. EXPRESSIONS ARE GIVEN FROM WHICH THE POSITIONS OF THE LINES OF THRUST FOR TOTAL AND EFFECTIVE STRESS CAN BE OBTAINED. SOLUTIONS ARE GIVEN TO TWO SERIES OF PROBLEMS. IN THE FIRST SERIES THERE IS NO TENSION CRACK BUT VARIOUS SHAPES ARE ASSUMED FOR THE SHAPE OF THE SLIP SURFACE AND DIFFERENT ASSUMPTIONS MADE REGARDING THE SLOPES OF THE INTER-SLICE FORCES. HOWEVER, NONE OF THESE SOLUTIONS LEADS TO A SATISFACTORY POSITION FOR THE LINE OF THRUST FOR EFFECTIVE STRESS. IN THE SECOND SERIES A TENSION CRACK WITH WATER PRESSURE ACTING IN IT IS ASSUMED PRESENT. IT IS SHOWN THAT A SATISFACTORY THRUST LINE IS OBTAINED WHEN THE DEPTH OF THE TENSION CRACK IS TAKEN TO BE THE DEPTH OF ZERO ACTIVE EFFECTIVE STRESS AND THE SLOPE OF THE INTER-SLICE FORCES IS CONSTANT, EXCEPT FOR A REDUCTION AT THE UPPER END OF THE SLIP SURFACE. THE INCLUSION OF THE TENSION CRACK WITH WATER PRESSURE ACTING IN IT DOES NOT AFFECT THE VALUE OF THE FACTOR OF SAFETY IN THIS PROBLEM. /TRRL/

The effect of slip on the motion of a sphere close to a wall and of two adjacent spheres

Abstract: The motion of a sphere towards a plane or another sphere is opposed by the fluid between them with a force which is inversely proportional to the gap. In consequence, it is impossible for a constant force to produce contact in a finite time, unless the Stokes equations are modified. When the gap is of the same order as the mean free path of the air molecules, the Stokes theory for the motion of the air must be modified. The Maxwell slip flow approximation is used in this paper to show that, when the gap is small, the resisting force between the approaching surfaces becomes only logarithmically dependent on the gap, and contact can be achieved in a finite time. The difficulty in applying the Stokes theory to the problem of determining collision efficiencies for cloud droplets is thereby removed. The calculated values of the resistance to approach are used to determine the motion of a sphere falling towards a plane. If the motion is compared with the corresponding motion when no allowance is made for slip flow, the sphere without slip would still be at a distance of 1.3 times the mean free path from the plane, when the sphere with slip has made contact. Transverse motion must also be considered if the trajectory of a particle close to a collector is required. The forces and couples on the sphere in that situation have a logarithmic dependence on the gap without slip, but they tend to constant values when the effect of slip is included. Some calculations of collision efficiency of drops falling under gravity (Hocking and Jonas [1]) have been amended to include the effect of slip when the colliding drops are very close together, and show a significant increase in the collision efficiency.

San Fernando Earthquake series, 1971: Focal mechanisms and tectonics

Abstract: The largest events in the San Fernando earthquake series, initiated by the main shock at 14h 00m 41.8s UT on February 9, 1971, were chosen for analysis from the first three months of activity, 87 events in all. C. R. Allen and his co-workers assigned the main shock parameters: 34°24.7′N, 118°24.0′W, focal depth h = 8.4 km, and local magnitude M_L = 6.4. The initial rupture location coincides with the lower, northernmost edge of the main north-dipping thrust fault and the aftershock distribution. The best focal mechanism fit to the main shock P wave first motions constrains the fault plane parameters to: strike, N67°(±6°)W; dip, 52°(±3°)NE; rake, 72° (67°−95°) left lateral. Focal mechanisms of the aftershocks clearly outline a down step of the western edge of the main thrust fault surface along a northeast-trending flexure. Faulting on this down step is left lateral strike slip and dominates the strain release of the aftershock series, which indicates that the down step limited the main event rupture on the west. The main thrust fault surface dips at about 35° to the northeast at shallow depths and probably steepens to 50° below a depth of 8 km. This steep dip at depth is a characteristic of other thrust faults in the Transverse ranges and indicates the presence at depth of laterally varying vertical forces that are probably due to buckling or overriding that causes some upward redirection of a dominant north-south horizontal compression. Two sets of events exhibit normal dip slip motion with shallow hypocenters and correlate with areas of ground subsidence deduced from gravity data. One set in the northeastern aftershock area is related to shallow extensional stresses caused by the steepening of the main fault plane. The other set is probably caused by a deviation of displacements along the down step of the main fault surface that resulted in localized ground subsidence near the western end of the main fault break. Several lines of evidence indicate that a horizontal compressional stress in a north or north-northwest direction was added to the stresses in the aftershock area 12 days after the main shock. After this change, events were contained in bursts along the down step, and sequencing within the bursts provides evidence for an earthquake-triggering phenomenon that propagates with speeds of 5–15 km/day. Seismicity before the San Fernando series and the mapped structure of the area suggest that the down step of the main fault surface is not a localized discontinuity but is part of a zone of weakness extending from Point Dume, near Malibu, to Palmdale on the San Andreas fault. This zone is interpreted as a decoupling boundary between crustal blocks that permits them to deform separately in the prevalent crustal shortening mode of the Transverse ranges region.

Deformation Twinning in Metals and Alloys

Abstract: Slip and twinning are the two fundamental modes by which metals and alloys can deform plastical1y. Slip occurs when crystal planes glide past each other. This is achieved by the passage of dislocations on different glide planes. Since the Burgers vector of the glide dislocations is always a lattice vector, the atoms during the slip motion move from one lattice site to the adjacent equivalent one. Consequently, the slipped and unslipped regions have identical orientation.

Experimental study of static and dynamic friction between soil and typical construction materials

Abstract: The limiting contact friction between sand and steel, cement mortar, graphite, and teflon surfaces was measured in the laboratory. The coefficients of (wall) friction were obtained using static and dynamic loadings with particular reference to conditions at the time slip was initiated. The coefficient of friction increases with the surface roughness and angularity of the sand grains, and as the roughness of the contact surface increases with respect to the size of the sand particles. For steel and mortar surfaces dynamic friction was greater than static friction by about 20 percent unless the surface was sufficiently rough that sand/sand slip was approached. The (static) angle of shearing resistance was the upper limit of the coefficient of friction for all static and dynamic tests where slip was initiated from 1–2 ms to 5 min (loading rates from 5 × 105 to 0.5 psi/min). Under static loading conditions teflon and graphite reduced wall friction by one-half to one-third; at high loading rates graphite was a more effective lubricant than teflon.

Slip Systems in Al2O3

Abstract: Crystallographic notation for Al2O3 is reviewed, with particular reference to the correct basis to be used in describing slip systems. A Groves-and-Kelly calculation showed that the combination of pyramidal slip on {11¯02} and basal slip on (0001){112¯0} will allow homogeneous deformation of Al2O3 polycrystals. Furthermore, operation of either the {101¯1} or the {011¯2} slip system will also satisfy the Von Mises criterion, since each system is capable of 5 independent deformation modes. Electron microscopy of an Al2O3 polycrystal deformed ≅5% at 1150°C under a hydrostatic confining pressure confirmed that pyramidal slip had occurred.

Kinetic Theory of Evaporation and Condensation

Abstract: The behavior of a gas in contact with its condensed phase is considered on the basis of a relaxation model of the linearized Boltzmann equation. The temperature and density distributions of the gas in the Knudsen layer as well as so called slip boundary condition on the interface of the gas and its condensed phase are obtained.

Initiation of fatigue cracks in 4340 steel

Abstract: Electron microscopy of surface replicas has been employed to determine the metallurgical micromechanics of fatigue crack initiation at surface and shallow subsurface inclusions in 4340 steel. The experimental results are considered in terms of current theoretical analyses of elastic stress distributions around hard inclusions imbedded in soft matrices. A model for crack nucleation at surface inclusions is suggested, based upon debonding of the inclusion/matrix interface at the tensile pole of the inclusion, followed by growth of the debond seam toward the inclusion “equator”. Subsequent generation of a matrix crack is associated with the initiation of “point” surface defects some distance from the inclusion/matrix boundary, but in the plane of the inclusion “equator”. Surface slip plays no discernible role in nucleation of surface inclusions, but slip bands are formed at crack sites above sub-surface inclusions. However, the microcracks continue to form through the link-up of point surface defects.

Focal depth and mechanism of mid‐ocean ridge earthquakes

Abstract: Rayleigh wave phase and amplitude spectra are used to determine the focal depths and mechanisms of mid-ocean ridge earthquakes. The effect of propagation on the spectra is removed by analyzing the differential phase and the amplitude ratio of the Rayleigh waves from a pair of close events with different focal mechanisms. This analysis preserves the difference between the source spectra. By matching the observations with theoretical models, a best description of the source is derived. The two mid-Atlantic ridge dip slip events that we have studied have a focal depth of only 3 ± 2 km beneath the ocean floor. Two dip slip events in the northeast Pacific have depths consistent with these results but with an uncertainty of 20 km. The depths of two mid-Atlantic ridge strike slip events are 6 ± 3 km. Two strike slip events in the northeast Pacific are shallower than 25 km. The phase analysis greatly aids the amplitude analysis and, for these events, is indispensable.

The dislocation structures responsible for the optical effects in some naturally-deformed quartzes

Abstract: The optical features in naturally deformed quartzites, namely undulatory extinction, deformation bands, deformation lamellae and sub-grains, can be related to dislocation structures in the quartz grains. Dislocation walls forming mosaics of sub-grains are the principal cause of all the optical features. The irrational deformation lamellae common in metamorphic quartzes are sub-grain walls; only those which lie on slip planes are slip lines and these are normally emprinted (superimposed) on sub-grain structures. The dislocation structures are indicative of recovery and thus optical features cannot be used as stress or strain gauges.

Half‐space problems in the kinetic theory of gases

Abstract: The elementary solutions of the linearized and decomposed BGK equation are used to solve evaporation and heat‐conduction problems in a half‐space, and values of the microscopic and macroscopic temperature and density slip coefficients are reported, along with the complete temperature and density profiles.

Source parameters for stick-slip and for earthquakes.

Abstract: Source parameters of stick-slip friction events measured in the laboratory show particle and rupture propagation velocities which are similar to those observed for earthquakes and inferred from seismic source theory. This dynamic similarity strongly supports the idea that stick-slip is the mechanism for shallow earthquakes.

Experiental deformation of single crystals of biotite

Abstract: Single crystals of biotite have been shortened up to 20% in compression tests parallel to [100], [110] and [010] directions at 3 Kbar confining pressure and temperatures from 300 to 700° C, and at a strain rate of 10−4 sec−1 Thick metal constraining sleeves were used and led to a distribution of kinking throughout the crystals The orientation of kink boundaries, angle of bending and asymmetry of the basal plane across the kink boundaries and the axes of bending were measured A minor amount of unidentified non-basal slip must have occurred to account for the assymmetry, but basal slip predominates at all temperatures From the axes of bending, the discrete slip directions [100], [110] and [110] for basal slip are deduced Increase in temperature mainly leads to a simpler pattern of kinking associated with the kinks being wider and the kinking angle larger, presumably as a result of greater mobility of dislocation walls that form the kink boundaries

Multimode Surface Waves for Selected Focal Mechanisms I. Dip-Slip Sources on a Vertical Fault Plane

Abstract: Summary The characteristics of the Rayleigh wave response to dip-slip motion along a vertical fault plane are investigated. The sources are located at various depths in the crust of a shield structure. Results are given in the form of frequency spectra of the displacement at the free surface. Both individual modes and combinations of the modes are treated.