Showing papers on "Slip (materials science) published in 1970"

Mechanism of the Chilean Earthquakes of May 21 and 22, 1960

Abstract: The Chilean earthquake sequence of May 21–22, 1960, was accompanied by linear zones of tectonic warping, including both uplift and subsidence relative to sea level. The region involved is more than 200 km wide and about 1000 km long, and lies along the continental margin between latitude 37° and 48° S. Significant horizontal strains accompanied the vertical movements in parts of the subsided zone for which triangulation data are available. Displacements were initiated near the northern end of the deformed region during the opening earthquake of the sequence (M s ≅ 7.5) on May 21 at 10h 02m 50s GMT and were extended over the remainder of the region during the culminating shock (M s ≅ 8.5) on May 22 at 19h llm 17s GMT. During the latter event, sudden uplift of adjacent portions of the continental shelf and much or all of the continental slope apparently generated the destructive tsunami that immediately followed the main shock. Available data suggest that the primary fault or zone of faulting along which displacement occurred probably is a complex thrust fault roughly 1000 km long and at least 60 km wide; it dips eastward at a moderate angle beneath the continental margin and intersects the surface on the continental slope. Dip slip required to satisfy the surface displacements is at least 20 m and perhaps as large as 40 m. There is some evidence that there was a minor component of right-lateral slip on the fault plane.

Depositional and Dispersal Dynamics of Intertidal Sand Bars

Abstract: The intertidal sand bars of the Minas Basin, Nova Scotia, are asymmetrical in cross-section and linear in plan. They are formed and reworked by tidal currents which are characterized by an asymmetric time-velocity profile. A causal connection between time-velocity asymmetry of tidal currents and bar topography is demonstrated. Average bottom ebb current velocities (90 cm/sec) were found to exceed average bottom flood current velocities (65 cm/sec) over gently-sloping (2 to 3 degree) bar surfaces, whereas over steep-sloping (8 degree) bar surfaces, average bottom flood current velocities (90 cm/sec) were found to exceed average bottom ebb current velocities (65 cm/sec). Both bar topography and zones of flood- or ebb-dominated bottom tidal currents control the distribution of sediment texture and sedimentary structures. On steeper bar slopes, the sediment is fine-grained sand and is characterized by airholes, planar lamination, and surface dunes and ripples. On the gentler bar slopes, the texture of the sediment is medium-grained and coarse-grained sand which has been fashioned into current ripples, simple dunes, complex dunes, simple sand waves and complex sand waves. The internal organization of some dunes and sand waves is extremely complex, inasmuch as thickness of internal sets of cross-stratification is considerably less than dune and sand wave height. A total of 14 sedimentary bar facies are defined from combinations of texture, internal cross-stratification and surface bedforms. Both topography and zones of ebb- and flood-dominated bottom tidal currents control the orientation of directional current structures. Over steep faces of bars, the slip faces of sand waves are oriented in the same direction as flow directions of bottom flood tidal currents, although they do show evidence of reworking by ebb currents. Over gently sloping bar surfaces, slip faces of both dunes and sandwaves are oriented parallel to the direction of flow of bottom ebb current systems. Because dunes and sand waves migrate only during a single phase (ebb or flood) of a tidal cycle, their orientation is generally unimodal. Current ripples are formed in depths of water less than 0.6 meters, during late-stage sheet-like runoff that is controlled by local slope changes on the bar. Indi idual tracer grains are dispersed in a radial-elliptical pattern form a point source. The size of directional properties is hierarchically sensitive to dispersal history. Tracer grains (modeling mineral indicator grains) are dispersed in a radial-elliptical pattern from a point source. Trimodal, highly variant, current ripple slip face orientation develops during late stage sheet runoff at low water depths; this flow is controlled by local bar slope. Unimodal, low variant dune slip faces, sand wave slip faces and associated maximum dip direction of cross-stratification are aligned parallel to tidal current flow and basinal topographic trend. The sand bars are aligned parallel to basinal topographic trend and in turn segregate zones of flood- and ebb-dominated bottom current systems. The tidal sand bars of the Minas Basin are equilibrium forms. Sand is dispersed alternately around the bar through zones of ebb- and flood-dominated bottom tidal currents. As a consequence, the sedimentary facies distribution on the bars has remained essentially unchanged since 1938. Comparison of low-tide airphotos taken in 1938, 1947 and 1963 in one of the study areas shows a slight erosional regime. This erosional regime controls the extreme reworking of sediments, and the formation of an erosional sand wave bedform by wave processes. Physical criteria characteristic of tide-dominated sand bodies include: sharp erosional contacts between sets of cross-stratification; rounded upper set boundaries of cross-stratification; unimodal and bimodal distributions of orientation of cross-stratification; bimodal distributions of set thickness and dip angles of cross-stratification; orientation of dunes, sand waves and cross-stratification in the dominant direction of flood or ebb tidal flow, basinal topographic trend and sand body axis; trimodal orientation of current ripples; oblique or 90° superposition of smaller current ripples on larger current ripples; double-crested current ripples; superposition of current ripples at 90° or 180° on slip faces and crests of dunes and sand waves; complex organization of inte nal cross-stratification in sand waves; etch marks on slip faces of dunes and sand waves; and alignment of the long axis of sand bodies parallel to tidal current flow, basinal topographic trend and basin axis.

The mechanism of creep in gamma prime precipitation-hardened nickel-base alloys at intermediate temperatures

Abstract: The creep deformation of Mar-M200 single crystals of various orientations has been studied at a temperature of 1400°F. It was found by a combination of transmission microscopy and analysis of lattice rotations that shear of the γ−γ′ structure occurs by the glide of loosely coupled intrinsic/extrinsic fault pairs with a net Burgers vector ofa . The orientation dependencies of both the rate and extent of primary creep are correlated with the Schmid factors and multiplicity of slip for {111} systems. It is also shown that strain hardening due to intersecting slip is necessary to obtain the transition from primary to steady-state creep. In addition, it was found that the deformation mode is a function of strain rate at 1400°F. In contrast to the observed glide mechanism during creep, tensile deformation occurs by the shear of the γ and γ′ phases bya/2 superlattice pairs.

The Alaska Earthquake of 1964: Radiation of long-period surface waves and source mechanism

Abstract: The records of multiple Love and Rayleigh waves of the Alaska earthquake of 1964 were recovered from the 30–100 seismograph records at the WWSSN stations. The seismograms were equalized to a propagation distance of 9π/2 (equivalent to G5 and R5 at Δ = π/2). These seismograms were compared with synthetic seismograms for radiation pattern and amplitude to estimate various source parameters. The synthetic seismograms were computed from the normal mode solutions. One simple, yet plausible, source model was found. The nature of the fault is essentially that of a low-angle thrust faulting. The direction of rupture propagation does not coincide with the strike of the fault. This enables one to distinguish between the fault plane and the auxiliary plane. The source parameters determined are as follows: force system, double couple, reverse dip slip; fault plane, dip angle 20°, dip direction N 24°W; rupture length. 600 km; rupture velocity, 3.5 km/sec towards S25°W; moment, 7.5×10^(29) dyne-cm; average slip dislocation, 7 meters in N24°W direction; stress drop, 28 bars; strain drop, 0.4×10^(−4); released strain energy. 1.5×10^(25) ergs. The moment and the width of the fault plane of this earthquake are much larger than those of any other earthquakes reported.

First-Time Slides in Over-Consolidated Clays

Abstract: (a) After a slide has taken place the strength on the slip surface is equal to the residual value. The residual strength is associated with strong reorientation of the clay particles and is represented by an angle of shearing resistance $= which in most clays is considerably smaller than the value of 4’ at peak strength (Fig. 1). (b) First-time slides in slopes in non-fissured clays correspond to strengths only slightly less than the peak. (c) First-time slides in fissured clays correspond to strengths well below the peak. (d) Some form of progressive failure must be operative to take the clay past the peak. This could be simply the result of a non-uniform ratio of stress to strength along the potential slip surface; but probably the fissures play an important role as stress concentrators and in leading to softening of the clay mass. (e) Granted a progressive failure mechanism the limiting strength would be residual, and it is therefore reasonable to express the actual strength at the time of failure as a function of the upper (peak) and lower (residual) limits, i.e. by the residual factor. (f) In natural slopes of London CIay the strength has fallen approximateIy to the residual value. (g) The residual strength obtains on pre-existing shear surfaces, whether these are the result of tectonic shearing or old landslides.

Dislocation Dynamics and Single‐Crystal Constitutive Relations: Shock‐Wave Propagation and Precursor Decay

Abstract: Rate‐dependent constitutive relations for single crystals are derived in terms of dislocation dynamics. Contributions from slip on the individual glide planes are assumed to superpose linearly to give the total plastic strain. As an application of the theory, equations describing elastic precursor decay are developed for longitudinal plane‐wave propagation in fcc, bcc, and rocksalt structures with wave propagation in the [100], [110], and [111] directions. In addition, expressions for precursor decay in zinc (hcp structure) are derived for wave propagation both parallel and perpendicular to the c‐axis. Calculated theoretical results are compared with experimental data on precursor amplitudes for single‐crystal copper (fcc), tungsten (bcc), NaCl (rocksalt), and LiF (rocksalt). Dislocation mobilities determined from direct observation of dislocations are used in these calculations. In general the theory predicts the proper relative order of the precursor amplitudes for different propagation directions. The comparisons show that in order for theoretically determined amplitudes to agree with experimental data, initial mobile dislocation densities must be two or three orders‐of‐magnitude greater than initial total densities which are measured in the material prior to shock loading. Possible explanations for this discrepancy are discussed.

Accumulation of tectonic strain in California

Abstract: The shear-strain accumulation in five tectonically-active areas of California has been calculated from triangulation data supplied by the U. S. Coast and Geodetic Survey. Three of the areas lie along active sections of the San Andreas fault. Near Hollister, no appreciable strain accumulation was detected for the period 1930 to 1962. The movement of the fault blocks there appears to be accommodated by slip on the San Andreas and Calaveras faults. Near Cholame, the only appreciable accumulation of shear strain in the period 1932 to 1962 appears to be associated directly with slip on the San Andreas north of Cholame, slip which probably occurred during the 1934 Parkfield earthquake. Significant strain accumulation was confined to a zone centered on the San Andreas fault and extending 10 km on either side. Some of this strain was released in the 1966 Parkfield earthquake. In Imperial Valley, an average accumulation of γ = 0.4 μstrain per year right-lateral (referred to vertical planes parallel to the Imperial fault) shear strain extends over a zone perhaps 100 km wide centered on the Imperial fault. It appears that this shear pattern may be resolved into two zones of shear, one concentrated near the Imperial fault and the other near the San Andreas fault. No appreciable shear-strain accumulation was detected in the two areas that do not lie on the San Andreas fault—Santa Barbara channel for the period 1880 to 1923 and Owens Valley for the period 1934 to 1956.

Strength of a Model of Jointed Rock

Abstract: In an attempt to extend the presently limited state of knowledge of the strength of jointed rock masses, triaxial compression tests were carried out on idealized samples containing sets of preformed discontinuities inclined at various angles to the sample axes The 4 in by 4 in by 8 in samples were built up from one in cubes of a high strength gypsum plaster Triaxial tests were carried out on 5 sample types at each of 5 confining pressures in the range of 0 to 2000 psi The four major modes of failure were: (1) axial cleavage fractures at low confining pressures, (2) shear failure through the plaster and across joint planes, (3) slip on joint planes, and (4) ductile failure The strengths of block-jointed samples failing by mode (2) were less than those of the corresponding unjointed samples At the higher confining pressures of mode (4), the strengths were higher than those of the unjointed samples and were unaffected by joint orientation Friction parameters determined from tests in which mode (3) applied were the same as those determined for the plaster in direct shear tests Mohr's circle envelopes were curved, and could be described by a power law in which the normal stress index varied with joint orientation

Capillary flow instability of ethylene polymer melts

Abstract: The capillary flow instability resulting in extrudate distortion has been studied for ethylene polymer melts using a molecular structure approach. It is found that the instability initiates at a critical value of elastic strain energy independent of (average) molecular weight for linear polyethylene. Once the flow breaks down, a slip interface within the melt is formed near the capillary wall, causing an abrupt increase in volumetric throughput. The velocity gradient within the melt remains continuous through the instability, however. Low molecular weight species present in the molecular weight distribution of linear polyethylene tend to suppress slip. Blends of linear and branched polyethylene exhibit instability behavior characteristic of both components throughout the entire range of composition. Results are discussed in terms of specific molecular mechanisms.

Grain size effects in the strain hardening of polycrystals

Abstract: The degree to which the flow stress of a polycrystal is sensitive to grain size is discussed in terms of the distribution of slip and dislocation structure that develops in the vicinity of grain boundaries as deformation proceeds. The point of view is taken that the two principal classes of grain boundary hardening models, namely, those based on dislocation pile-ups and those based on dislocation density concepts respectively represent special cases of a single rationale developed in this paper. Grain boundary strengthening is intimately related to strain hardening which is affected by slip mode,i.e., the number of slip systems and the ability to cross slip. The effects of substitutional solute elements on grain boundary strengthenings is considered to be a consequence of their influence on slip modes rather than on their interaction with dislocation sources.

Deformation of Polycrystalline MgO Under Pressure

Abstract: Polycrystalline MgO appears to deform ductilely when it is strained under confining pressures greater than 2 kbars at room temperature. Although the {110}〈110〉 slip systems in MgO do not provide the five independent slip systems required for homogeneous deformation, the lack is apparently met in part by the activity of additional slip systems and in part by microfracture. The strong pressure dependence of the stress-strain curves probably arises from the pressure sensitivity of microfracture, which becomes less important as the temperature is raised; high-temperature experiments at 2 and 5 kbars confining pressure show that the pressure dependence virtually disappears at 750°C and that there is a simultaneous trend toward wavy slip. High-temperature experiments on single crystals oriented for cube slip produced only kinking below 300°C; above 300° there is some cube slip, but it is not clear that this is a major deformation mechanism. The pressure dependence of the fracture and flow stresses is interpreted in terms of recent theories of crack propagation under pressure.

Dislocation structures in single-crystal tungsten and tungsten alloys

Abstract: Deformation of tungsten single crystals as a function of strain, temperature, and alloying was studied by transmission electron microscopy. Single crystals oriented for (−101)[lll] slip were grown by electron beam zone refining. Compression specimens of tungsten, W-l and 3 pct Re and W-l and 3 pct Ta were deformed to 2 pct strain at 150°, 300°, and 590°K (0.04, 0.08, and 0.16T m). Specimens were also strained to 0.5 and 5.0 pct strain at 300°K. Transmission microscopy revealed that the dislocation substructures in single-crystal tungsten are similar to substructures in other refractory metals when compared on a homologous temperature basis. At temperatures greater than 0.1T m, the substructure is characterized primarily by edge dipoles. At temperatures less than 0.1T m, long screw dislocations lying parallel to the primary [111] slip direction characterize the substructure. Rhenium additions to tungsten promote formation of edge dipoles at temperatures of 300° and 150°K and increase dislocation density at all three temperatures. In addition, dislocations consistent with (1−12)[−111] slip were observed in the W-Re single crystals after deformation at 150°K. Tantalum additions had a lesser effect on the dislocation substructure compared to rhenium additions. The W-l and 3 pct Ta alloys exhibited higher dislocation densities than unalloyed tungsten after similar strains and, at 150°K, W-3 pct Ta contained a few dislocations consistent with (1−12)[−111] slip. It is concluded that the reduction in ductile-brittle transition temperature of poly crystalline tungsten containing dilute rhenium additions, 1 to 5 pct, can be attributed to an increase in dislocation mobility at temperatures less than 0.1 Tm.

Directional drilling apparatus

Abstract: This invention relates to a directional drilling apparatus. More particularly, the invention is a drilling tool including provisions for changing the direction of drilling of a borehole, the tool including a tubular body having means at the upper end for attachment of a drill string, a drill bit affixed to the lower end of the body by means of a slip clutch drill bit so that the drill bit is rotated when the tubular body is rotated while permitting the drill bit to be rotated independently of the body, means within the tubular body for rotating the drill bit, and means controllable from the surface of the earth of varying the angle of the drilling axis of the drill bit relative to the tubular body.

Structure and properties of tantalum carbide crystals

Abstract: Single crystals of tantalum carbide, up to 2 mm in size have been grown from solution in a bath of molten iron. The slip plane was found to be {111} using a two-surface analysis on etch-pitted crystals deformed by microindentation at room temperature. Observations of etch-pit patterns around inclusions suggest that slip occurs on other planes at elevated temperatures. Maximum microhardness values between 3800 and 5200 Knoop (100 gm load) were found at a composition TaC0.83±0.01. In regions of crystals with a carbon content less than TaC0.83 a phase transformation was seen close to microhardness indentations in samples decarburised below 2200† C. The mechanical behaviour of tantalum carbide is discussed with reference to a general model for the electronic structure of carbides.

Prismatic Slip in Beryllium and the Relative Ease of Glide in H.C.P. Metals

Abstract: The macroscopic C.R.S.S. for prismatic slip in Beryllium is found to increase with increasing temperature in the range −100 to +50 °C while the microyield limit decreases regularly. Slip is initiated on the prism planes from the edge dislocations present in the annealed material. Evidences of a thermally activated locking of screw dislocations are presented. This locking is thought to occur by the usual splitting in the basal plane. The assumption that the a dislocations can also dissociate in the prismatic plane seems necessary to account for the activation of this locking. Possible dissociations in the prismatic plane are proposed; the most probable of them is a a/3 + 2 a/3. It gives a ribbon of stacking fault corresponding to the transformation of two {1010} h.c.p. “flat planes” into two {112} b.c.c. planes. It is suggested that there is a relationship between the energy of the stacking fault on the prismatic plane and the temperature of the phase transformation h.c.p. b.c.c. This relationship permits to account for the relative ease of slip in h.c.p. metals.

The temperature dependence of the flow stress of the γ' phase based upon Ni 3 Al

Abstract: The temperature dependence of the ordinary flow stress, the microplastic yield stress, and the transient creep responses ofγ′ have been studied with respect to the effect of alloying additions, slip line topography, and dislocation structure. The increase observed in the flow stress with increase in temperature may be attributed to a change in the mechanism controlling the flow stress. An exhaustion hardening process at low temperatures appears to be supplanted by a debris hardening process at high temperatures. This transition arises from an increased propensity for {100} slip as the temperature is raised. Solute additions affect the temperature dependence of the flow stress probably by altering the tendency for {100} slip.

Yield-point phenomena in substitutional alloys

Abstract: A material exhibits a yield point when a larger stress is required to initiate deformation by slip than to continue it. In a normal tensile test this is usually observed as a drop in load at the start of gross yielding. Load drops may also be observed that are due to deformation twinning, but this will not be discussed here. Annealed mild steel was once thought to be unique in showing an initial yield point but it is now known that the effect is quite general, and many examples occur in substitutional alloys.

Stacking faults in gamma prime Ni3(Al,Ti) precipitation hardened nickel-base alloys

Abstract: Most high temperature nickel-base alloys are strengthened by a coherent, orderedγ′ precipitate of Ll2 structure Examination of thin foils of these materials after various thermal and/or mechanical treatments has shown the presence of stacking faults in a variety of forms Stacking faults are developed in conjunction with certain phase reactions, and during plastic deformation The experimental evidence indicates that stacking fault energy is an important parameter determing the slip mode and strength at low and intermediate temperatures

Hugoniot Elastic Limit of Single‐Crystal Sodium Chloride

Abstract: Single‐crystal specimens (7‐ and 12‐mm thick) of sodium chloride were impacted with flat‐nosed, gas‐driven projectiles, and the Hugoniot elastic limit (HEL) was determined by reducing quartz gauge measurements. The HEL for the [100], [110], and [111] crystal directions was 0.26, 0.77, and 7.4 kbar, respectively. Stress—time profiles for specimens shocked in the [100] and [111] direction show evidence of stress relaxation behind the elastic precursor. This phenomenon is more pronounced in 12‐mm‐thick specimens. The ratio of the resolved shear stress on the active slip systems for uniaxial strain (shock loading) conditions to that for uniaxial stress (static loading) indicates a strain‐rate effect. This ratio increases from 3.1 for loading in the [100] direction to 8 for the [110] direction and to 21 for the [111] direction. The anisotropy of the HEL with crystal direction is related to the resolved shear stress on the primary and secondary slip systems in single‐crystal sodium chloride. The large HEL for shock loading in the [111] direction is a consequence of the resolved shear stress on the primary slip systems being zero. Thus, for deformation by slip to occur, a secondary slip system (or systems) must be activated which will require a higher resolved shear stress. The experimental data for single crystals of copper and beryllium can also be explained in terms of the resolved shear stress.