Showing papers on "Slip (materials science) published in 1969"
TL;DR: In this article, the authors used the absence of a heat flow anomaly greater than ∼0.3 µcal/cm2/sec associated with the San Andreas fault to estimate the upper limit for the steady state or initial shear stress.
Abstract: The absence of a heat flow anomaly greater than ∼0.3 µcal/cm2/sec associated with the San Andreas fault is used to estimate the upper limit for the steady state or initial shear stress. Under the assumption that the long-term rate of motion along the fault is 5 cm/yr and occurs primarily in the form of creep, this upper limit is about 100 bars. If the motion is primarily accomplished by faulting during large earthquakes and if the frictional stress is equal to the final stress as suggested by E. Orowan (1960), the upper limit is estimated to be about 200 bars. Without Orowan's assumption, the estimation of the upper limit is about 250 bars, based on earthquake energy-magnitude-moment relations. If the long-term rate of motion along the San Andreas fault is only ∼2 cm/yr, these results are increased to 250, 350, and 400 bars, respectively.
419 citations
TL;DR: In this paper, a series of alloys containing Zn and Al solute have been deformed in tension over a range of temperatures in an orientation such as to induce first order {1010} −1120 −1) prismatic slip while suppressing both basal slip and twinning.
298 citations
TL;DR: In this article, the critical resolved shear stress for basal slip was found to increase with the square root of the solute concentration in two linear stages having a transition at 0.025 at. % Zn.
286 citations
TL;DR: In this article, a model for the formation and propagation of cracks is developed which satisfies many well known general features of fatigue as well as the results of new observations of the fracture surface features of single crystals of copper.
280 citations
TL;DR: In this article, Mohr generalized Coulomb's criterion by extending it to a three-dimensional state of stress, and by allowing for a variable coefficient of internal and external friction.
Abstract: Coulomb's criterion for the shear fracture of a brittle material is that total shearing resistance is the sum of the cohesive shear strength (independent of direction) and the product of the effective normal stress and the coefficient of internal friction (a constant independent of normal stress). Mohr generalized this criterion by extending it to a three-dimensional state of stress, and by allowing for a variable coefficient. The coefficients of internal and external (sliding) friction are not the same in general. Both tend to decrease with increasing normal stress, and their relative magnitudes may determine if failure occurs by new shear fracturing or by slip on pre-existing cohesionless surfaces like joints in rocks.
266 citations
TL;DR: In this paper, the dislocation sub-structure and surface markings formed during the early stages of fatigue in copper single crystals at room temperature were studied and the merits of various proposed mechanisms for fatigue are discussed.
Abstract: The dislocation sub-structure and surface markings formed during the early stages of fatigue in copper single crystals at room temperature were studied. For the first few cycles the structure is similar to that associated with stage I of tensile deformation. A three-dimensional network of interconnected veins packed tightly with mainly primary edge dislocations then develops. The scale of the structure decreases with increasing strain. The surface observations show that in the first few cycles long straight primary slip lines are formed, but later the new slip markings are fine and short, their length corresponding to the inter-obstacle distance. The merits of various proposed mechanisms for fatigue are discussed.
210 citations
TL;DR: The Parkfield earthquake of June 27, 1966 and its aftershock and creep sequences are examined as a detailed example of fault slippage that includes both types, seismic and aseismic as discussed by the authors.
Abstract: Field and experimental evidence are combined to deduce the mechanism of slip on shallow continental transcurrent faults, such as the San Andreas in California. Several lines of evidence portray the central section of the San Andreas fault as a very smooth and flat surface, with a very low frictional strength in comparison to the breaking strength of intact rock. The Parkfield earthquake of June 27, 1966, and its aftershock and creep sequences are examined as a detailed example of fault slippage that includes both types, seismic and aseismic. It is shown from considerable number of field data that during the main shock a region from about 4 to 10 km in depth slipped approximately 30 cm. In response to this slippage, creep and aftershocks were generated. The creep and aftershocks are not directly interrelated, but they are microscopically identical processes of time-dependent brittle friction occurring in parallel in different regions. The creep occurred by time-dependent stable frictional sliding in the 4-km-thick surface layer; the aftershocks, by time-dependent stick-slip at the ends of the initial slipped zone. This model is in good agreement with laboratory results which show that slippage should occur by stable (aseismic) friction in the upper 4 km, by stick-slip accompanied by earthquakes from about 4 to 12 km, and by stable sliding or plastic friction below 12 km on the fault. One feature not observed in the laboratory is the episodic nature of creep. These episodes can be predicted with an accuracy of about 1 week.
175 citations
TL;DR: In this paper, a general theory is developed to account for the mobility of a dislocation which is sessile in its low-energy form, and three distinct mechanisms for movement are possible, each controlling the mobility over a different stress range.
Abstract: A general theory is developed to account for the mobility of a dislocation which is sessile in its low-energy form. It is shown that three distinct mechanisms for movement are possible, each controlling the mobility over a different stress range. A specific core model is used to derive an expression for the mobility of screw dislocations in b.c.c. metals, and it is shown that the theory can account satisfactorily for the temperature and orientation dependence of the yield stress and slip geometry, and the stress dependence of the activation energy and volume in b.c.c. metals.
151 citations
TL;DR: In this article, a fine grid scribed on the Mg-Al alloy of several grain sizes over a wide range of strain rates was used to measure the contribution of grain strain and the strain associated with grain boundary deformation.
137 citations
TL;DR: In this article, a study of the stress-strain behavior, secondary slip geometry and slip line morphology of niobium single crystals purified by annealing in ultra-high vacuum was made.
Abstract: A study has been made of the stress-strain behaviour, secondary slip geometry and slip line morphology of niobium single crystals purified by annealing in ultra-high vacuum. Within favourable limits of orientation, temperature and strain rate the stress—strain curves exhibit well-defined three-stage hardening. The principal secondary slip system is not usually that bearing the highest proportion of the applied stress and this anomalous behaviour can account for the orientation dependence of overshoot. For temperatures below 250°K the stress-strain curve is non-linear and the initial hardening rate very high. The slip lines observed on crystals deformed at low temperatures belong to a {110} ⟨111⟩ system which, in extreme orientations, is only the sixth most highly stressed system. The slip appears as crystallographic lamellae, in contrast to the wavy slip observed for all other systems.
117 citations
TL;DR: In this article, the behavior of individual dislocations was investigated by stretching the foil single crystals of Fe-3% Si inside a 500 kV electron microscope, and the formation of dislocation dipole trails and loops were continuously observed under the microscope.
Abstract: Behavior of individual dislocations is investigated by stretching the foil single crystals of Fe-3% Si inside a 500 kV electron microscope. Formation of dislocation dipole trails and loops are continuously observed under the microscope, and is attributed to jogs caused by cross glide. Slip traces of individual dislocations are wavy even in the electron microscopic scale, but are nearly parallel to a low index plane. Dislocation activity is larger when the dislocation is moving in the outer part of a slip band, where the dislocations are less joggy. Evidences on mode of dislocation multiplication and interaction are obtained. Drag stress by jogs as well as long range force between dislocations amounts only to a small fraction of the flow stress. Peierls mechanism can be used to explain consistently the elongated screw dislocations, the single ended dislocation sources and the large frictional stresses observed in this material.
TL;DR: In this article, the problem of accommodation of constrained deformation by slip and twinning has been analyzed based on Taylor's least-work hypothesis, and the operative combination of slip-and twinning systems is found by minimizing the orientation factor M = ($Sigma\_i$s$\_I$ + $\alpha \Sigma ε + ε ϵ + ϵπ ϵσon), where ϵ is the ratio of the critical resolved shear stress for twinning against slip, and ϵ = the external strain.
Abstract: The problem of accommodation of constrained deformation by slip and twinning has been analysed. The analysis is based on Taylor's least work hypothesis. In this analysis, the operative combination of slip and twinning systems is found by minimizing the orientation factor M = ($\Sigma\_i$s$\_i$ + $\alpha \Sigma\_i$t$\_i$)/$\epsilon$, where s$\_i$ and t$\_i$ are the simple shears resulting from slip and twinning respectively, $\alpha$ is the ratio of the critical resolved shear stress for twinning against slip, and $\epsilon$ is the external strain. Detailed calculations have been made for face-centred cubic crystals deformed by plane strain compression. Experimental observations on deformed single crystals of a Co-8% Fe alloy indicate good agreement with the analysis. Implications of the present study to the twinning observations of Heye & Wassermann on rolled Ag crystals are discussed.
TL;DR: In this paper, electron diffraction patterns and diffraction contrast (g·b) analysis were used to identify the plane on which the dislocation channels formed in most cases and the strain corresponded to the passage of 1−3 slip dislocations per slip plane.
Abstract: Dislocation channels cleared of radiation‐produced defect clusters were observed by transmission electron microscopy in polycrystalline niobium irradiated to 4×1018 neutrons/cm2 (E>1 MeV) and then deformed in tension to 6.6% strain. From electron diffraction patterns and diffraction contrast (g·b) analysis, the {110} plane was determined to be the plane on which the dislocation channels formed in most cases. The strain due to the motion of slip dislocations in the channels was deduced from the offset at intersections between the channels and other microstructural features. The strain corresponded to the passage of 1–3 slip dislocations per slip plane. Several mechanisms for the clearing of defect clusters by slip dislocations are discussed. These include: annealing due to the heat of plastic deformation, chopping up or sweeping up of defect clusters by slip dislocations, and annihilation by antidefects.
TL;DR: In this paper, the Burgers vector was shown to be parallel to the 〈110〉 axes by transmission electron microscopy and slip was observed on {100, {110}, or {111} planes, depending on the orientation of the stress axis; it always occurred on the most favorably oriented slip system.
Abstract: High-temperature deformation in ZrC single crystals was studied. Seeded crystals were grown by a direct rf-coupling floating-zone process. Yield stresses were measured from 1080° to 2000°C as a function of stress axis orientation. The Burgers vector was shown to be parallel to the 〈110〉 axes by transmission electron microscopy. Slip was observed on {100}, {110}, or {111} planes, depending on the orientation of the stress axis; it always occurred on the most favorably oriented slip system. The dependence of steady-state creep rate on the applied stress indicated that recovery occurred by a dislocation climb mechanism. Examination of the dislocation structure in deformed crystals by transmission electron microscopy supported this conclusion.
TL;DR: In this article, the fracture of brittle coatings on a strained substrate was examined from two points of view, and the results for both cases were compared with experiment and found to be in essential agreement.
Abstract: The fracture of brittle coatings on a strained substrate is examined from two points of view. In the first case, the substrate deforms continuously and regularly spaced fractures occur in the coating. The spacing d at any strain e is given by In e/e0 = (4g/d) (1−d/d0), where d0, e0 are any convenient set of data points, and g is a parameter having the units of length. In the second case, the substrate deforms by crystallographic slip and fracture of the oxide may or may not occur at the slip step. The criteria for fracture are that the interface adhesive stresses be too large for the coating to sustain the necessary peel stress. Quantitative relations are given in terms of the coating thickness, fracture strain, and the orientation of the slip step with respect to the surface. The results for both cases are compared with experiment and found to be in essential agreement.
TL;DR: In this paper, the compressive deformation of polycrystalline ǫ-zirconium hydride has been investigated within the temperature range 22 to ∼ 400° C and over the composition range ZrH1.71 to Zrh1.92.
Abstract: The compressive deformation of polycrystalline ɛ-zirconium hydride has been investigated within the temperature range 22 to ∼ 400° C and over the composition range ZrH1.71 to ZrH1.92. The observed deformation modes included slip, creation of new lamellae of different orientations to those of the main transformation lamellae, and movement of lamellar boundaries. The results are considered in terms of the contribution of these three processes to the overall deformation behaviour.
TL;DR: In this paper, the deformation mechanism of the ordered alloy CuAu I was investigated by electron microscopy and it was found that the predominant mechanism is mechanical twinning and not slip.
Abstract: The ordered alloy CuAu I was deformed in tension at room temperature and the deformation mechanism was investigated by electron microscopy. It was found that the predominant deformation mechanism is {111} mechanical twinning and not slip, as has been proposed by Syutkina and Yakovleva (1967). The CuAu I microstructure is composed of microtwins on {101} planes formed during the ordering process and the interaction of mechanical {111} twins with the order twins was investigated. It is probable that the CuAu I crystal structure is changed by the deformation process to one resembling the CuPt ordered alloy in which {111} planes of like atoms alternate.
Journal Article•
TL;DR: In this paper, it is shown that since faults are finite and confined within an essentially incompressible crust, vertical separation and an important component of vertical slip must accompany lateral movement along wrench faults.
Abstract: Wrench faults are near vertical fractures characterized by Important lateral slip components. They form under regional compression when the greatest and least principal pressures (axes) lie In the horizontal plane. With the aid of conceptual models (block diagrams) it is shown that since faults are finite and confined within an essentially incompressible crust, vertical separation and an important component of vertical slip must accompany lateral movement along wrench faults. Thus separation and slip along wrench faults may vary importantly, a geometric condition considered singularly characteristic. The reversal of fault dip along a fault line (“propeller faulting”), the development of belts of en echelon parafolds (“drag folds”) or pinnate tension fractures, or abrupt stratigraphic change across the fault zone, also are considered indicative of wrench faulting. In the central Rocky Mountain foreland area many of these wrench fault features can be recognized along major west-northwest (left wrench) and northeast (right wrench) trending fault zones. Considering the nearly north-south orientation of primary folds and of the low angle thrust faults of the disturbed belt, therefore, it appears that a single north-northeast–south-southwest direction of principal horizontal stress (PHS) can account for all of the Laramide structural features of the central Rocky Mountain foreland. An idealized tectonic diagram and a regional tectonic map of the central Rocky Mountain area are presented to show graphically the writer’s interpretation of the various faults and folds of this area according to the wrench fault concept. These diagrams portray the genetic relationships between first and second order wrench fault zones and other structural features. A check list of characteristic features is also presented as an aid in identifications of other wrench fault zones in the Rocky Mountain Area. Such identifications are considered economically important as the structures around and along wrench fault zones commonly are the habitat of mineral deposits.
TL;DR: A least-squares procedure has been used to determine the dislocation surface which best fits the geodetic data for the Fairview Peak, Nevada, earthquake of December 16, 1954.
Abstract: Maruyama's equations have been used to calculate both vertical and horizontal surface displacements for a Volterra dislocation in a uniform half space. The shape of the dislocation surface is assumed to be a plane rectangle. A least-squares procedure has been used to determine the dislocation surface which best fits the geodetic data for the Fairview Peak, Nevada, earthquake of December 16, 1954. The best model strikes N9°E, has a total length of 50 km, a width of 8. ± 2. km, a dip of 57° ± 6°, and a fault displacement of 2.3 ± 0.4 m normal dip slip and 2.9 ± 0.4 m dextral strike slip. The width of the model is probably somewhat less than the true width of the fault, but the other parameters appear to be quite reasonable. The N9°E strike of the model is thought to be more realistic than the N4°W to N11°W strikes indicated by nodal-plane solutions. It appears that the Dixie Valley earthquake of December 16, 1954 was associated with normal slip on a fault plane parallel to, but offset from, the fault plane of the Fairview Peak earthquake.
Avco1
TL;DR: In this paper, a polycrystalline aluminum oxide was hot-worked at 1750° to 1950°C and at stresses <21, 000 psi using a press-forging technique, and maximum true strains and strain rates of -1.25 and 0.2/min, respectively, were observed.
Abstract: Polycrystalline aluminum oxide was hot-worked at 1750° to 1950°C and at stresses <21, 000 psi using a press-forging technique. No ductility problems were encountered, and maximum true strains and strain rates of -1.25 and 0.2/min, respectively, were observed. Deformed samples often showed grain elongation in addition to a marked basal crystallographic texture, which suggested that basal slip was the predominant deformation mode. However, nonbasal slip, grain boundary sliding, and diffusional deformation were all thought to contribute to the ductility. Primary recrystallization occurred during or after the deformation and resulted in equiaxed microstructures, although the basal texture was retained. Because of a severe shear strain gradient during deformation, nonuniform microstructures were usually obtained, and this provided a means for growing single crystals by strain anneal. Although no conclusions can be drawn concerning the origin of the recrystallization texture, it is suggested that pores are preferential sites for recrystallization nuclei. MgO in solid solution (1/4%) retarded primary recrystallization.
TL;DR: Skempton et al. as mentioned in this paper found slip surfaces to a depth of 15 feet below the existing ground-level on slopes of stiff fissured clay, where the slope angles are 3° and steeper.
Abstract: Summary Details are given of trial pits which have been excavated during site investigations carried out in Kent and Oxfordshire over the past two and a half years. Slip surfaces have been found to a depth of 15 ft below the existing ground-level on slopes of stiff fissured clay, where the slope angles are 3° and steeper. It is suggested that, whilst these slopes are stable under present day conditions, the slip surfaces must have been formed as the result of periglacial activity. The presence of these discontinuities, which have shearing resistances at or near their residual values (Skempton 1964), is the governing factor affecting the maximum possible natural slope angle and also the stability of any engineering works that may be constructed in the area. In the case of the investigations in Kent it has been possible to recognize three separate periods of solifluction corresponding to the Saale Glaciation, the Main Weichselian and Zone III of the Late Glacial.
TL;DR: In this article, the authors analyzed the patterns and rates at which strain is accumulating along the San Andreas fault in California from geodetic data and showed that nearly pure shear with a maximum shear plane nearly parallel to the fault is accumulating at a rate of about 0.7×10−6 yr−1 from San Francisco Bay to the Transverse Ranges.
Abstract: The patterns and rates at which strain is accumulating along the San Andreas fault in California are analyzed from geodetic data. Geodimeter and triangulation data indicate displacements near the fault that are a result of homogeneous strain to an approximation within the accuracy of the data. Both sets of data indicate that nearly pure shear with a maximum shear plane nearly parallel to the fault is accumulating at a rate of about 0.7×10−6 yr−1 from San Francisco Bay to the Transverse Ranges. The nearly east-west trending segment of the fault in the Transverse Ranges is accumulating nearly uniaxial compression normal to the fault at a rate of 1.1×10−6 yr−1, indicating a ‘locking’ mechanism. At no point, with the possible exception of the Cholame Valley, do fault creep and small earthquakes substantially release the accumulating strain. A more complete set of data in the Imperial Valley suggests that the strains accumulating there are such as would be released by fault slippage at a rate of 8.5 cm yr−1 to a depth of 25 to 40 km. Slip on the Imperial fault due to small earthquakes and creep, however, occurs at a rate of only 1.3 cm yr−1, and earthquakes occur only to a depth of approximately 10 km. Strains at greater depths must be relieved by aseismic slip or inelastic deformation.
TL;DR: In this paper, the mechanics of the build-up of large local plastic strains at the free surface of a polycrystal under fatigue loading is shown, and the increase of local plastic strain in the slices with cycles of loading is calculated by applying the analogy between plastic strain and external force.
Abstract: The mechanics of the build-up of large local plastic strains at the free surface of a polycrystal under fatigue loading is shown. Two closely located thin slices in a most-favourably-oriented crystal located at a free surface of the polycrystal are assumed to have an initial resolved shear stress of a few psi of opposite sign. Under cyclic loading, the two thin slices slide in opposite directions, one during the forward loading and the other during the reversed loading. Based on the dependency of slip on the resolved shear stress, the increase of local plastic strain in the slices with cycles of loading is calculated by applying the analogy between plastic strain and external force. The calculated local plastic shear strain in both slices (one positive and the other negative) reaches 100 per cent at the free surface in a few hundred cycles. These large plastic shear strains clearly cause the start of an extrusion or intrusion and the nucleation of a fatigue crack.
TL;DR: In this article, mechanical albite and pericline twins were induced in seven feldspars, (Na, Ca) (Al, Si)4O8, in triaxial compression tests at 800° C, 8 to 10 kb confining pressure.
Abstract: Mechanical albite and pericline twins were induced in seven feldspars, (Na, Ca) (Al, Si)4O8, in triaxial compression tests at 800° C, 8 to 10 kb confining pressure. Two were initially in a high temperature structural state (disordered) (An1, An59). Three (An32, An39, and An53) were slightly disordered, and two (An76 and An95) had the transitional and primitive anorthite structure, respectively. No microscopic twinning was detected in comparable tests on ordered albite and oligoclase (An1, An20), feldspars in the peristerite range (An11 An14) or in a low structural state labradorite (An51). Other deformational features include lamellae 60 to 80° from the c axis and (010) slip in the opposite sense for (010) twinning.
TL;DR: In this paper, a model of plastic deformation based upon activation of near-surface dislocation sources is presented in the context of the above observations, which shows that slip lines formed during active dissolution are stronger and more widely spaced than those produced on crystals deformed in air.
Patent•
31 Jan 1969TL;DR: In this article, the slip properties of multilayer films of thermoplastic organic polymers are improved by incorporating small amounts of a conventional slip additive, e.g., oleamide, into one or more of the inner layers of said films.
Abstract: Slip properties of multilayer films of thermoplastic organic polymers are improved by incorporating small amounts of a conventional slip additive, e.g., oleamide, into one or more of the inner layers of said films. Said films exhibit slip characteristics which are retained for relatively long periods of time.
TL;DR: An electron microscope investigation has been made of the decomposition of ⅓⟨ 1120⟩ slip dislocations when they penetrate {1012} twin boundaries in zinc as mentioned in this paper.
Abstract: An electron microscope investigation has been made of the decomposition of ⅓⟨1120⟩ slip dislocations when they penetrate {1012} twin boundaries in zinc. The results show that basal dislocations decompose into an integral number of zonal twinning dislocations and a glissile slip dislocation in the twin. The previously unreported {1100}; ⅓⟨1123⟩ slip system is shown to be operative in {1012} deformation twins in zinc and is a direct result of the decomposition of basal dislocations on penetrating twin boundaries.
TL;DR: In this article, it is suggested that the shape strain is the resultant of a lattice strain and an elastic plastic strain in the austenite ahead of the growing plate, and that the orientation of the specimen surface determines which of the predicted directions operates in any particular case.