Showing papers on "Fracture (geology) published in 1971"
TL;DR: In this paper, the effects of the stress states on the stability and the flow of rocks are investigated by using the ELASTIC AXIAL STRAIN from the total AXial STrain.
Abstract: A NEW TRIAXIAL COMPRESSION TECHNIQUE HAS MADE POSSIBLE THE STUDY ON GENERAL LAWS OF FRACTURE AND FLOW OF ROCKS UNDER GENERAL TRIAXIAL STRESS STATES, IN WHICH ALL THREE PRINCIPAL STRESSES ARE DIFFERENT. IN THIS PAPER, THE EFFECTS OF THE STRESS STATES ON FRACTURE AND YIELDING OF ROCKS ARE EXPERIMENTALLY STUDIED BY THIS METHOD. THE EXPERIMENTAL PROCEDURE IS DESCRIBED, AND THE EQUATIONS FOR STRESS STATES PRODUCING FRACTURE AND YIELDING ARE GIVEN AS MONOTONIC INCREASING FUNCTIONS OF THE THREE PRINCIPAL STRESSES. THE NEW FAILURE CRITERIA CORRESPONDING TO THE GENERALIZED VON MISES CRITERIA ARE INTERPRETED. THE DUCTILITY DEFINED AS THE PERMANENT STRAIN JUST BEFORE FRACTURE IS DETERMINED BY SUBTRACTING THE ELASTIC AXIAL STRAIN FROM THE TOTAL AXIAL STRAIN. FROM THE RESULTS ON THE EFFECT OF STRESS STATES, FRACTURE AND FLOW PROPERTIES OF THE EARTH'S UPPER MANTLE ARE DEDUCED. /AUTHOR/
506 citations
TL;DR: In this paper, the effective elastic compliance of rock that contains cracks is evaluated from energy considerations, as first proposed by Eshelby [1957], and the effective compliance is linearly elastic for small-amplitude elastic waves.
Abstract: The effective elastic compliance of rock that contains cracks is evaluated from energy considerations, as first proposed by Eshelby [1957]. The compliance of rock depends on the compliance of the solid matrix, the directional distribution of the cracks, an ‘inhomogeneity’ interaction tensor, and the shape distribution of cracks, which are assumed to be shaped like pennies. The effective compliance is linearly elastic for small-amplitude elastic waves. Anisotropic crack distribution causes elastic anisotropy, with associated acoustic birefringence. Nonhydrostatic stress causes stress-induced anisotropy, owing to anisotropic closure of cracks. Although velocities are uniquely determined from the distribution of cracks, the distribution cannot be determined uniquely from the velocities. The theoretical results compare favorably with measured compressional velocities and crack distribution in Salisbury granite and with measured stress-induced compressional and shear velocity anisotropy in Barre granite.
396 citations
TL;DR: In this article, a simplified model is proposed that can explain the evolution of marginal offsets, ridges, and fracture zones of the equatorial Atlantic margins and the results reaffirm the suggestion that the South Atlantic opened in two stages beginning about 140 m.y.
Abstract: A simplified model is proposed that can explain the evolution of marginal offsets, ridges, and fracture zones. Submarine features of the equatorial Atlantic margins are examined and are found to be in reasonable agreement with the model. The results reaffirm the suggestion that the South Atlantic opened in two stages beginning about 140 m.y. and 80 m.y. ago. The pole of rotation describing the relative motion of the South American and African plates changed radically when the constraints imposed by adjacent continental blocks were relaxed.
376 citations
TL;DR: In this article, a two-dimensional analysis of the stress field around a crack on the plane interface between two bonded dissimilar anisotropic elastic half-spaces is presented, which is then combined with the usual local form of the Griffith virtual work argument to give an explicit fracture criterion which involves a suitably defined stress concentration vector and the specific surface energy of the bonded surfaces.
Abstract: This paper contains a two-dimensional analysis of the stress field around a crack on the plane interface between two bonded dissimilar anisotropic elastic half-spaces. This analysis is then combined with the usual local form of the Griffith virtual work argument to give an explicit fracture criterion which involves a suitably defined ‘stress concentration vector’ and the specific surface energy of the bonded surfaces. This criterion has a simple structure and reduces to the conventional form of Irwin when the two half-spaces are isotropic and identical. The analysis is then extended to cracks moving uniformly and a local fracture criterion with the same structure as the static criterion is derived by an energy balance argument. The criterion is specialized to isotropic half-spaces for illustration, when it predicts that the speed of a crack on an interface between such media will be limited by a speed Vc which is slightly greater than the smaller of the two Rayleigh wave speeds. A by-product of the analysis is an expression for the displacement field of an arbitrary interfacial dislocation, either stationary or moving uniformly.
307 citations
TL;DR: In this article, a numerical stress analysis of an elastic three-dimensional specimen similar to the compact tension specimen used in fracture investigations is presented using singular integral equations which are analogous to Green's boundary formula in potential theory.
Abstract: A numerical stress analysis of an elastic three-dimensional specimen similar to the compact tension specimen used in fracture investigations is presented The numerical results are achieved using singular integral equations which are analogous to Green's boundary formula in potential theory The analysis yields details of the stresses near the crack tip and clearly shows their three-dimensional character Some results are also given to indicate the influence of thickness and Poisson's ratio on the stresses
192 citations
TL;DR: In this paper, the effect of carbon fiber/polyester composites on fracture toughness and interlaminar shear strength was investigated by means of Charpy V-notch impact tests and slow three-point bend tests on notched specimens of triangular cross-section.
Abstract: Fracturing of carbon fibre/polyester composites has been studied by means of mechanical testing and scanning electron microscopy. Carbon fibres were surface-treated in several ways so as to vary the interlaminar shear strength of the composites, and the effect of this variation on the work of fracture was determined by means of Charpy V-notch impact tests and slow three-point bend tests on notched specimens of triangular cross-section. The effect of moisture on the fracture toughness was also studied by measuring toughness and interlaminar shear strength after exposure to steam. Improvement of the fibre/resin bond results, as expected, in an increase in the brittleness of composites and it appears that a purely mechanical bond, such as might be obtained by acid-etching the fibre surface, is less proof against deterioration in humid atmospheres than a chemical bond, such as can be obtained by the use of coupling agents. Estimates of the magnitude of various contributions to the fracture toughness show that in carbon-fibre-reinforced resins the effect of increasing the stiffness or load-bearing ability of the matrix and the work done against friction in pulling broken fibres out of the matrix contribute approximately one fifth and four fifths, respectively, of the total work of fracture.
109 citations
100 citations
01 Jan 1971
TL;DR: In this paper, the lower limit of the fracture energy in polyurethane elastomer has been determined and good agreement between the theoretically and experimentally determined relationships for the rate-sensitive fracture energy is demonstrated.
Abstract: The energy required to form a unit of new surface in the fracture of a polyurethane elastomer is determined. The rate sensitivity of the material has been reduced by swelling it in toluene. This paper primarily describes the experimental work of measuring the lower limit of the fracture energy. With this value and the creep compliance as a basis, the rate dependence of fracture energy for the unswollen material has been determined. It is thus shown that the dependence of the fracture energy on the rate of crack propagation can be explained by energy dissipation around the tip of the crack. Good agreement between the theoretically and experimentally determined relationships for the rate-sensitive fracture energy is demonstrated.
74 citations
TL;DR: A new analytical method for calculating crack density distributions from Hertzian fracture data is presented in this paper, which is the first correct analysis to be reported within the limitations of the assumptions made and is also one which can be readily applied.
Abstract: A new analytical method for calculating crack density distributions from Hertzian fracture data is presented This is the first correct analysis to be reported within the limitations of the assumptions made and is also one which can be readily applied Results are presented for a piece of polished pure silica glass and their statistical significance is discussed
69 citations
01 Aug 1971
01 Jan 1971
TL;DR: In this paper, the effect of flaws in stressed bodies can be quantitatively characterized by methods of linear elastic fracture mechanics (LEFM), which is sometimes necessary to assess the fracture susceptibility using only conventional transition temperature tests.
Abstract: Although the effect of flaws in stressed bodies can be quantitatively characterized by methods of linear elastic fracture mechanics (LEFM), it is sometimes necessary to assess the fracture susceptibility using only conventional transition temperature tests. In order to gain the advantages and best features of each approach, a correlation between the two methods of fracture assessment is needed. The existing correlation between LEFM results and transition temperature test results are reviewed in light of new data on A533B steel. A complete series of test results obtained by the HSST Program (ORNL) for both LEFM and transition temperature tests in both unirradiated and irradiated conditions permit fracture toughness to be correlated with charpy V-notch energy, nil-ductility transition temperature, DT transition temperature, and low temperature cleavage stress. By following fundamentals of LEFM, whenever possible, a consistent pattern of fracture behavior is demonstrated for a class of pressure vessel steels similar to A533B. /Author/
01 Jan 1971
TL;DR: In this article, it was shown that the dynamic threshold strength of terrains should vary as the one-thirteenth power of strain energy or the inverse one-half power of rise time.
Abstract: THE DYNAMIC TENSILE STRENGTH OF PLAIN CONCRETE, FIBER REINFORCED CONCRETE, AND A POLYESTER CONCRETE IS EVALUATED IN TERMS OF THE CRITICAL FRACTURE STRAIN ENERGY. BASED ON THE FRACTURE STRAIN ENERGY REMAINING CONSTANT, IT WAS SHOWN THAT THE FRACTURE STRAIN SHOULD VARY AS THE ONE-THIRD POWER OF STRAINING RATE OR THE INVERSE ONE-HALF POWER OF RISE TIME. THIS WSA EXAMINED ON PRISMATIC SPECIMENS OF THREE TYPES OF CONCRETE AND FOUND TO AGREE WITH EXPERIMENTAL RESULTS. THE TESTS WERE ACCOMPLISHED USING AN IMPACT LOADER AND A STRAIN GAGE SYSTEM. THE PAPER ALSO POINTS OUT THE RELATIONSHIP OF THIS TYPE OF TEST TO THE GENERAL PROBLEM OF SPALLATION OF CONCRETE BY DYNAMIC TENSILE PULSES. /ACIJP/
TL;DR: In this article, a reaction-rate molecular model was proposed to explain some of the deformation and bond-rupture behavior leading to fracture of nylon 6 fibers, and the model was successfully correlated with experimental stress, strain, and bond•rupture results for creep, constant-rate‐ofloading, and cyclic stress tests.
Abstract: Electron paramagnetic resonance (EPR) techniques were used to determine the number of free radicals produced during deformation leading to fracture of nylon 6 fibers. A reaction‐rate molecular model is proposed to explain some of the deformation and bond‐rupture behavior leading to fracture. High‐strength polymer fibers are assumed to consist of a sandwich structure of crystalline‐block and amorphous‐flaw regions along the fiber axis. In the flaw regions, tie chains connecting the crystalline blocks are assumed to have a statistical distribution in length. These chains are, therefore, subjected to different stresses. The length distribution was determined by EPR. The probability of bond rupture was assumed to be controlled by reaction‐rate theory with a stress‐aided activation energy and behavior of various loadings determined by numerical techniques. The model is successfully correlated with experimental stress, strain, and bond‐rupture results for creep, constant‐rate‐of‐loading, and cyclic‐stress tests.
TL;DR: In this paper, a section-and-etch technique is used to study the mechanics of Hertzian cone-cracks growth in glass, and it is shown that the cone cracks propagate at a convenient rate through successive phases of stability at constant indenter load.
Abstract: A section‐and‐etch technique is used to study the mechanics of Hertzian cone‐crack growth in glass. With a suitable choice of test environment the cone cracks propagate at a convenient rate through successive phases of stability at constant indenter load. Systematic measurements of the etched‐crack lengths as a function of indentation time permit a detailed description of the fracture mechanics. Within a certain range of indenter load, the cone crack is observed to grow as a shallow surface ring to a critical depth prior to full development. This directly confirms a salient feature of the energy balance theory of Hertzian fracture outlined in earlier papers. The current status of the long‐standing Auerbach law, which relates the critical fracture load linearly to the indenter radius, is discussed in the light of the present evidence.
TL;DR: In this paper, the fracture stress, elastic modulus, and strain energy to fracture also increase with decreasing crystallite size at constant density, and fracture stress and Young's modulus were measured in three-point bending.
01 Jan 1971
TL;DR: In this article, the authors describe the use of linear crack-stress field analysis to characterize a wide range of macroscopic crack-extension behaviors, including fatigue and stress-corrosion cracking, and provide guidance for studies of the relationship of crack toughness to plastic flow properties.
Abstract: The analytical aspects of linear fracture mechanics are complete relative to basic formulation and two-dimensional static problems. Extensions of current analysis techniques are needed for certain three-dimensional and dynamic problems. The terminology of linear crack-stress field analysis permits descriptive characterization of a wide range of macroscopic crack-extension behaviors. Plasticity analysis aspects of cracks are less advanced. However, simple aspects can be treated in ways which permit an understanding of the brittle-ductile fracture mode transition and provide essential guidance for studies of the relationship of crack toughness to plastic flow properties. Attempts to provide general characterization factors for crack extension in terms of plasticity analysis (rather than linear analysis) have been only partially successful. Although advancement in certain fields of fracture behavior may be delayed pending clarification of factors dependent on nonlinear analysis, applications of the linear fracture mechanics treatment to fatigue and stress-corrosion cracking, as well as to other fields, have become established, and these provide ample scope for continued growth of the fracture mechanics movement.
TL;DR: In this paper, the effect of stress loading path on fracture or maximum stress is investigated for several rocks using a special testing apparatus constructed for this study, which used conventional cylindrical specimens under pressures up to 7 kb, but with the unique features that the ratio of the two independent principal stresses could be controlled by means of electrohydraulic servo-systems.
TL;DR: For isotropic carbons with constant density, the Young's modulus and fracture stress increase with decreasing crystallite size possibly due to cross-linking either between crystallites or between layer planes as discussed by the authors.
TL;DR: In the majority of applications of polymers, we are interested in one or more of three basic mechanical properties-stiffness, strength and toughness as discussed by the authors, and to these can be added creep, which becomes important in many engineering applications.
Abstract: In the majority of applications of polymers, we are interested in one or more of three basic mechanical properties-stiffness, strength and toughness. To these can be added creep, which becomes important in many engineering applications. Stiffness represents resistance to deformation, and is a much simpler property than strength and toughness, which relate to failure. Strength is the ultimate stress which a material can withstand, before it fails, whether by fracture or by excessive deformation, whilst toughness represents the work required to fracture a material
Patent•
30 Jul 1971
TL;DR: In this article, the times of arrival of the seismic wave can be determined from a display, and the average velocity of seismic waves in the earth can also be determined based on the previously determined velocity.
Abstract: In the process of inducing fractures in the earth in the vicinity of a bore hole, fluid under high pressure is pumped down the well bore, and a portion of the wall of the well bore is exposed to this pressure at a known position in the earth. As the fluid pressure is increased, the rock will part, or rupture, and form a fracture. As the fluid rapidly flows into this fracture the pressure sharply falls, and this drop in pressure is transmitted to the surface, where at some time later, the pressure in the well fluid at the surface will show a corresponding drop. Sensors are placed in the earth around the well bore to receive the seismic wave that is generated by the rock fracture. The times of arrival of the seismic wave can be determined from a display, and the average velocity of seismic waves in the earth can be determined. As the flow of fluid continues, the pressurized fluid flows into the fracture, causing it to widen and extend to greater distances from the well bore. This extension is discontinuous and intermittent, involving additional rock fractures and corresponding seismic signals. The times of arrival of the later fracture signals are determined. From these determinations and the previously determined velocity of seismic waves, the position in the earth of the successive fractures are determined.
TL;DR: In this paper, the failure mechanism of diametrically-compressed glass cylinders was examined and it was shown that fracture always initiates at the contact surface, and not within the cylinder as predicted by conventional theory.
Abstract: This paper considers the failure mechanism of diametrically-compressed glass cylinders. Examination of failed specimens shows that fracture always initiates at the contact surface, and not within the cylinder as predicted by conventional theory. A tentative explanation for this phenomenon is given in terms of the three-dimensional stress system in the contact region and also of the frictional effects at the interface; in this connection, an analytical solution is given to the problem of adhesive contact between normally-loaded dissimilar elastic cylinders. The results have some relevance to the application of the well-known indirect tensile test for materials such as concrete and rock, and also to the general design of roller bearings.
TL;DR: In this article, a technique is described for varying the precompression stress wave magnitude σc relative to the magnitude of the rarefaction wave, which produces the spall, in the range of σ c/σr≥1.
Abstract: In impact‐produced spall fracture, a material undergoes drastic dynamic precompression immediately prior to the time of fracture. In this paper a technique is described for varying the precompression stress wave magnitude σc relative to the magnitude σr of the rarefaction wave, which produces the spall, in the range of σc/σr≥1. The method is used to determine the spall strength of 1020 steel and 6061‐T6 aluminum following precompression stress amplitudes up to 120 kbar. The results show that for these two materials neither the spall strengths nor the modes of fracture initiation and crack growth depend on the amount of precompression in the range attained in these experiments.
TL;DR: Fracture of the medial wall without fracture of the floor did not occur in this series of fractures of the orbit.
Abstract: Medial wall fractures of the orbit should be considered a frequent component of the entity termed blowout fracture. Fracture of the medial wall without fracture of the floor did not occur in this series. Hypocycloidal tomography affords the best radiologic technique for diagnosing orbital fractures.
Patent•
27 Aug 1971
TL;DR: In this paper, a process for hydraulically fracturing a permeable underground formation is described, in which the fracture faces are treated to reduce their permeability to the fracturing fluid and propping agent is placed in the fracture in a conventional manner.
Abstract: A process for hydraulically fracturing a permeable subterranean formation in which the fracture faces are treated to reduce their permeability to the fracturing fluid and propping agent is placed in the fracture in a conventional manner whereby the bulk of the propping agent is deposited in the fracture at a location remote from the well, and thereafter the fracture faces are treated to restore their permeability to subsequently injected fluids and propping agent is again injected into the fracture whereby the bulk of the propping agent is deposited in the fracture adjacent to the well In this manner, fluid conductively through the fracture is assured
TL;DR: In this article, the Griffith-Irwin-Orowan theory is applied to the fracture of unidirectional composites, and lower bounds on the fracture propagation stress are derived.
Abstract: A n analysis is presented of the mechanics of failure of notched unidirectional composites subjected to tensile load in the fiber direction. The applicability of the Griffith-Irwin-Orowan theory to the fracture of composites is discussed. The effects of fiber debonding, matrix and fiber plasticity, and scatter in fiber strength are considered. Statistical lower bounds on the fracture propagation stress are developed.
Patent•
19 Jan 1971TL;DR: In this article, the authors describe a cascade fracture in a substantially impermeable underground earth formation that tends to fracture along nonintersecting vertical planes of natural weakness, and the cascade fracture is extended into communication with an adjacent well or a fracture extending from the adjacent well by filling the fracture with a granular material and refracturing the well borehole by pumping in a viscous fluid at a rate causing the pressure to rise above the pressure at which the first fracture was formed.
Abstract: Wells in a substantially impermeable subterranean earth formation that tends to fracture along non-intersecting vertical planes of natural weakness are interconnected by initially fracturing at least one of the well boreholes along its vertical plane of natural weakness, filling the fracture with a granular material, and refracturing the well borehole by pumping in a viscous fluid at a rate causing the pressure to rise above the pressure at which the first fracture was formed. The lastmentioned fracture is extended into communication with an adjacent well or a fracture extending from the adjacent well.
01 Jan 1971
TL;DR: In this article, the authors present the critical normal fracture strain energy theory and suggest its potential for some rocks, such as concrete and quartz monzonite, and make recommendations for the potential application to and extension of the slabbing problem.
Abstract: An attempt is made to shed some light on the mechanisms of scabbing, spalling or slabbing by stress waves created by explosives or impacts. The dynamic tensile strength behavior under various stress waves is examined. The primary objective is to present the critical normal fracture strain energy theory and suggest its potential for some rocks. Also, it is pointed out that the dynamic tensile strength of rock and concrete (a pseudo rock) is not constant and varies with straining rate. Generally, the significance of the slabbing problem has been examined, and it's relation to dynamic tensile strength has been pointed out. The significance of the basic critical fracture strain energy is discussed, and its application to concrete is shown. Some work with quartz monzonite rock is presented. Recommendations are made for the potential application to and extension of the slabbing problem. A theory is propounded to explain dynamic tensile strength behavior, tests having verified the theory in the laboratory. The theory is extrapolated from concretes to a specific rock. (12 refs.)
TL;DR: In this article, an analysis based on the theory of dislocations was proposed to provide a quantitative description of the inelastic deformation that occurs near the edges of thin tabular excavations (stopes) at deep levels in brittle rock.
Abstract: Analysis based on the theory of dislocations can provide a quantitative description of the inelastic deformation that occurs near the edges of thin tabular excavations (stopes) at deep levels in brittle rock. The stope is modeled as an array of edge dislocations that climb from the center of the stope toward the edges as the stope is enlarged. The dislocations representing the stope interact with dislocations representing inelastic deformation in the surrounding rock and with the virgin stress field. One type of interaction leads to the formation of a zone of fractured rock, represented as an array of dislocations extending ahead of the stope. The continuous migration of dislocations into the plane of the stope results in the production of a ‘fracture zone’ and the continuous convergence of the center of the stope. This process consumes much of the energy released by extending the stope, and also relaxes the intense stress field near the edge of the stope.