Showing papers on "Fracture (geology) published in 1978"
TL;DR: Aamodt et al. as mentioned in this paper used a large fracture connecting the two pipes serving as the heat exchanger to determine the state of stress at mid-crustal depths.
Abstract: Measurements ofthe stress field within the crust can provide perhaps the most useful information concerning the forces responsible for various tectonic processes, such as earthquakes Advances in knowledge of the state of stress at mid-crustal depths are essential if further progress is to be made toward solving a broad class of problems in geodynamics Most stress measurements have been, and will continue to be, motivated by engineering needs rather than the needs of geologists engaged in fundamental research Knowledge of the state of stress is critical to the design of underground excavations for mining and for nuclear waste disposal (eg Jaeger & Cook 1969, pp 435-64) The massive hydraulic fracturing of formations in oil and gas fields to stimulate production is another application for which knowledge of the stress field at depth is very important and, in fact, many of the deeper stress determinations have been by-products of these "hydrofrac" operations (eg Howard & Fast 1970) A recent and exciting application of hydraulic fracturing is the Hot-Dry-Rock Geothermal Energy Program (Aamodt 1977) Heat is extracted from the rock by circulating fluid down a pipe into hot rock and then up through a second pipe A large fracture connecting the two pipes serves as the heat exchanger Knowing the state of stress is critical in the solution to the problem of creating and maintaining such a crack There is little argument about the applicability of information on the state of stress to these and many other engineering problems The application of stress measurements to the solution of problems in tectonics is not so straightforward as in engineering design Whereas the engineer is concerned with the stress field affecting the rock, the geologist attempts to deduce the processes that might have caused the stresses Before the measured stress field can be related
527 citations
TL;DR: In this paper, the authors used the disk test in which a circular specimen with an internal crack is subjected to diametral compression to investigate combined mode I and mode II fracture.
Abstract: The disk test in which a circular specimen with an internal crack is subjected to diametral compression is used to investigate combined mode I and mode II fracture. The stress intensity factors in the disk test are calculated numerically by means of the boundary collocation procedure and the dislocation method. Special care was taken to analyze the effect of the compression anvils. This method has the advantage, of allowing successive measurement of mode I, mode II and the combined mode fracture toughness under the same conditions. Some kinds of graphite, plaster and marble are examined to obtain the fracture toughness values, KIC , KIIC and the combined mode fracture criterion.
331 citations
TL;DR: In this paper, the authors outline the mechanisms of flow and fracture which appear to be relevant in the deformation of materials of interest to the geophysicist, and the way pressure affects them.
Abstract: Crystalline solids respond to stress by deforming elastically and plastically, and by fracturing. The dominant response of a given material depends on the magnitude of the shear stress (0 s ), on the temperature (T) and on the time (t) of its application. This is because a number of alternative mechanisms exist which permit the solid to flow, and its fracture, too, occurs by one of a number of competing mechanisms. Their rates depend on 0 8 , T and t: it is the fastest one which appears as dominant. In geophysical problems, pressure appears as an additional variable. At pressures corresponding to depths of a few kilometres below the surface of the Earth, the mechanisms of fracture are the most affected; but at depths of a few hundred kilometres, plasticity, too, is influenced in important ways. This paper outlines the mechanisms of flow and fracture which appear to be relevant in the deformation of materials of interest to the geophysicist, and the way pressure affects them. The results are illustrated and their shortcomings emphasized by using them to calculate the mechanisms of flow and fracture to be expected in the upper mantle of the Earth.
276 citations
TL;DR: In this paper, it was shown that there is a general relationship between the ferrite grain size and the size of the largest carbide particle in mild steels which are simply cooled after austenitization.
Abstract: It is shown, by compiling data from the literature, that there is a general relationship between the ferrite grain size and the size of the largest carbide particle in mild steels which are simply cooled after austenitization. By using this relationship, a cleavage fracture criterion derived by Smith is shown to predict a grain size dependence for the cleavage fracture stress of mild steel that is in good agreement with the results of many workers. These results indicate a value of 14 J m−2 for the effective surface energy of ferrite.Experimental results are presented showing the variation of the cleavage fracture stress of spheroidized steels with carbide particle radius. These support the suggestion that cleavage in such steels is due to the propagation of penny-shaped crack nuclei prod uced when spheroidal carbide particles crack. If the 95th percentile carbide radius is taken to represent the crack nucleus radius, an effective surface energy value of 14 Jm−2 is found to satisfy the fracture st...
264 citations
TL;DR: In this article, it is proved that a rule for accomplishing this (given without proof by Weibull) is valid for shear-insensitive cracks, i.e. on the assumption that only the component of stress normal to a crack plane contributes to its fracture.
Abstract: A primary objective of statistical fracture theory is to predict the probability of failure for an arbitrary stress state when the failure statistics are known for a particular stress state, e.g. simple tension. It is proved that a rule for accomplishing this (given without proof by Weibull) is valid for shear-insensitive cracks, i.e. on the assumption that only the component of stress normal to a crack plane contributes to its fracture. Four failure criteria for shear-sensitive cracks are considered and the results are compared with test data.
253 citations
TL;DR: In this paper, a general approach for the statistical analysis of fracture under multiaxial states of stress was developed, which invokes a critical coplanar strain-energy release-rate fracture criterion and considers distributions of penny cracks in random and preferred orientations.
Abstract: A general approach for the statistical analysis of fracture under multiaxial states of stress was developed. The approach invokes a critical coplanar strain-energy release-rate fracture criterion and considers distributions of penny cracks in random and preferred orientations. The analysis predicts strength ratios that depend on the strength dispersion and the proximity to the lower bound. For example, the uniaxial and equibiaxial strength ratios well above the lower bound are 1.25 to 1.09 for a typical range of dispersions. Uniaxial and equibiaxial fracture data for alumina were analyzed and compared with the theory. A good correlation was obtained.
229 citations
TL;DR: In this paper, the authors suggest that the anomalous transverse ridges are not the result of excess volcanism, but rather of tectonic uplift of upper mantle and crustal blocks.
214 citations
TL;DR: Large-scale gravity creep is the very slow downward and outward movement of a mass of earth material adjoining a slope, generally without the formation of a continuous rupture surface as discussed by the authors, which is a type of slow landsliding, in which zones of creep can extend a hundred metres or so below the surface.
Abstract: Large-scale gravitational creep of rock masses on slopes is a type of slow landsliding, in which zones of creep can extend a hundred metres or so below the surface. It excludes movement of surficial materials, such as solifluction and debris flows. As used in this report, creep is the very slow downward and outward movement of a mass of earth material adjoining a slope, generally without the formation of a continuous rupture surface. Measured rates of large-scale rock creep range from about 2 cm per year to 20 cm per day. Large-scale rock creep on slopes has been observed, measured, and described in various parts of the world, including Europe, New Zealand, Iran, South America, and the United States. Numerous examples from these places show that creep proceeds in several different ways in different geologic settings: (1) by valley ward squeezing out of weak ductile rocks overlain by or interbedded with more rigid rocks, causing tensional fracturing and outward movement of the more rigid rocks as well, sometimes with upward bulging in the centers of valleys; (2) by distortion and buckling of dipping interbedded strong and weak rocks or by creeping of rigid over soft rocks without buckling; (3) by movement distributed over a thick zone in relatively uniform material; (4) by incremental movement along a dipping rough-surfaced plane; (5) by deep-seated bending, folding, and plastic flow of rocks on slopes; and (6) by bulging, spreading, and fracturing of steep-sided ridges in mountainous areas. There may be still other types of creep that have not yet been recognized. In some places creep of rock masses proceeds continuously, under normal gravitational stresses; in other places it occurs in increments and may or may not require a trigger, such as an earthquake. Creep is known to precede sudden, catastrophic sliding (creep rupture), as at the Vaiont Reservoir in Italy, but it also may continue for years with no sign of sudden or accelerated movement. The mechanism that produces “spreading” of mountain ridges with uphill-facing scarps and trenches on hillsides is still not completely understood. Earthquake shaking, tectonic uplift, rapid stream erosion, and steepening of valley sides with removal of lateral support by glaciers now melted, could all have acted, separately or in combination, to cause this type of movement. Gravitational forces acting on steep-sided ridges probably cause tensional spreading of the ridge, which causes the sides of the ridge to fracture. Movement along these fractures or along pre-existing discontinuities forms trenches and uphill-facing scarps as the sides of the ridge bulge outward and the top subsides. Recognition and understanding of large-scale gravitational creep is vital in site selection and design of major engineering structures, particularly in high mountains. Gravitational creep may change to sudden catastrophic slide movement, as well illustrated by the slide at Vaiont. In places where valley sides are moving horizontally or bulging outward, engineering structures in the valley bottom will be subjected to both upward and lateral pressure, owing to bowing up of the valley bottom or closing in of the sides.
192 citations
TL;DR: A recent development in the area of stress measurements in rock is the use of hydrofracturing as discussed by the authors, which directly determines average stresses over large areas by recording two hydraulic pressures, one necessary to crack open a segment of the test-hole and the other required to keep the fracture open.
179 citations
Journal Article•
TL;DR: In this article, the tensile deformation and fracture of pearlite were studied using high-resolution 200-kV semi-volumetric sensors and a high-frequency 200-KV semiuser.
Abstract: Dynamic studies of the tensile deformation and fracture of pearlite using high-resolution 200-KV sem
178 citations
TL;DR: In this article, the authors defined the complexities of compression failure in terms of the three well known failure modes: yielding, cone failure, and axial splitting, and proposed new failure criteria for compression cracking based on the energy balance theory of fracture.
Abstract: The complexities of compression failure are defined in terms of the three well known failure modes: yielding, cone failure, and axial splitting. The notion of compressive strength is shown to be useful only in the case of yielding. For compression cracking, where the stress at failure varies with geometry and manner of force application, compressive strength is not such a useful parameter. Therefore, new failure criteria are suggested for compression cracking based on the energy balance theory of fracture. These criteria explain why the force required for failure depends on the mode of cracking, on the fracture surface energy of the material, and on the geometry and elasticity of the specimen. Fracture surface energy, and not strength, is found to be the fundamental material property dictating compression cracking. These ideas are verified by detailed theoretical and experimental investigation of compression splitting in glassy materials. In particular, the effects of size on compression failure are interpreted, both platen and specimen dimensions influencing the fracture force. It is further shown that the mode of failure can change from brittle to ductile under certain conditions, for example, as the platens are widened or as the sample is reduced in size. Finally, the inhibiting effect of lateral forces on compression cracking is explained.
01 Jan 1978
TL;DR: In this paper, the authors presented some data on FRACTURE CRITERIA, and outlined the BRITTLE FRACTure Theories and studied exact solutions to the PROBLEMS of FISSURATION.
Abstract: AFTER PRESENTING SOME DATA ON FRACTURE CRITERIA, THE AUTHOR OUTLINES THE BRITTLE FRACTURE THEORIES AND STUDIES EXACT SOLUTIONS TO THE PROBLEMS OF FISSURATION. ONE CHAPTER DEALS WITH INTEGRAL CONCEPTS; ANOTHER PRESENTS KNOWN METHODS OF DETERMINING INTENSITY FACTORS; THREE-DIMENSIONAL PROBLEMS ARE CONSIDERED; THE LAST CHAPTER AND APPENDICES ARE DEVOTED TO PROBLEMS OF THE DYNAMIC PROPAGATION OF CRACKS: SOME VERY SPECIFIC PROBLEMS OF THERMOELASTICITY, ROCK MECHANICS AND PLATE THEORIES ARE EXAMINED.
TL;DR: In this paper, a model for predicting ductile-fracture initiation and propagation is proposed based on plastic strain, which is calibrated by simulation of simple and notched round-bar tension tests and a precracked compact tension test.
Abstract: We describe a computer model for predicting ductile-fracture initiation and propagation. The model is based on plastic strain. Fracture starts or a crack extends when the integrated product of the equivalent plastic-strain increment and a function of the mean stress exceeds a critical value over a critical length. This critical length is characteristic of the microstructure of the material. The computer fracture model is calibrated by computer simulation of simple and notched round-bar tension tests and a precracked compact tension test. The model is then used to predict fracture initiation and propagation in the standard Charpy V-notch specimen. The computed results are compared with experiments. The model predicts fracture toughness from tests of standard surveillance specimens from nuclear-reactor pressure vessels and can be applied to fracture calculations for these vessels.
TL;DR: In this paper, the onset of dilatancy has not been identified, but most of the dilatance occurs within about 10 percent of the fracture stress difference, and the actual pore volume increase is larger in high initial porosity.
Abstract: Volume changes in geologic materials have been measured with strain gauges, cantilever displacement gauges, or through observation of either pore or total volume. When porosity is less than 0.05, compaction is small or absent; apart from elastic strains in the minerals, dilatancy predominates, beginning at 50 to 75 percent of the fracture stress difference. When initial porosity exceeds about 0.05, compaction and dilatancy may overlap. The onset of dilatancy has not been identified, but most of the dilatancy occurs within about 10 percent of the fracture stress difference. In low porosity rocks, dilatancy increases initial porosity by a factor of 2 or more; in porous rocks or granular aggregates the increase is only 20 to 50 percent. However, the actual pore volume increase is larger in rocks of high initial porosity. Hence, earthquake precursors which depend on the magnitude of dilatancy should be more pronounced in porous rocks or in fault gouge. In contrast, precursors which are based on fractional changes in some porosity-related property may be more pronounced in rocks of low initial porosity. Future work is particularly needed on constitutive relations suitable for major classes of rocks, on the effects of stress cycling in porous rocks, on the effects of high temperature and pore fluids on dilatancy and compaction, and on the degree of localization of strain prior to fracture.
TL;DR: In this article, the authors made an analysis of the relationship between load and crack extension in the Hertzian indentation of a solid surface with a spherical indentor and proposed that the minimum load for ring-crack formation becomes independent of the flaws in the solid if these have a size above a certain threshold value.
TL;DR: In this article, an experimental technique has been developed for implanting water vapor bubbles (H2O(v) of fixed size and spacing along the grain boundaries of polycrystalline silver.
TL;DR: In this article, the fracture toughness of WCCo alloys has been determined on single-edge notched beam (SENB) specimens precracked by electron discharge machining (EDM).
01 Jul 1978
TL;DR: The fracture energy of BaTiO3 increased with increasing grain size at 25°C in the ferroelectric 4 mm symmetry state and remained constant at 150°C at paraelectric m 3m state as discussed by the authors.
Abstract: The fracture energy of BaTiO3 increased with increasing grain size at 25°C in the ferroelectric 4 mm symmetry state and remained constant at 150°C in the paraelectric m 3m state. In general, observed flaw sizes agreed with those predicted from fracture mechanics equations. The fracture energy measurements combined with previously reported strength measurements were analyzed in terms of fracture mechanics principles to determine the effect of internal stresses on fracture. The analysis showed that the effect of internal stress on fracture for a given flaw size can be determined from a combination of fracture energy and strength measurements at two temperatures. The increase in fracture energy with grain size in the ferroelectric state is attributed to ferroelastic twin formation and wall motion.
TL;DR: In this article, the authors studied the fracture behavior of an epoxy resin by a method which involves the pressurization of an internal circular crack and derived fracture energy as a function of crack velocity.
Abstract: The fracture behaviour of an epoxy resin has been studied by a method which involves the pressurization of an internal circular crack. The method can be used to study both cohesive fracture and the adhesive failure of an interface. Plane strain conditions are assured because the crack does not intersect a free surface and (for adhesive failure) shrinkage stresses are eliminated as a crack driving force. Using high speed photography, the dependence of crack speed on critical pressure and specimen geometry was determined. An elastic analysis permits the derivation of fracture energy as a function of crack velocity. Fracture energy values lay between 100 and 200 Jm−3 at 35° C with a peak at a crack velocity of 37 m sec−1.
01 Jan 1978
TL;DR: The fracture mechanics parameters associated with the fracture of transversely oriented bovine femur compact tension specimens have been determined for a slowly propagating and stable crack, as a function of cross head speed.
TL;DR: In this paper, generalized relations between the strength distribution function and derivatives of the fracture probability are developed for five widely used testing methods for measuring the strength of ceramic materials, and the derived relations for three of these methods are used to analyze room-temperature fracture strength data for hot-pressed silicon nitride.
Abstract: Generalized relations between the strength distribution function and derivatives of the fracture probability are developed for five widely used testing methods for measuring the strengths of ceramic materials. The derived relations for three of these methods are used to analyze room-temperature fracture strength data for hot-pressed silicon nitride. Fracture of this material is shown to be controlled by internal flaws at strength levels up to and including the range where the tensile and flexural distributions overlap, but it is primarily surface-flaw-controlled toward the upper end of the flexural distribution.
TL;DR: In this article, the shape of the craze at the tip of a loaded crack has been determined by optical microscopy for polycarbonate, and the effect of temperature was examined, and measurements were made on samples of different molecular weight.
TL;DR: In this article, an effective engineering solution for the type of cracks that have been discovered in boiling water Reactor (BWR) plants was first developed, based upon a simple net section flow stress criterion.
TL;DR: In this article, the authors explained the influence of external stress on the manner of extension of linepipe linepipe fracture by stress analysis around a hydrogen gas pressurized crack-like cavity under stress.
Abstract: Hydrogen induced fracture in linepipe steels is characterized by the formation of internal blisters caused by hydrogen precipitation at an inclusion-matrix interface, followed by the formation of blister-crack array by cracking the region connecting the blisters through the action of internal hydrogen pressure and external stress. The manner of extension of the hydrogen induced fracture of this type is considerably influenced by the presence of external stress: in the absence of the external stress fracture develops by linking the blisters which are formed in stacked arrays out of a plane approximately perpendicular to the external stress axis. Shear stress distribution induced around the blister is sensi-tively influenced by the external stress applied parallel to the blister plane; therefore, it is expected that the manner of extension of the blister-crack array should be influenced by the external stress. In the present paper the above mentioned influence of the external stress on the manner of extension of the hydrogen induced fracture is explained based on stress analysis around a hydrogen gas pressurized crack-like cavity under stress.
TL;DR: In this article, the fracture energy of a model carbon fiber/glass fiber/epoxy resin hybrid composite system has been evaluated as a function of the carbon fibre/glass fibre ratio, and it was found that post-debond friction energy provided a major contribution to the fracture energies of the glass fibres.
Abstract: The fracture energy of a model carbon fibre/glass fibre/epoxy resin hybrid composite system has been evaluated as a function of the carbon fibre/glass fibre ratio. Work of fracture measurements were less than a rule of mixtures prediction and a pronounced negative synergistic effect was observed at high carbon fibre and high glass fibre contents. Fibre debonded lengths and fibre pull-out lengths for the carbon and glass fibres were accurately measured using a projection microscope technique. Models of microscopic fracture behaviour, together with these measurements, were successful in quantitatively describing the observed fracture behaviour of the hybrid fibrous composites. It was found that post-debond friction energy provided a major contribution to the fracture energy of the glass fibres. The post debond sliding mechanism was also shown to be primarily responsible for the non-linear behaviour of the work of fracture of the hybrid composite.
TL;DR: In this paper, the first results from an experiment to measure the fracture toughness of ice were described, and two experimental techniques have been used; fracture of pre-notched rectangular specimens in three-and four-point bending, and from the observation of the cracks which formed underneath an indenter forced into the ice surface.
Abstract: This paper describes the first results from an experiment to measure the fracture toughness of ice. Two experimental techniques have been used; fracture of pre-notched rectangular specimens in three- and four-point bending, and from the observation of the cracks which form underneath an indenter forced into the ice surface. In the latter test the indenter behaves like a wedge. We have observed that for indenters with large interior angles the plastic zone beneath the indenter may itself behave like a wedge. Data obtained over a range of temperatures has been compared with the little other data available. We find a decrease of fracture toughness as the temperature is lowered, which is the reverse of that observed by H. W. Liu and L. W. Loop.