Showing papers on "Fracture (geology) published in 1968"
2,452 citations
TL;DR: In this paper, a new experimental method which increased the sensitivity of detection by several orders of magnitude over that of previous studies was used, and the pattern of crack occurrence for a wide variety of rocks and at confining pressures up to 5 kb was found to be closely related to the stress-strain behavior.
Abstract: The cracking that occurs during the deformation of rock in compression was studied by detecting and analyzing the radiated elastic waves. A new experimental method which increased the sensitivity of detection by several orders of magnitude over that of previous studies was used. The pattern of crack occurrence for a wide variety of rocks and at confining pressures up to 5 kb was found to be closely related to the stress-strain behavior. Dilatancy in the region above half the fracture stress was found to be directly proportional to cracking. Microfracturing, i.e. cracking, of brittle rock was compared with the microfracturing observed in frictional sliding and in the deformation of ductile rock. Cataclastic deformation of marble was found to be similar to frictional sliding in this respect but distinctly different than brittle deformation. The marble was found to undergo a gradual transition from cataclastic to fully plastic flow as confining pressure was increased in tests up to 4 kb. A model of deformation of an inhomogeneous brittle material is introduced which predicts the observed microfracturing activity and inelastic stress-strain behavior of rock. According to this model, microfracturing events in the dilatant region below about 95% of the fracture stress can be considered randomly independent. At higher stresses, where a rapid acceleration of activity is observed, the events cannot be considered independent and are correlated with the formation of the fault.
601 citations
TL;DR: In this paper, the deformational characteristics of two limestones, one gabbro, and one dunite have been investigated as a function of confining pressure, and it was found that friction of these rocks and friction of granite and serpentinite studied elsewhere are nearly identical, and that the brittle-ductile transition pressure is simply the pressure at which the stress required to form a fault is equal to the pressure required to cause sliding on the fault.
Abstract: The deformational characteristics of 2 limestones, one gabbro, and one dunite have been investigated as a function of confining pressure. It was found, that friction of these rocks and friction of granite and serpentinite studied elsewhere are nearly identical, and that the brittle-ductile transition pressure is simply the pressure at which the stress required to form a fault is equal to the stress required to cause sliding on the fault. The transition pressure is higher in extension than it is in compression. This difference occurs because the frictional shear stress required to cause sliding is determined not by confining pressure but by the principal stresses and the angle of the fault. For the same frictional shear stress on a fault surface, the confining pressure is much higher in extension than it is in compression. (19 refs.)
531 citations
01 Jan 1968
TL;DR: In this article, the authors studied the strain energy for two and three dimensional crack systems subjected to varying loads, detailing loading and crack geometry effects on fracture criterion, and showed that crack geometry and crack loading effects affect fracture performance.
Abstract: Strain energy for two and three dimensional crack systems subjected to varying loads, detailing loading and crack geometry effects on fracture criterion
531 citations
Abstract: The amount of grout to inject into a given volume of fractured foundation rock depends on the fracture porosity and on the spacing and sizes of fracture openings. These properties cannot be measured directly but can be calculated from water-pressure tests if several simplifying assumptions are made. The method is valid for fractured rock masses whose intergranular permeability is very small compared to the fracture permeability, and if solution cavities or pervious interbeds are absent. Studies of 35 dam sites indicate that maximum fracture porosities are about 0.05% near the surface, decreasing to about 0.005% at the 200-ft depth. The volume of grout required for impregnation is correspondingly small. Fracture openings decrease from about 100 microns to 50 microns in the same depth interval. Cement grout penetration is accordingly limited to a small proportion, only the largest, of fractures. The minimum spacing of open fractures increases from 4 ft to 14 ft. All rock types appear to be similar in fracture properties.
488 citations
TL;DR: In this paper, a variety of crystalline silicate rocks of low porosity (0·001-0·03) were fractured in triaxial experiments at strain rates from about 10−3 to 10−1 sec−1.
317 citations
TL;DR: Magnetic anomalies and fracture zones make distinctive patterns when the direction of sea floor spreading changes as has occurred repeatedly in the north-eastern Pacific as mentioned in this paper, where the mode of deformation is such that the spreading centres between transform faults become uniformly reoriented essentially perpendicular to the faults.
Abstract: Magnetic anomalies and fracture zones make distinctive patterns when the direction of sea floor spreading changes as has occurred repeatedly in the north-eastern Pacific. The mode of deformation is such that the spreading centres between transform faults become uniformly reoriented essentially perpendicular to the faults.
300 citations
TL;DR: In this paper, it was shown that in about 92% of the cases, a rAPid acceleration of MICRO-ACTURING ACTIVITY OCCURRED.
Abstract: MANY SMALL CRACKING EVENTS OR MICROFRACTURES PRECEDE FRACTURE IN LABORATORY COMPRESSION TESTS ON ROCK. EACH EVENT RADIATES ELASTIC WAVES. DURING THE COMPRESSION OF GRANITE TO FRACTURE, TWENTY TWO OF THE LARGEST MICROFRACTURE EVENTS WERE LOCATED IN SPACE BY USING FIRST ARRIVALS OF S WAVES DETECTED WITH A MULTITRANSDUCER ARRAY. AT ABOUT 92% OF THE FRACTURE STRESS, A RAPID ACCELERATION OF MICROFRACTURING ACTIVITY OCCURRED. THE LOCATION OF THE EVENTS THAT OCCURRED BELOW THIS POINT SHOWED NO OBVIOUS RELATION TO THE EVENTUAL FAULT. AT STRESSES WITHIN THE REGION OF ACCELERATED ACTIVITY, HOWEVER, THERE WAS A MARKED CLUSTERING OF MICROFRACTURES ON THE EVENTUAL FAULT PLANE. THESE OBSERVATIONS SUGGEST THAT THE APPROXIMATE TIME AND PLACE OF FRACTURE COULD HAVE BEEN PREDICTED. IN THE LIGHT OF THE SIMILARITY OF MICROFRACTURES AND EARTHQUAKES, THIS SUGGESTS A POSSIBLE METHOD FOR PREDICTING EARTHQUAKES. /AUTHOR/
298 citations
TL;DR: In this article, the leading edge of a crack is treated as a line disturbance zone in a manner similar to the treatment of dislocation lines in dislocation mechanics, and the authors discuss interpretation of the brittle-ductile transition in terms of relative plastic zone size, and allowable load estimates which include fracture strength in a rational way.
276 citations
TL;DR: In this paper, changes in electrical resistivity were observed as a function of compressive stress in a variety of crystalline rocks that were subjected to confining pressure of up to 5 kb and to pore pressure of water of 500 bars.
Abstract: Changes in electrical resistivity were observed as a function of compressive stress in a variety of crystalline rocks that were subjected to confining pressure of up to 5 kb and to pore pressure of water of 500 bars In the majority of the rocks, resistivity increased slightly up to about half the fracture stress; just the reverse effect has been noted elsewhere for rocks that were apparently partially saturated Beyond half and particularly within about 20 per cent of the fracture stress, resistivity dropped typically by an order of magnitude This sharp decrease corresponded closely to an increase in porosity, or dilatancy, which took place under compressive stress Detailed study of one rock, Westerly granite, showed that changes in resistivity and, hence, porosity with stress were insensitive to effective pressure, when stress was normalized with respect to fracture stress This suggests that fracture occurred at a critical crack porosity that was pressure independent The changes in resistivity with stress that accompany frictional sliding on a fault are insignificant when the measurement volume contains the fault, even though faulted rock under pressure can support high stress
237 citations
TL;DR: In this paper, a model based on a network of cracks in an elastic medium was proposed to account for the inelasticity observed at interfaces in the rock structure and is insensitive to temperature but highly pressure dependent.
Abstract: The mechanical properties of crystalline rock have been studied in the laboratory as a function of temperature and pressure at the low frequencies and the strain amplitudes characteristic of seismic waves. The inelasticity observed arises at interfaces in the rock structure and is insensitive to temperature but highly pressure dependent. It cannot be described in terms of viscoelasticity but causes the rock to display static hysteresis. The internal friction ϕ of the rock is accompanied by a large modulus defect, δM/M; both ϕ and δM/M are shown to be independent of frequency and strain amplitude throughout a very wide range. A model based on a network of cracks in an elastic medium accounts for these properties. The presence of a fluid phase in the rock does not in itself significantly increase the internal friction in the range of frequencies of seismic waves, but the presence of a small amount of intergranular fluid can make interface inelasticity persist in the presence of a large confining pressure. Interface inelasticity can occur at substantial depths in the earth, resulting in low seismic velocities and low Q. The low velocity zones in certain areas are interpreted in this way as arising from the presence of a fluid phase.
TL;DR: In this article, the Griffith energy criterion, the Barenblatt cohesion modulus theory, and the assumption of a critical mean stress at an end-region of fixed size are compared.
Abstract: Several theories in fracture mechanics apparently approach the problem of crack extension from different points of view but lead to the same main result. Thus, in the case of brittle cracks, an equivalence exists between the Griffith energy criterion, the Barenblatt cohesion modulus theory, and the assumption of a critical mean stress at an end-region of fixed size. It is shown that the feature common to these theories is the adoption (explicitly stated or not) of an autonomous end-region, and that this assumption alone is sufficient for arriving at the principal results. In the case of brittle materials, the end-region acts as an instability kernel. This region develops into an instable region at a certain load, and crack extension takes place. The instability is clearly associated with the atomic force-distance relations. The interatomic distance thus provides the characteristic length needed to assure the existence of an autonomous end-region. It is suggested that similar instable end-regions may develop also in non-brittle materials. The characteristic length is here given by different kinds of imperfections. If no other characteristic length than the dimensions of the crack can be found, then a conclusion must be that the fracture stress is independent of the size of the crack.
TL;DR: Gulf Coast faults are normal faults with the exception of those around fault domes as mentioned in this paper, and the accumulation of all horizontal components of these faults in the Gulf Coast embayment makes considerable horizontal displacement of the sedimentary blanket necessary.
Abstract: Gulf Coast faults are normal faults with the exception of those around fault domes. The accumulation of all horizontal components of these faults in the Gulf Coast embayment makes considerable horizontal displacement of the sedimentary blanket necessary. The regional Gulf Coast fault pattern and its many local variations are therefore thought to be caused by regional gravity creep of the sedimentary blanket into the basin. As creep takes place the sliding sediments break away from the stationary ones forming a marginal graben, and, nearer the coast, asymmetrical down-to-basin faults with reverse drag, and antithetic faults.
TL;DR: In this paper, the authors present results of acoustic emission studies on flawed and unflawed specimens of aluminum and beryllium and show that acoustic emission from the flawed specimens is found to begin at stress levels far below the general yield stress.
TL;DR: In this paper, a theoretical model for predicting elastic-plastic, plane strain stress distributions in notched bars under bend loading has been developed by combining the elastic solutions of Neuber with the slipline field solutions of Hill.
TL;DR: Fracture mechanisms for filament reinforced composite materials, discussing epoxy matrix critical fracture modes were discussed in this paper, where the authors proposed a fracture mechanism based on filament reinforced composites.
Abstract: Fracture mechanisms for filament reinforced composite materials, discussing epoxy matrix critical fracture modes
TL;DR: In this paper, the authors discussed the fracture of thermally tempered glass in terms of both the stored elastic strain energy in the glass due to tempering and the elastic energy release rate Of crack extension, 9.
Abstract: The fracture of thermally tempered glass is discussed in terms Of both the stored elastic strain energy in the glass due to tempering and the elastic energy release rate Of crack extension, 9. The latter is used to obtain an analytical correlation between the maximum tensile stress and the average particle size at time of fracture. The theoretical predictions are supported by experimental data obtained for various glass thicknesses and temper levels.
01 Dec 1968
TL;DR: In this paper, a concept of fracture dynamics of rock is introduced, three aspects of fracture being discussed, namely: stability of fracture propagation, terminal fracture velocity and dynamic stresses created by a propagating crack.
Abstract: A concept of fracture dynamics of rock is introduced, three aspects of fracture being discussed, namely: stability of fracture propagation, terminal fracture velocity and dynamic stresses created by a propagating crack. Work related to this new field of research is reviewed and theoretical and experimental studies on rock are reported. The practical significance of the fracture dynamics concept in rock mechanics is outlined.
Patent•
28 Oct 1968
TL;DR: An angular compression plate for compressing a transverse fracture in a tibia bone, or the like, and including first and second flanges connected together along their adjacent edges is described in this article.
Abstract: An angular compression plate for compressing a transverse fracture in a tibia bone, or the like, and including first and second flanges connected together along their adjacent edges. The flanges are slightly flexible with respect to one another for adjustment to accommodate varying angles between the first and second sides of the tibia. Thus, the plate may be placed across the fracture and secured to such adjacent sides of the tibia for maintaining the fracture in compression and will likewise provide support along two sides of the tibia.
01 Apr 1968
TL;DR: In this article, the authors present calculations of the temperature elevations accompanying rapid plastic deformation near a crack tip, and show that the localized tip temperature elevation alone alone governs fracture toughness at very fast rates.
Abstract: : This paper presents calculations of the temperature elevations accompanying rapid plastic deformation near a crack tip. Solutions for the stress and strain distribution in non-hardening materials are employed as a basis for the heating rate distribution. Results are approximate in that temperature independent mechanical and thermal properties are assumed and thermal stressing is neglected. Two cases are considered: a stationary crack under increasing load, and a running crack with locally constant speed and plastic zone size. Numerical results are presented as based on properties of 2024 aluminum alloy, 6Al-4V titanium alloy, and mild steel. Temperature rises predicted for test conditions on these metals seldom exceed 100C. This may, nevertheless, be large enough to influence fracture and to account for the observed rise in roughness at very fast rates. Consequences are examined for the assumption that the localized tip temperature elevation alone governs fracture toughness at very fast rates. (Author)
TL;DR: In this paper, the advantages and disadvantages of different strengthening methods are discussed with relation to the observed strength values (measured either by quasi-static loading or by impact loading) and the fracture behaviour of reinforced glass objects.
Abstract: One of the methods most frequently used for reinforcing glass objects is to introduce compressive stresses at the surface Such stresses can be produced physically, as in the thermal toughening process, or chemically, by applying a film of a lower coefficient of thermal expansion than the glass body itself, or by producing a compressive surface layer making use of the “ion stuffing” technique The advantages and disadvantages of the different strengthening methods are discussed with relation to the observed strength values (measured either by quasi-static loading or by impact loading) and the fracture behaviour of reinforced glass objects
TL;DR: In this article, the phenomological fracture properties of glass bead filled polyphenylene oxide composites were investigated and yield strength and Young's modulus were obtained as a function of volume fraction of filler using standard microtensile testing techniques.
Abstract: The phenomological fracture properties of glass bead filled polyphenylene oxide composites were investigated.Yield strength and Young's modulus were obtained as a function of volume fraction of filler using standard microtensile testing techniques. Fracture toughness was measured using double edge notched tensile bars. The effects of adhesion were studied by using untreated and A-1100 silane-treated glass beads. The nature of the fracture surfaces was observed by use of an optical microscope, a scanning electron microscope and a transmission electron microscope.It was found that the fracture toughness of these materials de creased by increasing the filler content and by improving the adhesion. In general, an increase in strength and stiffness was accompanied by a decrease in toughness.The fractographic studies gave a detailed mapping of the frac ture front as it propagated through the material. Fracture occurred in two stages. The initial stage was a region of stable crack growth accompanied by, crazing, ...
TL;DR: A quantitative assessment of the density of hyperbolic markings in the fracture surfaces of polymethyl methacrylate has been made showing that the density is proportional to the fracture toughness as discussed by the authors.
Abstract: A quantitative assessment of the density of hyperbolic markings in the fracture surfaces of polymethyl methacrylate has been made showing that the density is proportional to the fracture toughness. In general the fracture toughness at any instance is a random function, but there is a definite tendency for it to increase with velocity of fracture propagation. It is suggested that the craze material ahead of the true crack tip may be assumed to have constant strength and Dugdale's model for elasto—plastic materials applied to organic glasses as well.
TL;DR: In this paper, a relation between the time duration of the radiated pulses and the time durations observed at the surface of the earth is established to correct the times of observed long-period P waves so as to recover the original time-duration radiation pattern.
Abstract: The theory for propagating earthquake sources predicts a ‘Doppler-type’ effect in the time duration of the radiated body wave pulses. With the assumption of a constant fracture velocity, the time duration of these pulses is directly related to the length of the fault but has different spatial patterns of variation for the unilateral and bilateral faulting cases. To relate this time duration of energy release to the observed long-period P waves, various pulse forms are postulated whose time history is controlled by the fault parameters of length and fracture velocity. These pulses are convolved with the impulse response of a standard crust-seismograph system to yield theoretical P-wave seismograms. A relation is thereby established between the time durations of the radiated pulses and the time durations observed at the surface of the earth. This relationship is employed to correct the times of observed long-period P waves so as to recover the original time-duration radiation pattern. By a minimum deviation technique, the fault length and fracture velocity can be found that best fits this observed pattern. This procedure is shown to yield reasonable results for four different earthquakes from three different regions.
TL;DR: In this article, the fracture toughness of a variety of sharply notched tension, bending and rotating disc specimens of PMMA was examined using linear fracture mechanics, and it was observed that rapid fracture with a brittle glassy appearance usually follows a period of slow crack growth, denoted by fan shaped markings of local ductility.
Abstract: The fracture toughness of a variety of sharply notched tension, bending and rotating disc specimens of PMMA is examined using linear fracture mechanics. It is observed that rapid fracture with a brittle glassy appearance usually follows a period of slow crack growth, denoted by fan shaped markings of local ductility, though still brittle overall. In this near brittle regime the fracture toughness is sensitive to strain rate so that high values of effective surface energy are easily induced by rapid testing or notch bluntness. At impact rates the toughness increases again. For design purposes, in the absence of environmental effects, the onset of slow cracking and rapid (glassy) fracture, can be associated with fracture toughness K1c of about 800 Ibf/in3/2 (90 kg/cm3/2) and 1600 Ibf/in3/2 (180 kg/cm3/2) respectively. Detailed studies have not been made on other materials but a guide to the levels of notch toughness and notch brittle temperatures are given for several plastics.
TL;DR: In this paper, the role of the interface between glass filters and matrix resins has been investigated as a function of chemical structure of the coupling agent and solvents used for deposition, and the inner layer extends the region of modified resins.