Showing papers on "Fracture (geology) published in 1972"

Propagation of a Vertical Hydraulic Fracture

Abstract: The propagation of hydraulic fractures of limited vertical extent and elliptic cross section is discussed, with the effect of fluid loss included. Numerical and asymptotic approximate solutions in dimensionless form give the fracture length and width at any value of time for any set of physical parameters. The insight provided by the dimensionless results and approximate solutions should be useful in the design of fracture treatments. (14 refs.)

The j integral as a fracture criterion

Abstract: The path independent J integral, as formulated by Rice, can be viewed as a parameter which is an average measure of the crack tip elastic-plastic fied. This together with the fact that J can be evaluated experimentally, makes a critical J value an attractive elastic-plastic fracture criterion. The critical J value fracture criterion refers to crack initiation under plane strain conditions from essentially elastic to fully plastic behavior. Experiments supporting the validity of a critical J value fracture criterion are presented in this paper. Values of the J integral were determined experimentally for two steel alloys, one of low and the other of intermediate strength. A review is given of the analytical support for the critical J value fracture criterion. The range of applicability of the critical J value concept, its limitations, and its advantages are also discussed. /Author/

Plastic flow and fracture of metallic glass

Abstract: The tensile flow and fracture behavior of three Pdo.8Sio2-based alloys in the glassy, “microcrystalline,” and fully crystalline condition has been studied. The glassy alloys flow plastically to a total strain of approximately 0.5 pct e, and exhibit proportional limit stresses of approximatelyE x 10~2 whereE is Young’s modulus. This plastic flow is accompanied by the formation of shear deformation bands on the specimen surfaces. Fully crystalline alloys are extremely brittle and fracture via intergranular cracking. Fracture surfaces of the amorphous and “microcrystalline” alloys are inclined at 45 deg to the tensile axis and exhibit two morphologically distinct zones. One zone is relatively featureless while the other contains a “river” pattern of local necking protrusions. Detailed comparison of opposing surfaces indicates that fracture is preceded by large local plastic shear which produces the smooth zone while the local necking pattern is produced during rupture. These observations form the basis for the hypothesis that plastic flow in the glassy material occurs via localized strain concentrations and that fracture is initiated by catastrophic, “adiabatic” shear.

Deformation and Fracture of Ice Under Uniaxial Stress

Abstract: Techniques for making precise uniaxial tests for strength and deformability of ice are described. Results are given for tests made in uniaxial tension and uniaxial compression at constant displacement rate, using bubbly polycrystalline ice. These results include stress/strain curves, elastic moduli, rupture or yield strengths, and failure strains, all for a range of strain-rates. A few results for ice doped with hydrogen fluoride are also given. The fracture mechanism for ice is discussed, and the test results are compared with data reported by previous investigators.

Criteria of Ductile Fracture Strain

Abstract: Two criteria of ductile fracture strain are suggested. From the theory of plasticity for porous materials, the following criterion of fracture for a triaxial state of stress is obtained: [numerical formula] where ee_qf is the equivalent fracture strain, σm the mean stress, σe_q the equivalent stress, a0 and b0 are constants. Except under certain conditions, this criterion shows reasonable agreement with experiment. To improve the accuracy of the prediction of the fracture strain, the above criterion is modified as follows: [numerical formula] where c0 is a constant. It is found that this criterion provides a greater accuracy for prediction of the fracture strain.

Fracture of plain concrete

Abstract: The application of linear fracture mechanics to the crack propagation load of pre-cracked concrete specimens is shown to depend upon the size of the specimen. The results of twenty-four tests on cracked beams with depths ranging from 3-in to 15-in (75-mm to 375-mm) are presented in support of this conclusion. /AUTHOR/

Ridge transform fault spreading pattern in freezing wax.

Abstract: A laboratory experiment shows that ridge-ridge transform faults, inactive fracture zones, and other features characteristic of spreading oceanic ridges can be produced in a variety of paraffins. Although the resultant pattern depends upon the temperature of the wax and the ratio of spreading rate to surface cooling, the characteristic orthogonal ridge transform fault system is a preferred mode of separation. Symmetric spreading occurs under conditions of no tensile strength across the ridge, and the stability of transform faults is a consequence of their lack of shear strength. The experiment also shows that properties characteristic of oceanic ridges occur under conditions of passive convection where upwelling of material at the ridge crest is a result only of hydrostatic forces in the fluid; that is, the plate separation is caused not by large convective forces beneath the ridge but rather by tensile forces in the plate.

The fracture energy of carbon-fibre reinforced glass

Abstract: The fracture energy of carbon-fibre reinforced glass has been measured by the work of fracture technique, using specimens of varied geometry, Meaningful material properties were obtained only when crack propagation was controlled throughout failure. The work of fracture (γ F) depended on strain-rate and fibre volume fraction, and was typically ∼3 kJm−2 for a 40 vol % specimen. Variations of work of fracture due to strain-rates have been related to the microstructure of the fracture surfaces and estimates have been obtained of the fibre-matrix interfacial shear stress during pull-out. Approximate estimates have been made of the fracture initiation energy (γ I) by fracture mechanics analyses, γ I was less than γ F and no strain-rate sensitivity was detected. An attempt has been made to explain γ I in terms of the initial rate of release of strain energy during fibre fracture.

Fracture Mechanics Approach to Adhesive Joints

Abstract: This study investigates the problem of applying fracture mechanics to the opening mode fracture of a two-material (aluminum-epoxy-aluminum) system. The results of a finite element analysis of a two-material, single- edge-notch (SEN) plate are used with a compliance method in order to obtain strain energy rates, g, and with a displacement method to obtain stress intensity factors, K. Approximate relationships between the homo geneous system and the adhesive system for both K and g are determined. The relationship between K and g for the adhesive system is obtained. The experimental investigation provides an experimental compliance calibration for the same adhesive system and loading. Good reproducibility of the fracture toughness values obtained for the two-material system with SEN and tapered DCB specimens indicates the geometry independence of the fracture toughness. The effect of the notch root radius and proper specimen preparation are also considered.

The Fracture of Glassy Polymers

Abstract: The fracture of glassy polymers starts with the separation of molecule bundles which then form a craze; this is followed by the fracture or rupture of the craze by sliding of the molecule bundles The first process has the approximate characteristics of brittle fracture, the second those of viscous flow; at low velocities, therefore, the crack extends by the essentially viscous mechanism in the craze layer, whereas at higher velocity the stress required for this rises so high that either a quasi-brittle fracture occurs between the craze and the adjacent bulk polymer (for example, in polystyrene), or patches of craze arise in the bulk ahead of, and away from, the propagating fracture front, as in cast polymethylmethacrylate (PMMA) When the craze wedge ahead of the ‘ viscous ’ crack in the craze layer suddenly peels off the adjacent bulk polymer, either multiple crazes and cracks arise, radiating from its edge, or a new craze wedge is initiated In either case only one craze wedge propagates, and it drops off the adjacent bulk when the rate of stretching of the craze (normal to its plane) reaches a critical magnitude The repetition of this process results in the well known striation of the surface of fracture in polystyrene and other polymers Since the fracture mechanism includes an essentially velocity-dependent viscous process, the Griffith theory cannot be applied to glassy polymers even as an approximation The work of fracture oscillates by orders of magnitude within microseconds in the region of striations

Reservoirs in Fractured Rock: Geologic Exploration Methods

Abstract: In recent years three developments which have evolved more or less independently, when related, may be of value to the petroleum industry. First is the recognition, through normal oil field development, that fractures are significant to both reservoir capacity and performance. Second is the fact that controlled laboratory experiments have produced, in increasing quality and quantity, empirical data on rupture in sedimentary rocks. These data have been segregated to demonstrate the individual control on rupture of several important parameters: rock type, depth of burial, pore pressure, and temperature. The third development consists of the discovery of new methods to recognize, evaluate, use, and, in some cases, see fractures in the subsurface. This discussion of these thr e developments may help geologists and engineers to find new approaches to exploration and exploitation of fractured reservoirs. Reservoir and production engineers presently make the greatest use of fracture data, but geologists should find this information useful in exploration for oil and gas trapped in subsurface fractures. Except in the search for extensions to proved fracture reservoirs, there is in the literature a paucity of clear-cut examples of the use of fracture porosity data in advance of drilling. For this reason, several speculative exploration methods discussed herein implement mapping of fracture facies as well as stratigraphic facies.

THE SCAPHO-CAPITATE FRACTURE SYNDROME: A Mechanism of Injury

Abstract: 1. A case of the scapho-capitate fracture syndrome is described. 2. At operation the proximal fragment of the capitate bone was found to have rotated on a transverse and not on a vertical axis.

Fracture behavior in nylon 6 fibers

Abstract: Electron paramagnetic resonance (EPR) techniques are 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 disordered and ordered regions along the fiber axis. In the disordered or critical flaw regions, tie chains connecting the ordered or crystalline block regions are assumed to have a statistical distribution in length. These chains are, therefore, subjected to different stresses. The effective 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 loadings, cyclic stress, stress relaxation and step strain tests at room temperature.