Showing papers on "Stress field published in 1984"

Determination of stress from slip data: Faults and folds

Abstract: A new technique is derived to invert slickenside data for the stress field that caused the faulting episode. This inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes, at the time of rupture, is similar. Study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption. Hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion. Application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes. Comparison of the inversion results with the geometry of the folds shows this application to be successful, greatly increasing the number of data sets that can be used to find the paleostress field.

The determination of dynamic fracture toughness of AISI 4340 steel by the shadow spot method

Abstract: Dynamic crack propagation experiments have been performed using wedge loaded double cantilever beam specimens of an austenitized, quenched and tempered 4340 steel. Measurements of the dynamic stress intensity factor have been made by means of the optical method of caustics. The interpretation of experimental data, obtained from the shadow spot patterns photographed with a Cranz-Schardin high speed camera, is based on an elastodynamic analysis. The instantaneous value of the dynamic stress intensity factor KdI is obtained as a function of crack tip velocity. Finally, the interaction of reflected shear and Rayleigh waves with the moving crack tip stress field is considered.

Lithospheric stress near a ridge‐transform intersection

Abstract: Oceanic lithosphere at a ridge-transform intersection has distinct structural characteristics. The spreading axis and normal fault scarps, which parallel the ridge axis away from the intersection, locally curve towards the transform fault. This implies that the least compressive stress direction becomes oblique to the spreading direction near a ridge-transform intersection. This stress field may be the result of a tensile ridge axis stress resisting plate separation and a transform shear stress resisting relative plate motion. A plane stress plate model with prescribed plate boundary stresses is formulated to explore this hypothesis. The orientation of the least compressive horizontal stress near an intersection depends strongly on the ratio of the applied boundary stresses. Thus ridge axis curvature may place an important constraint on plate boundary forces.

“Pressure solution” creep: Some causes and mechanisms

Abstract: Despite the widespread evidence of stress-controlled dissolution and precipitation in diagenetically altered and low-grade metamorphic rocks, a great deal of controversy remains concerning the driving forces and transport mechanisms involved. To clarify the various driving forces, the free enthalpy equation is expanded here to allow identification of different terms contributing to the overall phenomenon. It is argued that under diagenetic conditions, stress concentrations at grain-to-grain contacts will be the largest source of chemical potential gradients and that upon burial and cementation these inhomogeneities decline and the orientation dependence of normal stress in a quasi-homogeneous stress field becomes important as well. These mechanisms operate efficiently enough under these relatively cold, H2O-rich conditions that stresses can remain below the threshold for crystal plastic deformation. Water on grain boundaries provides at the very least a high diffusivity path and in cases of large volume losses must also contribute directly through fluid flow. Most experimental work on this phenomenon has not distinguished carefully between stress-enhanced solubility and solubility enhancement due to plastic deformation or microcracking. A new thermodynamic analysis of the results of some experiments by Sprunt and Nur suggests that in at least some of their experiments, true pressure solution creep has been activated. A related phenomenon, volume transfer creep during phase transformations which involve significant volume change, displays many of the characteristics of pressure solution.

Postglacial rebound and the focal mechanisms of eastern Canadian earthquakes

Abstract: A detailed numerical model of postglacial rebound for the eastern Canadian Arctic is described with special attention being paid to Baffin Island. This numerical model is able to account for the observed uplift patterns as recorded by the relative sea-level histories of discrete sites distributed throughout the study area. These uplift patterns show regional trends, so the same model can be used to interpolate between data sites and to estimate the uplift history at any arbitrary site within the study area.By treating the lithosphere as a thin elastic plate, spatial variations in the uplift pattern can be translated into estimates of lithospheric stress. The model predicts the variations in uplift as a function of both space and time since deglaciation and can therefore be used to estimate the temporal evolution of lithospheric stress following deglaciation.The stress so calculated is treated as a perturbation to an ambient stress field having its origin in other processes. Postglacial rebound is shown to...

Shear properties and a stress analysis obtained from vinyl-ester losipescu specimens

Abstract: The use of losipescu specimens for the determination of the shear properties of a vinyl-ester resin was investigated. The antisymmetric four-point bend and the Adams and Walrath fixtures were studied for their suitability in loading these specimens. Photoelastic and strain-gage data in addition to published finite-element results show that the latter fixture distorts the stress field in the gage section. The antisymmetric four-point bend fixture is found to give the purest shear-stress field in the gage section and to yield the most reliable shear-modulus values. A refined photoelastic analysis shows that the shear-stress distribution between the notch roots is essentially uniform with a relative maximum or minimum at the centroid depending on the depths of the notches. Also, stress risers of up to 30 percent are observed near the notch roots. Except at the roots, finite-element predictions are presented which are in excellent agreement with photoelastic data. The failure mode of this vinyl-ester resin is tensile and the corresponding tensile stress calculated from the average shear stress in the gage section of the losipescu specimen is in excellent agreement with failure data acquired in tension.

Elementary engineering fracture mechanics. 3rd edition

Abstract: During the last five years a considerable amount of research on elastic-plastic fracture mechanics has been conducted. The aim of this book is to show the use and application of fracture mechanics to practical problems. The book deals with the following aspects: basic problems and concepts; mechanisms of fracture and crack growth; the elastic crack-tip stress field; the crack tip plastic zone; the energy principle; dynamics and crack arrest; plane strain fracture toughness; plane stress and transitional behaviour; elastic-plastic fracture; fatigue crack propagation; fracture resistance of materials; fail-safety and damage tolerance; determination of stress intensity factors; practical problems; fracture of structures; stiffened sheet structures; and prediction of fatigue crack growth. (TRRL)

An invariant eight‐node hybrid‐stress element for thin and thick multilayer laminated plates

Abstract: A hybrid-stress eight-node isoparametric element is developed for the analysis of thin or thick multilayer fiber-reinforced composite plates. Transverse shear deformation effects are included by allowing for individual layer cross-section warping for thick laminates, or alternatively, laminate non-normal cross-section rotations for thin to moderately thick laminates. All stress components are included and are interpolated independently within each layer. Interlayer surface traction continuity and appropriate upper/lower surface traction-free conditions are exactly satisfied. The layer stress field is selected on the basis of earlier single-layer element studies so that the resulting element is naturally invariant with respect to co-ordinate translation or rotations, is non-locking in the thin-plate limit, and the element stiffness is of correct rank. An example for which an elasticity solution is available is used to demonstrate the element performance. Schemes for reduction of element stiffness computation time are also presented.

The strain distribution in anisotropic polycrystalline aggregates subjected to an external stress field

Abstract: When a stress field is applied to a, polycrystalline aggregate, an inhomogeneous strain field develops because of the elastic anisotropy of the crystallites in the sample. The distribution of strains can be investigated using neutron diffraction since, because of the low attenuation of neutrons in most solids, a large number of crystallites contribute to the diffraction profile. The distribution of strains is obtained theoretically for aggregates with textures typical of those found in rolled steels. These results have application to the determination of residual stresses in metals using neutron diffraction.

Oscillatory boundary layer flow over rippled beds

Abstract: Characteristics of the oscillatory boundary layer flow above rippled beds were investigated through experiments and numerical calculations. Experiments were conducted in an oscillatory flow tunnel. Velocities above symmetric and asymmetric ripples were measured with split-hot-film sensors under conditions of both sinusoidal and asymmetric oscillations. The stress field in the boundary layer was evaluated based on the distributions of the measured velocity and Reynolds stress. Relations between vortex formation and turbulence were examined, and effects of the asymmetry of oscillatory main flow and of ripple form on the velocity field were discussed. Numerical calculations were carried out by integrating the Navier-Stokes equations with an implicit finite difference scheme. Formation of a lee vortex above ripples was simulated in the calculations. The bottom shear stress and the energy dissipation rate were estimated based on the results of the experiments and calculations.

Near‐surface in situ stress: 1. Strain relaxation measurements along the San Andreas Fault in southern California

Abstract: Strain relaxation stress measurements were made in the Mojave Desert southeast of Palmdale, California, at two sites during the summers of 1979 and 1980, using the U.S. Bureau of Mines technique to depths of about 30 m. The field data and finite element modeling studies demonstrate that thermally induced stress dominates the results obtained in the upper 6 m. At depths greater than 6 m the average orientation for the horizontal maximum compressive stress at these sites is N22°W±9° at 2 km south of the San Andreas fault and N13°W±2° at 20 km north of the fault. These azimuths compare favorably with the average of N21°W determined with nearby hydrofracture stress measurements (Zoback et al, 1980). Savage et al. (1981) also found a NNW orientation for the maximum shortening from a geodetic network with a 15-km aperature in the Palmdale area. The fact that essentially the same orientation is recovered by three different techniques which sample to different depths and over different areal extents argues strongly for a contemporary tectonic origin for the stress. Finite element models of the San Andreas fault in southern California develop a stress field similar to that observed regionally (∼15°E for the maximum compressive stress) away from the fault when displacements corresponding to relative motion between lithospheric plates are applied on the boundaries of the models. Near the fault, however, the model principal stresses are rotated counterclockwise similar to those measured near Palmdale, demonstrating the influence of the faults on the principal stress orientations.

On continuous distributions of dislocations in nonlocal elasticity

Abstract: A linear, nonlocal continuum theory of dislocations is developed. The field equations are given for the dislocation density and the stress field due to continuous distribution of dislocations. Green’s functions are obtained for two‐ and three‐dimensional media and an integral formula is given for line distribution of dislocations generalizing Peach–Koehler formula of the classical (local) theory. Unlike the classical theory, no stress singularities occur so that self‐stress and energies of dislocation loops can be calculated involving no divergences. Exact solutions given for the line and circular distributions of dislocations verify these expectations.

Mode II dynamic fields near a crack tip growing in an elastic-perfectly-plastic solid

Abstract: A n asymptotic solution is given for Mode II dynamic fields in the neighborhood of the tip of a steadily advancing crack in an incompressible elastic—perfectly-plastic solid (plane strain). It is shown that, like for Modes I and III (G ao and N emat -N asser , 1983), the complete dynamic solution for Mode II predicts a logarithmic singularity for the strain field, but unlike for those modes which involve no elastic unloading, the pure Mode II solution includes two elastic sectors next to the stress-free crack surfaces. This is in contradiction to the quasi-static solution which predicts a small central plastic zone, followed by two large elastic zones, and then two very small plastic zones adjacent to the stress-free crack faces. The stress field for the complete dynamic solution varies throughout the entire crack tip neighborhood, admitting finite jumps at two shock fronts within the central plastic sector. This dynamic stress field is consistent with that of the stationary crack solution, and indeed reduces to it as the crack growth speed becomes zero.

Rapid expansion of a cylindrical cavity in a rate‐type soil

Abstract: An analytical solution for rapid (undrained) expansion of a long cylindrical cavity from initially zero radius is presented. A simple rate-type soil model possessing the salient features of the modified Cambridge critical state model is used. Application of the solution to determination of the stress field surrounding a pile immediately after driving is discussed.

Power-law creep of a material being compressed between parallel plates: a singular perturbation problem

Abstract: The flow of a power-law creeping or viscous material which is being compressed in a narrow gap between parallel plates is studied. A perturbation scheme based on the small gap size is developed and the approximations which lead to classical lubrication theory are formally identified. The solution obtained from lubrication theory is shown to correspond to an outer solution which is not uniformly valid because it predicts infinite longitudinal stresses along both the centerline of the gap and across the entire gap on the line connecting the plate midpoints. The failure of lubrication theory to describe the flow in these regions is not due to an inherent failure of the power-law constitutive equation to model material behavior, but is due to a breakdown in the approximations made in lubrication theory. The solution is corrected by constructing inner solutions in the regions where lubrication theory fails and a uniformly valid solution for the stress field and velocity field is obtained.

Nonuniform residual-stress measurement by hole-drilling method

Abstract: Considering the general stress field as the summation of two terms of a power series, a method for the measurement of nonuniform stress fields in thin plates by the hole-drilling method has been devised. The relieved-strain equations for the uniform and linear terms of the assumed power series have been calculated and the related constants of these equations for a range of hole diameter have been plotted.

Three-dimensional crack problems

Abstract: The present chapter is devoted to the investigation of the growth characteristics of arbitrary cracks embedded in three-dimensional bodies. The general equations of the strain energy density criterion developed in chapter one are used to determine the critical loads for crack extension, as well as the new shape of the crack after propagation. The determination of the stress field along the crack front in three-dimensional crack problems is more complicated than in two-dimensional problems. A thorough study of three-dimensional crack problems was provided by Sih and his coworkers [1–6] who expressed the local stress field along the crack front in a form analogous to the two-dimensional case. Three stress intensity factors were used, all of which are independent of the local coordinates, depending only on the crack geometry, the form of loading and the location of the point along the crack border. This result is fundamental, in analyzing the fracture behavior of cracks, and provides uniform expressions for the local stresses under various geometrical and loading conditions where only the values of stress intensity factors differ. Kassir and Sih [7] analyzed three-dimensional crack problems under a variety of loads. They presented the stress field around embedded and external elliptical or circular cracks in a uniform form and gave the values of stress intensity factors under various loading forms. The variety of problems considered covers most of the corresponding cases of two-dimensional problems as presented by Sih [8], including single or interacting circular and elliptical cracks under normal, shear, torsional and thermal loads; semi-infinite plane cracks under a variety of loads; cracks along the interface of dissimilar materials; cracks in anisotropic and nonhomogeneous materials; and penny-shaped cracks under dynamic loads.

Evaluatin of the higashitani and pritchard analysis of the hole pressure using flow birefingence

Abstract: Higashitani and Pritchard (H-P) carried out an analysis of the hole pressure (PH) for viscoelastic fluids which leads to expressions relating PH to the shear stress (σ), the wall shear stress (σw), and the normal stress differneces (N1 and N2). Although very good agreement their theory and experimental results has been obtained for several polymer solutions and three polymer melts, it is known that at least two of the key assumptions in the theory are violated. In this study flow birefingence has been used to determine the stress field (i.e. σ and the normal stress difference, σ11 — σ22) in the region of a slot placed perpendicular to the flow direction for a polystyrene melt. Values of σ and σ11 — σ22 were then used to evaluate the integrand in the expression relating Pe1 where Pe1 is the hole pressure measured at the base of the rectangular slot, σ and N1. Values of Pe1 evaluated using flow birefringence data agreed well with those obtained using the same integral expression and cone-and-plate values of N1 and σ, and with directly measured values of Pe1. This agreement occurred even though the stress field was found to be asymmetric around the centerline of the slot and with secondary flow in the slot. A detailed evaluation of the values of N1/2σ, which constitute the integral in the H-P theory, along the centerline of the slot revealed most of the contributions to the integral canceled in integrating from the base of the slot where σ is zero at the centerline of the slit-die. The main contributions to the integral occurred from the integration taken from the centerline of the slit-die to the upperdie

A Symmetric Rail Shear Test for Mode II Fracture Toughness (GIIC) of Composite Materials—Finite Element Analysis

Abstract: Using a high precision triangular finite element model, the elastic stress field in a symmetric rail shear test specimen is determined. The results are graphically presented and discussed. A simple finite element technique for energy release rate analysis of the precracked test specimen is presented. Numerical results showing the effects of material properties and crack length are tabulated as normalized stress-intensity factors. Based on this numerical study, it is fair to say that the symmetric rail shear test with some modifications is a viable method for shear characterization of composite materials in general and for G(IIc) determination in particular. Final acceptance of the test method, however, awaits experimental verification

Stress field in the fuyun, xinjiang earthquake fracture zone determined by fitting fault slip vector data

Abstract: Based on the horizontal and vertical offset data of 42 faults obtained from field survey in the epiceutral zone, caused by the great 1931 Fuyun earthquake of magnitude 8, the slip directions on the fault planes are deduced. The mean stress fields corresponding to 4 segments, from north to south, of the fracture zone have been estimated by minimizing the angle between the calculated shear stress and the observed slip vector on each fault.The result indicates that for the 4 segments the maximum and minimum compressive principal stress axes are all horizontal, while the maximum compressive principal stress axes take approximately the azimuths between N15°E to N30 °E. The overall stress field in the entire fracture zone is rather homogeneous, this implies that the underline cause for the great Fuyun earthquake could hardly be some local factors, but possibly tectonic movement on a large scale.

Elastic interaction of a crack with microcracks

Abstract: Elastic interactions of a crack with an array of microcracks located near the tip and imitating “damage” is analyzed. The stress field and the effective stress intensity factor are considered based on the double layer potential technique (known also as representation of cracks by dislocations) and polynomial conservation theorem. Two examples are given: (1) one microcrack on continuation of the crack line (stress “amplification”) and (2) two microcracks parallel to the main crack and located at certain distance from the crack line; in this case, both stress “amplification” and stress “shielding” are possible depending on the microcrack's location.

X-ray line profile analysis of dislocations and stacking faults in deformed copper

Abstract: Dislocation configurations and stacking faults in commercial copper rods after 20% and 70% cold-rolling, fatigue and unidirectional tension here studied by x-ray line profile analysis. The analysis of dislocation is based on the Stokes method, the Warren-Averbach analysis and the Wilkens theory for Gaussian or mixed type of strain broadening profiles. For the Cauchy type the range of stress field of dislocations is small, and a model of regular distribution of dislocation dipoles is proposed instead of the Wilkens model of a restrictedly random distribution of dislocations. Due to the obvious texture in all four kinds of deformed samples, the possible glide systems are obtained by using a biaxial stress system. The analysis of stacking faults is based on theories of Patterson, Warren, and Wagner by measuring profile peak shifts, asymmetry and broadening. The broadening due to perfect dislocations and stacking faults can easily be separated. The configuration parameters and density of dislocations, the probabilities of intrinsic, extrinsic and twin stacking faults were deduced in all cases.

Borehole elongation and its relation to tectonic stress at the Nevada Test Site

Abstract: This paper documents the borehole spalling pattern in relation to lithology, geologic structure, stress, and depth of two Nevada Test Site (NTS) areas, Yucca Flat and Pahute Mesa. Downhole movies and stereo photographs from 58 large-diameter test holes at NTS reveal a strong NW-SE elongation due to sidewall spalling. This trend is found in Yucca Flat and Pahute Mesa, which have distinctly different geologies, and is parallel to the direction of regional extension. The directionality is due to tangential stress concentration at the wellbore, which has a peak value along the azimuth of minimum horizontal regional stress. The percentage of borehole length affected by spalling varies from 5% near the surface to 30% at depths over 500 m. The severity of spalling is also a function of lithology; however, geologic discontinuities apparently have little effect on the orientation and occurrence of elongations. Directional spalling was observed in relatively shallow alluvial deposits, suggesting the persistence of horizontal stress differences at shallow depths. If the elongations are truly controlled by the deviatoric stress field, this implies that the regional stress direction is fairly uniform throughout NTS. A simple relation is given for the in situ stress and material strength conditions associated withmore » borehole elongation. 24 references, 13 figures, 2 tables.« less