Showing papers by "Brown University published in 1973"
TL;DR: In this paper, the critical value of tensile stress (a) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions.
Abstract: SUMMARY AN ANALYSIS is presented which relates the critical value of tensile stress (a,) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions. The correlation is based on (i) the model for cleavage cracking developed by E. Smith and (ii) accurate plastic*lastic solutions for the stress distributions ahead of a sharp crack derived by J. R. Rice and co-workers. Unstable fracture is found to be consistent with the attainment of a stress intensification close to the tip such that the maximum principal stress a,, exceeds a, over a characteristic distance, determined as twice the grain size. The model is seen to predict the experimentally determined variation of K,, with temperature over the range -150 to -75°C from a knowledge of the yield stress and hardening properties. It is further shown that the onset of fibrous fracture ahead of the tip can be deduced from the position of the maximum achievable stress intensiiication. The relationship between the model for fracture ahead of a sharp crack, and that ahead of a rounded notch, is discussed in detail.
1,374 citations
TL;DR: In this article, the authors used fracture mechanics to derive conditions for the propagation of a concentrated shear band in heavily overconsolidated clays and found that the mean resolved shear stress on that surface is markedly less than the peak shear strength.
Abstract: In heavily over-consolidated clays there is a marked peak in the observed relation between shear stress and shear strain. As the strain increases, the stress falls from a peak to a much smaller residual stress. Slopes made from such a clay often fail progressively many years after construction. Sliding occurs on a concentrated slip surface, and it is found that the mean resolved shear stress on that surface is markedly less than the peak shear strength. Concepts from fracture mechanics, and in particular the J -integral, are used to derive conditions for the propagation of a concentrated shear band of this kind. The results indicate the presence of a strong size effect, which has important implications for the use of models in soil mechanics. An elastic analysis makes it possible to determine the size of the end zone in which the shear stress on the shear band falls to its residual value. An attempt is made to assess the possible sources of the time-dependence governing propagation speed of the shear band. They include pore-water diffusion to the dilating tip of the band (which governs the rate at which local strength reductions can occur), viscoelastic deformation of the clay (which allows a gradual build-up of strain concentration at the tip of the band), and the weathering break-down of diagenetic bonds.
883 citations
Book•
01 Jan 1973TL;DR: In this paper, experimental and theoretical aspects of the mobility and diffusion of ions in gases are studied in detail, including ion-ion interaction, boundary condition and ion and electron behavior, and the problems of the diffusion coefficients and the afterglow techniques.
Abstract: Experimental and theoretical aspects of the mobility and diffusion of ions in gases are studied in detail. Some of the subjects discussed include ion-ion interaction, boundary condition and ion and electron behavior. Also discussed in separate chapters are the problems of the diffusion coefficients and the afterglow techniques. Finally, a special chapter studies the kinetic theory of diffusion and mobility, stressing the low-, medium- and high-field theory.
858 citations
TL;DR: In this article, complex-variable forms for the conservation laws in the cases of linear, isotropic, plane elasticity are presented for the case of linear and isotropically elasticity.
Abstract: New path-independent integrals recently discovered by Knowles and Sternberg are related to energy-release rates associated with cavity or crack rotation and expansion. Complex-variable forms are presented for the conservation laws in the cases of linear, isotropic, plane elasticity. A special point concerning plastic stress distributions around cracks is discussed briefly.
657 citations
628 citations
TL;DR: In this paper, an exact renormalization equation is derived by making an infinitesimal change in the cutoff in momentum space, and the expansion for critical exponents around dimensionality 4 and the limit of the $n$-vector model are calculated.
Abstract: An exact renormalization equation is derived by making an infinitesimal change in the cutoff in momentum space. From this equation the expansion for critical exponents around dimensionality 4 and the limit $n=\ensuremath{\infty}$ of the $n$-vector model are calculated. We obtain agreement with the results of Wilson and Fisher, and with the spherical model.
598 citations
574 citations
TL;DR: In this article, it was shown that the J-integral can be directly evaluated from single load-displacement records for a series of crack toughness specimens having the common feature that their only significant length dimension is that of the uncracked ligament.
Abstract: It is shown that the J-integral can be directly evaluated from single load-displacement records for a series of crack toughness specimens having the common feature that their only significant length dimension is that of the uncracked ligament. For the special case of bending loads on the ligament of a deeply cracked bar, J is shown to be twice the work of deformation divided by the ligament area. This and like results are employed to discuss Charpy and 'equivalent energy' toughness measures and also to evolve yet simpler estimating procedures for the J-integral.
560 citations
TL;DR: The authors used a selective adaptation procedure to obtain evidence for the existence of linguistic feature detectors analogous to visual feature detectors, which are each sensitive to a restricted range of voice onset times, the physical continuum underlying the perceived phonetic distinctions between voiced and voiceless stop consonants.
473 citations
469 citations
TL;DR: In this article, an expression for radial thickness variations in lunar impact crater ejecta was proposed, which was inferred from available cratering data and semi-empirical calculations for approximate modeling of variations in ejecta thickness with the increasing range of lunar craters.
01 Jan 1973
TL;DR: In this article, a finite element solution to the large-scale yielding of a circumferentially cracked round tension bar is obtained, and the three-dimensional aspects of flawed structures and numerical methods of treating them are studied.
Abstract: Numerical procedures for accurate determination of elastic stress intensity factors for the general two-dimensional crack problem are reviewed. The elastic perfectly plastic state of crack tip deformation is studied by a finite element procedure. Elastic-plastic fields in the immediate vicinity of a crack tip are determined numerically by finite element procedures based on asymptotic studies of crack tip singularities in plastic materials. The small-scale yielding problem is modeled, and expressions for crack tip opening displacement, shear singularity amplitude, and plastic zone extent are derived. A finite element solution to the large-scale yielding of a circumferentially cracked round tension bar is obtained. The three-dimensional aspects of flawed structures and numerical methods of treating them are studied. Ductile fracture mechanisms, in particular crack tip fracture on the microscale, are discussed.
TL;DR: In this paper, an approximation scheme for a class of optimal control problems is presented, and an order of convergence estimate is developed for the error in the approximation of both the optimal control and the solution of the control equation.
TL;DR: In this article, a numerical model is developed for the welding and subsequent loading of a fabricated structure, which treats the weld process as a thermo-mechanical problem, and the model includes finite strain effects during isothermal loading, so that it may be used in the modeling of distortion sensitive structure.
TL;DR: The unit in monkey striate cortex, at least with respect to eye dominance, was a long slab-shaped column of cortex rather than the vertical cylinder originally proposed by Lorente de N6, however, one possible reason for this difference not discussed is that the 'eye preference column' may not be a unitary structure.
TL;DR: In this article, the asymptotic behavior of weak solutions of weak contraction semigroup is characterized via a characterization of ω-limit sets of the contraction semiigroup generated by −A.
TL;DR: In this article, the shape of the cavity surfaces is determined based on the assumption that this is governed by surface diffusion, and that steady state conditions prevail, so that the cavity advances as a profile retaining a constant shape near its tip.
TL;DR: In this paper, the entropy rate admissibility criterion for solutions of hyperbolic conservation laws is numerically analyzed and the equivalence of this criterion and viscosity criterion is established for the single equation and the system of equations of one dimensional nonlinear elasticity.
TL;DR: In this paper, the authors determined the stress intensity factor of a half-plane crack extending non-uniformly in an isotropic elastic solid subjected to stress wave loading.
Abstract: T he stress intensity factor of a half-plane crack extending non-uniformly in an isotropic elastic solid subjected to stress wave loading is determined. A plane stress pulse strikes the crack at time t = 0, the wavefront being parallel to the plane of the crack. At some arbitrary later time t = τ, the crack begins to extend at a non-uniform rate. It is found that the stress intensity factor is a universal function of instantaneous crack-tip velocity times the stress intensity factor for an equivalent stationary crack. An energy rate balance fracture criterion is applied to obtain an equation of motion for the crack tip. The delay time between the arrival of the incident pulse and the onset of fracture is also calculated for this fracture criterion.
TL;DR: The fairly rapid onset of epinephrine stimulation of gluconeogenesis and the results with inhibitors suggest that RNA and protein synthesis are not required for the epine cortisol action, and the increase in cyclic AMP accumulation due to epinphrine is apparently unrelated to its stimulation in rat liver cells.
TL;DR: A simplified and more accurate version of the quantitative paleoenvironmental method proposed by Imbrie and Kipp (1971) is described in this article, which is based on untransformed rather than transformed species per cent data.
TL;DR: In this paper, the alpha effect was surveyed in the context of possible explanations for this phenomenon and four factors (ground-state destabilization of the nucleophile, transition-state stabilization, solvent effect differences for alpha and non-alpha nucleophiles, and product stability) may be involved in contributory roles.
Abstract: Instances of high reactivity (as signaled by a positive Bronsted deviation) by nucleophiles bearing one or more unshared pairs of electrons on an atom adjacent to the nucleophilic center (the alpha effect) are surveyed in the context of possible explanations for this phenomenon. No single cause appears to account satisfactorily for all the data. However, four factors (ground-state destabilization of the nucleophile, transition-state stabilization, solvent effect differences for alpha and nonalpha nucleophiles, and product stability) may be involved in contributory roles. The response to proton basicity of a substrate is probably not related to its susceptibility to the alpha effect. Carbon electrophiles seem to be receptive to the alpha effect in the order digonal > trigonal > tetrahedral. The inconsistent behavior of alpha nucleophiles makes the prediction of alpha effects rather risky and confirms the complicated nature of nucleophilic substitutions.
TL;DR: Because of the long lifetime, N-(3-pyrene)maleimide is useful for fluorescence polarization studies of high molecular weight proteins and other macro-molecules having reactive sulfhydryl groups.
TL;DR: Within the Pliocene twelve planktonic foraminiferal and seven calcareous nannoplankton datum levels can be calibrated to the palaeomagnetic time scale as discussed by the authors.
Abstract: The Pliocene spans the interval between 5 and 1.8 m.y.; its lower and upper limits can be determined by multiple micropalaeontological criteria. Within the Pliocene twelve planktonic foraminiferal and seven calcareous nannoplankton datum levels can be calibrated to the palaeomagnetic time scale.
TL;DR: The transition metal phosphorus trisulfide compounds with the general formula MPS3, with M = Mn, Fe, Ni, have been prepared by chemical vapor transport, vapor sublimation and direct combination of the elements.