Showing papers by "Lehigh University published in 1975"

Constitutive relations for concrete

Abstract: A constitutive relation and failure criterion for concrete material under general three-dimensional stress states have been formulated using the work-hardening theory of plasticity. The formulation considers the weak tensile strength, strain-hardening, and fracture behavior of concrete. The resulting stress-strain relationships are compared with existing biaxial loading experimental results and good agreement is generally observed. The relation is suitable for use in the finite element analysis of reinforced or prestressed concrete.

Electronic structure of E 1 ′ centers in Si O 2

Abstract: A linear combination of localized orbitals-molecular orbital (LCLO-MO) cluster method is applied to calculate the electronic structure of ${{E}_{1}}^{\ensuremath{'}}$ centers in the $\ensuremath{\alpha}$-quartz structure of Si${\mathrm{O}}_{2}$ An ${\mathrm{O}}^{\ensuremath{-}}$ vacancy model, implying a net charge of $|e|$, is used This corresponds to the ${F}^{+}$ center in simpler oxides Calculations on the intrinsic ${{E}_{1}}^{\ensuremath{'}}$ center predict a highly asymmetric relaxation of the two silicons adjacent to the ${\mathrm{O}}^{\ensuremath{-}}$ vacancy Detailed calculations of hyperfine parameters are carried out, and reasonable agreement with experiment is obtained The asymmetric relaxation of the two silicons is an example of a pseudo-Jahn-Teller effect; parameters associated with this description are obtained and appear to be reasonable Calculations on the extrinsic ${{E}_{1}}^{\ensuremath{'}}$ (Ge) center in Si${\mathrm{O}}_{2}$ also give satisfactory results

The inclusion problem with a crack crossing the boundary

Abstract: The problem of an elastic plane containing an elastic inclusion is considered. It is assumed that both the plane and the inclusion contain a radial crack and the two cracks are collinear. The problem is formulated in terms of a system of singular integral equations. In the interesting limiting cases in which the crack tips approach the interface from either one or both sides, the dominant parts of the kernels become generalized Cauchy kernels giving rise to stress singularities of other than 13-1 power. For these unusual cases of a crack terminating at or crossing the interface stress intensity factors are defined and some detailed results are given for various crack-inclusion geometries and material combinations.

Frequency sensitivity of fatigue processes in polymeric solids

Abstract: One is faced with an interesting challenge when trying to explain the effect of test frequency on polymer fatigue performance. While hysteretic heating arguments appear sufficient to explain a diminution of fatigue resistance with increasing cyclic frequency in unnotched test samples, the enhancement of fatigue resistance in many polymers with increasing cyclic frequency in notched samples is still not clearly understood. In large measure, this is due to contradictory trends in fre-quency-sensitive material properties which affect the fatigue process. In this paper, a number of proposed fatigue models dealing with the time and strain rate dependence of elastic modulus, yield strength, creep and localized crack tip heating are examined and confronted with available data from the literature. Additional fatigue crack propagation data for poly(methyl methacrylate), poly (vinyl chloride), polystyrene, poly-carbonate, nylon 66, poly(vinylidene fluoride) and poly(2,6-dimethylphenylene oxide) were obtained and are reported herein. These data were obtained over a maximum frequency range of 0.1 to 100 Hz and, for selected polymers, with various waveforms. Frequency sensitivity is shown to be greatest in those polymers that show a high tendency for crazing. Relative fatigue behavior is found to reflect a competition between strain rate and creep effects. Where creep effects dominate, the total crack growth rate may be viewed as consisting of the summation of pure fatigue and creep components, respectively. Finally, the β transition appears to have a role, with frequency sensitivity being at a maximum for polymers where the β transition at room temperature occurs in the range of the experimental test frequency.

Immobilized‐enzyme continuous‐flow reactor incorporating continuous electrochemical regeneration of NAD

Abstract: Electrochemical regeneration of the cofactor nicotinamide adenine dinucleotide (NAD) from its reduced form (NADH) has been coupled with the alcoholdehydrogenation reaction which consumes NAD and produces NADU using alcohol dehydrogenase bound to alumina. Alcohol (reactant) is added directly to the system while aldehyde (product) leaves the system through an ultrafiltration membrane which prevents loss of the cofactor. This system provides a continuous-flow process for carrying out a cofactor-requiring enzymatic reaction with no net loss or consumption of enzyme or cofactor and without the use of reagents for regenerating the cofactor. Although the process shown here is not economically practical, it may be a harbinger of useful and technically feasible chemical reaction systems based on immobilized enzymes requiring cofactors.

Capture and emission of electrons at 2.4-eV-deep trap level in Si O 2 films

Abstract: Capture, photoionization, and impact-ionization cross sections for a 2.4-eV-deep electron trapping center in the silicon-dioxide layer of a metal-oxide-semiconductor structure have been determined using the photoinjection-photodepopulation technique. The electric field dependence of both capture and impact-ionization cross sections have been determined for accelerating fields in the range 0.1-1.0 MV/cm. Capture cross sections are of order ${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$ and uv photoionization cross sections greater than ${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$. High-field impact-ionization rates are 1-10 ${\mathrm{cm}}^{\ensuremath{-}1}$ for filled trap densities of order 5 \ifmmode\times\else\texttimes\fi{} ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$.

Material Characterization on the Fracture of Filament-Reinforced Composites

Abstract: The mixed mode fracture of unidirectional composites is investigated by application of the strain energy density theory. Two analytical models are used. The first assumes that the composite is an ideal homogeneous anisotropic body, and the second assumes that failure takes place in a layer of matrix material whose edges are bonded to two orthotropic plates. The expressions for the strain energy density factor, S, are derived for both models, and brittle fracture is assumed to occur when the S-factor in an element of material ahead of the crack reaches a critical value, Sc. Results are presented for E-glass fiber reinforced plastics, stainless steel fiber reinforced aluminum and graphite fiber epoxy materials and compared with available experimental data. The latter model is preferred as it accounts for the effect of nonhomogeneity that is inherent in the filament-reinforced composites.

Electron-Beam-Specimen Interactions

Abstract: A large number of interactions occur when a focused electron beam impinges on a specimen surface. Among the signals produced are secondary electrons, backscattered electrons, characteristic and continuum x-rays, Auger electrons, and photons of various energies. These signals are obtained from specific emission volumes within the sample, and these emission volumes are strong functions of the electron beam energy E 0 and the atomic number of the specimen Z. In fact the resolution for a particular signal in the electron microprobe or scanning electron microscope is primarily determined by its excitation volume and not by the electron probe size. This chapter will discuss scattering and electron penetration in solids in order to provide a basis for understanding how the electron beam interacts with the sample. In addition we will discuss, in turn, each of the signals as well as the spatial resolution that can be obtained in these instruments.

Package construction for opening only by a predetermined procedure

Abstract: A package construction resistant to tampering including a pair of laminated layers, one layer having a pocket for receiving product and a cut-out spaced from the pocket, the other layer extending across both the pocket and cut-out, and a line of weakening for severing the layers to expose a finger-grip portion of said other layer peelably retained in position across said cut-out

Noise and vibration damping with latex interpenetrating polymer networks

Abstract: Damping systems based on interpenetrating polymer networks (IPN's) provide noise and vibration attenuation over broad temperature and frequency ranges. Semicompatible latex IPN's are employed in both extensional and constrained layer configurations. The damping behavior of IPN's of compositions poly(ethyl methacrylate)/poly(n-butyl acrylate) [PEMA/PnBA], poly(ethyl methacrylate–co–ethyl acrylate)/poly(n-butyl acrylate–co–ethyl acrylate) [P(EMA–co–EA)/P(nBA–co–EA)], and poly(vinyl chloride)/poly(butadiene–co–acrylonitrile) [PVC/P(B–co–AN)] were investigated and compared to both commercially available materials and to theory. The damping of both the PEMA/PnBA and the P(EMA–co–EA)/P(nBA–co–EA) IPN's in a constrained layer configuration was significantly better, over a broad temperature range of −10° to 60°C, than the commercial materials. In addition, the P(EMA–co–EA)/P(nBA–co–EA) IPN was found to be effective in damping phenolic-impregnated Kevlar cloth laminates. A reduction of 10 dB in impact noise resulted with a 6–8% by weight layer inserted between the Kevlar-phenolic panels. The relationship between the peak damping temperature of a constrained layer system to maximum tan δ along with that of an extensional damping system to maximum E″ was also demonstrated. Although the amount of damping predicted by the theory approached that found experimentally, sufficient differences existed such that the exact detail of the damping curve was not described.

Ultrasonic evaluation of superficial masses.

Abstract: While superficial masses are usually apparent and easily palpated, it is sometimes difficult to determine whether they are cystic, solid, or mixed. Ultrasound was used to evaluate superficial masses determining their size, relationship to other structures and internal characteristics. In a series of 34 patients, ultrasound was able to differentiate among cystic, solid, or complex masses with a 94% accuracy.

Non-isothermal finite diffusion-controlled growth in ternary systems

Abstract: A mathematical model has been developed for diffusion controlled phase growth in ternary systems. Local equilibrium at phase boundaries and one dimensional diffusion controlled growth is assumed. The model includes a method of determining phase growth velocity and interface compositions consistent with the diffusion rate of both solute elements. This method also accounts for the effects of overlapping diffusion fields and nonisothermal growth. Initial conditions can be any curvilinear composition gradients and boundary conditions can be fixed or vary with time and/or temperature. The Crank-Nicolson finite difference equations are used to provide numerical stability and flexibility. Other capabilities of the model include treatment of finite systems, of nonisothermal phase growth and of off-diagonal ternary coefficients (D 21 3,D 12 3). Several sample simulations of the constant cooling of a 2.1 wt pct P, 4.1 wt pct Ni, 93.8 wt pct Fe alloy are presented. Three cooling rates are used: 5×10−3, 5×l0−4, and 5×l0−5 °C/s. An Fe-Ni-P alloy of this same composition was cooled in the laboratory for five days at 5×lo−4 °C/s from 900 to 685°C. Excellent agreement was found for the predicted and measured composition gradients and precipitate sizes.

On the Distribution of the Difference of Two t-Variables

Abstract: Formulas and values of the percentage points and the incomplete probability integral are provided for the distribution of the sum or the difference of two independent t-variables. Approximations are also given and compared with an earlier one. Some applications are cited.

Flow-induced crystallization from solution: The relative effects of extension and shearing flow fields

Abstract: Calculations have been performed to evaluate the relative effects of extensional and shearing flow fields on both the chain elongation and crystal nucleation rate enhancement for polyethylene crystallizing from xylene solutions. Rheological behavior was evaluated by means of the elastic dumbbell model modified for nonlinear effects at high elongations, and nucleation rate effects were considered from an essentially phenomenological view point. Molecular weight effects were also incorporated explicitly in the computations. Results show that chain elongation and nucleation rate enhancement is far greater for extensional than for shearing flows. Semiquantitative comparisons with experimental results reported in the literature for various aspects of the flow induced process, including the important fractionation effects, are discussed. Modification of the dumbbell model to account for shear rate effects on the intrinsic viscosity is also discussed.

Bonded wedges with an interface crack under anti-plane shear loading*

Abstract: The primary aim of this paper is to describe an analytical technique which may be used in connection with the general problem of bonded wedges containing radial cracks. The technique consists of the reduction of the related dual integral equations of the problem to a singular integral equation in a systematic manner, and is described by applying it to a relatively simple anti-plane shear problem. The paper also presents the results of various numerical examples and the closed form solution for the special case of two bonded wedges with equal angles and an interface crack.

A half plane and a strip with an arbitrarily located crack

Abstract: A technique is presented for dealing with the problem of an elastic domain containing an arbitrarily oriented internal crack. The problem is formulated as a system of integral equations for a fictitious layer of body forces imbedded in the plane along a closed smooth curve encircling the original domain. The problems of a half plane with a crack in the neighborhood of its free boundary and of an infinite strip containing a symmetrically located internal crack with an arbitrary orientation are considered as examples. In each case the stress intensity factors are computed and are given as functions of the crack angle.

The High Temperature Deformation Properties of Gold and Thermocompression Bonding

Abstract: The flow stress of a high purity gold has been determined so that the contribution of plastic flow to the gold

A Two-Stage Procedure for the Behrens-Fisher Problem

Abstract: We consider the problem of constructing a fixed-width confidence interval for the difference between the means of two normal populations with unknown variances. A Stein-type two-stage procedure is presented and some of its properties are investigated. It is shown that the procedure is generally more efficient than Chapman's [1] solution.

Retrieval of answer-sentences and answer-figures from papers by text searching

Abstract: Retrieval of passages from documents rather than whole documents as units speeds both user access to wanted information and the screening out of false retrievals. Passage retrieval services are already available to many lawyers. Results of an experiment reported here suggest that high quality passage retrieval services for scientists are now feasible. The experimental results are for biomedical retrieval questions, but reasons are given which support generalizing them. Since only titles, abstracts and words from figures (tables graphs, etc.) need be in computer-readable form, the retrieval procedures used are now economically feasible. Several characteristics of the results are especially noteworthy. (1) Search words for input to the computer search were selected by a person with only limited biomedical knowledge, aided primarily by a medical dictionary and medical textbooks (no thesauri or other cross-reference systems were used). (2) Recall averaged 90% and the lowest recall for any question was 75%. (3) The false retrieval rate averaged three falsely retrieved sentences per answer-paper retrieved, though for one question this value rose to 12. (4) Each answer-paper was retrieved by retrieval of a sentence, figure or (occasionally) title which was either in itself an answer-passage or became so when “automatically augmented”. In the latter case the computer annotated the passage with a qualification such as “multiple-case result” on the basis of words in the title or abstract. (5) Search of the words in figures in addition to those in titles and abstracts raised recall from 35% to 80%.