scispace - formally typeset
Search or ask a question

Showing papers by "Lehigh University published in 1970"


Journal ArticleDOI
TL;DR: In this paper, a model of the underlying processes is sketched which proposes that words of higher frequency are recognized sooner because their lexical entries are marked earlier for comparison against the stimulus information.

490 citations


Journal ArticleDOI
01 May 1970
TL;DR: Simulation results show the optimum detector under a fixed delay constraint D to outperform a transversal equalizer even for relatively small values of D.
Abstract: The optimum detector under a fixed delay constraint D is derived for channels having memory and additive noise. The resulting receiver is recursive and does not grow with the message length. Its structure is presented for linear channels (AM and PSK) with known (or estimated) impulse response and noise statistics. The intersymbol interference is assumed to extend for L sampling periods and the receiver is allowed a "look-ahead" at D future received samples. Simulation results using actual channel characteristics show the detector to outperform a transversal equalizer even for relatively small values of D.

304 citations


Journal ArticleDOI
TL;DR: In this article, the authors reviewed the effects of pile ups of dislocations on the relation between yield or flow stress and grain size, and some non-pileup theories of yielding are critically reviewed.
Abstract: Calculations involving pile ups of dislocations, both analytical and numerical, using either discrete dislocations or continuous distribution of dislocations of infinitesimal Burgers vectors, are reviewed in the light of their effects on the relation between yield or flow stress and grain size. The limitations of the pileup models are discussed and some nonpileup theories of yielding are critically reviewed also. More critical experiments are still needed to reveal the fundamental mechanicm of yielding.

268 citations


Journal ArticleDOI
TL;DR: In this paper, a theory of electron tunneling from the metal through the insulator and into the semiconductor of a MIS-structure is developed using a square well model, the interface states are represented by a distribution of δ-function potentials, and their wave functions calculated.
Abstract: A theory of electron tunneling from the metal through the insulator and into the semiconductor of a MIS-structure is developed. Using a square well model, the interface states are represented by a distribution of δ-function potentials, and their wave functions calculated. Following the method of Bardeen, the tunneling matrix element and current are found and used with an extension of Shockley-Read recombination theory to determine a tunnelling time constant, τ To , similar to the surface recombination time constant, τ. Small signal solutions are calculated and presented in the form of equivalent circuits. For a single level state the equivalent circuit consists of the thick insulator, non-tunneling MIS-capacitor plus a tunneling current, j 1 , injected from the metal into the midpoint of the recombination RC circuit. j 1 is made up of three terms caused by modulation of the effective barrier height, and by modulation of the metal and trap occupancy functions. For τ To ⪡ τ , the case of an ideal Schottky barrier, the tunneling current is controlled by the recombination time, τ. If τ To > τ , the tunneling limited case, j 1 is controlled by τ To . This case is discussed in detail. The model's current and conductance characteristics are numerically calculated and graphically presented as a function of interface state density and distribution, interface potential, insulator thickness, and a.c. frequency.

166 citations


Journal ArticleDOI
Robert P. Wei1
TL;DR: In this paper, a critical review and analysis of existing fatigue-crack-growth data on high-strength aluminum and titanium alloys and high strength steels has been made.

160 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the fracture and fatigue in elastic cylindrical shells with circumferential crack under axial tension and noted precracked specimens with precariness.
Abstract: Fatigue and fracture in elastic cylindrical shells with circumferential crack under axial tension, noting precracked specimens

146 citations


Journal ArticleDOI
01 Jun 1970
TL;DR: In this paper, both wedge force loading and remote loading techniques were employed to achieve the desired ΔK levels, and preliminary experiments were designed to test their compatibility, and the observed crack growth rates compared with those in desiccated air.
Abstract: Environmental fatigue crack propagation in 2024-T3, 7075-T6, and 7178-T6 has been studied at low levels of cyclic amplitude of stress intensity, ΔK. Both wedge force loading and remote loading techniques were employed to achieve the desired ΔK levels, and preliminary experiments were designed to test their compatibility. Testing was carried out in humid air, distilled water, and 3.5 pct sodium chloride solution, and the observed crack growth rates compared with those in desiccated air. Later studies were also conducted in an inert reference environment with a total water content of less than 2 ppm. When the data are plotted as log ΔK vs log d2a /dN, alloy 2024-T3 exhibits a marked slope transition, alloy 7075-T6 a slight slope transition, and alloy 7178-T6 a rectilinear behavior throughout the whole range of ΔK studied. The basic shape of these curves is discussed in terms of state-of-stress conditions at the crack tip, frequency effects, environmental effects, strain rate sensitivity, and metallurgical structure. An attempt is also made to correlate the rate of fatigue crack propagation in a particular environment and at a particular ΔK level with the fracture topography.

138 citations


Journal ArticleDOI
TL;DR: Elastic plate uniform extension with rectangular crack by three dimensional bending theory, using variational principle as discussed by the authors, was proposed to solve the problem of 3D bending in elastic plate uniform extensions.

130 citations


Journal ArticleDOI
01 Jun 1970
TL;DR: The phase boundary compositions of the two-and three-phase fields are listed and compared with the three binary diagrams in this article, and nineteen isotherms were determined in this study.
Abstract: In order to provide the necessary phase equilibria data for understanding the development of the Widmanstatten pattern in iron meteorites, we have redetermined the Fe-Ni-P phase diagram from 0 to 100 pct Ni, 0 to 16.5 wt pct P, in the temperature range 1100° to 550°C. Long term heat treatments and 130 selected alloys were used. The electron microprobe was employed to measure the composition of the coexisting phases directly. We found that the fourphase reaction isotherm, where α+ liq ⇌ γ+ Ph, occurs at 1000° ± 5°C. Above this temperature the ternary fields α+ Ph + liq and α+ γ+ liq are stable and below 1000°C, the ternary fields ⇌+ γ + Ph and γ + Ph + liq are stable. Below 875°C a eutectic reaction, liq → γ + Ph, occurs at the Ni-P edge of the diagram. Altogether nineteen isotherms were determined in this study. The phase boundary compositions of the two-and three-phase fields are listed and are compared with the three binary diagrams. The α + γ + Ph field expands in area in each isotherm as the temperature decreases from 1000°C. Below 800°C the nickel content in all three phases increases with decreasing temperature. The phosphorus solubility in α and γ decreases from 2.7 and 1.4 wt pct at 1000°C to 0.25 and 0.08 wt pct at 550°C. The addition of phosphorus to binary Fe-Ni greatly affects the α/α + γ and γ/α + γ boundaries below 900°C. It stabilizes the α phase by increasing the solubility of nickel (α/α +γ boundary) and above 700°C, it decreases the stability field of the γ phase by decreasing the solubility of nickel(@#@ γ/α + γ boundary). However below 700°C, phosphorus reverses its role in γ and acts as a γ stabilizer, increasing the nickel solubility range. The addition of phosphorus to Fe-Ni caused significant changes in the nucleation and growth processes. Phosphorus contents of 0.1 wt pct or more allow the direct precipitation ofa from the parent γ phase by the reaction γ ⇌ α + γ. The growth rate of the α phase is substantially higher than that predicted from the binary diffusion coefficients.

127 citations


Journal ArticleDOI
TL;DR: In this article, an analytical and experimental program was conducted to determine if a biaxial stress field produces a significant effect on the fatigue and fracture behavior of thin plates, and it was shown that the effect of nonsingular stresses on the behavior of a crack is examined from both a linear elastic and an elastic-plastic viewpoint.
Abstract: The results are presented of an analytical and experimental program which was conducted to determine if a biaxial stress field produces a significant effect on the fatigue and fracture behavior of thin plates. The materials tested were 6061-T4 and 6061-T6 aluminum sheets and plexiglas sheets. The experimental program included fracture tests with various magnitudes of biaxial load at fracture and fatigue tests with sinusoidal loading normal to the crack and either constant or sinusoidal stresses applied parallel to the crack. The effect of nonsingular stresses on the behavior of a crack is examined from both a linear elastic and an elastic-plastic viewpoint. The experimental study indicates that a biaxial stress field does affect the behavior of a crack in a thin sheet. An increase in the apparent fracture toughness with increasing biaxial load was observed experimentally but as yet cannot be adequately explained using linear fracture mechanics theory. Biaxial stresses were found to produce a shift in the fatigue crack growth rate data, and it is shown that this shift can be predicted using several empirical fatigue crack propagation models.

85 citations



Journal ArticleDOI
TL;DR: In this article, a series of fatigue tests were performed on several different polymer materials representing different classes of mechanical response and a strong correlation was found between the fatigue crack propagation rate and the stress intensity factor range prevailing at the advancing crack tip.
Abstract: In order to gain a better understanding of matrix-controlled fatigue failure processes in non-metallic materials a series of fatigue tests were performed on several different polymer materials representing different classes of mechanical response Fatigue crack propagation rates between 5×10−6 in cycle−1 (127 nm cycle−1) and 4×10−4 in cycle−1 (10 300 nm cycle−1) were measured in nylon, polycarbonate, ABS resin, low-density polyethylene and polymethyl methacrylate A strong correlation was found between the fatigue crack propagation rate and the stress intensity factor range prevailing at the advancing crack tip Whereas metals exhibit comparable fatigue growth rates for a given stress intensity range when normalised with respect to their static elastic modulus, the polymer materials exhibited a 1300-fold difference in crack growth rate for a given normalised stress intensity range This observation dramatically illustrates the importance of understanding molecular motion and energy dissipation processes in polymer materials as related to their chemistry and architecture The relative behaviour of the different polymer materials could be generally correlated with their reported damping characteristics

Journal ArticleDOI
TL;DR: In this article, an analysis of stresses and deflections produced in a thin, complete spherical shell when it is compressed between two parallel rigid plates is presented, and the deformation state at which the contact region buckles is given.
Abstract: Abstract : The paper presents an analysis of stresses and deflections produced in a thin, complete spherical shell when it is compressed between two parallel rigid plates. The analysis accounts for finite deflections and rotations, but assumes that the material remains linearly elastic throughout the deformation. It is also assumed that the region of the shell which is in contact with the plate remains flat. The deformation state at which the contact region buckles is given. (Author)


Journal ArticleDOI
01 Nov 1970
TL;DR: In this article, the properties of solid surfaces required for effective heterogeneous nucleation of ice from the vapor were investigated and the spatial distribution of the polar adsorption sites on the surface was examined by a steric hindrance method employing isopropanol adsorptions.
Abstract: The properties of solid surfaces required for effective heterogeneous nucleation of ice from the vapor were investigated. Amorphous silicas were modified in various ways and tested in a cloud chamber. The surface properties of these substrates were then determined by gas adsorption techniques. The spatial distribution of the polar adsorption sites on the surface was examined by a steric hindrance method employing isopropanol adsorption. It was found that silicas heat treated in the presence of sodium chloride had satisfactory nucleating ability in the cloud chamber. Furthermore, the polar adsorption sites on these good nucleants were found to cover approximately half the available surface area and were distributed in clusters on a low-energy surface. Adsorption studies of several silver iodide preparations, on the other hand, showed the polar adsorption sites to be related to the impurity content of the substrates, which also yield polar sites in a hydrophobic matrix. A comparison of the nucleating properties of silver iodide preparations and modified silicas in water vapor and in bulk water indicated that good crystallographic match between substrate and ice is of primary importance, especially in bulk nucleation. In the absence of a favorable substrate structure, heterogeneous nucleation from the vapor is largely controlled by the water adsorption properties of the substrate. A partially hydrophilic substrate, which is an effective ice-nucleating agent in water vapor, is less effective in bulk water possibly because the site adsorption and clustering mechanism is rendered inoperative when the surface is covered with water.

Journal ArticleDOI
TL;DR: It was apparent that the recipients were capable of differentiating between allogsrafts and xenografts since host reactions directed at the latter were more rapid and generally more severe.

Journal ArticleDOI
TL;DR: In this paper, a series of interpenetrating polymer networks were prepared containing PMMA and PEA as their two components, and the results indicated one very broad transition for the IPN's rather than two transitions expected for incompatible polymer pairs.
Abstract: A series of interpenetrating polymer networks were prepared containing PMMA and PEA as their two components. Corresponding telomer mixtures and random copolymers were also prepared for comparison purposes. The glass-rubber transition studies were made via shear modulus and dilatometric measurements. The results indicate one very broad transition for the IPN's rather than two transitions expected for incompatible polymer pairs. An interpretation based on the compatibility or near-compatibility of the PEA/PMMA pair is offered.

Journal ArticleDOI
01 Jun 1970
TL;DR: In this article, the effect of carbon content, grain size, quench rate, and retained austenite on microcracking in Fe-C martensites was investigated.
Abstract: Metallographic analysis was used to study the effect of carbon content, grain size, quench rate, and retained austenite on microcracking in Fe-C martensites. It was found that microcracking is directly related to an increase in the carbon content of the martensite and that there exists a carbon content which corresponds to both the onset of microcracking and the formation of plate martensite. Retained austenite indirectly affects microcracking in that more complete transformation yields more martensite and consequently more microcracking. Grain size changes from 100 to 1200 μ, introduced by varying the austenitizing temperature from 1800° to 2400°F and varying the time at 2000°F for 15 hr, did not affect microcracking or the amount of retained austenite. Finally, the investigation emphasizes that microcracking is a manifestation of the impingement of martensite plates and is not a function of the stress state introduced by the quenching medium.

Journal ArticleDOI
A. Barry Kunz1
TL;DR: Using the relativistic mixed basis (M.B.) technique and the non-relativistic O.P.W. technique, electron energy bands are obtained for KI and RbI under a variety of conditions as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, a physically adsorbed monolayer of water vapor on hydroxylated α-Fe2O3 is shown to be immobile through application of adsorption thermodynamics and statistical mechanics.

Journal ArticleDOI
TL;DR: In this article, the stretching of a nonlinear elastic panel of finite length is described in the limit when the strains are small but the strain rates are comparable with the natural frequency of the panel.
Abstract: The equations governing the stretching of a nonlinear elastic panel of finite length are integrated in the limit when the strains are small but the strain rates are comparable with the natural frequency of the panel. Such a theory is needed to describe many small amplitude but nonlinear phenomena, such as near-resonant oscillations. It is shown that such a theory must be used when investigating the distortion and decay of free vibrations. These are discussed in detail. A brief discussion of the effect of friction on such vibrations is also given. The mathematical problem reduces to solving nonlinear difference equations and involves functions whose values repeat at a sequence of times which are separated by a time interval which depends on the value repeated. Although the problem is stated in the language of elasticity theory the results are directly applicable to nonlinear optical systems and gas flows in Kundt tubes.

Journal ArticleDOI
TL;DR: In this article, the creep behavior of poly(ethyl acrylate) and poly(methyl methacrylate)-interpenetrating polymer networks was investigated using a modified Tobolsky-Aklonis-Dupre glass-rubber theory, and it was found that the breadth of the transition could be attributed to a near continuum of phase compositions in the material, each phase composition making its specific contribution to the relaxation spectrum.
Abstract: The creep behavior of a series of poly(ethyl acrylate)–poly(methyl methacrylate) interpenetrating polymer networks was investigated. For comparison purposes, some stress relaxation data were included. Master curves containing a single broad transition covering approximately 20 decades of time were found for midrange compositions. Although the time–temperature superposition principle and the WLF equation should not strictly apply, reasonable agreement was found over a large portion of shift factor versus temperature plots. Application of a modified Tobolsky-Aklonis-Dupre glass–rubber theory suggested that the breadth of the transition could be attributed to a near continuum of phase compositions in the material, each phase composition making its specific contribution to the relaxation spectrum. Whether or not these phase regions are so small as to arise from random concentration fluctuations in an otherwise compatible polymer pair remains unknown.

Journal ArticleDOI
G.C. Sih1, E.P. Chen1
TL;DR: In this article, a semi-infinite crack traveling with constant velocity in an infinitely long strip of finite width is considered and the effect of strip width on the dynamic stresses is examined.
Abstract: This paper is concerned with the anti-plane stress distribution around a semi-infinite crack traveling with constant velocity in an infinitely long strip of finite width. The problem is reduced to the solution of the Riemann-Hilbert problem by application of the Schwarz-Christoffel transformation and the theory of complex functions. Closed-form solutions are obtained for two cases of practical interest: (1) the boundaries of the strip are clamped and displaced in equal and opposite directions causing a tearing motion along the leading edge of the crack and (2) the crack is sheared longitudinally by a pair of concentrated forces moving with the crack while the strip boundaries are free of tractions. In both cases, the effect of strip width on the dynamic stresses is examined. A dynamic crack extension force is defined by a line integral the value of which is independent of the path of integration and requires only a knowledge of the local stress and displacement fields. The information gained in this study is useful in that it can assist interpretation of results from dynamic experiments on moving cracks.

Journal ArticleDOI
TL;DR: In this paper, a rule of thumb based on extensive study of the distribution of 0 in small samples is given as an aid in judging when the χ2 approximation is satisfactory for practical purposes.
Abstract: Cochran's Q test for differences between related-sample percentages or proportions has generally been incorrectly presented in secondary sources. The most common mistake results from failure to recognize that rows containing only 1's or only 0's, i.e., only successes or only failures, do not affect the value of Q. The F test, however, is affected by such rows. The probabilities from the χ2 and F approximations are compared with the exact probabilities in three sets of data. A rule of thumb, based on extensive study of the distribution of 0 in small samples, is given as an aid in judging when the χ2 approximation is satisfactory for practical purposes.


Journal ArticleDOI
TL;DR: In this article, a theory is developed describing finite amplitude, high frequency, periodic disturbances in dissipative systems, where the transmitting medium is taken to be a viscoelastic string and the results are applicable to nonlinear transmission lines and nonlinear dielectrics.
Abstract: A theory is developed describing finite amplitude, high frequency, periodic disturbances in dissipative systems. Although, for definiteness, the transmitting medium is taken to be a viscoelastic string, the results are applicable to nonlinear transmission lines and nonlinear dielectrics, as well as relaxing and reacting gas mixtures. Part I of the paper describes small amplitude but finite rate processes: part II will describe disturbances of unrestricted amplitude. It is shown that by interpreting high frequency waves as modulated simple waves with slowly changing Riemann invariants, the parameter expansion techniques of geometrical optics can be modified to include finite amplitude waves. The roles of the linear models of viscoelasticity and elasticity as well as that of nonlinear elasticity as approximations to the nonlinear viscoelastic model are elucidated.

Journal ArticleDOI
E. Sommer1
TL;DR: In this paper, a simple interference method has been used to measure the opening displacement of cracks in glass plates under eccentric tension load, and a K-calibration curve for the crack-line-loaded, single-edge notched plate has been established.

Journal ArticleDOI
TL;DR: In this paper, the convergence properties of the sequences of positive linear operators of the form {Ln(f)} to for each f ∈ C[a, b] have been studied.
Abstract: Let {Ln} be a sequence of positive linear operators defined on C[a, b] of the form where xnk ∈ [a, b] for each k = 0, 1,…, n = 1, 2,…. The convergence properties of the sequences {Ln(f)} to for each f ∈ C[a, b] have been the object of much recent research (see e.g. [4], [8], [11], [13]). In many cases positive linear operators of the form (1) give rise to interesting summability matrices A = (ank(x)) and vice- versa.


Journal ArticleDOI
TL;DR: In this article, the significance of the limit analysis in terms of real behavior of soils and their idealizations is discussed, and the power and simplicity of application of limit analysis method is demonstrated.