PM flake material prepared by mechanical chopping of rapidly quenched metallic ribbon

Ductile metallic ribbons prepared by melt spinning can be easily cut into flakes suitable for $\text{P}\text{M}$ processing by a mechanical chopper designed to tear off ribbon flakes by combining a rotating blade and a bed knife. Details of the design features are described.     

Interrelation of crack opening displacement and J-integral

The relationship between $\text{J-}\text{integral}$ and crack opening displacement δ is based on theoretical as well as experimental investigations and is of the general form $\text{J = Mσ}{}_{\mathrm{r\delta }}$. The significance of M and its possible dependence on specimen geometry and material properties is unknown. An attempt is made in the present paper to identify the different variables and to account for them in $\text{H-δ}$ relationship. It is observed that if the material properties remain constant, $\text{M}$ increases with $\text{a/W}$ ratio upto 0.5 and then probably decreases for higher $\text{a/W}$ ratios. If the specimen geometry and size is maintained constant then it is observed that $\text{M}$ increases with decreasing yield strength and a corresponding increase in work hardening exponent.     

Fracture of round bars loaded in mode III and a procedure for KIIIc determination

The available literature reports few studies on Mode $\text{III}$ fracture. In fact, even though the Mode $\text{III}$ fracture toughness, $\text{K}{}_{\mathrm{IIIc}}$ is an important factor in design and analysis of fractures under torsional loading, the procedure for the measurement of $\text{K}{}_{\mathrm{III}}$ is yet to be standardized.In this paper, the results of a simple analysis, which determines the displacement produced by the size dependent plasticity and the growth of crack in a circumferentially cracked round bar subjected to Mode $\text{III}$ loading, are presented. It is shown that plastic zone size decreases as bar diameter increases. This implies that whereas a small diameter bar can fail in a ductile manner, a large diameter bar may undergo a predominantly linear, elastic and brittle fracture even though the material is ductile.The analytical results are verified by experimental measurements on circumferentially cracked specimens loaded in Mode $\text{III}$. Based on this, one can determine the limiting value of the bar diameter, which must be tested to obtain a $\text{K}{}_{\mathrm{IIIc}}$ in a predominantly linear elastic condition. Further, a new and simple procedure for the determination of $\text{K}{}_{\mathrm{IIIc}}$ is proposed. This procedure enables one to determine the stress intensity factor at which a crack starts extension in the specimen under Mode $\text{III}$ loading.     

Computer controlled decreasing ΔK fatigue threshold test

An automated fatigue threshold test was developed which decreases testing time, eliminates need for constant operator attention, and produces a plot of fatigue crack growth rate (FCGR) data as the test proceeds. A minicomputer interfaced to a servo-hydraulic test stand adjusts loads during the FCGR test to achieve a specified stress intensity range (AA). The value of $\text{ΔK}$ is decreased exponentially with crack growth to get the fastest load shedding without crack arrest. The procedure is as follows: apply load levels to obtain desired $\text{ΔK}$ for the crack length, $\text{a}$; using the specimen compliance, compute a new value for $\text{a}$; adjust loads to obtain corresponding $\text{ΔK}$ for that $\text{a}$; record $\text{a}$, $\text{ΔK}$, and cycle count ($\text{N}$); repeat. Plots of $\text{a}$ vs $\text{N}$, and $\text{da/dN}$ vs $\text{ΔK}$ are made by a separate program. The optimized load shedding and 24hr/day operation result in a considerable reduction in test time. The program was written in BASIC on a MTS Automated Test System. Visual crack growth measurements showed good agreement with computer acquired data for a test of ETP Cu.     

On the relationship between J-integral and crack opening displacement

This paper describes a simple method of calculating the material-dependent nondimensional factor β used in the well known relation $\text{J = βσ}{}_0\text{δ}$, or, in other words, of improving the most simple relation $\text{J = σ}{}_0\text{δ. β}$ as derived in this paper accounts for the effect of hardening and prior cold-work of the material. The results obtained by this very simple procedure compare quite favorably with experimental and numerical results of other authors.     

Tunneling barrier structure of NbPb and Nb(PbIn) thin film Josephson junctions studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis

The structure of the insulant barrier of $\text{Nb}\text{Pb}$ and $\text{Nb}\text{(PbIn)}$ thin film Josephson tunnel junctions is studied in detail by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis. The properties of these two types of junction are strictly related to the thin (2–3 nm) oxide acting as a barrier between the superconducting electrodes. Two oxides were found in each barrier: Nb₂O₅ and PbO in the $\text{Nb}\text{Pb}$ junction and Nb₂O₅ and In₂O₃ in the $\text{Nb}\text{(PbIn)}$ junction. In addition, the present analysis shows a change with time of the PbO in contact with Nb₂O₅: this result is correlated with junction aging. Finally, a comparison in terms of the stability of the two junctions is made: $\text{Nb}\text{(PbIn)}$ devices seem to display a more stable behaviour with time.     

Low temperature compound formation in CuSn thin film couples

Transmission electron microscopy (TEM) and Auger electron spectroscopy have been used to study the morphology and kinetics of compound formation in vapor-deposited polycrystalline bimetallic $\text{Cu}\text{Sn}$ thin film diffused at low transport temperatures. The TEM observations show that two concurrent mechanisms, namely the interstitial transport of copper in tin and the grain boundary diffusion of tin in copper, lead to the sequential formation of η′ (Cu₆Sn₅) and ε (Cu₃Sn) intermetallic compounds. Preliminary Auger depth profiling data indicate linear growth kinetics for the η′ compound at 86°C implying that interfacial reaction kinetics is the rate-controlling step. A detailed model for the interdiffusion and reaction process in $\text{Cu}\text{Sn}$ thin films is presented.     

On the computation of mixed-mode K-factors for a dynamically propagating crack,using path-independent integrals J'k

The path-independent integral $\text{J'}{}_{\mathrm{k}}$, which has the meaning of energy release rate in elastodynamic crack-propagation, is used to numerically obtain the mixed-mode dynamic stressintensity factors for a crack propagating in a prescribed direction with a prescribed velocity. Moving isoparametric (non-singular) elements are used to model crack propagation. Even though J' is a vector integral and hence is coordinate invariant, the desirability of using specific coordinate systems to improve the accuracies of the numerical solutions for $\text{K-}\text{factors}$ is pointed out. Two procedures for extracting the mixed-mode $\text{K-}\text{factors}$ from the J' integral for a propagating crack are given. It is found that the component of J' along the crack-axis, i.e. $\text{J'}{}_1{}^0$, is always equal to or greater than the product of a crack-velocity-function and the component normal to the crack-axis, $\text{J'}{}_2{}^0$. Several examples of a slanted crack are presented to demonstrate the practical utility of the J' integral. A discussion is also presented concerning the velocity factors for dynamic $\text{K-}\text{factors}$, and energy release rate, in a finite body.     

A single test method for evaluation of the J integral as a fracture parameter

A semi-analytical method for the evaluation of the Rice fracture parameter $\text{J}$ is presented. The method is such that a value of $\text{J}$ may be determined from a single load-displacement test record, and procedures are set out, together with appropriate equations, for evaluating center cracked sheets, compact tension specimens and single edge notched beams. The method utilizes the elastic stress intensity relationships in conjunction with a modified form of the Irwin plastic zone size correction factor. Tests were carried out on center cracked sheets and compact tension specimens manufactured from a high strength aluminium alloy of a thickness (3.2 mm) for which conditions of plane stress prevailed. The $\text{J}$ values are shown to be dependent on specimen dimensions. The results are compared with those obtained by a graphical procedure. Some anomalies are noted and comparison of center cracked sheets with compact tension specimens discussed.     

The J-integral fracture criterion under opening and tearing modes and unloading effects

Measurements of $\text{J}$ from certain formulae agree well with compliance measurements for a round notched bar specimen subjected to tensile (Mode I) and torsional (Mode III) loadings. Crack growth resistance curves ($\text{R-}\text{curves}$) obtained by a three parameter technique are compared with those obtained by two current approaches. The $\text{J}{}_{\mathrm{IC}}$ values (Mode I) at initial crack growth are in good agreement with the $\text{j}{}_{\mathrm{IIIC}}$ values (Mode III). In addition, the effect of unloading on fracture toughness is examined.     

The origin of dark spot defects in InPInGaAsP aged light emitting diodes

The formation of dark spot defects (DSDs) in $\text{InP}\text{InGaAsP}$ aged light emitting diodes has been investigated by spatially resolved cathodoluminescence, transmission electron microscopy and Rutherford backscattering. It is shown that DSDs are caused by the migration of Au from the p-contact. This migration occurs during device processing and aging. As a consequence, Au-In intermetallics and inclusions associated with glide dislocations and multiple faults form, respectively, within the contact and p-InP confining layers. These features are responsible for dark spot contrast observed in electroluminescent images.     

On the path independent integral-Ĵ

The path independent integral, $\text{J}\text{?}$, is presented as the rate of energy flux during crack extension. This integral is an extension of the J-integral proposed by Rice and includes the existence of a fracture process region and the effect of plastic deformations, body forces, thermal strains and inertial of material.It is shown that the $\text{J}\text{?}\text{-}\text{integral}$ can include as special cases other fracture mechanics parameters such as J by Rice, $\text{G}\text{?}$ by Eftis et al., J¹ by Blackburn or f by Strifors.A definition of the $\text{J}\text{?}\text{-}\text{integral}$ in a three-dimensional problem is presented and possibility of applying the $\text{J}\text{?}\text{-}\text{integral}$ as fracture criterion is discussed.     

Modified manjoine WOL specimen for JIc and δi tests

A procedure is presented by which a modified WOL specimen can be designed to withstand the load required to achieve a $\text{δ}{}_{\mathrm{i}}$, or $\text{J}{}_{\mathrm{Ic}}$ test for a low yield strength, high toughness material, using information from the test of a standard WOL specimen that has suffered plastic collapse of its loading arms. The $\text{K-}\text{calibration}$ for the family of geometries used is obtained from published data fitted to a 2-dimensional half-power series, and the load point and guage point compliances are obtained through a connected beam model that is calibrated from existing compliance data to imitate a WOL specimen. Prom these calibrations the $\text{J-}\text{integral}$ tensile component correction factor is evaluated and found to be applicable for this type of specimen.     

Lithium intercalation via n-Butyllithium of the layered transition metal dichalcogenides

$\text{n}$-Butyllithium in hexane solution serves as an excellent reagent to effect the intercalation of lithium into the Group IVb and Vb layered dichalcogenides. Under mild conditions, highly crystalline, uncontaminated stoichiometric products are afforded. In addition, the course of the reaction can be monitored by titration of aliquots of the supernatant.     

Contact resistance characteristics of the low cost CuNiCr thin film resistor system

In this paper an investigation of the use of copper as a contact and interconnecting material for thin film resistors and hybrid circuits is reported. The current-voltage characteristics of Nichrome thin film resistors with copper contacts and the contact resistance of $\text{Cu}\text{NiCr}$ metallizations were measured. The effect of thermal annealing on the contact characteristics was also studied.     

On the use of the theory of v-fluids for the construction of models of turbulence

The class of $\text{v-}\text{fluids}$, defined by Proudman[1] to be non-Newtonian fluids all of whose properties depend on a single dimensional constant whose dimensions are those of viscosity, is examined further as a source of possible models of turbulence at high Reynolds number. It is found that, while the general definition is valuable, certain aspects of Proudman's associated concept of a regular $\text{v-}\text{fluids}$ have a number of features that bring its value as a source of models of inhomogeneous turbulence into question. The nature of these problems suggests a suitable modification to the definition of a regular $\text{v-}\text{fluids}$. A number of constraints on the form and solution of the equations of a model of turbulence are proposed with the intention of improving the generality of models of a given degree of complexity, and their justification and significance discussed. In the light of these proposals the simplest modified regular $\text{v-}\text{fluids}$ that can be used to model homogeneous turbulence at infinite Reynolds number is described, and it is seen to include all the most desirable features of earlier models of this type, and is in addition capable of extension in a natural way to describe inhomogeneous turbulence.     

The effect of temperature and R ratio on fatigue crack growth in A612 grade B steel

Fatigue-crack propagation rates in ASTM$\text{A612}$ Grade B steel were investigated at room temperature and ?100°F (?73°C) with $\text{R}\text{ratio}\text{= ?0.1}\text{and}\text{+0.67}$. The data were evaluated in terms of the crack propagation rates ($\text{d}\text{a/}\text{d}\text{N}$) as a function of the alternating stress intensition ($\text{ΔK}$), according to $\text{d}\text{a/}\text{d}\text{N = e+(v ? e)(? 1}\text{n}\text{(1 ?}\text{Δ}\text{K/K}{}_{\mathrm{b}}\text{))}{}^{\mathrm{t/k}}$. It was found that crack growth rates were increased due to increasing $\text{R}$ ratio. Also the dependence of crack growth rates on $\text{R}$ ratio is strongest at the lowest crack growth rates where a $\text{ΔK}$ fatigue threshold is established. Crack growth rates were decreased due to decreasing test temperature in the slow crack growth region. However, it was found that crack growth rates were increased due to decreasing test temperature in the fast crack growth region near the upper instability asymptote. Decreased test temperature and increased $\text{R}$ ratio interact synergistically to increase crack growth rates for the entire range of $\text{ΔK}$.     

Dynamic stress intensity factors using Ĵ-integral and finite element method

A formula is derived for determining the stress intensity factors from the path independent $\text{J}\text{?}\text{-}\text{integral}$ which has been formulated in the previous paper as the energy release rate by taking the effect of inertia into account. Both pure and mixed mode problems of a suddenly loaded crack can be analyzed by making use of the formula together with the conventional finite element method. Several computational examples have been given to demonstrate the accuracy of this method.     

Application of the ac potential drop technique to the determination of R curves of tough ferritic steels

The suitability of the AC potential drop (ACPD) technique for detecting crack initiation and monitoring crack extension during slow stable growth has been investigated using side-grooved Charpy size specimens tested in three point bending. For ferritic steels with widely differing initiation and growth characteristics, the potential drop (PD) vs clip gauge opening displacement (CGOD) trace shows consistent behaviour, the most important feature being the occurrence of a minimum around the point of crack initiation. At low current frequency (150 Hz), there is close agreement between $\text{δ}{}_{\min }$, the COD corresponding to the minimum of the PD/CGOD trace and $\text{δ}{}_{\mathrm{i}}$ estimated by the recommended multispecimen technique for $\text{δ}{}_{\mathrm{i}}$ ranging from 0.02 to 0.37mm. In steels with $\text{δ}{}_{\mathrm{i}}$ less than about 0.1 mm, the minimum occurs at the same value of δ for both low (150 Hz) and high (4.7 kHz) frequencies. However, for steels with higher toughness, the minimum shifts to lower δ values as the frequency is increased. It appears that for any steel, there is a maximum frequency below which the minimum corresponds to $\text{δ}{}_{\mathrm{i}}$. It is demonstrated that the ACPD method can be employed to determine $\text{R}$ curves from single specimens.