Electron spin resonance and electrical conductivity of vanadate glasses

Electron spin resonance (ESR) and d.c. conductivity were measured for a series of vanadium borophosphate glasses before and after heat treatment. The ESR spectra showed the presence of vanadium in the V⁴⁺ state in all untreated and heat-treated samples free from iron. The variable temperature ESR and d.c. conductivity results obtained on the sample free from iron showed an inflexion at about 140°C. The electrical conductivity was found to decrease on substitution of 1 mol.% V₂O₅ by 1 mol.% Fe₂O₃ which may be due to a decrease in the V⁴⁺/V ratio. However, the electrical conductivity was found to increase on addition of more than 1 mol.% Fe₂O₃ which may be due to possible hopping conduction between Fe²⁺−Fe³⁺, V⁴⁺−Fe³⁺ and Fe²⁺−V⁵⁺. The increase in conductivity in the sample heat treated at 350°C relative to those heat treated at 300°C and 400°C may be due to the variation in the V⁴⁺/V total ratio. The activation energy values for untreated and heat-treated samples were calculated and were found to depend on the variation in the V⁴⁺/V ratio and the microstructure.     

Ti-content and annealing temperature dependence of transformation behavior of TiXNi(92-XCu8 shape memory alloys

Ti-content and annealing temperature dependence of the transformation behavior of Ti_XNi_(92-X)Cu_8.0 (at,%) (X = 49.0–5l.0) alloys was investigated by varying the annealing temperature from 573 to 1273 K. It was found that the peak temperature of B2–B19 transformation (O^*) increases with increasing annealing temperature from 673 to 873 K for all of the alloys. With annealing at temperatures above 873 K, the influence of annealing on O^* depends on Ti-content. In the range of 50.4–51.0 at.% Ti, O^* shows little dependence on annealing temperature. In the range of 49.3–50.2 at.% Ti, O^* firstly decreases and then keeps constant with increasing annealing temperature. For the alloy of 49.0 at.% Ti, O^* continuously decreases with increasing annealing temperature from 873 to 1273 K. On the basis of the above data, a partial phase diagram of Ti-Ni-8.0Cu (at.%) was proposed. The transformation hysteresis also showed unique Ti-content and annealing temperature dependence.     

Application of the T-integral and S criteria in finite element analysis of impact damage at fastener holes in graphite/epoxy laminates under compression

This paper illustrates the application of two fracture criteria, Atluri's T^*-integral and Sih's strain energy density factor S for estimating the residual strength of an impact damaged fastener hole in a composite laminate. Finite element analyses are performed, and the magnitude and distribution of T^* and S are determined around the delamination. It is found that the profiles of these distributions are extremely complex and sensitive to the modelling of the stress fields close to the delamination. The effects of local closure, shear moduli and cracktip singularity are investigated. It is also shown that the representation of the stress singularity in the finite element model has a strong effect on the distribution of T^* and S. The distribution of both T^* and S is such that three local maxima occur and are situated at the same locations around the delamination. These locations approximately coincide with the points of maximum growth as revealed by ultrasonic C-scan of the damage growth of several specimens. The T^*-integral is shown to be more sensitive to the values of interlaminar shear moduli than S. The results of the analyses suggest that both the T^*-integral and S criteria may be successfully employed in the prediction of residual strength. However, S is better at predicting the direction of damage growth provided the stress fields near the delamination can be accurately modelled.     

Representation of the displacement rate between the loading points in terms of applied stress and temperature and its relation to creep crack growth rate, C, P and Q parameters

The displacement rate between the loading points in SUS 304 stainless steel has been experimentally obtained under several applied gross stress and high temperatures, and the equation for has been obtained experimentally as a function of applied gross stress σ_g and absolute temperature T. Then, the relation of δ to creep crack growth rate da/dt was clearly shown in terms of equation. Furthermore, the relation has been clarified between the energy rate line integral C^* as affected by , and P parameter. In this way, it is clearly shown why log (da/dt) data plotted against log C^* deviates in some systematic trend with the increase of temperature and gross stress, respectively, whereas log da/dt vs the P parameter becomes exactly the same and one straight line independent of temperature and gross stress. The discussion is made on that the similar relation will hold between the evaluation by C^* and that by _gQ or by Q^*.     

Anomalous elastic response of amorphous alloys suggesting collective motions of many atoms

The dynamic Young’s modulus, E, of amorphous (a-) Zr₆₀Cu₃₀Al₁₀ (numbers indicate at.%) alloy was measured as a function of frequency, f, with a strain amplitude, _t, of 10⁻⁶, E(10⁻⁶,f), and also as a function of _t for f near 10² Hz, E(_t,10² Hz), by means of the vibrating reed methods. The elasticity study under the passing of electric current (PEC) was carried out too. E(10⁻⁶,f) is lower than E₀ for f between 10 and 10⁴ Hz showing local minima near 5×10, 5×10² and 5×10³ Hz, which are indicative of the resonant collective motion of many atoms, where E₀ is the static Young’s modulus. E(_t,10² Hz) increases showing saturation with increasing _t. Qualitatively, the outlines of E(10⁻⁶,f) and E(_t,10² Hz) observed for a-Zr₆₀Cu₃₀Al₁₀ are similar to those reported for various a-alloys. Quantitatively, a change in E(_t,10² Hz) for a-Zr₆₀Cu₃₀Al₁₀ is smallest among that reported for various a-alloys, presumably reflecting that the crystallization volume, (ΔV/V)_x, is smallest for a-Zr₆₀Cu₃₀Al₁₀. The effective charge number, Z^*, estimated from the change in E(10⁻⁶,10² Hz) due to PEC is 3.0×10⁵, which is comparable with Z^* reported for various a-alloys. We surmise that the number of atoms in the collective motions excited near 10² Hz is similar among various a-alloys. The E(10⁻⁶,f) data suggest that the spatial sizes of the density fluctuations may show a distribution.     

Further studies on elastic-plastic stable fracture utilizing the T integral

Herein, the T^* fracture parameter is shown to have relevance to the mechanics of elastic-plastic fracture. Specifically, it is shown to have certain advantages over the currently established plastic fracture parameters such as J and CTOA. Finite element analyses of experimental data were carried out as a means to obtain a comparison of the effectiveness of the plastic fracture parameters. T^* is clearly superior. A note on problems associated with satisfying the plastic incompressibility constraint is also included.     

Review of the fracture mechanics approach to creep crack growth in structural alloys

The application of the fracture mechanics approach to time-dependent high temperature crack growth has been reviewed. Available data on several structural alloys indicate that depending on the environmental sensitivity and creep ductility of the material, creep crack growth can be characterized by either linear elastic parameter, K, non-linear elastic-plastic parameter, J^*-integral, or reference stress, σ_ref. In particular for materials that are significantly sensitive to environment, K can adequately characterize the growth rate, and for materials that are significantly creep ductile, σ_ref can be used to predict creep life of a cracked body. Finally, for materials that are relatively ductile and wherein crack growth occurs predominantly by a deformation process, J^* integral appears to be the characterizing parameter for the growth rate. Data for several materials indicate that under steady state crack growth conditions, there may be a unique growth rate-J^* relation independent of temperature and material. This would have a profound impact in terms of the utility of fracture mechanics approach to predict creep crack growth rate and needs to be examined further. Conditions under which K, J^* or σ_ref is applicable are discussed in detail.     

On the influence of residual stresses on the fracture behavior of a structural steel in the KIc temperature range

The increase with increasing temperature of K_Ic, measured with 2CT and 1'CT specimens, from about 10³N mm at 77 K to about 2.10³ N mm at about 170 K is attributed to the increasing proportion of dimple to cleavage fracture as revealed by scanning electron microscope investigation.

The specimens were prestrained to different partial scale yielding states by the same kind of loading, performed at 298 K, as in the later K_Ictests, performed at 77 K. After pretension K_Ic = K^*_Ic is increased by a maximum amount of about half of the value K⁰_Icof nonprestrained specimens, after precompression it is reduced by the same amount if this value is evaluated from the load at which a pop-in occurs. The value K_Ic = K^**_Ic for the final fracture lies between K^*_Ic and K⁰_Ic. These results are interpretated in terms of the residual stress states due to prestraining.     

The effect of multiple damage in composite structures: a theoretical investigation

This paper focuses on the problem of damage in composite structures and discusses the theoretical analysis of the effect of multiple damaged composite laminates subject to uniaxial and bi-axial loading. The interaction effect between two 27.5 mm diameter delaminations, with 9.5 mm diameter holes, was studied using a 3-D finite element analysis as a function of damage spacing. The compressive loads required for delamination growth were predicted using a Strain Energy Release Rate approach, viz. T^*-integral. The results indicated that, for the particular layup analysed, the damage interaction can be considerable as the distance between the damage is reduced. The interaction effect appears to substantially increase T^* i.e. reduce the compressive load required for delamination growth, if the row of multiple damage is perpendicular to the applied load. T^* also appears to increase, for all the cases considered, when bi-axial loading is applied.     

Variations of color with alloying elements in Pd-free Au–Pt-based high noble dental alloys

The effects of alloying addition of a small amount of base metals (In, Sn, Fe, Zn) on color variations in Pd-free Au–Pt-based high noble dental alloys were investigated in terms of rectilinear and polar color coordinates. The ternary Au–Pt–X (X = In, Sn, Fe, Zn) and quaternary Au–Pt–In–Y (Y = Sn, Fe, Zn) alloys were prepared from high purity component metals. The amount of alloying base metals, X and Y, were restricted up to 2 at.%. The alloying addition of a small amount of Fe, In, Sn, to a binary Au–10 at.% Pt alloy (referred to as AP10) effectively increased chroma, C^*. On the other hand, the addition of Zn to the parent alloy AP10 did not change color coordinates greatly. The increase in chroma in the present Au–Pt-based high noble alloys was attributed to the increase in the slope of spectral reflectance curve at its absorption edge near 515 nm. It was found that the addition of a small amount of Fe to the parent alloy AP10 markedly increased lightness, L^*, and the addition of Sn gave a very light tint of red to the parent alloy. Although red–green chromaticity index a^* contributed to chroma to some extent, contribution of yellow–blue chromaticity index b^* was much greater in determining chroma in this Pd-free Au–Pt-based multi-component alloys. The present results are expected to be valuable in case color is to be taken into account in designing Pd-free Au–Pt-based high noble dental alloys.     

Finite element simulation of elastic-creep growth of a semicircular surface crack

An initially semicircular crack loaded in Mode I tension with a material model similar to 316 SS at 600°C has been simulated using the finite element method. Two techniques have been used to predict creep crack growth. One technique assumes that the rate of crack growth does not effect the crack tip stress and strain rate distributions and that crack growth is determined by the stationary state conditions. A second technique is a more general approach. The crack is extended by the node release technique. Crack growth was predicted throughout on the basis of the C^* contour integral. When the stresses were non-stationary, this is termed C(t) and was used instead of C^* in the creep crack growth rate expression. Stresses, creep strains and displacements are discussed for this simulation.     

The crack initiation and growth under high temperature creep, fatigue and creep-fatigue multiplication

This article concerns some of our recent studies on the crack initiation, early stage crack growth and its subsequent crack growth under high temperature creep, fatigue and creep-fatigue multiplication. The criteria for these and some new ideas are proposed. For instance, the relative notch opening displacement (RNOD) criterion for the crack initiation and the Q^* parameter for the crack growth are critically reviewed. Early stage crack growth and its subsequent crack growth as affected by notch tip acuity were studied. The behaviour of the tail part in the log da/dN vs log C^* curve has been attempted to explain in terms of the curve of the creep behaviour and of the crack length against time. Furthermore it was proposed that early stage crack growth, say, the so-called first stage crack growth in terms of log da/dN vs log K curve may be characterized by the parameter different from those for the so-called second stage crack growth.     

Stage II fatigue crack growth

The linear part of the fatigue crack growth diagram is found to be divided into Stages IIa and IIb by the point O whose coordinates K^* and A are dependent on the physical and structural characteristics of the material. In Stage IIa K_eff remains constant as the microcrack advances in increments corresponding to the dislocation cell structure size, λ, pausing for (dN−1) cycles to accumulate the elastic energy required for the crack opening. During Stage IIb K_op remains constant and the microcrack opens during each cycle and advances irrespective of the substructure but in accordance with an increasing value of K_eff. The effects of temperature and vacuum on K^* are considered; the A values correspond to those of λ and are independent of the above effects.     

Field-lowering carrier excitation in cadmium arsenide thin films

Cadmium arsenide is a II–V semiconductor which exhibits n-type intrinsic conductivity with high mobility up to μ_n=1.0–1.5 m²/V s. Potential applications include magnetoresistors and both thermal and photodetectors, which require electrical characterization over a wide range of deposition and measurement conditions. The films were prepared by vacuum evaporation with deposition rates in the range 0.5–6.0 nm/s and substrate temperatures maintained at constant values of 20–120°C. Sandwich-type samples were deposited with film thicknesses of 0.1–1.1 μm using evaporated electrodes of Ag and occasionally Au or Al. Above a typical electric field F_b of up to 5×10⁷ V/m all samples showed instabilities characteristic of dielectric breakdown or electroforming. Below this field they showed a high-field conduction process with logJ∝V^1/2, where J is the current density and V the applied voltage. This type of dependence is indicative of carrier excitation over a potential barrier whose effective barrier height has been lowered by the high electric field. The field-lowering coefficient β had a value of (1.2–5.3)×10⁻⁵ eV m^1/2/V^1/2 which is reasonably consistent with the theoretical value of β_PF=2.19×10⁻⁵ eV m^1/2/V^1/2 expected when the field-lowering occurs at donor-like centres in the semiconductor (Poole–Frenkel effect). For thinner films Schottky emission was more probable. The effects of the film thickness, electrode materials, deposition rate, and substrate temperature on the conductivity behaviour are discussed.     

The nuclear fluctuation width and the method of maxima in excitation curves

The method of counting maxima of excitation curves in the region of the occurrence of nuclear cross section fluctuations is extended to the case of the more realistic maxima defined as a sequence of five points instead of the simpler and commonly used case of a sequence of three points of an excitation curve. The dependence of the coefficient b⁽⁵⁾(κ), relating the number of five-point maxima and the mean level width Γ of the compound nucleus, on the relative distance κ of excitation curve points is calculated. The influence of the random background on the coefficient b⁽⁵⁾(κ) is discussed and a comparison with the properties of the three-point coefficient b⁽³⁾(κ) is made — also in connection with the contribution of the random background. The calculated values of b⁽⁵⁾(κ) are well reproduced by the data obtained from the analysis of artificial excitation curves.     

Crystal structure and spectroscopic studies of NaGd(PO3)4

Single crystals of gadolinium–sodium polyphosphate NaGd(PO₃)₄ were grown for the first time using a flux method and characterized by X-ray diffraction. This phosphate crystallizes in a monoclinic system with P2₁/n space group and with the following unit-cell dimensions: a = 9.767(3) Å, b = 13.017(1) Å, c = 7.160(2) Å, β = 90.564(5)°, V = 910.3(4) Å³ and Z = 4. The crystal structure was solved from 3451 X-ray independent reflections with final R(F²) = 0.0219 and R_w(F²) = 0.056 refined with 164 parameters (). The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO₃)∝ chains with a period of eight tetrahedra run along the [0 1 1] direction. The structure of NaGd(PO₃)₄ consists of GdO₈ polyhedra sharing oxygen atoms with phosphoric group PO₄. Each Na⁺ ion is bonded to eight oxygen atoms.     

On constructing T2 control charts for on-line process monitoring

In this paper we study the performance of X² control limits on T² control charts during on-line process monitoring. We make recommendations on the minimum number of subgroups necessary for control charts based on estimated parameters to perform similar to control charts based on true parameters when the X² control limit is used. We discuss an exact procedure for constructing T² control charts using estimated parameters that perform similar to control charts based on true parameters regardless of the number of preliminary subgroups. Furthermore, we suggest an implementation approach for using Alt's control limit on T² control charts until the accumulation of recommended minimum number of subgroups.     

Investigation of the dependence of the contact resistance on the external gold layer in AuNiGeAu/n-GaAs

The contact resistance of an Au/Ni/Ge/Au metallization system on n-GaAs exhibits a drop in contact resistance from 13.3 × 10⁻⁶ ω cm² to 8.6 × 10⁻⁶ ω cm² when the external gold layer is varied from 800 Å to 6000 Å in thickness. Secondary ion mass spectroscopy indicates that the improvement in contact resistance is due to the gold's “regulating” the amount of NiAs formed, leading to an increase in the area fraction covered by the Ni₂GeAs. The result shows that the external gold layer deposited to improve bonding should be optimized in thickness. This role played by the external gold layer of the metal system in affecting the contact resistance has not been previously studied.     

Non-collinear structure of Cr trimer on the surface of non-magnetic metals

Magnetic structure of Cr trimer clusters on non-magnetic metal substrate has been calculated by recursion method within Anderson model. The values of the moments are enhanced relatively to bulk bcc Cr due to the reduction of coordination number. Angles between the moments depend on the relations between hopping parameters V_ij, determined by the interatomic distance in the cluster. We performed systematic calculations of the ground state for different values of parameters V₁₂=V₁₃ and V₂₃. For V₁₂V₂₃ ground state corresponds to moments on the atoms 2 and 3 with opposite direction, whereas the moment on atom 1 is perpendicular to them. For V₁₂=V₂₃ the angle between each pair of moments equals 2π/3 and the total moment of the trimer is zero. A decrease of V₂₃ versus V₁₂ leads to collinear state with moment on the atom 1 antiparallel to the moments on second and third. Calculation in external magnetic field reveals the co-existence of two self-consistent states with essentially different total magnetic moments. In weak field these solutions are very close in energy whereas with the increase of the field the state with larger moment is stabilized.     

A theoretical framework and efficiency study of multivariate statistical process control charts

A multivariate T² chart is developed based on the Generalized Likelihood Ratio Test (GLRT) without a priori information about potential mean deviations. Identification of response variables from a T² chart is challenging and has received considerable attention recently. By highlighting the intrinsic relationship between various multivariate control charts and statistical hypothesis testing, this paper presents a theoretical framework for various individual multivariate control charts including the T² chart, regression-adjusted chart and M chart. The performance of these control charts is compared under different correlation structures among variables and different mean deviations. A hybrid control chart is also proposed based on the GLRT and union-intersection test, which can serve as a complementary diagnosis tool for the T² chart.