A comparison on the effect of the ratio on the fracture behaviour between ductile and brittle materials

The effect of the ratio on the fracture behaviour of ductile and brittle materials has been studied by measuring the crack-opening displacement and J-integral for ductile material and the stress intensity factor for brittle material in three-point bend specimens with shallow and deep notches. It is shown that, for ductile material, the values of δ_i and J_i, for specimens with shallow notches are larger than those of deep notches. On the contrary, for brittle material, the values of K_IC for specimens with shallow notches are smaller than those of deep notches. The reason for this is explained.     

Kr and 4He Adsorption on Individual Suspended Single-Walled Carbon Nanotubes

We report mass and conductance adsorption isotherms of Kr on individual, single-walled, suspended carbon nanotubes for 53?K<T<90?K for several devices, and of ⁴He for 5?K<T<8?K for two devices. Different nanotubes, probably of different diameter and/or chirality, yield different phase diagrams, full monolayer coverages, and partial wetting characteristics for Kr. The ⁴He results show, for one of the devices, a greatly reduced heat of adsorption as compared to the well studied system of ⁴He on graphite.     

Evaluation of VOC recovery strategies

Many manufactured items receive surface coatings for decoration and/or protection against damage. In a number of places along the production line emissions of (VOC) Volatile Organic Compounds can occur. Because VOC are a major contributor to photochemical smog, control of VOC emissions is a major concern for the industries' commitment to the environment. Approaches for process optimisation have a long tradition within chemical and process engineering for the systematic identification of cost- and resource-efficient production options. The challenge in the context of supply chain management is the optimal recovery and reuse of materials not only for single substances or energy flows in large chemical installations, but also for smaller production processes and various mass and energy flows within and between enterprises. Based on a case study from the industrial coating of bicycle frames, an approach for Multi Objective Pinch Analysis (MOPA) for the evaluation of overall recovery potentials for energy, water and VOC is presented. Moreover, a metric for resource efficiency is introduced as a measure for the possible savings potential and for the savings ultimately realised. This integrated approach requires a tight coupling of mass, energy, economic and environmental assessment methods and demands a highly interdisciplinary approach.

Compositional effects on the fracture behaviour of alkali–silicate glasses

The two-point bend strength and the fracture toughness of a series of soda–potassia–silicate and soda–potassia–calcia–silicate glass fibres have been measured. There is a clear variation of mean strength with composition for the soda–potassia–silicate glasses, however, there is much less variation of mean strength with composition for the soda–potassia–calcia–silicate glasses. There is also a greater variation of fracture toughness with composition for the soda–potassia–silicate glasses than for the soda–potassia–calcia–silicate glasses. The mean strength, fracture toughness and inferred flaw sizes for the soda–potassia–calcia–silicate glasses are all less than the equivalent values for the soda–potassia–silicate glasses. These results are related to the structural models and durability of the glasses tested.     

Spectral Emissivities and Emissivity X-Points of Pure Molybdenum and Tungsten

Prediction methods for thermophysical properties of metals and alloys such as emissivity are of great interest not only for science but also for the metal working industry as time-consuming and often expensive measurements may not be required. As recent results have shown, an assumed Hagen–Rubens relation for the prediction of emissivity based on electrical resistivity results was not found in the visible spectra. Within this work normal spectral emissivity results obtained with two complete different techniques are presented. On one hand, a multi-wavelength-pyrometry (MWLP) approach has been used to obtain emissivity as a function of temperature at 684.5, 902, and 1570 nm, and on the other hand, a radiance-comparison method was used to obtain emissivity isotherms as a function of wavelength for a range starting from 1 to 24 μm. From results of the radiance-comparison measurements an intersection of the isotherms, often referred to as the emissivity x-point, was found for both investigated materials, tungsten and molybdenum. According to these results, the x-point wavelengths are given by λ _x = 1.41 μm for tungsten and λ _x = 1.55 μm for molybdenum. Based on these x-points and the MWLP measurements, a new prediction method for the liquid-phase behavior of emissivity is developed and discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Structure and properties of Ge–Sb–S–CsCl glass–ceramics

We annealed Ge–Sb–S–CsCl glass and investigated the evolution of the structural, optical and mechanical properties as a function of annealing temperature. It was found that, for the glass annealed at 280 °C for 210 h, a CsCl crystalline phase with mono-dispersedly spherical shape was formed; while for the glass annealed at 370 °C for 5 h, both β-GeS₂ and CsCl crystalline phases with irregular distribution of large grains was observed. While the density and the microhardness of the glasses increase with increasing annealing temperature, it was found that, optical loss in the glass annealed at 370 °C for 5 h was much larger than that annealed at 280 °C for 210 h.     

T-stress of cracks loaded by near-tip tractions

T-stress solutions were derived for tractions acting on the crack-faces near a crack tip. Such solutions are of interest for the determination of the leading term of a weight function representation of T-stresses and the computation of an “intrinsic” T-stress for cracks growing in a material with a rising crack growth resistance. First, the type of the Green’s function for T-stresses is theoretically established. Then, results of finite element computations are reported for edge-cracked bars, DCB and CT specimens, which are suited for the determination of the first series term. As an application of the Green’s functions, the T-stresses caused by bridging interactions very close to the crack tip are computed.     

Faster synthesis of A-type carbonated hydroxyapatite powders prepared by high-temperature reaction

Synthesis of A-type carbonated hydroxyapatite (CHA) materials has typically involved heating of a hydroxyapatite composition for 24 h or greater. In this study, a hydroxyapatite powder was heated at 800, 900 or 1000 °C for 1, 8 or 16 h in dry CO₂. Samples heated for 8 and 16 h at 900/1000 °C were fully-carbonated A-type CHAs. After only one hour at 1000 °C, the carbonate content approached 95% of the theoretical maximum. Preparing compositions with more than 95% of the theoretical maximum with reduced thermal energy (1000 °C for 1 h, or 900 °C for 8 h) results in powders with higher surface areas and a reduced level of sintering, compared to powders prepared with typical thermal treatments reported for A-type CHAs, such as 1000 °C for 16 h. As far as the authors are aware, these are the shortest heating times reported for the preparation of fully-carbonated A-type CHAs which is significant for future applications of such powders, particularly in applications beyond medical devices such as chromatography, remediation and carbon capture.     

Elastic T-stress solutions for semi-elliptical surface cracks in finite thickness plates

Three-dimensional finite element analyses have been conducted to calculate the elastic T-stress for semi-elliptical surface cracks in finite thickness plates. Far-field tension and bending loads were considered. The analysis procedures and results were verified using both exact solutions and approximate solutions. The T-stress solutions are presented along the crack front for cracks with a/t values of 0.2, 0.4, 0.6 or 0.8 and a/c values of 0.2, 0.4, 0.6 or 1.0. Based on the present finite element calculations for T-stress, empirical equations for the T-stress at three locations: the deepest, the surface and the middle points of the crack front under tension or bending are presented. The numerical results are approximated by empirical formulae fitted with an accuracy of 1% or better. They are valid for 0.2?a/c?1 and 0?a/t?0.8. These T-stress results together with the corresponding K or J values for surface cracks are suitable for the analysis of constraint effects for surface cracked components.     

A modified model for calculating lattice thermal expansion of I2-IV-VI3 and I3-V-VI4 tetrahedral compounds

A general empirical formula was found for calculating lattice thermal expansion for compounds having their properties extended for compound groups having different mean ionicity as well as more than one type of cation atoms with that of different numbers of them such as I₂-IV-VI₃ and I₃-V-VI₄. The difference in the valence electrons for cations and anions in the compound was used to correlate the deviations caused by the compound ionicity. The ionicity effects, which are due to their different numbers for their types, were also added to the correlation equation. In general, the lattice thermal expansion for a compound semiconductor can be calculated from a relation containing melting point, mean atomic distance and number of valence electrons for the atoms forming the compound. The mean ionicity for the group compounds forming I₂-IV-VI₃ was found to be 0.323 and 0.785 for the ternary group compounds of I₃-V-VI₄.     

Mechanical properties of single- and double-gated injection moulded short glass fibre reinforced PBT/PC composites

Tensile and flexural properties of single-gated (SG) and double-gated (DG) injection moulded blend of polybutylene terephthalate (PBT) and polycarbonate (PC) and its composites containing 15, 20 and 30 wt.% short glass fibres were investigated. In the DG mouldings, a weldline was formed by direct impingement of two opposing melt fronts (i.e. cold weld). It was found that tensile modulus was not affected by the weldline but flexural modulus decreased in the presence of weldline. For both specimen types, modulus increased linearly with volume fraction of fibres (ϕ _f), according to the rule-of-mixtures for moduli. The weldline integrity (WIF) factor for flexural modulus decreased linearly with increasing ϕ _f. Results showed that tensile and flexural strengths for SG mouldings increase with increasing ϕ _f in a linear manner according to the “rule-of-mixtures” for strengths. The presence of weldline affected both strengths in a significant way; WIF factor decreased linearly with increasing ϕ _f and was independent of loading mode. It was noted also, that the overall fibre efficiency parameter for tensile modulus was independent of specimen type but for flexural modulus it was lower in the case of DG mouldings. In all cases, efficiency parameter for strength was considerably lower than for the modulus. Impact strength and fracture toughness of SG mouldings were significantly greater than for DG mouldings. Although these properties for SG mouldings increased with increasing ϕ _f, they decreased significantly for DG mouldings. Results showed that WIF factor for impact strength and fracture toughness decreased linearly with increasing ϕ _f.     

Radioisotope generators of short-lived α-emitting radionuclides promising for use in nuclear medicine

α-Emitting radionuclides open unique possibilities for nuclear medicine owing to short range of α-particles and high linear energy transfer values. The use of radioactive generators is the simplest and the most efficient method for production of short-lived α-emitting radionuclides. The designs of radioisotope generators and generator systems used for repeated production of short-lived α-emitting radionuclides ²²⁵Ac, ²¹³Bi, ²¹¹Pb/²¹¹Bi, ²¹²Pb/²¹²Bi, ²²³Ra, and ²²⁴Ra, promising for targeted radiotherapy, are described in detail. Particular attention is paid to the methods for production and purification of short-lived α-emitting radionuclides and for their isolation in the form suitable for use in medicobiological studies. Other procedures for producing alternative α-emitting radionuclides (²¹¹At, ²²⁷Th, ²³⁰U, ²⁵³Es, ²⁵⁵Fm, ¹⁴⁹Tb) and possibilities of their use are also considered. The objectives and prospects of radiochemical studies in the field of production and isolation of α-emitting radionuclides meeting the requirements of nuclear medicine are discussed.     

Fully plastic J-integral solutions for surface cracked plates under biaxial loading

In this paper, surface cracked plates under biaxial tension are studied. Three-dimensional elastic-plastic finite element analyses have been carried out to calculate the J-integral for surface cracked plate for a wide range of geometry, biaxiality and material properties. Fully plastic J-integral solutions along the front of the surface cracks are presented for Ramberg-Osgood power law hardening material of n = 3, 5, 10 and 15. Geometries considered are a/c = 0.2, 1.0 and a/t = 0.2, 0.4, 0.6 and 0.8 and the biaxial ratios of 0, 0.5 and 1. Based on these results, the J-integral along the crack front for general elastic-plastic loading conditions can be estimated using the EPRI scheme. These solutions are suitable for fracture analyses for surface cracked plates under biaxial loading.     

Optical modelling of fluorine doped ZnO

A model for the complex dielectric function appropriate for use with fluorine doped ZnO transparent conductors has been developed. The model uses three components; a Drude term, a Lorentz oscillator, and a term accounting for inter-band transitions. It was used to generate the complex dielectric permittivity for ZnO:F, which in turn was used to fit experimentally determined optical transmission data for sputtered films. Use of this methodology to provide data for modelling the optical transmission through the window layer stacks of solar cell devices is commented upon. The experimentally determined Burstein-Moss shifts and carrier concentrations for a series of films were used to calculate a value of m_e = 0.33 ± 0.8 m₀ according to the model's assumptions.     

Correlation and prediction of dense fluid transport coefficients. I. n-alkanes

Recent accurate measurements of the self-diffusion coefficient for n-hexadecane and n-octane and of the viscosity coefficient for n-heptane, n-nonane, and n-undecane over wide pressure ranges have been used to provide a critical test of a previously described method, based on consideration of hard-sphere theory, for the correlation of transport coefficient data. It is found that changes are required to the universal curve for the reduced viscosity coefficient as a function of reduced volume and, also, to the parameters R _D, R , and R which were introduced to account for effects of nonspherical molecular shape. The scheme now accounts most satisfactorily for the self-diffusion, viscosity, and thermal conductivity coefficient data for all n-alkanes from methane to hexadecane at densities greater than the critical density.     

An improved technique for the solution of edge crack problem for finite plate

This paper provides a detailed examination for the edge crack problem of finite plate. The Williams expansion for the crack problem is used first. Secondly, the complex potentials for the central crack problem are used in the present study, which is called the improved technique hereafter. In both techniques, the eigenfunction expansion variational method (EEVM) is used for evaluating the undetermined coefficients in the expansion form. The ratio of height versus width of plate (h/w) is varying from 1.5, 1.0, 0.75, 0.5, 0.4, 0.3 to 0.25. The ratio of edge crack length versus width of plate (a/w) takes two sets: (1) a/w = 0.1, 0.2, … to 0.9, (2) a/w = 0.01, 0.02, … to 0.09. The detailed computation proves that for moderate cases of the a/w ratio, for example, 0.2 < a/w < 08, the deviations for SIFs and T-stress from two techniques are minor. However, for the case of short edge crack length, for example, a/w < 0.05, the deviations for SIFs and T-stress from two techniques are significant. It is found that the Williams expansion may not be suitable for the short edge crack, for example, a/w < 0.05.     

Annealing study of palladium–silver dental alloys: Vickers hardness measurements and SEM microstructural observations

Three Pd–Ag dental alloys for metal-ceramic restorations, W-1 (Ivoclar Vivadent), Rx 91 (Pentron) and Super Star (Heraeus Kulzer), were subjected to isothermal annealing for 0.5 hr periods in a nitrogen atmosphere at temperatures from approximately 400 ^∘ to 950 ^∘ C. The annealing behavior was investigated by Vickers hardness measurements (1 kg load) and SEM microstructural observations. The highest Vickers hardness occurred at approximately 700 ^∘ C for W-1 and 650 ^∘ C for Rx 91. For Super Star, there were two peaks in hardness at approximately 500 ^∘ and 650 ^∘ C. Additional use of light indenting loads (25 g for W-1; 10 g for Rx 91 and Super Star) revealed that hardness variations during annealing for W-1 and Rx 91 were related to the palladium solid solution matrix phase. For Super Star, the lower-temperature peak was controlled by multi-phase regions and the higher-temperature peak by the matrix phase. While microstructural changes due to annealing were evident with the SEM for Rx 91 and Super Star, no correlation was possible for W-1 because of its finer-scale microstructure. Although commercial Pd–Ag alloys have a relatively narrow composition range, their microstructures and annealing behavior can vary because of differences in proportions of secondary elements utilized for porcelain adherence and grain refinement elements, as well as other proprietary strategies employed by the manufacturers.     

Multistage homogenization process of aluminum alloy 2618

Single-, two-, and three-stage homogenization treatments of heat-resistant alloy 2618 were conducted in this study. Results reveal a low melting point Al₂CuMg phase and high melting point Al₂Cu phase in the as-cast aluminum alloy 2618. After single-stage homogenization at 495 °C for 10 h, the Al₂CuMg phase dissolves completely, but the Al₂Cu phase cannot be completely dissolved even once the homogenization time is prolonged to 18 h. After the alloy 2618 are homogenized using two stages: 495 °C for 10 h and 520 °C for 8 h, a portion of the Al₂Cu phase remains in the alloy. The Al₂Cu phase remains undissolved even after prolonged time. After the two-stage homogenization treatment at 495 °C for 10 h and 540 °C for 5 h, the high melting point Al₂Cu phase completely dissolves but overburn occurs. After the alloy 2618 are homogenized using three stages at 495 °C for 10 h, 520 °C for 5 h, and 540 °C for 3 h, the Al₂Cu phase completely dissolves and no overburn is detected. The three-stage homogenization treatment is an effective method for dissolving the high melting point Al₂Cu phase in the alloy 2618 and increasing their overburn temperature and solid solution temperature.     

An investigation of the edge-sliding mode in fracture mechanics

A boundary collocation procedure has been applied to the Williams stress function to determine the elastic stress distribution for the crack tip region of a finite, edge-cracked plate subjected to mode II loading at the crack tips. The asymmetric specimen selected was particularly suitable for the determination of plane strain fracture toughness for mode II loading. Numerical solutions for stress intensity factors for the edge-sliding mode obtained by the boundary collocation method were in close agreement with values obtained from photoelastic experiments.Fracture tests of several compact shear specimens of 2024-T4 aluminum were conducted in order to experimentally investigate the behavior of the edge-sliding mode. In each case a brittle shear failure was observed and mode II fracture toughness values were obtained. The average value for K_IIc obtained from two tests was 39.5 ksi(in)^{$\text{1}\text{2}$}. No K_Ic. data for 2024-T4 were available for comparison purposes; however, K_Ic values for a similar alloy, 2024-T351, have been reported as 34ksi(in)^{$\text{1}\text{2}$} which is only about 15 per cent below the corresponding K_IIc value.     

Magnetic Interaction Force and a Couple on a Superconducting Sphere in an Arbitrary Dipole Field

The calculation of the magnetostatic potential and levitation force due to a point magnetic dipole placed in front of a superconducting sphere in the Meissner state is readdressed. Closed-form analytical expression for the scalar potential function that yields the image system for an arbitrarily oriented magnetic dipole located in the vicinity of a superconducting sphere is given. Analytic expression for the lifting or levitation force acting on the sphere is extracted from the solution for a general dipole. A special case of our expression where the initial magnetic dipole makes an angle with the z-axis is derived. Our expression for the force in this particular case shows that a recently obtained result (J. Supercond. Nov. Magn. 21:93–96, 2008) for an arbitrary dipole is incorrect. A brief discussion of another erroneous result (J. Supercond. Nov. Magn. 15:257–262, 2002) for a transverse/tangential dipole–sphere configuration, corrected elsewhere recently, is reproduced. Correct expressions for the interaction energy with some limiting cases are also provided. The result derived here demonstrates that the value of the levitation force for a dipole that makes an angle with z-axis lies between the values for a radial dipole–sphere and transverse dipole–sphere configurations providing upper and lower bounds. It is found that for a magnetic dipole making an angle with z-axis, there exits a second force component along the negative y-direction, which influences a couple acting on the superconducting sphere. It is also shown that the couple is proportional to the second force component and that both the couple and second force components vanish for a radial dipole–sphere and transverse dipole–sphere configurations, respectively. These results appear to be new and have not had received due attention in the context of superconductivity.