Effect of moisture absorption on damping performance and dynamic stiffness of NY-6/CF commingled yarn composite

The damping performance of a unidirectional (0 °) nylon 6-carbon fibre (NY-6/CF) commingled yarn composite was experimentally studied with special concern for the effect of moisture absorption. Dried specimens were immersed in distilled water for a certain time to allow water to diffuse into the material. The damping measurements were conducted on double-cantilever and cantilever beam specimens using sinusoidal and impact-hammering techniques. The damping loss factor , flexural dynamic stiffness E and loss modulus E were evaluated as a function of the moisture content up to 8.2 wt %. and E initially increased significantly with increasing moisture content up to 5–6%. Further increase of the moisture content up to 8.2% caused a slight reduction in damping ability. The reverse was true of E although the variation amplitude was smaller. The moisture content dependency of the damping performance obtained is discussed.On leave from Tashkent Technical University (Uzbekistan) as a postdoctoral research fellow of the Japan Society for the Promotion of Science.     

Fluidity of mica particle dispersed aluminium alloy

Cast aluminium alloy-mica particle composites were made by dispersing mica particles in a vortex produced by stirring the liquid Al-4 wt% Cu-1.5 wt% Mg alloy and then casting the melt containing the suspended particles into permanent moulds. Spiral fluidity and casting fluidity of the alloy containing mica particles in suspension were determined. Both the spiral fluidity and the casting fluidity of the base alloy were found to decrease with an increase in volume or weight percent of mica particles (of a given size), and with a decrease in particle size (for a given amount of particles). The fluidities of Al-4 wt% Cu-1.5 wt% Mg alloys containing suspended mica particles were found to correlate very well with the surface area of suspended mica particles. The regression equation for spiral fluidity Y (cm) as a function of surface area of mica particles per gram of spiral X (cm² g^–1) at 700° C was found to be Y=42.62–0.42X with a correlation coefficient of 0.9634. The regression equations for casting fluidity Y (cm) as a functiono of surface area of mica particles per gram of fluidity test piece X (cm² g^–1) at 710 and 670° C were found to be Y=19.71–0.17X and Y=13.52–0.105X with correlation coefficients of 0.9194 and 0.9612 respectively. The percentage decrease in casting fluidity of composite melts containing up to 2.5 wt% mica with a drop in temperature is quite similar to the corresponding decrease in the casting fluidity of base alloy melts (without mica). The change in fluidity due to mica dispersions has been discussed in terms of changes in viscosity of the composite melts. However, the fluidities of these composite alloys containing up to 2.5 wt% mica are adequate for making a variety of simple castings including bearings for which these alloys have been developed.     

Characterization of commercial soft liners by dynamic mechanical analysis

Although there is a significant clinical interest in suitable polymer-based soft liners, none have proven fully satisfactory in actual use. As a result there has been continued interest in the development of new materials. One major weakness in the development of improved materials has been the lack of clear understanding of structure/property relationships. This paper deals with the determination of visco-elastic properties such as E (Storage modulus) and tan (damping factor) of four commercial materials. They represent the broad range of chemical types available for denture base soft liners. A DMA study of four materials: (1) Molloplast B (silicone); (2) Novus (phosphazine); (3) Kurepeet (fluropolymer); and (4) Super Soft (acrylic) was made using a Perkin-Elmer DMA-7. Samples were made following the manufacturers' instructions, in the form of sheets 1.5 mm thick and 15.0 mm square. The samples were tested compressively using a 3 mm flat tip probe cycled at a frequency of 1 Hz. Wet and dry specimens were evaluated for E and tan over a 5–95°C temperature range. Water sorption was determined gravimetrically at 37°C. Changes in E between the wet and dry conditions for Molloplast (B), Kurepeet and Super Soft were insignificant. A significant increase in tan for wet Novus was observed, suggesting that the material is capable of dissipating more energy. The wet modulus (E) is about 42% lower than the dry modulus (E). This difference may be attributed to the very high water sorption (34%) of Novus. i.e. the significant decrease in E indicates plasticization due to sorbed water. Changes in visco-elastic properties seem to occur for materials which take up large amounts of water at 37°C. DMA is found to be a useful supplement for the evaluation of soft lining materials in conjunction with the standard mechanical test methods.     

Viscoelastic properties of composites of calcium alginate and hydroxyapatite

Calcium alginate was reinforced with hydroxyapatite (HA) particles, whose dimensions were a few micrometres, with mass fraction, m _f, values in the range 0–0.8. Cylindrical samples of these composite materials were subjected to cyclic compression in the frequency range f = 0.001–20 Hz; in these tests a sinusoidal load of amplitude 1 N was applied either side of a static compression of 2 N. Storage and loss moduli, E′ and E′′, respectively, were found to be independent of particle size; however, E′ increased with frequency consistent with the materials undergoing a glass transition. Above frequencies of about 0.05 Hz, for all materials. For each frequency, the dependence of the moduli on log₁₀ f could be represented by a third order polynomial; these equations can be used to calculate E′ and E′′ for a range of compositions. Approximate values of are predicted by a Reuss model.     

Coarsening of precipitates and dispersoids in aluminium alloy matrices: a consolidation of the available experimental data

Experimental data on the coarsening of precipitates and dispersoids in aluminium-based matrices are reviewed. Available data are tabulated as K=(r ³–r ₀ ³ )/t where r ₀ is the initial particle radius and r is its value after time t at temperature T, and then plotted as log (KT) against 1/T for consolidation and assessment. The considerable body of data for -A₃Li in Li-containing alloys is well represented by K=(K ₀/T) exp (–Q/RT) with K ₀=(1.3 _–0.5 ^+3.0 ) × 10^–13m³Ks^–1 and Q=115±4kJ mol^–1. The relatively limited data for and in Cucontaining alloys are representable by the same relationship with K ₀4 × 10^–8 and — 4 × 10^–10 m³ Ks^–1, respectively, and Q — 140 kJ mol^–1. Available data for coarsening of L1₂ ^– Al₃(Zr, V) and related phases in Zr-containing alloys and of Al₁₂Fe₃Si and related phases in Al-Fe based alloys indicate (i) rates of coarsening at 375 to 475 °C (0.7 to 0.8T_m) five to eight orders of magnitude less than would be expected for , and in this temperature range, and (ii) high activation energies of 300 and 180 kJ mol^–1, respectively.     

Experimental determination of dynamic Young's modulus and mechanical damping,and theoretical prediction of dislocation density for depleted uranium-0.75 wt% titanium using the PUCOT

Dynamic Young's modulus (E) and mechanical damping (Q ^–1) measurements were made for three microstructures (, + , and ) of a depleted uranium-0.75 wt% titanium alloy. The temperature range covered was 298 to 1123 K. The apparatus was the piezoelectric ultrasonic composite oscillator technique (PUCOT) operated at 80 kHz. The ranges of values for E and Q ^–1 were 193 to 99 GPa and 3×10^–3 to 8×10^–2, respectively. Correlations for E of each heat treatment as functions of temperature are presented. In addition, the mechanical damping against strain amplitude plots generated from PUCOT data were analysed using the Granato-Luecke zero Kelvin and high-temperature theories of dislocation damping. Computed dislocation densities ranged up to 10¹⁶m^–2.     

γ′ particle coarsening and yield in Alloy 800

The age strengthening of Alloy 800 by ordered particles of-Ni₃(Al, Ti) phase has been studied by using both transmission electron microscopy and room-temperature tensile tests on aged specimens. The samples have been aged in the temperature range 525 to 650° C up to a maximum time of 10⁴ h. Two groups of samples with different Ti/Al ratios have been investigated in order to obtain more reliable information on the role played by these alloying elements on the age-hardening behaviour. The linear dimension increases with time,t, ast ^1/3 and an activation energy of 70.0 kcal mol^–1 was derived from the temperature dependence of the coarsening rate. The particle volume-fraction, as measured by electron microscopy, has been found to remain constant on ageing in the temperature range 525 to 600° C. The increase in the critical shear stress due to the particles is found to agree quantitatively with the equations of Brown and Ham which describe hardening by ordered particles. Antiphase boundary energies of 227 and 279 mJ m^–2 have been measured, respectively, for the two groups of samples investigated.     

Piecewise polynomials and the partition method for nonlinear ordinary differential equations

Summary An efficient numerical method, used previously for linear differential equations [1], is here extended to systems of nonlinear ordinary differential equations. Spline functions are used as the basic approximations. Residuals are liquidated by setting their integrals equal to zero over specified subintervals of the intervals of analyticity. Several diverse examples are given.Notation a Radius of circular membrane - [C _j ] An unsymmetrical 4×4 matrix, defined by Eq. (6) - [C _j ] An unsymmetrical 6×6 matrix, defined by Eq. (8) - E Young's modulus - F _i Algebraic or transcendental functions - L Differential operator - R Closed interval - T Dimensionless radius stress for the circular membrane - [Y _j ] The transpose of the row matrix [y _j –1,y _j –1,y _j ,y _j ] - [Y _j ] The transpose of the row matrix [y _j –1,y _j –1,y _j–1 ,y _j ,y _j ,y _j ] - Residual - Poisson's ratio Formerly with Department of Theoretical and Applied Mechanics, University of Illinois, Urbana, Illinois, USA.     

The Static Dielectric Constant of Liquid Water Between 274 and 418 K Near the Saturated Vapor Pressure

The complex dielectric constant (relative electric permittivity) of liquid water was redetermined in the temperature range 0°C<;t<145°C at pressures less than 440 kPa. In this work, _r was deduced from measurements of the resonant frequencies f of a novel, re-entrant, two-mode, radio-frequency resonator. The frequencies ranged from 23 to 84 MHz and were well within the low-frequency limit for because (2f _max)²<5×10^–5 where _max=1.8×10^–11 s is the maximum relaxation time of water under the conditions studied. The data for for two water samples differing in conductivity by a factor of 3.6 and for the two resonant modes differing in frequency by a factor of 2.6 were simultaneously fit by the polynomial function (t)=87.9144–0.404399t+9.58726×10^–4 t ²–1.32802×10^–6 t ³ with a remarkably small residual standard deviation of 0.0055. The present data are consistent with previously published data; however, they are more precise and internally consistent. The present apparatus was also tested with cyclohexane and yielded the values (t)=2.0551–0.00156t for 20°C<t<30°C, in excellent agreement with previously published values.     

In situ production and defect characterization of laser PVD layers from YBaCuO HTSC targets inside a scanning electron microscope

In situ generation and defect characterization of YBa₂Cu₃O_7–x layers are carried out inside a scanning electron microscope (SEM) to investigate the process of pulsed laser PVD. A Nd-glass laser with a wavelength =1.06 µm and an energy densityE<200 MJ m^–2 was combined with a SEM and used for experiments. By the irradiation of a YBa₂Cu₃O_7–x target the laser PVD process and the deposition on Si substrates were originated. At high pulse energies and/or long laser pulses heating and evaporation processes of target material dominated. For laser irradiation without Q-switch (=10 ms) the defect particles incorporated into laser PVD layers were mainly big droplets originated from the liquid phase. Otherwise, for very short pulses (Q-switch mode) the layer defects were also particles of irregular size generated by material ablation on the target surface. In contrast to the droplets these irregular particles and also the layer itself showed the same stoichiometry as the target. Both the particle density and the layer thickness showed the same plane distribution function. Therefore the particle density in the plasma seemed to possess the same solid angle distribution as the plasma itself.     

Lead zinc niobate pyrochlore: Structure and dielectric properties

In Pb(B _x B_1–x )O₃ ceramic compositions, it is customary to find a mixture of cubic pyrochlore and perovskite phases after calcination. Based on X-ray diffraction analysis, we concluded that both phases are made up of the same structural unit of BO₆ octahedra. The B and B ions occupy the B sites randomly to the extent that local charge equilibrium is maintained. Thus a general formula for the pyrochlore phase can be expressed as Pb(B _x B_1–x )O₃ · O_p where O p 0.5. An extensive study of the Pb(Zn _x Nb_1–x )O_3.5–1.5x pyrochlore system was made by varying the zinc concentration. We interpret changes in the X-ray diffraction pattern and the lattice constant as indicative of the changing occupancy of the seventh oxygen sites in order to maintain local charge balance. The best combination of the dielectric properties, with a dielectric constant of130 and a factor greater than 1000 at10 MHz, is achieved at a composition of 0.3 x 0.4 and a sintering temperature of 980° C. The temperature coefficient of the dielectric constant measures –0.75 × 10^–3° C^–1. It decreases to –0.54 × 10^–3° C^–1 when5 mol% of PbTiO₃ was mixed with the nominal pyrochlore compositions and sintered. Thus, it may be possible to effect a larger change in the temperature coefficient by judiciously including selective amounts of a second phase which has the best compensating temperature coefficient.     

High-field electrical conduction in m Hgl2

The electrical and dielectric properties of illuminated Hgl₂ were studied at room temperature under various a.c.-signal amplitudes in the frequency range 1 Hz to 10 kHz. Below 40 H, We real part of the dielectric constant, ,was found to vag slightly with voltege for low electric fields (E < 10³V cm^–1, above which it showed a steady increase with the applied voltage. At higher frequencies, no voltage dependence of (or the geometrical capacitance) of the crystal was observed. On the other hand, the imaginary part of the dielectric constant, or the a.c. conductivity, (=_o) was found to decrease considerably with the applied voltage forE < 10³V cm^–1 at all frequencies. For higher fields (E > 10³V cm^–1), exp [C(E/)^1/2], whereC is e constant. Above 40 Hz, this variation was in good agreement with the behaviour of the bulk, resistance of the crystal. Such behaviour is discussed in the view of Richardnon-Schottky and Poole-Frenkel conduction mechanisms, which seem to be operative in Hgl₂ at room temperature.     

Influence of rhenium on the microstructures and mechanical properties of a mechanically alloyed oxide dispersion-strengthened nickel-base superalloy

The influence of a 3 wt% Re addition on the creep strength and microstructure of a mechanically alloyed and oxide dispersion-strengthened nickel-base superalloy was investigated. Two alloys, Ni–8Cr–6.5Al–6W–3Ta–1.5Mo–6Co–1Ti–3Re–0.15Zr–0.05C–0.01B–0.9Y₂O₃ (3Re alloy) and a non-rhenium containing (0Re) alloy were prepared for this study.The 3Re alloy showed two-fold improvement in creep life compared with that of 0Re alloy, presumably due to a change in the mode of the precipitate-dislocation interaction. For the 3Re alloy, finer, more cuboidal and aligned precipitates are formed, which force the mobile dislocations at the – interfaces to cut precipitates in order to proceed. Shearing of precipitates is evinced by the existence of stacking faults and results in an increase of creep strength. In constrast, lower creep strength was observed for 0Re alloy because a dislocation looping mode is dominant with coarser and more irregularly shaped precipitates present in this alloy. Another possible explanation for an improved creep strength of 3Re alloy is related to the tangled dislocation structure formed by the interaction between glide dislocation and interfacial dislocation, which also acts as an effective barrier for further glide dislocation motion. A 3 wt% Re addition significantly retards coarsening kinetics. Rhenium acts as a rate-controlling species upon the volume diffusion-controlled coarsening process because it is a heavy elemenet and also it almost solely partitions to the matrix. X-ray diffraction experiments showed that the magnitude of the lattice mismatch between and increased with the 3 wt% Re addition from 0% to –0.26% at room temperature. Increased lattice mismatch for 3Re alloy causes the formation of more aligned and cuboidal precipitates rather than random and odd-shaped precipitates for 0Re alloy, and it also accelerates the coalescence between cuboidal precipitates.     

Surface tension of liquid3He and4He near the liquid-gas critical point

The surface tension of liquid³He and⁴He was measured near the gas-liquid critical points in the reduced temperature range 3×10^–4–1, where t (T _c –T)/T _c . The critical exponents were found to be ₃=1.289±0.015 for³He and ₄=1.306±0.017 for⁴He. These values are very close to those for classical liquids, and are consistent with the value of 1.28 predicted by Widom, but are apparently different from the exponents previously obtained for liquid helium isotopes, which are near unity. The critical coefficients show good agreement with the quantum-corrected corresponding states theory for the Lennard-Jones 6–12 potential discussed by Young. The interface thickness is deduced from Widom's theory to bed=d ₀t^–v withd ₃₀=0.14±0.03nm and v₃=0.57±0.04 for³He, andd ₄₀=0.37±0.07 nm and v₄=0.58±0.01 for⁴He.     

Microsegration and homogenization of Ni-7.5wt%Al-2.0wt%Ta dendritic monocrystals

Dendritic monocrystals of nickel-7.5 wt% aluminium-2.0 wt% tantalum alloy were solidified at growth rates of 0.05 and 0.25 m h^–1, under average thermal gradients of 6×10³ and 16×10³ Km^–1. The segregation ratios of aluminium and tantalum were found to depend on growth conditions. That of aluminium increases only slightly with increasing local cooling rate, whereas that of tantalum increases more substantially. A diffusion model was introduced to analyse homogenization kinetics. Predictions of the index of residual segregation were in reasonable agreement with experimental measurements. Aluminium homogenizes much faster than tantalum during an isothermal treatment. It also homogenizes appreciably during crystal pulling.In the as-cast material, the particle size is finer at locations that are poorer in aluminium and tantalum and coarser at locations that are richer in these two metals. Following a homogenization treatment, the particle size distribution becomes more uniform.     

The dielectric properties of alumina substrates for microelectronic packaging

The dielectric characterization of alumina substrate materials used in high-performance microelectronic packaging is described. These materials included both pure and impure polycrystalline substrates and, as a reference standard, pure and chromium-doped single crystals of alumina. For each material the permittivity () and dielectric loss () has been measured over a frequency range of 0.5 kHz to 10 MHz, at room temperature, and correlated with the structure and composition as determined by supplementary techniques. At room temperature the pure substrates show the frequency independence of both and , characteristic of pure single-crystal material. The permittivity (= 10.1) agrees closely with the average of the anisotropic values for the single crystal but the dielectric loss is an order of magnitude higher than in the single crystal, giving tan 1.5 × 10^–3. The impure substrates compared with the pure, show a small increase in and a marked, frequency-dependent increase in dielectric loss. Measurements have also been made in both the high- and low-temperature ranges (i.e. 20 to 600 ° C and 77 to 293 K, respectively) in order to establish the variation of permittivity with temperature and frequency. At temperatures below 200 °C the temperature coefficient of permittivity, [( –1)( + 2)]^–1 (/T) _p is about 9 × 10^–6 K^–1 for the pure materials but this increases rapidly with impurity addition.     

Microstructural characterization of CO2 laser welds in the Al-Li based alloy 8090

The microstructural development of the Al-Li-Cu-Mg-Zr alloy 8090 has been studied after autogenous CO₂ laser welding. Sheets ranging in thickness from 1–4 mm were welded at speeds of between 20–120 mm s^–1 and powers from 1.5–3.8 kW. Optical microscopy, scanning and transmission electron microscopy were used to study the as-received base metal, the heat-affected zone and the solidified fusion zone. The base metal was supplied in a superplastically formable condition and thus had an unrecrystallized grain structure containing 1–2 m sized sub-grains with sub-micrometre and precipitates in the matrix. In the fusion zone, the as-solidified grain structure was columnar at the interface with the base metal but became equiaxed in the central region of the weld pool. The weld depth and top bead width both increased with decreasing welding speed and increasing beam power within the limits investigated. The fusion zone microstructure was cellular-dendritic. Intermetallic precipitates, which are rich in copper, magnesium, silicon (and presumably lithium), formed in the cell/dendrite boundaries. Very fine-scale precipitates were present in the as-solidified -Al matrix but there was no evidence for the , S and T₁ phases. The heat-affected zone was only 100 m wide and was characterized by regions of partial melting. Radiographs of welds reveal that porosity occurred predominantly along the weld centre-line. In partial penetration welds, two types of pores were observed: near spherical and irregular. However, in fully penetrating welds, only the spherical type of porosity was present. Overall volume fractions of porosity were measured from metallographic sections and were found to vary with welding speed and weld type, i.e. partial or full penetration.     

Magnetic measurements of the reverse martensite to austenite transformation in a rolled austenitic stainless steel

The reverse (-) transformation in 304 stainless steel (SS) has been studied by magnetic measurements. Specimens rolled 15 to 55% reduction in thickness were annealed at various temperatures and times. After annealing at temperatures between 300–;600°C for 5 min the saturation magnetization values increased when compared to the saturation magnetization values after rolling. Specimens rolled to 40 to 55% reduction after annealing at 500°C showed the highest saturation magnetization. Saturation magnetization sharply decreases at annealing temperature above 625°C which indicates the start of reverse (-) transformation. The decrease in saturation magnetization is rapid for annealing time from 5 to 40 min, whereas, the decrease in saturation magnetization is relatively low for annealing time above 40 min. The hardness values after reverse (-) transformation at temperatures between 300–;600°C is slightly greater attributed to the increase in martensite and above this temperature the hardness dropped substantially as a result of recovery and recrystallization. The results show that there is a decrease in coercive force at temperatures between 300–;500°C and may be due to an increase in martensite phase. A further decrease in coercive force at temperature between 500 and 625°C may be attributed to the sweeping out of some dislocation from the martensite phase. This is followed by a sharp increase in coercive force at temperature up to 800°C and is attributed to a shape magnetic anisotropy effect. At temperatures between 800–;900°C a rapid decreased in coercive force occurs. At temperatures between 900–;1100°C the decrease in coercive force is not so sharp dominant. The decrease in coercive force above 800°C corresponds to softening of the stainless steel due to recrystallization. From the changes in the values of saturation magnetization the A _s temperature is estimated to be between 625–;650°C, and the A _f to be between 900–;950°C.     

Photoluminescence of Eu3+-activated GdTaO4 with both M type and M′ type structures

A series of Eu³⁺ doped M and M type gadolinium orthotantalate Gd_{1– x}Eu_xTaO₄ (x = 0–0.20) have been synthesized by high temperature solid state reaction. The emission and excitation spectra for M and M type gadolinium orthotantalate are studied in detail. The structural difference between M and M type structure obviously influences their luminescence properties. The main excitation bands in M type Gd_{1– x}Eu_xTaO₄ shift to shorter wavelength because of a shorter distance of Ta-O in comparison with M type. The strong evidence from excitation spectra, emission spectra and diffusive reflection spectra of these two system show Gd³⁺ can play an intermediate role of energy transfer in the process of luminescence. There is energy transfer from TaO₄ ^3– to Gd³⁺ and finally to Eu³⁺ via the charge transfer states and spectral overlap.     

The relationship between the mean dopant-ion radii and conductivity of co-doped ZnO systems, Zn1−x−y M x M′ y O (M, M′ = Al, In, Ga, Y)

The conductivities of the Zn_1–x–y M _x M _y O (M, M = Al, In, Ga, Y) and Zn_1–x M _x O (M = Al, In, Ga) systems were measured from room temperature to 1173 K in order to elucidate a dominant parameter of the conducting mechanism. The conductivity at 873 K first increased with the dopant content. However, it showed a maximum value at a given dopant content, and then gradually decreased. For the samples with the same dopant content, their conductivity at 873 K was strongly dependent on the mean dopant-ion radii, and reached a maximum value at around 0.51 Å of the mean dopant-ion radii. The results suggested that the conductivity of the system would be influenced not only by the dopant content, but also by the mean dopant-ion radii. It was found that the co-doped ZnO system of Zn_0.995Al_0.003In_0.003O had a conductivity higher than that of the other usual mono-doped system.