Temperature dependences of Young’s modulus of biomorphic silicon carbide ceramics

Temperature dependences of the Young’s modulus E of wood-derived biomorphic SiC ceramics fabricated through pyrolysis of eucalyptus and oak with subsequent silicon infiltration were studied using electrostatic resonance excitation of longitudinal vibrations. The decrease in E with increasing temperature observed to occur in eucalyptus SiC in the temperature interval 20–1000°C was found to be accompanied by several jumps (splittings) in the resonance frequency, which persist after the sample is heated to 1000°C. The oak-SiC ceramic exhibits only one jump, which vanishes after heating to 1000°C. The observed anomalies are assigned to the presence of defects (including pores) in the materials studied.     

Hardness and elastic modulus of zircon as a function of heavy-particle irradiation dose: I. In situ α-decay event damage

Abstract

For a natural single crystal of zircon, ZrSiO₄, from Sri Lanka, exhibiting zonation in U and Th contents, the hardness and elastic modulus have been determined as a function of α-decay dose using a mechanical properties microprobe (MPM). The zones vary in thickness from one to hundreds of micrometers, and have uranium and thorium concentrations such that the α-decay dose varies between 2 × 10¹⁵ and 1 × 10¹⁶ α-decay events/mg (0.15 to 0.65 dpa, displacement per atom). The transition from the crystalline to the aperiodic metamict state occurs over this dose range. For a traverse of 75 indent pairs across layers sampling a large portion of the crystalline-to-metamict transition (3.7 × 10¹⁵ to 9.7 × 10¹⁵ α-decay events/mg) both the hardness and elastic modulus decrease linearly with increasing α-decay dose. The radiation-induced softening follows a behavior similar to other radiation-induced changes, that is with the expansion of the unit cell parameters there is a decrease in density, birefringence, hardness and bulk modulus.     

Shear modulus of shock-compressed LY12 aluminium up to melting point

Asymmetric plate impact experiments are conducted on LY12 aluminium alloy in a pressure range of 85-131 GPa. The longitudinal sound speeds axe obtained from the time-resolved particle speed profiles of the specimen measured with Velocity Interferometer System for Any Reflector （VISAR） technique, and they are shown to be good agreement with our previously reported data of this alloy in a pressure range of 20-70 GPa, and also with those of 2024 aluminium reported by McQueen. Using all of the longitudinal speeds and the corresponding bulk speeds calculated from the Gruneisen equation of state （EOS）, shear moduli of LY12 aluminium alloy are obtained. A comparison of the shear moduli in the solid phase region with those estimated from the Steinberg model demonstrate that the latter are systematically lower than the measurements. By re-analysing the pressure effect on the shear modulus, a modified equation is proposed, in which the pressure term of P/η^1/3 in the Steinberg model is replaced by a linear term. Good agreement between experiments and the modified equation is obtained, which implies that the shear modulus of LY12 aluminium varies linearly both with pressure and with temperature throughout the whole solid phase region. On the other hand, shear modulus of aluminium in a solid-liquid mixed phrase region decreases gradually and smoothly, a feature that is very different from the drastic dropping at the melting point under static conditions.     

Amplitude dependence of the internal friction and Young’s modulus defect of polycrystalline indium

The dependences of the internal friction and the Young’s modulus defect of polycrystalline indium on the oscillatory strain amplitude have been studied over a wide range of temperatures (7–320 K) and oscillatory strain amplitudes (10⁻⁷−3.5 × 10⁻⁴) at oscillatory loading frequencies of about 100 kHz. It has been revealed that the amplitude dependences of the internal friction and the Young’s modulus defect include stages associated with the interaction of dislocations with point defects and the interdislocation interaction. The temperature range characterized by the formation of point-defect atmospheres (the Cottrell atmospheres) near dislocations in indium has been determined.     

Blind equalization of underwater acoustic channelusing a combined constant modulus algorithm

A kind of Combined Constant Modulus Algorithm (CCMA) is presented to compensate the defects of the Constant Modulus Algorithm (CMA) and the Sign Error CMA (SECMA). And CCMA is applied to the equalization of the underwater acoustic channel (UWAC). Based on the decision of the equalizer‘s output, its iteration process switches between CMA and SECMA automatically. It is more robust than SECMA, and more computationally efficient than CMA. Therefore, it is very suitable for the recovery of the underwater data transmission. The performance of CCMA is proven by computer simulation for the equalization of the UWAC.     

The influence of defects on the effective Young’s modulus of a defective solid

It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method (FEM) and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.     

Confirmation of bulk modulus model of III–V compounds under pressure effect using tight-binding method

The electronic band structure for GaAs, GaSb and GaP is studied using semi-empirical tight-binding sp³s* method for tetrahedrally coordinated cubic materials. By means of our empirical model, the structural property of bulk modulus at critical transition pressure is calculated. Also, the GaAs, GaSb and GaP compounds are found to be indirect-gap semiconductors under pressure effect. The noticed behaviour of the bonding character reflects the structural phase transition. These results are in good agreement with experimental and theoretical data.     

Investigation on method for measuring dynamic shear modulus of underwater acoustic structure materials

1IfltroductionSince6o's,withthedevelopmentoflargemolecularmaterialsandcompositematerials,structurematerialsinunderwateracousticapplicationshavemadeagreatchanges.Forex-ample,thepropertiesofsonardomesthatmadefromreinforcedpolymersinsteadofstainlesssteelhavebeenimprovedobviously.Inordertodesignrationally,itisnecessaryforengineerstofindouttheiracousticpropertiescompletely.Accordingtotheelastictheories,twokindsofwave:longitudinalwaveandshearwavewillbeexcitedontheboundaryoftwomediumswhilethesoundsar…     

Experimental studies on the multistage constant modulus array for the estimation of directions-of-arrival

The performance of the multistage Constant Modulus (CM) array, one of the most striking blind beamforming algorithms, for the source Directions-of-Arrival (DOA) estimation was analyzed via computer simulations and water tank experiments, and was compared to that of other DOA estimation algorithms including the ‘non-blind‘ and the ‘blind‘. Firstly, a nominal array model and an array model with gain and phase perturbations were established,respectively. Secondly, the multistage CM array algorithm was described and computer simulations were conducted. Simulation results showed that the multistage CM array could correctly estimate the DOA at the same time when the sources were blindly recovered, and the angle separating ability of the algorithm was beyond the Rayleigh resolution limit. By changing the variance of the array model errors, it was also verified that the multistage CM array was more robust to the errors than some other algorithms mentioned in this paper. Finally, water tank experiments and data processing results were provided. Situations with different array sizes and source angular separations were considered. It was shown that the results were in good agreement with computer simulations. Results of computer simulations and water tank experiments verified that the DOAs of the multiple independent sources could be blindly and robustly estimated with the multistage CM array.     

The influence of grain size and texture on the Young's modulus of nanocrystalline nickel and nickel–iron alloys

Hardness and Young's modulus were measured by nanoindentation on a series of electrodeposited nanocrystalline nickel and nickel–iron alloys. Hardness values showed a transition from regular to inverse Hall–Petch behaviour, consistent with previous studies. There was no significant influence of grain size on the Young's modulus of nanocrystalline nickel and nickel–iron alloys with grain sizes greater than 20?nm. The Young's modulus values for nanocrystalline nickel and nickel–iron alloys for grain sizes less than 20?nm were slightly reduced when compared to their conventional (randomly oriented) polycrystalline counterparts. The observed trend with decreasing grain size was found to be consistent with composite model predictions that consider the influence of intercrystalline defects. However, there was some notable variability of the measured values when compared to the model predictions. Three theoretical relationships were used to characterise the anisotropic elastic behaviour of these materials. As a result, texture was also considered to have an influence on the measured Young's modulus and used to explain some of the observed variability for the entire grain size range (9.8–81?nm).     

Toward a theory of the third-order elastic modulus of crystals with A2 structure: The case of α-Fe

The third-order elastic modulus of α-Fe were calculated based on the computation of lattice sums. The lattice sums were determined using an integer rational basis of invariants composed by vectors connecting equilibrium atomic positions in the crystal lattice. Irreducible interactions within clusters consisting of atomic pairs and triplets were taken into account in performing the calculations. Comparison with experimental data showed that the potential can be written in the form of e₉ = - ?_i,k A₁₉ r_ik ^{- 6} + ?_i,k A₂₉ r_ik ^{- 12} + ?_i,k,l Q₉ I₉ ^{- 1}\varepsilon _9 = - \sum\nolimits_{i,k} {A_{19} r_{ik}^{ - 6} } + \sum\nolimits_{i,k} {A_{29} r_{ik}^{ - 12} + \sum\nolimits_{i,k,l} {Q_9 I_9^{ - 1} } }, where I₉ = [(r)\vec]_ik² [ ( [(r)\vec]_ik [(r)\vec]_kl )² + ( [(r)\vec]_li [(r)\vec]_ik )² ] + [(r)\vec]_kl² [ ( [(r)\vec]_ik [(r)\vec]_kl )² + ( [(r)\vec]_kl [(r)\vec]_li )² ] + [(r)\vec]_li² [ ( [(r)\vec]_li [(r)\vec]_ik )² + ( [(r)\vec]_kl [(r)\vec]_li )² ]I_9 = \vec r_{ik}^2 \left[ {\left( {\vec r_{ik} \vec r_{kl} } \right)^2 + \left( {\vec r_{li} \vec r_{ik} } \right)^2 } \right] + \vec r_{kl}^2 \left[ {\left( {\vec r_{ik} \vec r_{kl} } \right)^2 + \left( {\vec r_{kl} \vec r_{li} } \right)^2 } \right] + \vec r_{li}^2 \left[ {\left( {\vec r_{li} \vec r_{ik} } \right)^2 + \left( {\vec r_{kl} \vec r_{li} } \right)^2 } \right]. If the values of [(r)\vec]_ik\vec r_{ik} are scaled in half-lattice constant units, then A₁₉ = 1.22 ë t⁹ û GPa, A₂₉ = 5.07 ×10² ë t¹⁵ û GPa, Q₉ = 5.31 ë t⁹ û GPaA_{19} = 1.22\left\lfloor {\tau ^9 } \right\rfloor GPa, A_{29} = 5.07 \times 10^2 \left\lfloor {\tau ^{15} } \right\rfloor GPa, Q_9 = 5.31\left\lfloor {\tau ^9 } \right\rfloor GPa, and τ = 1.26 ?. It is shown that the condition of thermodynamic stability of a crystal requires that we allow for irreducible interactions in atom triplets in at least four coordination spheres. The analytical expressions for the lattice sums determining the contributions from irreducible interactions in the atom triplets to the second- and third-order elastic moduli of cubic crystals in the case of interactions determined by I ₉ are presented in the appendix.     

‘Factors of ignorance’ and the rationalized M.K.S.A. system of units

An attempt is made, by means of an allusive (rather than a systematic) historical account of the development of the subject, to exhibit the essentially unique character of the rationalized M.K.S.A. system of units. The establishment of this system involved one arbitrary decision—the determination to retain unaltered the size of the previously accepted unit of current. Thereafter, any choice of derived units, other than the choice actually made, would have destroyed the basic symmetry of the formulation.     

Young’s modulus and the Poisson’s ratio of planar and nanotubular supracrystalline structures

A method has been proposed for calculating the two-dimensional Young??s modulus and the Poisson??s ratio for planar and nanotubular structures through the components of the two-dimensional elastic rigidity tensor obtained by numerical methods. The method has been tested for graphene and two-dimensional supracrystalline sheets.     

Dynamic effective elastic modulus of polymer matrix composites with dense piezoelectric nano-fibers considering surface/interface effect

Based on effective field method,the dynamic effective elastic modulus of polymer matrix composites embedded with dense piezoelectric nano-fibers is obtained,and the interacting effect of piezoelectric surfaces/interfaces around the nano-fibers is considered.The multiple scattering effects of harmonic anti-plane shear waves between the piezoelectric nano-fibers with surface/interface are averaged by effective field method.To analyze the interacting results among the random nano-fibers,the problem of two typical piezoelectric nano-fibers is introduced by employing the addition theorem of Bessel functions.Through numerical calculations,the influence of the distance between the randomly distributed piezoelectric nano-fibers under different surface/interface parameters is analyzed.The effect of piezoelectric property of surface/interface on the effective shear modulus under different volume fractions is also examined.Comparison with the simplified cases is given to validate this dynamic electro-elastic model.     

List of Ya.A. Smorodinsky’s publications

A list of Ya. Smorodinsky’s articles published in science journals is presented. The text was submitted by the author in English.     

Characterization of Young’s modulus of silicon versus temperature using a “beam deflection” method with a four-point bending fixture

Young’s modulus (E) and Poisson’s ratio (ν) are dependent upon the direction on the silicon surface. In this work, E and ν of silicon have been calculated analytically for any crystallographic direction of silicon by using compliance coefficients (s₁₁, s₁₂, and s₄₄), and the values of E are confirmed experimentally by using a “beam deflection” method with a four-point bending fixture. Experimental results for E as a function of temperature from −150 °C to +150 °C are presented for (0 0 1) and (1 1 1) silicon wafers.     

N.M.R. spectra of the XnAA′ Xn′ type

The method described previously for the calculation of the X spectrum for spin systems of of the X_nAA′X_n′ type is extended by means of magnetic equivalence factoring to cases in which the long-range coupling constant J_x is non-zero. This coupling is treated as a first-order perturbation to the energy levels obtained when J_x =0, and it is found that J_x may be measured directly from the separations between easily identified lines in the spectrum. A detailed account of the X ₃ AA′X ₃′ system is given, and the N.M.R. spectrum of fluoro-N,N′-dimethyl-1,3,2,4-diazadiphosphetidine is analysed. The spectral parameters obtained are discussed. A computer programme which calculates the spectra of systems involving magnetic equivalence is used to examine the validity of the approximations in the method.     

Free radicals in pyrimidines: E.S.R. of a γ-irradiated single crystal of 5-nitrouracil

Free radicals are observed in γ-irradiated single crystals of 5-nitrouracil with the unpaired electron showing hyperfine interaction with one nitrogen atom. The principal values of hyperfine coupling are A_x = 22·5 g, A_y = 25·2 g, and A_z = 40·0 g, and the principal values of the spectroscopic splitting factor are g_u = 2·0117, g_v = 2·0064 and g_w = 2·0027. The relationship of the directions of the corresponding principal axes to the molecular orientations show that the unpaired electron must be located in an sp ² orbital on either N₍₁₎ or N₍₅₎. Considerations of the mechanism of radical formation and comparison to radiation damage in other molecules make the N₍₁₎ location seem more probable. The π interaction of the nitro group on C₍₅₎ evidently prevents the formulation of free radicals with the unpaired electron on C₍₅₎. That carbon atom is the most common location of unpaired electron density in other pyrimidine free radicals.     

Second‐Order Dispersion Forces. I. Equations of Motion

Equations of motion for polarization on the S–P atomic transition in a weak resonance field have been derived taking into account the Van der Waals interaction between atoms. The case of two atoms is considered within the Wigner–Weisskopf formalism and generalized to the case of identical atoms in a weak resonance field, where the saturation is negligible. It is found that two equations of motion are necessary: one of them for the polarization and another one for an effective polarization relaxation rate.     

Digital discrimination of neutron and γ ray using an organic scintillation detector based on wavelet transform modulus maximum

A novel algorithm for the discrimination of neutron and γ -ray events with wavelet transform modulus maximum (WTMM) in an organic scintillation has been investigated. Voltage pulses arising from a BC501A organic liquid scintillation detector in a mixed radiation field have been recorded with a fast digital sampling oscilloscope. The WTMM method using frequency-domain features exhibits a strong insensitivity to noise and can be used to discriminate neutron and γ -ray events based on their different asymptotic decay trend between the positive modulus maximum curve and the negative modulus maximum curve in the scale-space plane. This technique has been verified by the corresponding mixed-field data assessed by the time-of-flight (TOF) method and the charge comparison (CC) method. It is shown that the characterization of neutron and γ ray achieved by the discrimination method based on WTMM is consistent with that afforded by the TOF method and better than the CC method. Moreover, the WTMM method itself has presented its ability to eliminate the noise without any pretreatment to the pulses.