Variation of the yield stress and latent strain energy in the course of plastic deformation of a neutron-irradiated chromium-nickel steel

The laws of variation of the flow stress (σ) and latent strain energy (E_s) in the course of plastic deformation have been studied in the samples of a titanium-doped chromium-nickel steel (12Kh18N10T grade) before and after neutron irradiation to a dose of 5×10²²m^?2 (neutron energy E>0.1 MeV). The E_s versus σ curve can be divided into several characteristic regions, the first of which is described by a relation of the type E_s～E₀+kσ² (E₀ and k being certain coefficients). It is established that neutron irradiation shifts the E_s versus σ curve toward smaller latent energies.     

Mixed-Mode Crack Propagation in Cruciform Joint using Franc2D

The focus of this research was on determining the cracking behavior when parameter such as the biaxiality ratio was varied. The crack propagation under mixed-mode loading was simulated by means of finite element method. The stress intensity factors have been calculated by the linear elastic fracture mechanics approach using fracture analysis code-2D (Franc2D). The crack growth under opening mode-I was considered because the crack growth occurs mainly along the direction where the mode-I stress component becomes the maximum. The numerical integration of Paris’ equation was carried out. The effect of normal and transverse applied load (σ _x, and σ _y, respectively) on crack propagation was presented. It was found that the fatigue crack growth was faster at a smaller biaxial stress ratio (λ), i.e., higher σ _y on the horizontal crack plan. Moreover, fatigue strength values decrease as λ decreases. The results confirm the use of fracture mechanics approach in biaxial fracture.     

The surface energy of cryocrystals

An expression for the surface energy σ₀₀ of a crystal at T = 0 and P = 0 is obtained with allowance for the zero-point vibrations of atoms in the crystal. Particular calculations are performed for the cryocrystals of inert gases and hydrogen isotopes, in which the energy of zero-point vibrations is comparable with the energy of interatomic interactions. It is established that σ₀₀ exhibits highly correlated dependences of the same kind on the atomic (molecular) mass m, the melting temperature T_m, and the interatomic interaction potential D/k_B (k_B is the Boltzmann constant), whereby the function σ₀₀(m, T_m, D/k_B) exhibits nonlinear growth with each argument. The ratio σ₀₀/σ_liquid, where σ_liquid is the surface tension of the liquid phase at T = T_m, also exhibits highly correlated dependences on m, T_m, and D/k_B, which can be divided into two parts of linear growth corresponding to the quantum and classical domains. The σ₀₀/σ_liquid ratio, being smaller in the quantum case than in the classical one, grows with m, T_m, and D/k_B much faster in the quantum than in the classical domain.     

A dimensionless criterion of dispersion for crystalline solids

A dimensionless criterion of dispersion for crystalline solids is proposed based on a comparison of the excess free energy in the compact and disperse state: D_L=12σ/Gb²pL, where σ is the surface energy, G is the shear modulus, b is the Burgers vector, p is the dislocation density, and L is the particle size. According to this, the critical size of particles corresponding to D_L=1 is approximately the same (L₁=500 nm) for all metals. Classification of disperse crystalline solids with respect to the parameter D_L is more justified thermodynamically than characterization by the particle size.     

Triaxial compression tests of QH-E lunar soil simulant under constant mean principal stress path using discrete element method simulations

In this paper, discrete element method (DEM) simulations are applied to investigate the triaxial compression tests of QH-E lunar soil simulant (developed by Tsinghua University, China) under constant mean principal (P) stress path. The P stress path is achieved by controlling the loading speed and direction of the axial stress and confining stress in the DEM simulations, the strain softening and dilatancy characteristics of QH-E lunar soil simulant both at low and conventional P stress levels are discussed. The results show that the deviatoric stress–strain curve is divided into hardening, softening descending, and residual strain stages, and the shear strength and residual strength increase with the increase of P stress, which are similar to the conventional triaxial compression tests. The volumetric strain versus shear strain curve shows a good linear relationship both at the linear shear dilatancy and residual shear dilatancy stages, but the slope of the linear dilatancy stage is larger than that of the residual dilatancy stage. Furthermore, it is found that the variations of shear dilatancy characteristic parameters with regard to P stress also show a good linear relationship, and the values of these parameters increase with the increase of P stress.     

Quadrature frequency resolved spectroscopy of upconversion photoluminescence in GeGaS:Er<Superscript>3+</Superscript>: I. Determination of energy transfer upconversion parameter

The article presents the formulas of quadrature frequency resolved spectroscopy (QFRS) on the upconversion photoluminescence (UCPL) of rare-earth (RE) doped materials on the general M-level model. The formulas are derived in matrix-equation form with the first-order perturbation on the rate equations at the M energy-levels of RE ion. The QFRS spectra for three different UCPL processes, i.e., the excited state absorption (ESA), energy transfer upconversion (ETU) and photon avalanche (PA) via cross relaxation process (CRP) in a particular case of M?=?3 are demonstrated with the respective salient features of the excitation power dependence. We have measured the QFRS on the UCPL (⁴ S _3/2 → ⁴ I _15/2) by systematically varying Er-doping in Ge_28.1Ga_6.3S_65.6 chalcogenide glass from 0.01 to 0.5 at.% as well as 975 nm excitation power. Thereby the relaxation rates k ₁ at the intermediate level ⁴ I _11/2, k ₂ at the top level ⁴ S _3/2 and ETU parameter w are determined as a function of Er concentration. The UCPL dynamics on the basis of the formulas for the 3-level model is interpreted in terms of the determined parameters.     

A new niobate-based CaO–2CuO–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> microwave dielectric ceramic composite for LTCC applications

A novel CaO–2CuO–Nb₂O₅ (CCN) ceramic composite was prepared by the solid-state reaction method in the temperature range of 810–890 °C. Typically, the CCN sintered at 870 °C exhibited the excellent microwave properties of ε _r ?=?15.7, Q?×?f?=?28,700 GHz, τ _f = ? 38.4 ppm/°C. The τ _f of CCN was turned to be near zero by adding TiO₂, while the ε _r increased slightly and the Q?×?f decreased. The 0.91CCN–0.09TiO₂ ceramic sintered at 920 °C showed modified properties of ε _r ?=?16.9, Q?×?f?=?21,500 GHz, τ _f = ? 1.6 ppm/°C, which shows potential in LTCC applications.     

Strongly consistent model selection for densities

Let f be an unknown multivariate density belonging to a set of densities \(\mathcal{F}_{k^{*}}\) of finite associated Vapnik–Chervonenkis dimension, where the complexity k ^* is unknown, and ? _k ?? _k+1 for all k. Given an i.i.d. sample of size n drawn from f, this article presents a density estimate \(\hat{f}_{K_{n}}\) yielding almost sure convergence of the estimated complexity K _n to the true but unknown k ^* and with the property \(\mathbf{E}\{\int|\hat{f}_{K_{n}}-f|\}=\mbox{O}(1/\sqrt{n}\,)\). The methodology is inspired by the combinatorial tools developed in Devroye and Lugosi (Combinatorial methods in density estimation. Springer, New York, 2001) and it includes a wide range of density models, such as mixture models and exponential families.     

Structural relaxation and electrical conductivity of molybdovanadate glass

⁵⁷Fe Mössbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe₂O₃·70V₂O₅ (in mol%) showed paramagnetic doublet peak due to distorted Fe^IIIO₄ tetrahedra with isomer shift (δ) value of 0.37 (±?0.01) mm s^?1. Mössbauer spectra of 20BaO·10Fe₂O₃·xMoO₃·(70???x)V₂O₅ glasses (x?=?20–50) showed paramagnetic doublet peaks due to distorted Fe^IIIO₆ octahedra with δ’s of 0.40–0.41 (±?0.01) mm s^?1. These results evidently show a composition-dependent change of the 3D-skeleton structure from “vanadate glass” phase, composed of distorted VO₄ tetrahedra and VO₅ pyramids, to “molybdate glass” composed of distorted MoO₆ octahedra. After isothermal annealing at 500 °C for 60 min, Mössbauer spectra also showed a marked decrease in the quadrupole splitting (Δ) of Fe^III from 0.70 to 0.77 to 0.58–0.62 (±?0.02) mm s^?1, which proved “structural relaxation” of distorted VO₄ tetrahedra which were randomly connected to FeO₄, VO₅, MoO₆, FeO₆ and MoO₄ units by sharing corner oxygen atoms or edges. DC-conductivity (σ) of barium iron vanadate glass (x?=?0) measured at room temperature was 3.2?×?10^?6 S cm^?1, which increased to 3.4?×?10^?1 S cm^?1 after the annealing at 500 °C for 60 min. The σ’s of as-cast molybdovanadate glasses with x’s of 20–50 were ca. 1.1?×?10^?7 or 1.2?×?10^?7S cm^?1, which increased to 2.1?×?10^?2 (x?=?20), 6.7?×?10^?3 (x?=?35) and 1.9?×?10^?4 S cm^?1 (x?=?50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO₄ tetrahedra was directly related to the marked increase in the σ, as generally observed in several vanadate glasses.     

Dual relaxation behaviors and large electrostrictive properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Sr<Subscript>0.85</Subscript>Bi<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> ceramics

Lead-free ceramics (1???x)Bi_0.5Na_0.5TiO₃–xSr_0.85Bi_0.1TiO₃ (BNT–xSBT, x?=?0.4, 0.5, 0.6 and 0.7) were prepared by a solid-state reaction process. Coexistence of ferroelectric relaxation at low temperature and Maxwell–Wagner dielectric relaxation at high temperature was revealed for the first time in this system. Meanwhile, hysteresis-free P–E loops combined with a very high piezoelectric strain coefficient (d₃₃) of 1658 pC/N concurrently with large electrostrictive coefficient Q?=?0.287 m⁴C^?2 were achieved. The ferroelectric relaxor behavior and large electrostrictive strain might be linked to easy reorientation and reversal of ergodic PNRs and the combined effect of Bi off-center position and lone pair electrons.     

A diffusion criterion of the crystal-liquid phase transition

A diffusion criterion of the crystal-liquid phase transition (PT) is proposed according to which the PT begins when the E _d/k _b ratio reaches a threshold value of E _d(s)/k _b T _m, where E _d is the self-diffusion energy, k _B is the Boltzmann constant, T is the absolute temperature, and E _d(s) is the self-diffusion energy in the solid phase at the melting temperature T _m. It is shown that this criterion is a generalization of the Lindemann criterion and is applicable both to solids exhibiting normal melting and to those melting with a decrease in the specific volume. Based on the new criterion, it is possible to explain the relation T _N < T _m, where T _N, is the crystallization onset temperature. The results of calculations of the T _N/T _m ratio well coincide with experimental data.     

Influence of Nd doping on microwave dielectric properties of SrTiO<Subscript>3</Subscript> ceramics

Sr_1?x Nd _x TiO₃ (x?=?0.08–0.14) ceramics were prepared by conventional solid-state methods. The analysis of crystal structure suggested Sr_1?x Nd _x TiO₃ ceramics appeared to form tetragonal perovskite structure. The relationship between charge compensation mechanism, microstructure feature and microwave dielectric properties were investigated. Trivalent Nd³⁺ substituting Sr²⁺ could effectively decrease oxygen vacancies. This reduction and relative density were critical to improve Q?×?f values of Sr_1?x Nd _x TiO₃ ceramics. For ε _r values, incorporation of Nd could restrain the rattling of Ti⁴⁺ cations and led to the reduction of dielectric constant. The τ _f values were strongly influenced by tilting of oxygen octahedral. The τ _f values decreased from 883 to 650 ppm/°C with x increasing from 0.08 to 0.14. A better microwave dielectric property was achieved for composition Sr_0.92Nd_0.08TiO₃ at 1460 °C: ε _r ?=?160, Q?×?f?=?6602 GHz, τ _f ?=?883 ppm/°C.     

Influence of the Hybrid Combination of Multiwalled Carbon Nanotubes and Graphene Oxide on Interlaminar Mechanical Properties of Carbon Fiber/Epoxy Laminates

An effective strategy to improve the mode I and mode II interlaminar fracture toughness (G _IC and G _IIC ) of unidirectional carbon fiber/epoxy (CF/E) laminates using a hybrid combination of multiwalled carbon nanotubes (MWCNTs) and graphene oxide (GO) is reported. Double cantilever beam (DCB) and end notched flexure (ENF) tests were conducted to evaluate the G _IC and G _IIC of the CF/E laminates fabricated with sprayed MWCNTs, GO and MWCNTs/GO hybrid. Scanning electron microscopy was employed to observe the fracture surfaces of tested DCB and ENF specimens. Experimental results showed the positive effect on the G _IC and G _IIC by 17% and 14% improvements on CF/E laminates with 0.25 wt.% MWCNTs/GO hybrid content compared to the neat CF/E. Also, the interlaminar shear strength value was increased for MWCNTs/GO-CF/E laminates. A synergetic effect between MWCNTs and GO resulted in improved interlaminar mechanical properties of CF/E laminates made by prepregs.     

Stress and strain mapping of micro-domain bundles in barium titanate using electron backscatter diffraction

Cross-correlation of electron backscatter diffraction patterns has been used to generate stress and strain maps of a single crystal of tetragonal barium titanate (BaTiO₃) containing bundles of small, (0.2–5) μm, a- and c-domains separated by 90° domain boundaries. The strains peaked at the domain boundaries, and approximately equal, but opposite, values were observed in the a- and c-domains; the peak strain magnitudes were slightly less than half the tetragonal distortion of BaTiO₃, about 0.004, consistent with a tendency to a cubic structure at domain boundaries. The strain state was dominated by two normal strains: in-plane, perpendicular to domain wall intersections with the surface, and out-of-plane, perpendicular to the surface. In distinction to larger, lamellar domains, significant shear strains were also observed. Stress maps were constructed from strain maps using a method that does not require zero stress at reference locations. Peak in-plane normal stresses of approximately 700 MPa were observed. The variation of the stress component parallel to the domain walls was used to determine numerically a microstructurally based stress intensity factor for crack propagation perpendicular to the domain walls. The conditions for stable micro-crack formation in the microstructural stress field and unstable crack propagation under the action of a superposed applied stress were considered in the context of multi-layer ceramic capacitor reliability.     

Phase equilibria and crystal structures of phases in the La-Fe-Ni-O system at 1370 K in air

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-O phase diagram at constant temperature and pressure has been constructed. Based on x-ray diffraction results for samples prepared by standard solid-state reactions and via citrate and nitrate routes, the following solid solutions have been shown to exist at 1370 K in air: LaFe_{1 ? x} Ni _x O_{3 ? δ} (0 < x ≤ 0.4, sp. gr. Pbnm; 0.6 ≤ x ≤ 0.8, sp. gr. R-3 c), La₄(Ni_{1 ? y} Fe _y )₃O_{10 ? δ} (0 < y ≤ 0.3), La₃(Ni_{1 ? z} Fe _z )₂O_{7 ? δ} (0 < z ≤ 0.05), La₂Ni_{1 ? v} Fe _v O_{4 + δ} (0 < v ≤ 0.05), Ni_kFe_{3 ? k} O₄ (0.81 ≤ k ≤ 1.05), Ni_{1 ? m} Fe _m O (0 < m ≤ 0.05), and Fe_{2 ? p} Ni _p O₃ (0 < p ≤ 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.     

Effect of methyltrimethoxysilane hydrolysis and condensation conditions on the properties of thin polymethylsilsesquioxane films

We have studied the influence of methyltrimethoxysilane hydrolysis and condensation conditions in aprotic solvents on the formation, composition, and properties of thin polymethylsilsesquioxane films. The condensation of silanol groups and the structuring of the silicon–oxygen skeleton at different heat-treatment temperatures have been investigated by IR spectroscopy. The dielectric permittivity k and refractive index n of the films have been determined as functions of annealing temperature t_a: at t_a = 430°C, k = 2.75 and n = 1.38.     

Effect of Tb<Superscript>3+</Superscript> ion substitution on structural,optical and magnetic properties of CdS nanoparticles

Cd_1?xTb_xS (x?=?0.00, 0.05, 0.10, 0.15) nanoparticles were synthesized by hydrothermal technique. The effect of Tb-doping on structural, optical and magnetic properties were studied. The X-ray diffraction (XRD) confirmed wurtzite phase without any impurity. HR-TEM micrographs revealed the particle size of ~?18 nm with spherical morphology. Band gap calculated from UV–Visible absorption spectra showed an initial decrease from 2.49 eV (x?=?0) to 2.45 eV (x?=?0.10). Further, increasing Tb-doping to x?=?0.15 band gap increased to 2.54 eV. Photoluminescence emission spectra showed peaks at 430 and 490 nm for x?=?0 and 0.05 which corresponds to blue emission. Further increase in Tb doping, peaks found to be quenched. Peak at 530 nm is due to green emission and shifted to higher wavelength with Tb-doping. Magnetic analysis confirmed ferromagnetism in both undoped and Tb-doped nanoparticles. Saturation magnetization found to decrease upto x?=?0.10 and increased for x?=?0.15.     

Modified inelastic bouncing ball model of the Brazil nut effect and its reverse

We developed the modified inelastic bouncing ball model (mIBBM) to describe the emergence of the Brazil nut effect (BNE) and its reverse (RBNE) in a vertically-vibrated binary granular mixture. The mIBBM incorporates the container-to-grains force-transmission efficiency (transmissibility) T_r to quantify the dimensionless mean void lifetime \( \omega \langle \delta t\rangle \) that acts as the segregation phase indicator where ω is the vibration angular frequency. The mixture is represented as two non-interacting inelastic balls, Ball A and Ball B. Each ball bounces with a time-of-flight τ_A (or τ_B) that depends on transmissibility T_rA (or T_rB) and the dimensionless container acceleration Γ, i.e., τ_A?=?τ_A(Γ, T_rA) and τ_B?=?τ_B(Γ, T_rB). The ball dynamics are described by the bifurcation diagrams of the dimensionless times-of-flight, ωτ_A(Γ, T_rA) and ωτ_B(Γ, T_rB). The probability-weighted difference \( \omega \langle \delta t\rangle \) between branches of the two diagrams is computed and interpreted as follows: \( \omega \langle \delta t\rangle > 0 \) (occurrence of BNE), \( \omega \langle \delta t\rangle < 0 \) (RBNE) and \( \omega \langle \delta t\rangle \)?=?0 (no segregation). Segregation phases are revealed as varying shifts and widths of \( \omega \langle \delta t\rangle \) across the Γ axis. The phase boundaries in the \( \omega \langle \delta t\rangle \)-versus-Γ diagram are sensitive to changes in T_rA, T_rB and ΔT_r?=?(T_rA???T_rB). The mIBBM explains why the BNE is a more likely than the RBNE and predicts a segregation phase sequence that is generally consistent with related experimental results taken over a limited ω-range. Additional experiments are needed to enable a more comprehensive and precise evaluation of the mIBBM.     

Microstructure and properties of the Ba<Subscript>0.75−x</Subscript>Ca<Subscript>x</Subscript>La<Subscript>0.25</Subscript>Fe<Subscript>11.6</Subscript>Co<Subscript>0.25</Subscript>Ti<Subscript>0.15</Subscript>O<Subscript>19</Subscript> hexaferrites

In the case of Ti⁴⁺ remain unchanged, the Ca²⁺ substituted Ba_0.75?xCa_xLa_0.25Fe_11.6Co_0.25Ti_0.15O₁₉ (0?≤?x?≤?0.05) were prepared by conventional solid-state reaction method at temperature of 1280 °C. A ball-to-power weight ratio of 10:1. Their crystal structure and magnetic properties were mainly investigated. The results show that the single magnetoplumbite phase structure transformed into the multiphase structure. Meanwhile, the small amount of α-Fe₂O₃ phase existed in M-type phase. The micrographs were observed by a field emission scanning electron microscopy (SEM). Vibrating sample magnetometer (VSM) was used to analyze the magnetic properties. The saturation magnetization (M _s ) first increases then decreases when x from 0 to 0.03. But, when x from 0.03 to 0.05, the saturation magnetization (M _s ) first increases then decreases too. The maximum value is at x?=?0.04 (M _s ?=?70.73 emu/g). The value of coercivity (H _c ) first increases then decreases when x from 0 to 0.04. But, the value increased when x from 0.04 to 0.05. The maximum value is at x?=?0.02 (H _c ?=?1691 Oe).     

Explanation of Non-linear In-Plane Resistivity and Hall Coefficient in the Normal State of Cuprates: Polaronic Approach

We present a theoretical study of the in-plane resistivity ρ _{a b} (T) and Hall coefficient R _H (T) within the polaronic model and precursor pairing scenario by considering a two-component charge carrier picture in the normal state of high-temperature superconducting cuprates (HTSC). Here, we use a Boltzmann-equation approach and extended BCS-like model to compute ρ _{a b} (T) and R _H (T) in the τ-approximation. The opening of the pseudogap (PG) in the normal state of the cuprates should affect their transport properties. We have found that the transition to the PG regime and the effective conductivity of charge carriers in the normal state are responsible for the pronounced non-linear temperature dependence of ρ _{a b} and R _H . With the two-component model analysis, we conclude that the opening of the BCS-like PG, while the non-linear temperature dependence of ρ _{a b} and R _H could be understood as a consequence of pairing fluctuations in the PG state of cuprate superconductors. The calculated results for ρ _{a b} (T) and R _H (T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also show that the energy scales of the binding energies of charge carriers are identified by PG crossover temperature on the cuprate phase diagram.