Influence Of Uniaxial Stress Research Articles

Influence of moisture on ultrasonic propagation, acoustic emission activity, and failure mechanism in concrete media

Free water in a concrete medium significantly influences its bearing capacity and failure mechanism. In this study, the mechanical properties and failure mechanism in concrete specimens with different moisture contents were investigated with the objective of enhancing the safety of concrete structures. Uniaxial compression tests were employed to study bearing capacity, ultrasonic propagation, acoustic emission activity and failure mechanism of concrete specimens with moisture contents of 0%, 2%, 4%, and 5.5%. The results implied that the crack initiation stress and compressive strength of concrete first increased and then decreased with the increase in moisture content, and the elastic modulus and Poisson’ s ratio first decreased and then increased. The inflection points were observed in the fitting curves for moisture contents within 1.15–1.65%. With the increase in the moisture in the concrete specimens, the ultrasonic propagation velocity in the material increased, the acoustic emission activity decreased, and the proportion of high-frequency acoustic emission signals decreased. The acoustic emission activity in the concrete specimens was observed predominantly in the failure stage under the influence of uniaxial stress. Based on the moment tensor inversion of acoustic emission, the proportion of shear damage in the failure process of concrete increased with the increase in moisture content. The failure mechanism was analyzed by obtaining the ISO and DC values of acoustic emission events, the moment tensor T–k diagram, and the P–T diagram. The geometric orientation of the acoustic emission events was consistent with the macroscopic fracture mode of the specimens. The ultrasonic propagation, acoustic emission characteristics and the deterioration mechanism of bearing capacity in water-saturated concrete were analyzed. The findings of this study can be applied in health monitoring and for the safe operation of concrete structures in water environments.

Influence of uniaxial stress on phonon-assisted relaxation in bismuth-doped silicon

The relaxation of electrons bound to bismuth donors in silicon and the effect of uniaxial stress have been studied using the time-resolved single color pump-probe technique. In unstressed Si:Bi, an excited 2p0 donor state is resonantly coupled with the donor 1s(A1) ground state via an intervalley f-TO optical phonon. This results in a very short lifetime (a few ps) of the excited state. Even a slight deformation of the silicon crystal leads to modification of particular interstate energies of the donor, which resolves the resonant coupling to intervalley phonons whose energies remain unchanged. We have shown that once the energy gap between the lower stress-split component of the 2p0 state and the ground state becomes less than the energy of the f-TO phonon, the relaxation of electrons from the excited state slows down to about 300 ps. The experimental data are compared with theoretical calculations of the 2p0 state relaxation rate, which are performed assuming that it is dominated by the emission of intervalley phonons.

Influence of Uniaxial Stress on the Shear-Wave Spectrum Propagating in Steel Members

Structural health monitoring technologies have provided extensive methods to sense the stress of steel structures. However, monitored stress is a relative value rather than an absolute value in the structure’s current state. Among all the stress measurement methods, ultrasonic methods have shown great promise. The shear-wave amplitude spectrum and phase spectrum contain stress information along the propagation path. In this study, the influence of uniaxial stress on the amplitude and phase spectra of a shear wave propagating in steel members was investigated. Furthermore, the shear-wave amplitude spectrum and phase spectrum were compared in terms of characteristic frequency (CF) collection, parametric calibration, and absolute stress measurement principles. Specifically, the theoretical expressions of the shear-wave amplitude and phase spectra were derived. Three steel members were used to investigate the effect of the uniaxial stress on the shear-wave amplitude and phase spectra. CFs were extracted and used to calibrate the parameters in the stress measurement formula. A linear relationship was established between the inverse of the CF and its corresponding stress value. The test results show that both the shear-wave amplitude and phase spectra can be used to evaluate uniaxial stress in structural steel members.

Внутрицентровая релаксация мелких доноров сурьмы в деформированном германии

Long-wave acoustic phonons assisted relaxation ratesof the lower excited states 1s(T), 2p0, 2s, 3p0, 2p±, 4p0,3p±of antimony donors in a germanium crystal are calculated.The influence of uniaxial stress in the crystallographic direction[111]on relaxation rates has been considered. The calculationresults have been compared with the measurement data ofrelaxation times of nonequilibrium donor states by the pump-probe method. A comparison is also made with the lifetimesobtained experimentally by the method of studying submillimeterphotoconductivity.

Interaction Between Fluid and Porous Media with Complex Geometries: A Direct Pore‐Scale Study

AbstractEffect of boundary stress on permeability in porous media at pore‐scale is investigated by means of numerical methods for computing deformation of rock material in the presence of pore fluid. We implement a partitioned, strongly coupled solver for transient fluid‐solid simulations with independent conformed interface meshes for the fluid and solid domains. Fluid flow and solid computations were performed using the finite element method. External load is prescribed along the solid boundary in gradual steps to examine the extent of pore‐scale deformation along internal grain walls while applying a fixed constraint at the opposite end to ensure uniform stress distribution across the media. Hydrodynamic interactions between the pore walls and the matrix leading to interface displacements by fluid viscous forces are also investigated by examining fluid flow with different combinations of Reynolds number. Coupling is achieved via traction and displacements boundary conditions at the interface with respect to Lagrangian coordinates. The role of particle shape in the matrix deformation process is also considered in this paper. In order to examine the how particle shape affects local affects local permeability/stress, we examine fluid movement based on varying Reynolds numbers in Berea sandstone obtained from Micro‐CT image scans at high resolution, and artificially constructed random polydisperse 3‐D sphere packs. It was found that permeability alteration under the influence of uniaxial stress was more in the sandstone sample than in the sphere‐pack and that the sphere‐pack deformed less than the actual sample due to pore geometry, surface smoothness, and homogeneity.

The analysis of the effect of homogeneous mechanical stress on the acoustic wave propagation in the “La3Ga5SiO14/fused silica” piezoelectric layered structure

The results of computer simulation taking into account the linear and nonlinear material constants have been presented. Study of the influence of external uniaxial mechanical stress on the dispersive characteristics of elastic waves in piezoelectric structures as “La3Ga5SiO14/fused silica” has been executed. The comparison of elastic wave velocity changes under the influence of an uniaxial stress while a full set of nonlinear material constants of crystalline layer+geometric nonlinearity, or only geometric nonlinearity of the layer induced by the static deformation of a substrate, has been fulfilled.

Influence of Uniaxial Stress on the Stress-Strain Curve Measured by Nanoindentation

A nanoindentation technique with a spherical indenter of tip radius 10 μm is applied to the evaluation of stress-strain curve at a local area of a pure iron under the uniaxial compressive stress exerted through the iron, and the influence of the compressive stress on the estimated stress-strain curve has been examined. A continuous multiple loading method is employed to determine the stress-strain curve. In the method, a set of 21 times of loading/unloading sequences with increasing terminal load are made and load-displacement curves with the different terminal loads from 0.1 mN to 100 mN are then continuously obtained and converted to a stress-strain curve. To examine the stress dependence of the stress-strain curve, the estimation by the nanoindentetion is performed under different uniaxial compressive stresses up to 250 MPa. It has been found that the stress-strain curve determined by the nanoindentation shifts upward as the compressive stress increases and the quantity of the shift is almost equal to the uniaxial stress acting on the iron specimen. It is also noted that the yield stress (0.2 % proof stress) estimated from the stress-strain curve increases almost proportionally to the uniaxial stress and the increase ratio tends to decrease as the stress reaches around 200 MPa.

Electronic band structure and influence of uniaxial stresses on the properties of K2SO4 crystal: ab initio study

Influence of the uniaxial stresses on the electronic band structure, density of states, and optical properties of the potassium sulphate crystal β-K2SO4 have been studied in the framework of the density functional theory using the ab initio code CASTEP (CAmbridge Serial Total Energy Package). Increase of the band gap Eg of the crystal takes place for there crystallographical directions and for moderate uniaxial stresses, σ<1.5GPa. Dependencies of principal refractive indices (nx, ny, nz) upon uniaxial stresses (σx, σy, σz) are discussed together with other features of electronic structure of the crystal.

Influence of uniaxial stress on the ferroelectric-to-paraelectric phase change in barium titanate

The dielectric behavior near the ferroelectric-to-paraelectric phase transition of 〈001〉C-oriented single crystal and polycrystalline barium titanate (BaTiO3) was investigated as a function of uniaxial compressive stress in the temperature range from 25 to 200 °C. An increase in the Curie point (TC) and decrease in the Curie-Weiss temperature (θ) were observed with increasing stress for both single crystal and polycrystalline samples, resulting in an increase in the first order nature of the phase transition as measured by the temperature difference (TC – θ). With increasing applied stress levels, the permittivity versus temperature curves of polycrystalline samples were found to broaden and flatten near the Curie point, which was not observed for the single crystals. The experimental results were analyzed using a classical 2-4-6 Landau polynomial. The observed increase in the first order nature of the ferroelectric-to-paraelectric phase transition with uniaxial stress was explained by a linear dependence of the quartic coefficient of the Landau series on stress.

Effect of uniaxial stress on substitutional Ni in ZnO

The influence of uniaxial stress on the electronic T13(F)→T23(F) transitions of Ni2+ (d8) in ZnO at 4216, 4240, and 4247cm−1 is studied. It is shown that the split pattern and polarized properties of IR absorption lines are consistent with a dynamic Jahn–Teller effect in the T23(F) state of the defect.

Analytical dispersion relation model for conduction band of uniaxial strained Si

In this paper, based on the framework of kp method, the influence of uniaxial stress on the conduction band energy-band structure of bulk-Si is analysed first, the coupling of 1 and 2 bands at the X point, and the influence of that band-band coupling on the minimum of energy valley are then separately discussed under the action of shear strain. On that basis, the dispersion relation close to the minimum is obtained. Furthermore, the different valley orientations need to be taken into account. Using the coordinate transformation, the modelling for dispersion relation of each valley with arbitrary uniaxial stress is finally achieved. The proposed analytical model in this paper is also suited to the understanding of the physical properties of uniaxial strained Si material and may provide some references for the study on bandstructure and electrical properties of the inversion layer in uniaxial strained Si nMOSFETs.

Energy-band structure for uniaxial stressed Germanium

The influence of uniaxial stress along the , and directions to the conduction band (CB) energy valley (Γ valley, Δ valleys, and L valleys) of Germanium was investigated by deformation potential theory. The valence band (VB) structure model of Germanium in uniaxial stressed was established by using a six-band k·p model and coupled with deformation potential theory, and the variation of valence band edge energy level with stress was analyzed. The uniaxial stress induced band edge structure change, such as CB splitting energy, VB splitting energy, and band-gap were elaborated. The obtained quantitative results can provide reference for the calculation of other physical parameters of uniaxial stressed Germanium.

Influence of uniaxial stress on ultrasonic wave propagation near the ferroelastic phase transition in LiCsSO4 crystal

Changes in velocity and attenuation of the longitudinal ultrasonic waves induced by the uniaxial stresses σX , σY and σZ in LiCsSO4 crystal in the vicinity of ferroelastic phase transition, are studied. Far from the phase transition, the stress derivatives of the relative velocity changes, being measures of nonlinear elasticity, are calculated. The stresses applied change the stepwise nature of the velocity changes at T C as a result of the nonlinear elasticity. The uniaxial stresses applied change the phase transition temperature too. The stress σX acting on the wave propagating in [0 1 0] direction drastically decreases the stepwise change in the wave velocity up to its disappearance at 2 MPa and in the temperature range between T C and T C−6 K it leads to increase in the wave velocity and decrease in its attenuation. This range was interpreted as that of co-existence of ferroelastic and incommensurate ordering.

Electroluminescence in quantum well heterostructures p‐AlxGa1–xAs/GaAs1–yPy/n‐AlxGa1–xAs under uniaxial stress

AbstractWe present new results on the influence of uniaxial stress up to P = 4 kbar on the electroluminescence spectra and current–voltage characteristics of p‐Alx Ga1–x As/GaAs1–y Py /n‐Alx Ga1–x As double heterostructures usually used in TM emitting 808 nm high‐power diode lasers. With increasing stress, the emission spectra demonstrate a blue shift of up to 25 meV at a pressure of P = 4 kbar, while the electroluminescence intensity increases under compression. The different behavior of the current–voltage characteristics under uniaxial stress along [110] and [1$ \bar 1 $0] directions is mainly determined by the arising piezoelectric field. The results are also discussed in terms of changes in the band structure under uniaxial compression. The construction of the cryostat for optical measurements under uniaxial stress at liquid nitrogen temperature is described in the paper. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Uniaxial compression influence on electroluminescence spectra in p-Al x Ga1−x As/GaAs1−y P y /n-Al x Ga1−x As heterostructures

We present new results on the influence of uniaxial stress up to P=400 MPa along [110] direction on the electroluminescence (EL) spectra of p-Al x Ga1−x As/GaAs1−y P y /n-Al x Ga1−x As double heterostructures. With increasing stress, the emission spectra demonstrate a blue shift of up to 20 meV at a pressure of P=400 MPa, while the EL intensity increases under compression. The results are discussed in terms of changes in the band structure under uniaxial compression.

Influence of uniaxial stress on stimulated terahertz emission from phosphor and antimony donors in silicon

The effect of uniaxial stress on terahertz stimulated emission from phosphor and antimony donors in silicon excited by CO2 laser radiation was studied. The laser action originates from 2p0→1s(T2) intracenter transitions. A compressive force applied to the silicon crystal decreases the laser threshold by one order of magnitude. The output power depends nonmonotonically on the stress, while the emission frequency does not change. The results are explained by changes of the donor electronic structure, which do not affect the energy gap between the laser states, and a resonant interaction with acoustic f-TA and g-TA phonons that disappears with increasing stress.

Uniaxial stress study of the Cu–H complex in ZnO

AbstractThe influence of uniaxial stress on the vibrational mode of the Cu–H complex at 3192 cm–1 in ZnO is studied. It is shown that the split patterns are consistent with the stretching mode of a bond‐centered hydrogen located in the basal plane between substitutional Cu and O. Quantitative analysis of the stress effects reveals two low energy modes with frequencies of 25 and 49 cm–1. Upon substituting deuterium for hydrogen they shift to 22 and 36 cm–1, respectively. The origin of the low energy modes is discussed. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Influence of Uniaxial Stress on the Polarization of Spontaneous Emission from p-Ge

The intensity of polarized spontaneous emission as a function of uniaxial stress in p-Ge is studied. It is found that with rising of stress dependence of the radiation polarization rotates by π/2. The effect is explained by the modification of the energy spectrum of free and impurity states under the uniaxial compression.

Metal–semiconductor transitions under uniaxial stress for single- and double-walled carbon nanotubes

The alignment defects observed in cylindrical carbon nanotubes are related to the band gaps in a 1-D tight binding scheme. The influence of uniaxial stress on the electronic properties is analyzed and evidence is put forward of possible experimentally observable semiconductor to metal transitions under compression for single- and double-walled nanotubes.

Influence of uniaxial stress on ultrasonic wave propagation near thephase transition in a TGSe crystal

Changes in the velocity and attenuation coefficient of quasilongitudinal wavespropagating in a TGSe crystal in the directions z' = z-4°and x, induced by uniaxial stress σx and σy, were measured in the temperature range of the ferroelectric phasetransition. The uniaxial stress applied was found to shift the phasetransition temperature by ∂TC/∂σx = -0.074 and∂TC/∂σy = -0.18 K MPa-1. Othereffects appearing under the influence of external stress, such as a change inthe jump of the wave velocity at the phase transition, increase in theattenuation coefficient and broadening of the phase transition range, arediscussed on the basis of the phenomenological theory. The relaxation time ofthe order parameter fluctuations was determined. For stress exceeding 2 MPa anadditional anomaly in the wave velocity and attenuation appeared, which wasinterpreted as a splitting of the phase transition. The nonlinear elasticeffects at the phase transition, in the para- and ferroelectric phases, arealso discussed.