Determination of fracture mechanics parameters on a base of local displacement measurements

New experimental technique for a determination of the stress intensity factor (SIF) and T-stressvalues is developed and verified. The approach assumes combining the crack compliance method and opticalinterferometric measurements of local deformation response on small crack length increment. Initialexperimental information has a form of in-plane displacement component values, which are measured byelectronic speckle-pattern interferometry at some specific points located near a crack tip. Required values offracture mechanics parameters follow from the first four coefficients of Williams’ series. A determination ofinitial experimental data at the nearest vicinity of notch tip is the main feature of the developed approach. Thatis why it is not necessary to involve complex numerical models, which include global geometrical parameters,loading and boundary conditions of the object under study, in a stage of experimental data interpretation. Anavailability of high-quality interference fringe patterns, which are free from rigid-body motions, serves as areliable indicator of real stress state around a crack tip. A verification of the technique is performed bycomparing experimental results with analogous data of FEM modelling. Experimentally determined mode I SIFfor DCB specimen with end crack is in 5 per cent agreement with the numerically simulated case. Proposedapproach is capable of estimating an influence of the notch radius on fracture mechanics parameters.Comparing SIF and T-stress obtained for U-notches of different radius both in actual and residual stress fieldconfirms this statement

Isolation of Peaks in TDS Spectra of Deuterium from Ion Irradiated Tungsten

AbstractInteraction of deuterium with radiation defects in tungsten was studied by means of thermal desorption spectroscopy. The displacement damage in a recrystallized tungsten foil was produced by irradiation with 10 keV/D ions to the fluences in the range of 3–8×1019 D/m2 at room temperature. The resulted thermal desorption spectra consisted of three wide overlapping peaks. It was shown that annealing of the damaged sample at 550 K and subsequent implantation with 0.67 keV/D ions allows to isolate the peak corresponding to deuterium release from vacancies

Independent ferroelectric contributions and rare-earth-induced polarization reversal in multiferroic TbMn2O5

Three independent contributions to the magnetically induced spontaneous polarization of multiferroic TbMn2O5 are uniquely separated by optical second harmonic generation and an analysis in terms of Landau theory. Two of them are related to the magnetic Mn3+/4+ order and are independent of applied fields of up to 7 T. The third contribution is related to the long-range antiferromagnetic Tb3+ order. It shows a drastic decrease upon the application of a magnetic field and mediates the change of sign of the spontaneous electric polarization in TbMn2O5. The close relationship between the rare-earth long-range order and the non-linear optical properties points to isotropic Tb-Tb exchange and oxygen spin polarization as mechanism for this rare-earth induced ferroelectricity.Comment: 8 pages, 5 figure

Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets

The impulsive generation of two-magnon modes in antiferromagnets by femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent longitudinal oscillations of the antiferromagnetic order parameter that cannot be described by a thermodynamic Landau-Lifshitz approach. We argue that this dynamics is triggered as a result of a laser-induced modification of the exchange interaction. In order to describe the oscillations we have formulated a quantum mechanical description in terms of magnon pair operators and coherent states. Such an approach allowed us to} derive an effective macroscopic equation of motion for the temporal evolution of the antiferromagnetic order parameter. An implication of the latter is that the photo-induced spin dynamics represents a macroscopic entanglement of pairs of magnons with femtosecond period and nanometer wavelength. By performing magneto-optical pump-probe experiments with 10 femtosecond resolution in the cubic KNiF$_3$ and the uniaxial K$_2$NiF$_4$ collinear Heisenberg antiferromagnets, we observed coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The detected frequencies as a function of the temperature ideally fit the two-magnon excitation up to the N\'eel point. The experimental signals are described as dynamics of magnetic linear dichroism due to longitudinal oscillations of the antiferromagnetic vector.Comment: 25 pages, 10 figure

Structural, electronic, vibrational and dielectric properties of LaBGeO5_5 from first principles

Structural, electronic, vibrational and dielectric properties of LaBGeO$_5$ with the stillwellite structure are determined based on \textit{ab initio} density functional theory. The theoretically relaxed structure is found to agree well with the existing experimental data with a deviation of less than $0.2\%$. Both the density of states and the electronic band structure are calculated, showing five distinct groups of valence bands. Furthermore, the Born effective charge, the dielectric permittivity tensors, and the vibrational frequencies at the center of the Brillouin zone are all obtained. Compared to existing model calculations, the vibrational frequencies are found in much better agreement with the published experimental infrared and Raman data, with absolute and relative rms values of 6.04 cm$^{-1}$, and $1.81\%$, respectively. Consequently, numerical values for both the parallel and perpendicular components of the permittivity tensor are established as 3.55 and 3.71 (10.34 and 12.28), respectively, for the high-(low-)frequency limit

Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3

Terahertz and far-infrared electric and magnetic responses of hexagonal piezomagnetic YMnO3 single crystals are investigated. Antiferromagnetic resonance is observed in the spectra of magnetic permeability mu_a [H(omega) oriented within the hexagonal plane] below the Neel temperature T_N. This excitation softens from 41 to 32 cm-1 on heating and finally disappears above T_N. An additional weak and heavily-damped excitation is seen in the spectra of complex dielectric permittivity epsilon_c within the same frequency range. This excitation contributes to the dielectric spectra in both antiferromagnetic and paramagnetic phases. Its oscillator strength significantly increases on heating towards room temperature thus providing evidence of piezomagnetic or higher-order couplings to polar phonons. Other heavily-damped dielectric excitations are detected near 100 cm-1 in the paramagnetic phase in both epsilon_c and epsilon_a spectra and they exhibit similar temperature behavior. These excitations appearing in the frequency range of magnon branches well below polar phonons could remind electromagnons; however, their temperature dependence is quite different. We have used density functional theory for calculating phonon dispersion branches in the whole Brillouin zone. A detailed analysis of these results and of previously published magnon dispersion branches brought us to the conclusion that the observed absorption bands stem from phonon-phonon and phonon- paramagnon differential absorption processes. The latter is enabled by a strong short-range in-plane spin correlations in the paramagnetic phase.Comment: subm. to PR

The effect of low-cycle fatigue on evolution of fracture mechanics parameters in residual stress field caused by cold hole expansion

Localized displacement measurements based on electronic speckle-pattern interferometry are used to obtain crack mouth opening displacement (CMOD), stress intensity factor (SIF) and T-stress values during crack growth around cold-expanded holes. The specimens with a central open hole are made from 2024 aluminium alloy. The expansion level is 5% of nominal interference. The results are obtained for the same stress range ??? = 350 MPa, but different stress ratio R = 0.4 and R = �1.0. A sequence of narrow notches, inserted under the constant external load, serves for crack modelling at different stages of cyclic loading. Initial experimental data represent in-plane displacement component values measured in the vicinity of the crack tip. The transition from in-plane displacement components to SIF and T-stress values follows from the relationships of modified version of the crack compliance method. The crack length curves of CMOD, SIF and Tstress profiles are obtained for different stages of cyclic loading. These data provide the construction of dependencies of fracture mechanics parameters for cracks of fixed lengths from the loading cycle numbe

Immunochemical determination of sulfamethazine in river water and medicinal preparations

A new variant of the immunochemical assay for determining sulfamethazine, an antimicrobial drug belonging to the class of sulfonamide derivatives, has been developed based on the fluorescence polarization technique. The immunoassay is carried out using a polyclonal antiserum against several sulfonamides (conjugated with bovine serum albumin) and a fluorescent label (tracer). The proposed fluorescence polarization immunoassay ensures sulfamethazine detection with a threshold of 6 ng/ml and has a dynamic range of linearity for drug concentrations from 0.05 to 25.7 μg/ml. The proposed method has been applied to the determination of sulfamethazine in river water and tablets. Various methods of tablet pretreatment using methanol, acetonitrile, potassium hydroxide solution, and hydrochloric acid have been tried and compared. The accuracy of the immunoassay was confirmed by the recovery test. The possibility of using the obtained antiserum and the proposed immunoassay scheme for the determination of some other sulfonamides is demonstrated. © 2005 Springer Science+Business Media, Inc