Internal Friction and Photoacoustic Effects in A2B6 and A2B7(HgI2) Single Crystals at Different Levels of Ultrasound Strain Amplitude

A comparison of effects in damping and Young modulus under the influence of illumination for ZnSe and HgI2 demonstrates quite different mechanisms of photoacoustic interaction in the crystals : a drift of photocarriers in the electric field which arises due to piezoelectricity for the first case and a dislocation pinning mechanism for the second one. Spectral responses of the photoacoustic effect in both amplitude independent and dependent damping range are presented for mercury iodide crystals. The newly found acousto- and photo-optic effects in the luminescence spectrum of HgI2 allow one to specify the photosensitive dislocation pinning centre as an exciton state of carriers on a stoichiometric point defect of the lattice (iodine or mercury vacancy or interstitial)

Low-temperature embrittlement and fracture of metals with different crystal lattices – Dislocation mechanisms

The state of a low-temperature embrittlement (cold brittleness) and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals) with various crystal lattices (BCC, FCC, HCP) are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength) as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation) and after a low-temperature damaging (neutron) irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron) irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed) due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics

Amplitude-dependent internal friction and magneto-acoustic effects in YBCO ceramics

The paper is concerned with effects in damping and Young's modulus observed in YBaCuO ceramic superconductors vibrating ultrasonically either in or without magnetic field. The amplitude and time dependencies which arise as a result of high amplitude vibrational excitation are presented for coarse-grained and fine-grained specimens. Weak magneto-acoustic effects were observed, and found to be strongly influenced by vibration amplitude and by thermal pre-history of the sample. Analysis of the results shows that, in the vicinity of liquid helium temperature, high amplitude ultrasonic stresses induce structural modifications in these YBaCuO ceramics. Dislocation point defect interaction mechanisms are proposed for explaining the micro-plastic behaviour of the YBaCuO samples observed in the ultrasonic experiments. The magneto-acoustic effects are discussed in the framework of flux line pinning models

Amplitude Dependent Internal Friction and Magneto-Acoustic Effects in YBCO Ceramics

The paper is concerned with effects in damping and Young's modulus observed in YBaCuO ceramic superconductors vibrating ultrasonically either in or without magnetic field. The amplitude and time dependencies which arise as a result of high amplitude vibrational excitation are presented for coarse-grained and fine-grained specimens. Weak magneto-acoustic effects were observed, and found to be strongly influenced by vibration amplitude and by thermal pre-history of the sample. Analysis of the results shows that, in the vicinity of liquid helium temperature, high amplitude ultrasonic stresses induce structural modifications in these YBaCuO ceramics. Dislocation point defect interaction mechanisms are proposed for explaining the micro-plastic behaviour of the YBaCuO samples observed in the ultrasonic experiments. The magneto-acoustic effects are discussed in the framework of flux line pinning models

Effect of carbonization temperature on the microplasticity of wood-derived biocarbon

The uniaxial compression strength under stepped loading and the 325-nm-stepped deformation rate of biocarbon samples obtained by carbonization of beech wood at different temperatures in the 600-1600°C range have been measured using high-precision interferometry. It has been shown that the strength depends on the content of nanocrystalline phase in biocarbon. The magnitude of deformation jumps at micro- and nanometer levels and their variation with a change in the structure of the material and loading time have been determined. For micro- and nanometer-scale jumps, standard deviations of the differences between the experimentally measured deformation rate at loading steps and its magnitude at the smoothed fitting curve have been calculated, and the correlation of the error with the deformation prior to destruction has been shown. The results obtained have been compared with the previously published data on measurements of the elastic properties and internal friction of these materials. © 2014 Pleiades Publishing, Ltd.Peer Reviewe