Nanoscale deformation irregularities of γ-irradiated poly(methyl methacrylate)

Development of deformation jumps in the creep of poly(methyl methacrylate) (PMMA) has been studied. The structural levels of deformation have been determined from the creep rate oscillation periods (deformation jumps) measured by the interferometric method. Special attention is given to a new method of data processing, which enables one to reveal previously undetectable nanoscale deformation jumps. By the example of PMMA specimens preliminarily exposed to γ radiation with doses D=55–330 kGy and unexposed specimens, the presence of nanoscale deformation jumps with the values dependent on the dose D and time of creep has been shown. The obtained results confirm the existence of 10–20-nm domains in amorphous polymers and make it possible to study the multilevel organization of the deformation process, starting from the nanoscale.     

Effect of the magnetic field on nanometer-scale deformation jumps in polymers

The effect of a constant magnetic field on the rate of jumplike creep under compression is investigated for vitreous polymers with a globular structure. The interferometric method used for recording the creep makes it possible to measure deformation jumps from 300 nm and larger. It is demonstrated that the sizes of deformation jumps in polyester and epoxy resins decrease in the magnetic field (B = 0.2 T). Taking into account that the deformation jump size corresponds to the size of structural inhomogeneities, it is assumed that macroglobules under the action of a constant magnetic field are separated into smaller structural units on the nanometer level.     

Serrated creep of zinc single crystals under compression in a magnetic field

The compressive creep rate of zinc single crystals was measured for sample deformation increments of 150 nm, which permits the measurement of deformation jumps larger than 300 nm. A weak magnetic field B = 0.2 T is shown to increase the average creep rate and decrease the height and sharpness of submicron-sized deformation jumps. Preliminary holding of a sample in a magnetic field also influences the creep rate and the characteristics of deformation jumps. The data are explained in terms of a model relating the effect of a magnetic field to the destruction of barriers to dislocation motion.     

The influence of measurement and relaxation time on flux jumps in high temperature superconductors

The influence of the magnetization and relaxation time on flux jumps in high temperature superconductors (HTSC) under varying magnetic field is studied using the fundamental electromagnetic field equations and the thermal diffusion equation; temperature variety corresponding to flux jump is also discussed. We find that for a low sweep rate of the applied magnetic field, the measurement and relaxation times can reduce flux jump and to constrain the number of flux jumps, even stabilizing the HTSC, since much heat produced by the motion of magnetic flux can transfer into coolant during the measurement and relaxation times. As high temperature superconductors are subjected to a high sweep rate or a strong pulsed magnetic field, magnetization undergoes from stability or oscillation to jump for different pause times. And the period of temperature oscillation is equal to the measurement and relaxation time.     

Inhomogeneity of the strain rate of polymer materials with different supramolecular structures

The characteristics of rate oscillations in submicron deformation increments in the course of creep under compression of polymer materials of different classes, namely, amorphous poly(vinyl butyral), amorphous-crystalline poly(tetrafluoroethylene), and a composite consisting of polyimide with graphite particles, have been investigated. The strain rate has been measured using an interferometer on a deformation base of 300 nm. The periods of rate oscillations have been used to determine the deformation jumps, and the amplitude of rate oscillations has been used to determine the jump sharpness. It has been demonstrated that the radical differences in the structure of materials manifest themselves in the parameters of deformation jumps at different stages of creep. The type of jumps makes it possible to reveal the type of molecular packing in the starting polymer or the packing formed during deformation.     

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.     

Jumplike deformation of γ-irradiated polymethyl methacrylate

Nonuniformity of the microdeformation rate and the parameters of microdeformation jumps were studied in the creep regime for a polymethyl methacrylate irradiated by various dozes of the Co-60 γ radiation. The creep rate during compression of the polymethyl methacrylate was measured by an interferogram on 300-nm deformation increments. It is shown that the periods L of rate oscillations (jumps of deformation) on three scale levels are dependent on the irradiation doze and are also changed after prolonged exposure of samples in air. In the doze range 0 to 330 kGy, both a decrease and an increase in L are observed, which corresponds to the unstable kinetics of radiation chemical processes. The deformation jumps permit estimates of the radiation effect on various structural levels. It is concluded that the effect of radiation on coarser microstructural formations is the largest.

     

Jumpwise deformation of polymethyl methacrylate in the microplasticity region

The deformation rate with a step of 325 nm has been measured under uniaxial compression at the initial stage of creep and shape recovery of a polymethyl methacrylate (PMMA) sample after unloading. The effect of low γ-ray doses and magnetic fields on the deformation has been studied. It has been shown that a weak pre-exposure of the PMMA sample structure to radiation and magnetic fields can cause a slight hardening in the microplasticity region. The deformation jump sizes have been determined on micro- and nanoscales. The effect of irradiation and magnetic fields manifests itself as redistributed contributions of various jumps to the deformation.     

Jumplike deformation of polymer materials on the micrometer and submicrometer structural levels

Jumplike creep is considered as a reflection of the structural heterogeneity of amorphous polymers on the mesoscopic and nanoscopic levels. The D-450 epoxy resin, poly(vinyl chloride), poly(vinyl butyral), and a composite consisting of the D-450 epoxy resin and diabase microparticles are studied at a temperature of 290 K. The creep rate of the specimens under compression is measured with a laser interferometer in submicrometer-scale deformation increments. Periodic variations of the creep rate with time or under deformation correspond to a jumplike (stepwise) behavior of the creep. It is shown that diabase particles (5–10 μm in size) are responsible for the appearance of micrometer-scale jumps in the creep of the composite and that the deformation jumps on the nanometer level are comparable to the sizes of the globules. The role of the resolution of the method employed in the evaluation of the scale of deformation jumps and structural units is considered.     

Micro- and nanoscale instabilities of deformation in polymers

The rate and magnitude of the deformation in polymers under constant compressive stresses at room temperature have been measured. The use of laser interferometer has made it possible to perform measurements at small intervals of variations in the specimen length Δl = 0.325 μm, and the analysis of the form of beats has made it possible to estimate oscillations of the strain rate in nanoscale displacements. It has been shown that the average strain rate of polymers continuously varies and no creeping interval with a constant rate is observed. At all stages of smooth variations in the average rate, jumps of its current values corresponding to Δl from several nanometers to a hundred and more nanometers have been found. Changes in the structure with an increase in the deformation manifest themselves in an increase in the size of nanoscale jumps and in a complication of their shape.     

Regularities of Microstrain of Ultrahigh-Molecular-Weight Polyethylene Modified with Halloysite Additives

The effect of additives of 1 and 3 wt % of halloysite on the rate and small jumps of deformation under uniaxial compression of ultrahigh-molecular-weight polyethylene was investigated. A procedure for precision interference measurement with a resolution of 325 nm for displacement and 1 kHz for frequency enabled the detection of several levels of deformation in the micro- and nanometer ranges. The addition of halloysite results in a decrease in the strain rate under the same loading conditions and a change in the characteristics of the strain jumps. Calorimetric measurements showed that melting of polyethylene with a different concentration of halloysite causes a change in the transition energy and the degree of crystallinity.     

Polymer creep in a static magnetic field

By noting changes in the color of samples in a polarization microscope with varying degree of birefringence, the effect of a weak static magnetic fields (2 and 4 kOe) on molecules of glassy polymers has been observed. Variations in the nonmonotonicity of the rate of discontinuous creep at +18° were studied interferometrically. It is shown that the abruptness of the deformation jumps varies in a magnetic field, where this abruptness is assumed to be due to the existence of strong physical junctions between the kinetic units of deformation. The reactivity of the polymers to the magnetic field stands in satisfactory correspondence with their magnetic susceptibilities. Results show that such nonmagnetic materials as glassy polymers can noticeably alter their deformational properties in response to the action of magnetic fields. Fiz. Tverd. Tela (St. Petersburg) 39, 1690–1692 (September 1997)     

Inhomogeneity of deformation of solids at the nanometer level

A new method for processing interferometrically recorded deformation data has been implemented for studying an inhomogeneity in the rate and parameters of deformation jumps at the nanostructure level, which provides detection of deformation jumps of less than 300 nm. It is shown that the lower limit for deformation jumps lies in the range 10–30 nm for aluminum and is 130 nm for amorphous polymer (poly(methyl methacrylate)). It is assumed that the sizes of jumps correspond to scales of ordered structures, as was previously established for higher level structures. The results obtained make it possible to investigate more thoroughly the multilevel character of deformation and to evaluate the sizes of the nanostructural units, their evolution during deformation and under the effect of external fields, as well as their relation to the microscopic and macroscopic inhomogeneities of deformation.     

熔融织构(Nd-Eu-Gd)-Ba-Cu-O超导体的各向异性磁通跳跃及其不稳定性研究

对c轴择优取向的熔融织构样品(Nd_0.33Eu_0.33Gd_0.33) Ba₂Cu₃O_7-δ（含Gd(211)相）的磁通跳跃现象进行 了系统研究.结果表明，在外加磁 场平行于样品c轴条件下，在2到3K的温度范围内明显观测到了部分磁通跳跃现象，而 在5K及以上温区并未出现.在磁场垂直于样品的c轴情况，在2K到T_c的整个温 区都没有观察到磁通跳跃现象.这种各向异性磁通跳跃现象可归因于各向异性钉扎力和几何 退磁因子的结果.随着温度的增加，磁通跳跃数目减少，且M(H)曲线的第三象限是磁通 跳跃的最不稳定过程.最后，研究了磁通跳跃对磁场扫描速率的依赖关系，并讨论了磁通蠕 动对磁通跳跃的影响. 关键词： 0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_7-δ超导体')" href="#">(Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_7-δ超导体 OCMG方法 磁通跳跃     

Jumplike microdeformation of nanostructured metals

The parameters of microdeformation jumps for copper, aluminum, titanium, and Armco iron with the initial (annealed) structure and after equal-channel angular pressing are investigated in a creep mode under low compressive stresses. The strain rate is measured with a laser interferometer in 0.15-μm linear displacements. It is demonstrated that the values of the microstrain rate and the mean sizes of jumps for the annealed metals are larger than those for the metals subjected to severe deformation. It is revealed that there is a correlation between the jumps of microplastic deformation and the size of nanometal grains. The inference is made that, for nanostructured metals, as for other materials, the structural heterogeneity is one of the factors responsible for the jumplike deformation.     

Strength and microplasticity of biocarbons prepared by carbonization in the presence of a catalyst

The microdeformation has been investigated under uniaxial compression of beech-derived biocarbons partially graphitized during carbonization in the presence of a Ni- or Fe-containing catalyst. The strength and ultimate fracture strain have been determined at different temperatures of carbonization of the samples in the absence or in the presence of a catalyst. It has been shown using high-precision interferometry that the deformation of biocarbon samples under uniaxial loading occurs through jumps (in magnitude and rate of deformation) with axial displacements in the nanometer and micrometer ranges. The use of a catalyst leads to a decrease in the size of nanometer-scale jumps and in the number of micrometer-scale jumps. The standard deviations of the strain rate on loading steps from the smooth average dependence of the strain rate on the displacement have been calculated for micrometer-scale jumps. A similar characteristic for nanometer- scale jumps has been determined from the distortion of the shape of beats in the primary interferogram. It has been shown that the variation in the standard deviation of the strain rate with a change in the carbonization temperature is similar to the corresponding dependence of the ultimate fracture strain.     

Role of solid-solution strengthening and interactions in the dislocation ensemble in the formation of flow stress in austenitic nitrogen steel

The paper reports on an experimental investigation of the role of structural levels of deformation in the formation of the flow stress of austenitic nitrided steel. The contributions to the yield stress and the flow stress from the structural levels of various scales have been determined and it has been found that small-scale levels make the main contribution to the strain resistance. A detailed study of the dislocation ensemble has shown that undergoes strong relaxation at different stages of deformation. The laws of solid-solution strengthening and its effect on substructural transformations are examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 33–56, March, 1996.     

Magnetic properties of a two-dimensional spatially ordered array of nickel nanowires

The structural and magnetic characteristics of two-dimensional spatially ordered arrays of magnetic nickel nanowires embedded in the anodized alumina template have been investigated. It has been shown using small-angle polarized-neutron diffraction that, there exists the samples under investigation, in a highly ordered hexagonal structure of pores and magnetic nanowires separated by a characteristic distance d = 106 ± 2 nm. An analysis has been made of different contributions to neutron scattering, such as the nonmagnetic (nuclear) contribution, the magnetic contribution dependent on the magnetic field, and the interference contribution indicating a correlation between the magnetic and nuclear structures. The performed analysis of the results obtained has demonstrated that, when the magnetic field is applied perpendicular to the longitudinal axis of the nanowire in a completely magnetized sample, there arise demagnetizing fields around each nanowire that form a regular hexagonal lattice.     

Magnetic-Field Dependence of Raman Coupling Strength in Ultracold ~(40)K Atomic Fermi Gas

We experimentally demonstrate the relation of Raman coupling strength with the external bias magnetic field in degenerate Fermi gas of ~(40)K atoms.Two Raman lasers couple two Zeeman energy levels,whose energy splitting depends on the external bias magnetic field.The Raman coupling strength is determined by measuring the Rabi oscillation frequency.The characteristics of the Rabi oscillation is to be damped after several periods due to Fermi atoms in different momentum states oscillating with different Rabi frequencies.The experimental results show that the Raman coupling strength will decrease as the external bias magnetic field increases,which is in good agreement with the theoretical prediction.     

Step deformation of solid amorphous polymers

The variation of step deformation kinetics in solids is studied as a function of morphological factors. Oscillations of creep rate at micrometer increments of the amount of deformation, which reflect the step nature of the process, are investigated from an interferogram. It is shown that the plasticization of polymethyl methacrylate by dibutyl phthalate blurs the steps, while their height varies insignificantly. The results are explained using the concept of the netlike structure of amorphous polymers. The data obtained confirm the universal nature of jumps as a mode of evolution of deformation in various solids. The jumps reflect the cooperative nature of motion of kinetic units, and the regular variation of the characteristics of the jumps lends support to the definition of creep as a process of structural self-organization.