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This study investigates the radiative relaxation of electronic excitations through luminescence spectroscopy techniques applied to high-purity KBr crystals subjected to low-temperature (85 K) uniaxial deformation along the <100> and <110> crystallographic directions. Results demonstrate that the most significant enhancement in the intensity of σ-(4.42 eV) and π-(2.3 eV) luminescence from self-trapped excitons in KBr crystals occurs with elastic deformation along the <110> direction, aligning with the axis of the hole component of the anion self-trapped exciton. Deformation-induced changes in X-ray, tunneling, and thermally stimulated luminescence spectra reveal a new band, denoted as Ex, peaking at approximately 3.58 eV, attributed to tunneling charge exchange between the F'- and VK-centers in their ground state. [ABSTRACT FROM AUTHOR]

Radiative relaxations of electronic excitations - self-trapped excitons (STE) in regular lattice sites (intrinsic luminescence) and exciton-like formations (ELF) in the field of homologous cations (exciton-like luminescence). It has been found that the maximum effect of luminescence enhancement occurs upon uniaxial deformation along the crystallographic direction (compared to ), which coincides with the direction of the self-trapped anion exciton () in the KBr crystal matrix. The exciton mechanism was estimated from the increase in the intensity of the intrinsic σ(4, 42eV) - and π(2, 3eV) - luminescences of STE, and the enhancement of luminescence intensity of near-single Na+ (2.85 eV), pair ions Na+ , Na+ (3.1 eV) and Na+ Pb++ (3.4 eV)- centers - recombination mechanism of radiative relaxation of electronic excitations.

This study investigates the radiative relaxation of electronic excitations through luminescence spectroscopy techniques applied to high-purity KBr crystals subjected to low-temperature (85 K) uniaxial deformation along the and crystallographic directions. Results demonstrate that the most significant enhancement in the intensity of σ-(4.42 eV) and π-(2.3 eV) luminescence from self-trapped excitons in KBr crystals occurs with elastic deformation along the direction, aligning with the axis of the hole component of the anion self-trapped exciton. Deformation-induced changes in X-ray, tunneling, and thermally stimulated luminescence spectra reveal a new band, denoted as Ex, peaking at approximately 3.58 eV, attributed to tunneling charge exchange between the F’- and VK-centers in their ground state.

This work develops a probability-based numerical method for quantifying mechanical properties of non-Gaussian chains subject to uniaxial deformation, with the intention of being able to incorporate polymer–polymer and polymer–filler interactions. The numerical method arises from a probabilistic approach for evaluating the elastic free energy change of chain end-to-end vectors under deformation. The elastic free energy change, force, and stress computed by applying the numerical method to uniaxial deformation of an ensemble of Gaussian chains were in excellent agreement with analytical solutions that were obtained with a Gaussian chain model. Next, the method was applied to configurations of cis- and trans-1,4-polybutadiene chains of various molecular weights that were generated under unperturbed conditions over a range of temperatures with a Rotational Isomeric State (RIS) approach in previous work (Polymer 2015, 62, 129–138). Forces and stresses increased with deformation, and further dependences on chain molecular weight and temperature were confirmed. Compression forces normal to the imposed deformation were much larger than tension forces on chains. Smaller molecular weight chains represent the equivalent of a much more tightly cross-linked network, resulting in greater moduli than larger chains. Young's moduli computed from the coarse-grained numerical model were in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Changes in the resistance of single crystals of p-type conductivity silicon under the action of mechanical loading were investigated in this research. Also, non-irradiated and pre-irradiated X-rays experimental samples were studied. It was found that at small deformation values when they are at the initial stage of the action of elastic deformation, a section forms and increases, on which the resistance practically does not depend on the applied mechanical load. In irradiated crystals, at small deformation values, electron generation processes dominate, which then recombine with the main carriers – holes. The consequence of such processes is the appearance of a maximum increase in electrical resistance at the initial stage of elastic deformation of experimental samples irradiated with X-rays. Charge carrier generation processes begin to dominate with further deformation. Such processes occur as a result of the release of acceptor centers from other complex defects, which are destroyed during the deformation of the Si crystal and captured by mobile dislocations. Thus, the processes of generation of charge carriers prevail over the processes of gettering and, accordingly, a mechano-stimulated decrease in the electrical resistance of p-Si samples occurs. [ABSTRACT FROM AUTHOR]

To study the effect of the melt-draw ratios (MDRs) on the structure and properties of the poly(4-methyl-1-pentene) (PMP) film, the crystal structure evolution and mechanical properties of the PMP film with an MDR of 40–160 were characterized using scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray scattering, and mechanical test. The results show that with the increase of MDR, the spherulite to platelet transition occurs in the PMP. When the MDR exceeds 100, a parallel platelet structure appears. Due to the side chains, with the increase of MDR, the distribution density of tie chains in PMP decreases and the entanglement density of amorphous chains increases. This leads to a decrease in the yield strength and the strain hardening becomes noticeable. Although the crystalline network becomes loose due to the decrease in tie chain density, the elastic recovery (ER) value still increases with the increase of MDR. This result indicates that the entanglement density of the amorphous region greatly contributes to the ER.

Optical properties of polymer-liquid-crystal composites (PLCCs) with controlled surface adhesion during uniaxial deformation have been studied. It has been experimentally shown that in PLCCs based on the 4-nheptyl- 4'-cyanobiphenyl nematic liquid crystal, the phenomenon of optical hysteresis can be observed during uniaxial deformation. The structure of such a film is a polymer matrix, in the volume of which elongated nematode droplets are distributed randomly, the long axes of which are oriented mainly along the direction of film stretching. The results of this work can be used used for creating elements of static memory for recording and long-term storage of information and optical switches of bistable states. [ABSTRACT FROM AUTHOR]

This work develops a probability-based numerical method for quantifying mechanical properties of non-Gaussian chains subject to uniaxial deformation, with the intention of being able to incorporate polymer–polymer and polymer–filler interactions. The numerical method arises from a probabilistic approach for evaluating the elastic free energy change of chain end-to-end vectors under deformation. The elastic free energy change, force, and stress computed by applying the numerical method to uniaxial deformation of an ensemble of Gaussian chains were in excellent agreement with analytical solutions that were obtained with a Gaussian chain model. Next, the method was applied to configurations of cis- and trans-1,4-polybutadiene chains of various molecular weights that were generated under unperturbed conditions over a range of temperatures with a Rotational Isomeric State (RIS) approach in previous work (Polymer 2015, 62, 129–138). Forces and stresses increased with deformation, and further dependences on chain molecular weight and temperature were confirmed. Compression forces normal to the imposed deformation were much larger than tension forces on chains. Smaller molecular weight chains represent the equivalent of a much more tightly cross-linked network, resulting in greater moduli than larger chains. Young’s moduli computed from the coarse-grained numerical model were in good agreement with experimental results.

Abstract Tungsten disulfide (WS2) nanotubes (NTs) are examined here as a filler for polylactide (PLA) for their ability to accelerate PLA crystallization and for their promising biocompatibility in relevant to biomedical applications of PLA-WS2 nanocomposites. In this work, we have studied the structural and thermal properties of PLA-WS2 nanocomposite films varying the concentration of WS2 NTs from 0 (neat PLA) to 0.6 wt%. The films were uniaxially drawn at 90 °C and annealed at the same temperature for 3 and 10 min. Using wide angle x-ray scattering, Raman spectroscopy and differential scanning calorimetry, we probed the effects of WS2 NT addition on the structure of the PLA films at various stages of processing (unstretched, stretching, annealing). We found that 0.6 wt% of WS2 induces the same level of crystallinity in as stretched PLA-WS2 as annealing in neat PLA for 10 min. These data provide useful insights into the role of WS2 NTs on the structural evolution of PLA-WS2 composites under uniaxial deformation, and extend their applicability to situations where fine tuning of PLA crystallinity is desirable.

Tungsten disulfide (WS2) nanotubes (NTs) are examined here as a filler for polylactide (PLA) for their ability to accelerate PLA crystallization and for their promising biocompatibility in relevant to biomedical applications of PLA-WS2 nanocomposites. In this work, we have studied the structural and thermal properties of PLA-WS2 nanocomposite films varying the concentration of WS2 NTs from 0 (neat PLA) to 0.6 wt%. The films were uniaxially drawn at 90 °C and annealed at the same temperature for 3 and 10 min. Using wide angle x-ray scattering, Raman spectroscopy and differential scanning calorimetry, we probed the effects of WS2 NT addition on the structure of the PLA films at various stages of processing (unstretched, stretching, annealing). We found that 0.6 wt% of WS2 induces the same level of crystallinity in as stretched PLA-WS2 as annealing in neat PLA for 10 min. These data provide useful insights into the role of WS2 NTs on the structural evolution of PLA-WS2 composites under uniaxial deformation, and extend their applicability to situations where fine tuning of PLA crystallinity is desirable. [ABSTRACT FROM AUTHOR]

Monocrystals of p-Si were used to study the changes in the electrical conductivity of silicon in the course of the action of a single-acting elastic load and X-radiation. An equation describing the dependence of the surface conductivity of irradiated silicon crystals on the amount of elastic deformation (σ) is proposed. This equation made it possible to quantitatively compare the role of the following three radiation-stimulated mechanisms that determine the surface conductivity of p-Si crystals in the course of elastic deformations: (1) reduction of hole mobility (µp); (2) increase of the value of the positive charge in the SiO2 oxidation layer (determined by the factor β1); (3) generation of point defects, which are stoppers for dislocations (determined by the factor β2). If we substitute in the equation for surface conduction the following expressions for a non-irradiated sample: β 1 = 1 0 17 m - 2 ; β 2 σ = 1 0 14 m - 2 + σ · 3.51 0 7 P a - 1 · m - 2 ; μ p σ = 0.05 m 2 / V · s + σ · 1.5 · 1 0 - 11 m 2 / P a · V · s , we can get a theoretical curve that almost coincides with the experimental one. By reducing the mobility of holes by 5%, the coefficient β2 by 39%, and by increasing β1 by 4.34%, the theoretical dependence of conductivity on the mechanical load can be obtained for irradiated specimens. [ABSTRACT FROM AUTHOR]

The effect of uniaxial elastic deformation on the current–voltage characteristic of surface–barrier Sb–p-Si〈Mn〉–Au diodes is studied. It is shown that reverse-current sensitivity to uniaxial compression exceeds the forward-current sensitivity at identical applied voltages. An increase in the forward current of these structures during deformation is caused by internal gain associated with redistribution of the applied voltage between the base and barrier. [ABSTRACT FROM AUTHOR]

Based on the decisions of electroneutrality equation and experimental results of measurements of the piezo-Hall-effect the dependences of activation energy of the deep level A-center depending on the uniaxial pressure along the crystallographic directions [100], [110] and [111] for n-Ge single crystals, irradiated by the electrons with energy 10 MeV are obtained. Using the method of least squares approximational polynomials for the calculation of these dependences are obtained. It is shown that the activation energy of A-center deep level decreases linearly for the entire range of uniaxial pressure along the crystallographic direction [100]. For the cases of uniaxial deformation along the crystallographic directions [110] and [111] decrease of the activation energy according to the linear law is observed only at high uniaxial pressures, when the A-center deep level interacts with the minima of the germanium conduction band, which proved the lower at the deformation. The various dependences of the activation energy of A-center depending on the orientation of the axis of deformation may be connected with features of its microstructure.

Abstract Changes in conductivity of irradiated and non-irradiated p-Si mono-crystals under the influence of elastic uniaxial mechanical stress were investigated in this paper. An analytical expression was suggested to describe the dependence of surface conductivity as a function of mechanical stress and X-ray irradiation dose. It was shown that 4-angular nano-particles on the surface of “solar” silicon affect the electroconductivity changes under mechanical stress. It was established that X-ray irradiation causes the generation of point defects in silicon. These defects suppress the dislocations movement. It was shown that the resistivity of previously irradiated samples of “electronic” silicon is only slightly sensitive to the influence of uniaxial compression at certain deformation rate.

In thе work, changes in the surface electrical resistance of p-Si crystals were investigated under the simultaneous action of the magnetic field and elastic uniaxial deformation. It was established that a sharp decrease (leap) of resistance occurs at the moment of transition from compression to unclamping at a magnitude of a mechanical load exceeding 18 MPa. Such a leap of resistance is not observed under the elastic uniaxial deformations, which do not exceed 14 MPa. This can be explained by the fact that due to the deeper and more prolonged penetration of the dislocation loops, and the corresponding increase in their length, they accumulate a significant number of charged defects that remain unplaced at the beginning of the release (reduction of the field of mechanical stress). A fluctuation of the resistance value in the direction of increase or towards the reduction occurs in the magnetic field. The diffusion of magnetically sensitive defects into the near-surface region can be explained by the repetition of the processes described in time. In a deformed crystalline lattice, diffusion processes occur more rapidly, which increases the frequency of oscillations of the resistance value. By investigating the IR absorption spectra of experimental samples, it was shown that the decay of defects on the surface (111) of p-Si crystals occurs during a long-term action (288 h) of a constant magnetic field (B = 0.354 T). Such defects are hydrogen-containing and oxygen-containing complexes (Si–O–Si, Si–Si, Si–H2, Si–C, O–Si–O, Si–O–C, Si–CH3, H–OH, H2O, Si–OH). This leads to an increase in the surface resistance of the experimental samples of silicon. [ABSTRACT FROM AUTHOR]

Temperature dependencies for Hall mobility of electrons for the uniaxially deformed n-Si single crystals, irradiated by the flow of electrons Ω=1·1017 el./cm2 with the energy of 12 MeV, are obtained on the basis of piezo-Hall effect measurements. From the analysis of these dependencies it follows that under the uniaxial pressure (0–0.42) GPa and (0–0.37) GPa along crystallographic directions [100] and [111], respectively, the deformation-induced increase of the Hall mobility has been observed. On the basis of the proposed theoretical model of mobility, this increase is explained by the decrease of the amplitude of a large-scale potential with an increase in the magnitude of uniaxial deformation and, accordingly, the probability of electron scattering on this potential. The slight discrepancy between the obtained experimental results and the relevant theoretical calculations at the low temperatures is due to the fact that the electron scattering on the radiation defects, created by the electron radiation, was not taken into account in the calculations. The decrease in Hall mobility of electrons along with an increase in temperature for unirradiated and irradiated silicon single crystals is explained by the growth of the probability of electron scattering on the optical phonons that are responsible for the intervalley scattering in silicon. The obtained results can be used in designing and modelling on the basis of n-Si single crystals of various electronic devices of micro- and nanoelectronics, which can be subject to the extreme conditions of action of the significant radiation and deformation fields. [ABSTRACT FROM AUTHOR]

Although innovative at the time of their inception, all the historic and extant instrumental texture profile analysis (TPA) versions have serious methodological flaws. Their measured and calculated parameters, for example, "hardness," "brittleness," and "cohesiveness," bear only a remote relationship to the same properties as understood in material science and other disciplines. The TPA parameters are supposedly objective measures of the tested food's textural attributes. But because they are all specimen size‐dependent, they cannot be considered intensive material properties. Also, because the arbitrary test conditions, notably the specimen and probe's geometries and the set deformation level significantly affect the TPA parameters' magnitudes, assigning them textural term leads to logical inconsistencies, making their relationship to the food's actual properties even more difficult to establish. It is doubtful that the instrumental TPA parameters indeed describe the same properties in different foods and sometimes even within the same food, as in ripening juicy fruits and certain soft cheeses. It is proposed that the TPA parameters currently in use be replaced by a list of mechanical and other physical properties determined by testing methods recognized by material scientists, such as "yield stress," "strain at failure," "stiffness," and "toughness," perhaps supplemented by a quantitative measure of "juiciness" and/or the acoustic signature's features, especially developed for the particular food. It is also proposed that instead of correlating such intensive material properties with sensory evaluations described by a predetermined sensory vocabulary, they should be used to study the distribution or spectrum of humans' verbal responses, expressed in their own chosen terms. [ABSTRACT FROM AUTHOR]

Metallic nanowires are widely employed as small-scale structural materials due to their characteristically small volume and high strength compared with their bulk counterparts. Nowadays, the mechanical properties of nanowires in pure metals are well understood with the help of experiments and simulations. However, the deformation of nanowires in metallic alloys remains elusive. In recent years, a new class of alloys called refractory multi-principal element alloys (RMPEAs) emerged. RMPEAs are alloys that form solid solution phases and consist of three or more principal elements, most of which are refractory metals. In this paper, we perform atomistic simulations to investigate the uniaxial deformation of nanowires in 16 body-centered cubic RMPEAs. For each RMPEA, three nanowires consisting of atoms randomly distributed in three different ways are used. The main finding is that dislocation slips on {110} planes and twinning on {112} planes, respectively, control the compressive and tensile plastic deformation of the nanowires. To provide references, we also study the deformation of nanowires in natural and A -atom potential-based artificial pure metals. Results show that the deformation of RMPEA nanowires cannot be predicted by simply extrapolating from those of pure metal nanowires, highlighting the significance of directly simulating RMPEAs using multiple random atomic structures. It is also found that RMPEAs possess a reduced tension-compression asymmetry compared with pure metals, regardless of the underlying plastic deformation mechanism. • Uniaxial deformation of nanowires in 16 RMPEAs are studied by atomistic simulations. • Compressive plastic deformation of the nanowires is controlled by dislocation slips. • Tensile plastic deformation of the nanowires is dominated by twinning. [ABSTRACT FROM AUTHOR]

Polymer laminated sheet metal (PLSM) is a layered material in which a thin polymer film is bonded to a sheet metal substrate by means of an adhesive layer. The PLSMs could potentially be used as the blank materials for forming applications such as sheet drawing and stamping. Due to the difference in formability of metallic and polymeric components in the PLSMs, deformation of these materials induces residual stress in the polymer adherend involving thin film and adhesive layer. The residual stress, consequently, may cause interfacial delamination of polymer adherend and hence limit forming applications of the PLSMs. This paper presents an experimental method based on shear punching of uniaxially deformed PLSMs for the assessment of interfacial delamination between metallic substrate and polymer adherend. The experimental results show that the interfacial delamination depends on the amount of deformation and type of the polymer adherend material. In addition, it is shown that the deformation-induced delamination at the interface between the polymer adherend and metallic substrate is a retardation process and can be characterized by the three-parameter Voigt rheological model. Beyond the capabilities of the experiment, the Voigt model can estimate the amount of pure elastic delamination, which occurs immediately upon load removal after deformation. [ABSTRACT FROM AUTHOR]

The mechanical behaviour, crystalline and macromorphology structure development during uniaxial deformation and annealing of poly- l -lactic acid (PLLA), with varying strain rate and draw temperatures ( T d ) above T g , have been investigated using small- and wide-angle X-ray scattering (SAXS/WAXS), microscopy, thermal and mechanical techniques. The mechanical behaviour of PLLA, was strongly dependent on T d where embrittlement and eventual failure were observed as T d was increased, during uniaxial drawing of the amorphous polymer. This was mirrored in the bulk surface morphology where crazing, microvoiding and cavitation occurred with increasing T d . SAXS/WAXS data showed that strain-induced crystallization occurs on drawing, but crystallite orientation decreased with increasing T d , due to chain relaxation at temperatures ≥30 °C above T g . However, no long-range oriented lamellar macromorphology was observed post-draw directly and only developed in the samples that were step annealed at temperatures above T d . Also, the disordered α′ crystal form was observed post-draw at T d between 60 and 80 °C, whereas T d  ≥ 90 °C, resulted in the ordered α crystal form directly. However, on annealing at temperatures of ≥110 °C, the α′-α crystal transition ensued and in all samples, an oriented lamellar macromorphology developed. Therefore, T d and post-draw annealing, have a significant influence on the mechanical properties, crystallinity and crystalline phase transformation in PLLA, which in-turn, affects the polymers medical and industrial applications. [ABSTRACT FROM AUTHOR]

It is shown that at a deformation rate of 0.41 kg/min, the characteristic feature of the dependence of the surface resistance of the p-Si sample on the magnitude of its elastic deformation (R(σ)) is the reduction of the resistance during compression and unclamping. With the increase in the number of “compression-unclamping” cycles, the difference between the positions of the compression and unclamping curves decreases. The transformation of two types of magnetically sensitive defects occurs under the impact of a magnetic field on p-Si crystals. The defects are interrelated with two factors that cause the mutually opposite influence on the conductivity of the crystal. The first factor is that the action of the magnetic field decreases the activation energy of the dislocation holders, which leads to an increase in the electrical conductivity of the sample. The second factor is that due to the decay of molecules of oxygen-containing impurities in the magnetic field, the stable chemisorption bonds appear in the crystal that leads to a decrease in its conductivity. If the sample stays in the magnetic field for a long time, the one or the other mechanism predominates, causing a slow growth or decrease in resistance around a certain (averaged) value. Moreover, the frequency of such changes is greater in the deformed sample. The value of the surface resistance of p-Si samples does not change for a long time without the influence of the magnetic field. [ABSTRACT FROM AUTHOR]

We obtain expressions for the determination of the shear moduli of n-Ge and n-Si single crystals subjected to uniaxial deformation. The proposed method is based on the mechanism of redistribution of electrons between the minima of conduction bands of germanium and silicon subjected to uniaxial compressive deformation along the crystallographic directions [111] and [100]. By using the obtained expressions and the results of the measurements of longitudinal piezoresistance for these single crystals, we determine their shear moduli. [ABSTRACT FROM AUTHOR]

Polymer composites are found throughout the world both natural and artificial in origin. In the vast majority of applications, composites serve as structural support or reinforcement roles. Demand for lightweight tough composites is growing in multiple application spaces such as areospace, biomaterials, and infrastructure with physical properties as diverse as the applications. The unifying component in all composites is the presence of an interphase. Many measurement techniques and measurement tools have been developed for the study of this crucial region in composite materials. Many of these methods are great for the measurment and study of bulk properties or model systems. However, development of methods that permit the direct observation of interactions at the interphase during applied stress are needed. Here we employ fluorescence lifetime imaging and hyperspectral imaging to observe activation of a fluorogenic dye at the composite interface as a result of applied stress. The advantages of this sytem include commercial availability of the dye precursor, and simple one-pot functionalization. The attachment of the dye at the interface is easily monitored through emission wavelength shifts and fluorescence lifetime variations. Interfacial mechano-responsive dyes have potential for both fundamental studies as well as industrial use as a structural health monitoring tool. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the decisions of electroneutrality equation and experimental results of measurements of the piezo-Halleffect the dependences of activation energy of the deep level A-center depending on the uniaxial pressure along the crystallographic directions [100], [110] and [111] for n-Ge single crystals, irradiated by the electrons with energy 10 MeV are obtained. Using the method of least squares approximational polynomials for the calculation of these dependences are obtained. It is shown that the activation energy of A-center deep level decreases linearly for the entire range of uniaxial pressure along the crystallographic direction [100]. For the cases of uniaxial deformation along the crystallographic directions [110] and [111] decrease of the activation energy according to the linear law is observed only at high uniaxial pressures, when the A-center deep level interacts with the minima of the germanium conduction band, which proved the lower at the deformation. The various dependences of the activation energy of A-center depending on the orientation of the axis of deformation may be connected with features of its microstructure. [ABSTRACT FROM AUTHOR]

The adhesion between adhesively bonded polymer film and a metallic sheet substrate in a polymer laminated sheet metal (PLSM) subjected to large deformation, such as in a forming process, is influenced by two deformation-induced factors. These are (i) evolution of surface roughness of metallic substrate with applied strain and (ii) development of residual stress in the polymer adherend (polymer film with a thin uniform adhesive layer on one side) arising from significant differences in the deformation behavior of metal and polymeric components. A new experimental methodology was devised in this study to decouple the effects of substrate surface roughness and residual stress on interfacial peel strength (IPS) of uniaxially deformed PLSMs. This methodology was based on 180° peel testing of PLSM specimens prepared under two different lamination conditions, one involving systematic pre-straining in uniaxial tension of the metallic substrate prior to laminations and the other involving post-lamination pre-straining of the PLSM. The role of pre-strain and peel test speed, for the above laminations conditions, were critically analyzed for their effect on IPS of two differently tailored PLSM systems. The IPS results were attributed to the effect of deformation-induced residual stress and metallic surface roughness. The analysis suggests that IPS is strongly dependent upon the residual stress induced by uniaxial deformation but only marginally on substrate surface roughness depending upon the constituents (film and adhesive) of the adherend. The magnitude of pre-strain was inversely and non-linearly related to IPS for both deformed PLSMs. Peel test speed, on the other hand, showed a more complex behavior in terms of IPS for the two PLSM systems. [ABSTRACT FROM AUTHOR]

A nanocrystalline metal contains grains that are extremely small, with a high proportion of grain boundary (GB). For understanding of the mechanical properties of nanocrystalline metals, it is indispensable to elucidate the influence of GBs on plastic deformation. In this study, molecular dynamics simulations of uniaxial deformation tests on magnesium bicrystals with [ 1 ¯ 1 0 0 ] symmetric tilt GBs were performed in order to reveal the role of GBs during the plastic deformation of hexagonal close-packed metals. We found that not only the critical resolved shear stress but also the active deformation mode itself is sensitively dependent on both the misorientation angle between the grains and the loading direction. In particular, ease of nucleation of basal dislocations from the GB could be qualitatively explained by the dependence of the GB energy on the misorientation angle, where dislocation nucleation from the GB is regarded as a process by which GBs accommodate changes in misorientation angle caused by elastic deformation due to an applied load. [ABSTRACT FROM AUTHOR]

We report on the first fully atomistic simulation of sulfur-crosslinked cis -1,4-polybutadiene (PB) rubbers, both unfilled and nanosilica-filled. A well-integrated network is built by crosslinking the coarse-grained precursor PB chains. The initial configurations for subsequent molecular dynamics simulations are obtained by reverse mapping of well-equilibrated coarse-grained systems. Thermal and mechanical properties of the PB-based elastomers are predicted in reasonable agreement with experiment. The inclusion of silica nanoparticles into the model rubber increases the glass transition temperature and elastic modulus. Under tensile loading conditions, the formation of structural defects (microcavities) within the polymer bulk is observed for nanocomposite at the elastomer/nanoparticle interfaces. [ABSTRACT FROM AUTHOR]

The mechanical response and the corresponding microstructure of polymer blends composed of styrene-isoprene-styrene block copolymer and deuterated polystyrene are studied via in situ small-angle neutron scattering (SANS) measurements during intermittent uniaxial extension. The initial blend morphologies consist of spherical PS glassy domains arranged in body-centered cubic (BCC) lattices. The spheres rearrange affinely with the macroscopic deformation up to Hencky strains ~0.35. Larger deformation is mechanically characterized by yield and strain hardening. In this regime, SANS measurements reveal a transition from a BCC crystal lattice to chevron-like patterns. Using electron microscopy, we found that the chevrons arise from a real-space structure described as spheres that have been stretched along one axis and aligned parallel to one another. Such configuration is unstable and reverts to BCC structure after stress release. After unloading the blends, remnant nano-deformation is observed, which is fully relaxed only in the transverse direction after more than 10 h. Permanent damage of the internal structure along the stretching direction impedes the full recovery of the initial sphere configuration. [ABSTRACT FROM AUTHOR]

The theoretical strength of LaB and MeB borides and a eutectic LaB-TiB system is calculated with quasiharmonic approximation for uniaxial strain in the temperature range between 0 and 2750 K. It is established that the linear temperature dependence of strength, typical of LaB, does not hold in the range 1300-2200 K. It is shown that the theoretical strength increases with higher temperatures. The same dependence is typical of the LaB-MeB systems (Me is Ti, Zr, Hf) at 0.7 mol.% LaB. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Nano- & Electronic Physics is the property of Sumy State University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An approach for molecular dynamics simulation of the formation of polycrystalline materials from a melt during its cooling is proposed. Atomic configurations of copper corresponding to polycrystals with the mean grain size from 2 to 16 nm are obtained. Isothermal uniaxial tension and compression of these polycrystals is studied by the molecular dynamics method. For the mean grain size of polycrystalline copper being smaller than 10 nm, it is shown that Young's modulus and yield stress decrease as the grain size decreases. Shock adiabats for polycrystalline copper are constructed. For a material with the grain size approximately equal to 2 nm, the temperature behind the shock wave front is demonstrated to be 10% higher than that in a polycrystal with the grain size greater than 10 nm. Molecular dynamics calculations predict the presence of copper with a body-centered cubic lattice behind the shock wave front at pressures ranging from 100 to 200 GPa. [ABSTRACT FROM AUTHOR]

Abstract: Natural rubber (NR) film was crosslinked by γ-irradiation under uniaxial extension. The degree of deformation defined as λ′=l′/l 0′ (l 0′ and l′ being the lengths of relaxed and uniaxially deformed sample, respectively) was constant and equal to 1.50, and the total irradiation dose was 300kGy. Deuterium NMR spectroscopy, known as an extremely sensitive method to detect anisotropic molecular motions, was applied for the study of dynamic behaviour of polyisoprene chain segments. Perdeuterated cyclohexane was used as deuterium probe. NMR spectra indicate that segmental motions in NR films crosslinked under deformation are anisotropic. Moreover, spectra of NR films stretched in the direction parallel and perpendicular to the direction of deformation applied during the crosslinking process show an intrinsic difference in orientational behaviour of chain segments. [Copyright &y& Elsevier]

Abstract: This study concerns the thermal and mechanical response of several commercial grades of ethylene – tetrafluoroethylene copolymer films. Differential scanning calorimetry was used to show that, although films have similar degrees of crystallinity and melting temperature, the melting endotherms and crystallisation exotherms differ between materials, suggesting small changes in composition between manufacturers. Films were deformed in tension at a range of temperatures and rates. Selected films were unloaded immediately after stretching, and measurement of the elastic recovery highlighted further differences between materials. Batches of films were pre-drawn uniaxially above the glass transition and immediately quenched. When these materials were subsequently re-drawn below the glass transition temperature, most of them exhibited much improved yield stress, modulus and tensile strength (improving by factors of 5, 5 and 4, respectively at a draw ratio of 3), but a reduced strain to failure. In most of the films, the pre-drawing, as well as the initial orientation of the films, is accounted for by a simple shift in the true strain axis. This is indicative of a material response dominated by entropic network stretch. It also suggests that, in the cases where strain superposition does not work, a different arrangement of crystalline lamellae may be present, limiting the extent to which improved properties can be achieved in some materials. [Copyright &y& Elsevier]

Linear low-density polyethylene (PE-LLD) films were mechanically deformed at room temperature in both parallel and perpendicular directions to their initial orientation obtained during the manufacturing process. The degree of deformation ${\lambda}$, defined as ${\lambda} = l/l_{0}, l$ and l0 being the length of the deformed and relaxed samples, respectively, was varied from 1.0 to 2.0. Oxygen transport was investigated by a manometric method and the results were correlated with differential scanning calorimetry and positron annihilation lifetime spectroscopy measurements in order to investigate the contribution of various factors that influence the permeability of deformed PE-LLD films. An electron spin resonance spin-probe method was employed to determine the influence of uniaxial deformation on the chain segmental mobility in the amorphous phase. The results show that the deformation process reduces oxygen permeability and diffusion coefficients. It was found that the reduction is a combined effect of an increased crystallinity and reduced fractional free volume. The decrease of the chain segmental mobility with deformation plays an important role in the gas diffusion mechanism. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: β phase isotactic polypropylene (β-iPP) with the β phase lamellae oriented parallel to the melt extrusion direction, was employed to investigate the deformation-induced structure evolution at various temperatures (25, 80, 110, 130 and 140 °C). The orientation change of β phase during deformation greatly influences the β to α phase transformation and its temperature dependence. At temperatures lower than 110 °C, the orientation of β phase is almost unchanged during deformation, and void or crack forms before fragmentation and reorientation of β phase. The crystal size change of β phase is small, and the defolding of the β lamellae triggers the β to α phase transformation. As the deformation temperature rises to 130 and 140 °C, the reorientation of β phase occurs gradually upon stretching, and the size of micro-voids decreases due to the fact that less β crystal fragmentation takes place at high draw temperature than that at low temperature. The β to α phase transformation is mainly induced by intra-lamella slip, and the trend of crystal size change of β phase is larger. The chains orientation changes from perpendicular to the stretching direction in β phase to parallel to the stretching direction in α phase is achieved by the chains defolding of β phase along the stretching direction at temperatures lower than 110 °C, and it is through the chains reorientation of β phase along the stretching direction at temperatures of 130 and 140 °C. The crystal size of α phase of the deformed β-iPP during deformation depends on the dynamic balance of the breakage of existing α crystal and the formation of new crystal through phase transformation. Specially, at draw temperature of 25 °C, the slippage of β phase relieves the breakage of α phase crystal, which indicates that the high content of β phase crystal really accounts for the toughening effect on iPP. [Copyright &y& Elsevier]