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1.
As a first attempt to study the dynamics of a heated structure with complicated boundaries, this paper deals with the thermal buckling and the natural vibration of a simply supported slender beam, which is subject to a uniformly distributed heating and has a frictional sliding end within a clearance. This sliding end is initially at a stick status under the friction force, but may be slightly slipping due to the thermal expansion of the beam until the sliding end contacts a stop, i.e., the bound of the clearance. The material properties of the beam are temperature-independent for low temperature, but temperature-dependent for high temperature. For each case, the analytic solutions for the critical buckling temperature and the natural frequencies of the heated beam are derived first. Then, discussions are made to reveal the effects of beam parameters, such as the ratio of beam length to beam thickness, the ratio of clearance to beam length and the temperature-dependent material properties, on the critical buckling temperature and the fundamental natural frequency of the heated beam. The study shows that both friction force and clearance have significant influences on the critical buckling temperature and the fundamental natural frequency of the beam. When the friction force is not very large, the clearance can greatly increase the critical buckling temperature. These conclusions enable one to properly design the stick–slip–stop boundary so as to improve the mechanical performance of the beam in thermal environments. 相似文献
2.
《Journal of Physics and Chemistry of Solids》2004,65(2-3):421-424
The present study describes a solid–solid transformation of nanocrystalline sodalite from the solid gel mixture of Al2O3-pillared montmorillonite (Al-PILC) with sodium hydroxide at room temperature (25 °C) under an ambient atmosphere. Powder X-ray diffraction (XRD) analysis confirms that the X-ray crystalline sodalite products are crystallized after 12 days, whereas infrared absorption (IR) spectra reveal that diagnostic IR absorption peaks due to single four-membered ring of sodalite framework is observed even after 1 day. Scanning electron microscopy (SEM) shows that Al-PILC is transformed into discrete nano-sized sodalite particles (∼50 nm). Although the induction period, the time elapsing before nucleation, for the solid–solid transformation takes much longer (12 days), the nanocrystalline sodalite is successfully obtained at this extremely mild synthetic condition through solid–solid transformation. 相似文献
3.
《Composite Interfaces》2013,20(7-9):869-890
Polylactide–flax fiber composites with 1, 10 and 20 wt% fiber were melt-compounded and subsequently molded via the conventional and microcellular injection-molding processes. Silane was used as a coupling agent. The effects of fiber and silane content on cell morphology, static and dynamic mechanical properties, and crystallization properties have been studied. The average cell size decreased while the cell density increased with the fiber content. The degree of crystallinity increased with the fiber content. Silane treatment of fibers affected neither the cell morphology nor the degree of crystallinity. The toughness and strain-at-break of solid samples decreased with the fiber content while silane treatment increased both properties; however, neither fiber content nor silane treatment had much influence on the toughness and strain-at-break of microcellular samples. The specific modulus of both solid and microcellular samples increased with the fiber content. The specific strength of the solid and microcellular PLA–flax composites were only slightly lower than that of their solid and microcellular pure PLA counterparts. Overall, the toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than that of their solid counterparts. The storage modulus of the PLA–flax composites with 10 and 20% fiber contents was higher than that of pure PLA. 相似文献
4.
《声学学报:英文版》1991,(4)
In this paper,a general model on sound reflection from a lay-ered solid medium with rigid and slip interfaces is proposed by using ma-trix method.Analytical expressions for reflection coefficients of bothlongitudinal and transverse waves from the layered solid medium with oneor two slip interfaces are derived.Numerical results of sound reflectioncoefficients from some typical adhesive joints with slip and rigid interfacesare presented,which may be useful for correct choice of technicalparameters in ultrasonic evaluation of their interface properties. 相似文献
5.
N. P. Kobelev I. G. Brodova Ya. M. Soifer A. N. Manukhin 《Physics of the Solid State》1999,41(4):501-505
The effect on the internal friction and Young’s modulus of the evolution of the structure of the amorphous alloy Mg84Ni12.5Y3.5 (relaxation of internal stresses, devitrification, nucleation and decay of nanocrystalline phases) was investigated as it
was heated. The measurements were performed on ribbon samples by flexural oscillations. Irreversible peaks of the internal
friction and anomalies in the behavior of Young’s modulus as a function of temperature were observed. The position of the
anomalies correlates with the characteristic temperatures of restructurings observed by differential thermal and x-ray diffraction.
Possible internal-friction mechanisms associated with various types of structural relaxation and nanocrystallization processes
in the alloy are discussed.
Fiz. Tverd. Tela (St. Petersburg) 41, 561–566 (April 1999) 相似文献
6.
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8.
Internal friction and dynamic shear modulus in an indium–21?at.% thallium alloy were measured as functions of frequency and cooling rate using broadband viscoelastic spectroscopy during the martensitic transformation which occurs in this material occurs around 50°C. Microstructural evolution of martensitic bands was captured using time-lapse optical microscopy. The amplitude of damping peaks due to the temperature-induced transformation in the polycrystalline alloy was found to exceed those reported by others for single crystals of similar alloy compositions, in contrast to the usual reduction in damping in polycrystals. The high temperature portion of the damping peak occurs before martensitic bands are observed; therefore this portion cannot be due to interfacial motion. Constrained negative stiffness of the grains can account for this damping, as well as for amplification of internal friction peaks in these polycrystals and for sigmoid-shaped anomalies in the shear modulus at high cooling rates. Surface features associated with a previously unreported pre-martensitic phenomenon are seen at temperatures above martensite-start. 相似文献
9.
First-principles study of elastic and slip properties of non-canonical β-based Al–Cu–Fe approximants
N. I. Medvedeva 《哲学杂志》2018,98(23):2135-2150
Ab initio calculations were carried out to compare the mechanical properties of β-based non-canonical Al–Cu–Fe approximants of quasicrystals with cubic (β), monoclinic (η) and orthorhombic (ξ1, ξ2) structures, which all demonstrate high strengthening. The aim was to elucidate the competitive effects of the η- and ξ-ordering and iron content on deformation behaviour of these phases. We found that the Young’s modulus, polycrystalline shear modulus, mechanical stability and shear elastic modulus G(n,m) for different slip planes decrease for β-Al50Cu1-xFex with lowering iron content, but they grow from β-Al50Cu31.25Fe18.75 to the ordered η-Al50Cu45Fe5, and ξ2-Al45.5Cu50Fe4.5 that indicates a growing resistance to plastic deformation due to ordering and agrees well with our experimental finding. The preferable slip systems were predicted based on the calculated generalised stacking fault (GSF) energies in β-(Cu,Fe)Al and η-(Cu,Fe)Al with similar Fe concentration. The GSF energies confirmed also that the strengthening observed in η-phase is related to ordering rather than the Fe effect in consistence with a stronger covalent bonding in η-phase. 相似文献
10.
NENGXian PANWen-Xia WUCheng-Kang 《中国物理快报》2003,20(5):685-687
The beat flux distributions were measured by using transient method for an argon dc laminar plasma-jet flow impinging normally on a plate surface embedded with copper probes.Different powders were coated on the probe surfaces and the effect of powder coating on the heat transfer from jet flow to the probe surface was examined Experimental results show that the maximum values of the heat flux to the probe increase with the coating of fine metal powders,while for the surfaces coated with fine ceramic powders,the maximum values of heat flux decrease,compared with that to the bare copper probe surface. 相似文献
11.
Single-wavelength anomalous diffraction (SAD) phasing is increasingly important in solving de novo protein structures. Direct methods have been proved very efficient in SAD phasing. This paper aims at probing the low-resolution limit of direct-method SAD phasing. Two known proteins TT0570 and Tom70p were used as test samples. Sulfur-SAD data of the protein TT0570 were collected with conventional Cu-Kα source at 0.18 nm resolution. Its truncated subsets respectively at 0.21, 0.30, 0.35 and 0.40 nm resolutions were used in the test. TT0570 Cu-Kα sulfur-SAD data have an expected Bijvoet ratio 〈 |△F| 〉 / 〈 F 〉 ~ 0.55%. In the 0.21 nm case, a single run of OASIS-DM-ARP/wARP led automatically to a model containing 1178 of the total 1206 residues all docked into the sequence. In 0.30 and 0.35 nm cases, SAD phasing by OASIS-DM led to traceable electron density maps. In the 0.40 nm case, SAD phasing by OASIS-DM resulted in a degraded electron density map, which may be difficult to trace but still contains useful secondary-structure information. Test on real 0.33 nm selenium-SAD data of the protein Tom70p showed that even automatic model building was not successful, the combination of manual tracing and direct-method fragment extension was capable of significantly improving the electron-density map. This provides the possibility of effectively improving the manually built model before structure refinement is performed. 相似文献
12.
Raman spectroscopy is applied to study the surfaces of a pair of tantalum and titanium alloy samples after high-speed dry friction. The surface of titanium alloy (Ti–6Al–4V) shows titanium oxides on the rubbing surfaces. Raman spectra enable to differentiate the allotropic phases of anatase or rutile. The presence of these phases is the signature of the local thermal history during the friction tests. Moreover, Raman mapping allows localizing area the flash temperatures that may have been produced by the friction between sample asperities. 相似文献
13.
N. Moutalibi A. M’chirgui J. Noudem 《Physica C: Superconductivity and its Applications》2010,470(13-14):568-574
The YBa2Cu3O7?x (Y123) textured bulk superconductors with various amounts of nanometer alumina particles were fabricated by a seeded infiltration and growth process. The addition of nanometer alumina was found to be effective for an improvement of the superconducting properties. The critical current density (Jc) values were increased twice in self field with a slight addition amount of nanometer alumina particles (maximum Jc at 0.01 wt.% alumina addition). The present work suggests that the use of insulating inclusions in the nanometer sub-scale can stabilize the flux-line lattice and greatly enhance the pinning capabilities of the infiltrated samples. No refinement of Y211 particles was observed with alumina addition. The Jc improvement by nanometer alumina inclusions is likely rendered to the insulating nano-pinning centers that have been successfully embedded into superconducting Y123 matrix. On the other hand, we examined the effect of the pinning centers size on the superconducting properties of infiltrated YBCO bulk samples. To this effect insulating nano-pinning centers with two different size distributions has been successfully incorporated within YBCO matrix of bulk superconductor by slightly doping with nano-particle alumina dispersions. Two alumina nano-particle dispersions with mean size diameters of about 20 nm and 130 nm were used. It was shown that the size of the pinning centers can affect considerably the Jc performances and the pinning mechanism. 相似文献
14.
Danilkin M. I. Klimonskii S. O. Koksharov Yu. A. Kuznetsov V. D. Must M. Nikiforov V. N. Primenko A. É. Solov'eva N. V. Seman V. O. 《Russian Physics Journal》2000,43(8):670-674
The electron paramagnetic resonance (EPR) spectra and the stationary magnetic susceptibility are investigated for Ca1–x
Eu
x
S and Sr1–x
Eu
x
S solid solutions (0.00005 < x < 0.0032). The EPR spectrum of Eu2+ in both matrices contains a wide structureless line in addition to the narrow lines of the superfine structure characteristic of ions with high local symmetry. Because of the extraordinary temperature dependence of this line in CaS:Eu, it is associated with strongly interacting magnetic centers, namely, exchange-coupling pairs and chains or more complex clusters of magnetic ions. At the same time, the dependence of the stationary magnetic susceptibility in the temperature range 4.2–50 K has no peculiarities for CaS:Eu and SrS:Eu and obeys the Curie law. 相似文献
15.
Anton Alekseev Florian Naef Xiaomeng Xu Chenchang Zhu 《Letters in Mathematical Physics》2018,108(3):757-778
Descent equations play an important role in the theory of characteristic classes and find applications in theoretical physics, e.g., in the Chern–Simons field theory and in the theory of anomalies. The second Chern class (the first Pontrjagin class) is defined as \(p= \langle F, F\rangle \) where F is the curvature 2-form and \(\langle \cdot , \cdot \rangle \) is an invariant scalar product on the corresponding Lie algebra \(\mathfrak g\). The descent for p gives rise to an element \(\omega =\omega _3+\omega _2+\omega _1+\omega _0\) of mixed degree. The 3-form part \(\omega _3\) is the Chern–Simons form. The 2-form part \(\omega _2\) is known as the Wess–Zumino action in physics. The 1-form component \(\omega _1\) is related to the canonical central extension of the loop group LG. In this paper, we give a new interpretation of the low degree components \(\omega _1\) and \(\omega _0\). Our main tool is the universal differential calculus on free Lie algebras due to Kontsevich. We establish a correspondence between solutions of the first Kashiwara–Vergne equation in Lie theory and universal solutions of the descent equation for the second Chern class p. In more detail, we define a 1-cocycle C which maps automorphisms of the free Lie algebra to one forms. A solution of the Kashiwara–Vergne equation F is mapped to \(\omega _1=C(F)\). Furthermore, the component \(\omega _0\) is related to the associator \(\Phi \) corresponding to F. It is surprising that while F and \(\Phi \) satisfy the highly nonlinear twist and pentagon equations, the elements \(\omega _1\) and \(\omega _0\) solve the linear descent equation. 相似文献
16.
Continuous transformation of icosahedral quasicrystals as observed in Al-Cu-Fe alloys proceeds through intermediate modulated structures towards rational approximants with a rhombohedral structure. Corresponding to the diffuse scattering in the electron diffraction during the transformation, a tweed contrast emerges throughout the icosahedral phase matrix. High-resolution electron microscopy reveals a complex modulated structure which tends to evolve into rhombohedral microdomains. The observed distortion of the reciprocal quasilattice due to the structural modulation has been simulated on a computer by introducing linear phason strains into the quasicrystals. 相似文献
17.
A. V. Golenishchev-Kutuzov V. A. Golenishchev-Kutuzov R. I. Kalimullin A. V. Semennikov 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(3):282-284
Elastic and ferroelectric characteristics of single crystals of lithium niobate and tantalate are investigated in a wide range of temperatures by complex acoustooptic means. The contribution from Jahn–Teller NbO6 and TaO6 systems to the characteristics of elastic moduli, ultrasonic attenuation, and nonlinear optical coefficients is analyzed using a new phenomenological model. It is hypothesized that the displacement of Nb5+ and Ta5+ ions, which exhibit the second-order Jahn–Teller effect along trigonal axis C, and the subsequent ordering of octahedral, result in unusual elastic and ferroelectric properties. 相似文献
18.
JETP Letters - In this study, the influence of two nanoscale parameters (e.g., ratios of energy and width of two different interfaces) and temperature have been investigated which drastically... 相似文献
19.
K. Nordlund T.T. Järvi K. Meinander J. Samela 《Applied Physics A: Materials Science & Processing》2008,91(4):561-566
The nature of cluster ion–surface interactions changes dramatically with the kinetic energy and mass of the incoming cluster
species. In this article we review some recent work on the nature of cluster–surface interactions spanning an energy range
from a few tens of meV/atom to several MeV/cluster and cluster sizes in the range of 1–300000 atoms/cluster. We describe five
possible distinct outcomes of a single cluster impact event: (i) deposition into a non-epitaxial configuration, (ii) deposition
into an epitaxial configuration, (iii) crater formation by liquid flow, (iv) crater formation by hydrostatic pressure, (v)
implantation.
PACS 65.80.+n; 82.60.Qr; 61.46.Hk; 02.70.Ns 相似文献