排序方式: 共有46条查询结果,搜索用时 265 毫秒
31.
This paper addresses quasi-static loading of the shear compression specimen (SCS), that has been especially developed to investigate the shear response of
materials at various strain rates. Previous work [4, 5] addressed bi-linear hardening materials, whereas the present work
concerns parabolic hardening materials. The investigation is done numerically using three-dimensional elastoplastic finite
element simulations. The analyses show that the averaged von Mises stress (
) and strain (
) on a mid-section of the gauge reflect accurately the prescribed parabolic hardening model. A method for finding the parabolic
hardening coefficients and reducing the measured load, P, and displacement, d, into equivalent stress
and strain
is introduced and tested. A very good agreement is observed, thus confirming the potential of the technique for large strain
testing of parabolic hardening materials. 相似文献
32.
A review of wave celerity in frictionless and axisymmetrical steel-lined pressure tunnels 总被引:1,自引:0,他引:1
Generally applicable approaches for estimating the “quasi-static”, which means without fluid-structure interaction and frequency-dependent water-hammer wave speed in steel-lined pressure tunnels are analyzed. The external constraints and assumptions of these approaches are discussed in detail. The reformulated formulas are then compared to commonly used expressions. Some special cases of wave speed calculation such as unlined pressure tunnels and open-air penstocks are investigated. The quasi-static wave speed is significantly influenced by the state of the backfill concrete and the near-field rock zone (cracked or uncracked). In the case when these two layers are cracked, the quasi-static wave speed is overestimated in between 1% and 8% compared to uncracked concrete and near-field rock layers. Depending on the stiffness of steel liner and penstock, the fluid-structure interaction leads to significant difference in wave speeds values. Compared to the quasi-static case, the fluid-structure interaction approach, applied to steel-lined tunnels, results up to 13% higher wave speed values in the high-frequency range (higher than 600 Hz) and up to 150% lower values for frequencies between 150 and 300 Hz in the considered test case. 相似文献
33.
The paper presents experimental and analytical studies on axial compression of aluminium spherical shells having Radius/wall thickness (R/t) ratios between 23 and 135. Quasi-static compressive load was applied centrally and with offset through a indenter having diameter of 22 mm. Testing was carried out on an INSTRON machine having 250 T capacity. Shells having different radius and wall thickness were tested, to classify their modes of collapse and their corresponding energy absorption mechanism. In experiments shells of lower R/t values were found to collapse due to formation of an inward dimple associated with a rolling plastic hinge in central as well as in offset loading. On the other hand, shells of higher R/t values were collapsed initially with formation of an axisymmetric inward dimple, but in later stage of compression showed buckling of non-symmetric shape consisting of integral number of lobes and stationary plastic hinges. The stationary hinges were formed between consecutive lobes. Experimental observations are used to propose an analytical model for prediction of load–compression and energy–compression curves. The results obtained from analytical model compared with the experimental results and found match fairly well. 相似文献
34.
Jian Zhu 《Journal of nanoparticle research》2009,11(4):785-792
In this paper, theoretical calculations based on dipole-limit are performed to investigate the effects of curvature on the
surface plasmon resonance (SPR) properties of nanometer size gold spheroid and shell. By comparing the aspect ratio with the
shell thickness, we demonstrated that the curvature radius is a common better factor that can be used to predict the SPR wavelength
and shift fashion. For nanospheroid, increasing the ratio of curvature radius corresponding to the climaxes leads to an increase
in the ratio of SPR wavelength, whereas increasing the ratio of curvature radius of outer and inner surface in nanoshell leads
to an decrease in the ratio of SPR wavelength. As a morphologic factor, curvature radius plays an important role in affecting
the distribution of electron density, and consequently controlling the SPR frequency. 相似文献
35.
A coupled-dipole approach is proposed in order to study the coupling between the probe tip and the rough sample in SNOM. In the present model both the optical probe tip and the sample protrusions are represented by polarizable dipole spheres. The induced polarization effects on the sample surface can be replaced by the image dipoles in the circumstance of quasi-static electromagnetic field approximation. Applying the radiation theory of the dipole, we have established a set of self-consistent equations to describe the field distribution at the sites of the probe tip and the sample protrusions. The results are completely the same as those obtained by means of the dyadic electromagnetic propagator formalism and also the derivation procedure is relatively simple. This method permits us to analyze the physical mechanisms of the interaction between the probe tip and the rough surface in SNOM intuitively. Based on this approach, we further discuss the influence of polarization of the incident light on the imaging quality. The calculating result shows that the shape and the contrast of the images of the sample are both sensitive to the field polarization, and the z-polarized mode is proved to give better resolution in SNOM. 相似文献
36.
The variation of stress field around an oscillating crack tip in a quenched thin glass plate is observed using instantaneous
phase-stepping photoelasticity. The successive images around the propagating crack are recorded by a CCD camera that is equipped
with a pixelated micro-retarder array. Then, the phase maps of the principal stress difference and the principal direction
are easily obtained even though the photoelastic fringes cannot be visualized. The path of the crack growth as well as the
stress intensity factors and the crack tip constraint are obtained from these phase distributions. Results show that the mode
I stress intensity factor and the crack tip constraint vary remarkably with the crack growth. In addition, the results show
that the mode-II stress intensity factor exists even though the crack propagates smoothly. 相似文献
37.
Igor Chueshov Stanislav Kolbasin 《Nonlinear Analysis: Theory, Methods & Applications》2010,73(6):1626-1262
We study long-time dynamics of a class of plate models with a state-dependent damping coefficient and their quasi-static limits. We first present the problem in abstract form and then prove the existence of finite-dimensional global attractors and their upper semicontinuity in the quasi-static limit, i.e., in the case when the mass density of plate tends to zero. Our proofs involve a recently developed method based on “compensated” compactness and quasi-stability estimates. As an application we consider the nonlinear Kirchhoff, von Karman and Berger plate models with different types of boundary conditions and damping coefficients. Our results can be also applied to the nonlinear wave equations in an arbitrary dimension. 相似文献
38.
Based on the three-dimensional quasi-static general solution of the transversely isotropic pyroelectric material, the Green's function for an infinite transversely isotropic pyroelectric material under a step point heat source is presented in this paper. Firstly, a suitable function with an undetermined constant is constructed. Secondly, the Green's function can be obtained by substituting this function into the general solution. The undetermined constant can be determined by the heat conservation equation. Finally, the numerical results are shown in form of contours at the different times. 相似文献
39.
One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions.This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains.The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames.Moreover,a force-measuring frame is designed and manufactured based on the quasi-static load series.The load decoupling model of the quasi-static load series is then established via calibration tests.Quasi-static load–time histories,together with online tests and decoupling analysis,are obtained for the intermediate range of the Beijing—Shanghai dedicated passenger line.The damage consistency calibration of the quasi-static discrete load spectra is performed according to a damage consistency criterion and a genetic algorithm.The calibrated damage that corresponds with the quasi-static discrete load spectra satisfies the safety requirements of bogie frames. 相似文献
40.
The present paper deals with the determination of a quasi-static thermal stresses in a thick circular plate subjected to arbitrary initial temperature on the upper face with lower face at zero temperature and the fixed circular edge thermally insulated. The results are obtained in series form in terms of Bessel’s functions and they are illustrated numerically. 相似文献