Sharif Digital Repository

Using Hamilton's principle, exact equations of motion for non-linear planar and spatial Euler-Bernoulli beams are derived. In the existing non-linear Euler-Bernoulli beam formulations, some elastic terms are dropped by differentiation from the incomplete Green-Lagrange strain tensor followed by negligible elastic deformations of cross-sectional frame. On the other hand, in this article, the exact strain field concerning considerable elastic deformations of cross-sectional frame is used as a source in differentiations. As a result, the achieved closed-form equations are exact and more accurate than formerly reported equations in the literature. Moreover, the applicable dynamic model of... 

Both theoretical and experimental results of an optical beam shaping system are investigated in this report. The described system is a two-stage beam shaping device including a fiber-bundle and a prism-duct. A source light is used to illuminate the fiber-bundle and the image of output beam is captured by a CCD camera. The fiber-bundle output beam shape shows a linear arrangement of circular spots lights, which are placed in a rectangular cross section of about 21.37 mm×2.44 mm. In another study, the photograph picture of the prism output beam is taken by a digital camera. The prism output beam cross section is a square shape with a dimension of about 4×4 mm2. According to the experimental... 

A closed form solution is presented in this paper to study the dynamics of a composite beam with a single delamination under the action of a moving constant force. The delaminated beam is divided into four interconnected beams using the delamination limits as their boundaries. Governing motion equations are derived in which the differential stretching and the bending-extension coupling are considered. The method of modal analysis is adopted to derive analytically the dynamic response of each beam. The obtained results for the free vibrations of delaminated beam are verified against reported similar results in the literature. Moreover, the maximum dynamic response of such a beam is compared... 

The characterization of ion beam current density distribution and beam uniformity is crucial for improving broad-beam ion source technologies. The design of the broad ion beam extraction system directly affects these two parameters, therefore, depending on the application, the design and geometry of the source is changed. In this study, the effect of the presence or the absence of a neutralization process on the ion beam density was investigated. Also, the effect of the probe bias on the ion beam current measurement was evaluated. Eventually, using a flat probe, the ion beam profiles obtained from the extraction system of the ion source (Model RFIS 60, ACECR, Iran) were measured at energies... 

Shape memory polymers (SMPs) are a class of smart materials which can recover their shape even after many shape changes in application of an external stimulus. In this paper, flexural behavior of a composite beam, constructed of a corrugated part filled with SMPs, is studied. This composite beam is applicable in sensor and actuator applications. Since the corrugated profiles display higher stiffness-to-mass ratio in the transverse to the corrugation direction, the beams with a corrugated part along the transverse direction are stiffer than ones with a corrugated part along the length. Employing a developed constitutive model for SMPs and the Euler–Bernoulli beam theory, the behavior of the... 

Discrete motion equations of an Euler-Bernoulli, Timoshenko and higher-order beams under a moving mass are derived for different boundary conditions. To this end, the reproducing kernel particle method (RKPM) has been utilized for spatial discretization, beside the extension of Newmark-β method for time discretization of the beams motion equations. The effects of significant parameters such as the beam's slenderness and velocity of the moving mass on the maximum deflection and bending moment of different beams are studied in some details. The results indicate the existence of a critical beam's slenderness mostly as a function of beam's boundary conditions, in which for slenderness lower than... 

A micro scale Timoshenko beam was modeled with strain gradient theory in "A micro scale Timoshenko beam model based on strain gradient elasticity theory" by Wang et al., European Journal of Mechanics - A/Solids, vol. 29, pp. 591-599, 7//2010. Looking at the modeling of the beam, a mistake in deriving the effect of classical moment has occurred. The classical boundary conditions of a Timoshenko beam could not be derived going backward from the strain gradient Timoshenko beam theory which has been presented in aforementioned paper. In this comment, the contradiction has been shown and the correct form of the boundary conditions and final equations has been derived  

Design and performance of two-stage optical beam shaping system based on a plastic fiberbundle, prism coupled waveguide, is described in this study. Such systems offer practical means to modify and change the output beam shape at two stages and also provide quantitative information concerning the output beam intensity. It is possible to investigate output power and image transmittance data by using a light source for illumination and image analysis by a CCD/digital camera. The photograph picture of the illuminating LED beam shows a circular shape with a diameter of about 10 mm at its output point. Picture of the fiber-bundle output beam is also taken, which shows a rectangular shape with a... 

A micro scale Timoshenko beam was modeled with strain gradient theory in “A micro scale Timoshenko beam model based on strain gradient elasticity theory” by Wang et al., European Journal of Mechanics – A/Solids, vol. 29, pp. 591–599, 7//2010. Looking at the modeling of the beam, a mistake in deriving the effect of classical moment has occurred. The classical boundary conditions of a Timoshenko beam could not be derived going backward from the strain gradient Timoshenko beam theory which has been presented in aforementioned paper. In this comment, the contradiction has been shown and the correct form of the boundary conditions and final equations has been derived  

In this paper, the vacuum film deposition through electron beam evaporation has been reviewed and the effect of magnetic field on the operation of this system has been explained. Then, the magnetic field distribution due to magnetic components configuartion of a commercial evaporation source with 270-degree electron beam gun (manufactured by Sharif University Branch of ACECR), has been simulated by means of a finite element software, ANSYS. The simulation result was verified by comparing with the results obtained from measurement by Hall Effect sensor. Furthermore, by using the ray-tracing capability of the software, the capability of the magnetic lens of this device for electron beam... 

A simple geometrical method is used here for divergence determination of a TEA N2 laser. Using beam cross-section (rectangle) monitoring on the fluorescence paper and geometrical method, the laser beam divergence is determined. Variations of the laser beam width (W) and height (H) with respect to the gap distance are investigated for propagation distances of 10, 30, and 50 cm from the laser aperture. For the 0.52 mm gap, the beam width (W) at a distance of 10 cm is about 2 cm and height is also 2 cm (H = 2 cm), while both increase to about W = 3.125 cm, and H = 2.4 cm at a distance of 50 cm. At 50 cm distance, for a gap distance range of 0.52 mm, W = 3.125, H = 2.4 cm, which increases to W =... 

A hybrid plasmonic-dielectric metasurface is proposed in order to manipulate beam propagation in desired manners. The metasurface is composed of patterned hybrid graphene-silicon nano-disks deposited on a low-index substrate, namely silica. It is shown that the proposed hybrid metasurface simultaneously benefits from the advantages of graphene-based metasurfaces and dielectric ones. Specially, we show that the proposed hybrid metasurface not only provides reconfigurability, just like previously proposed graphene-based metasurfaces, but also similar to dielectric metasurfaces, is of low loss and CMOS-compatible. Such exceptional features give the metasurface exceptional potentials to realize... 

A hybrid plasmonic-dielectric metasurface is proposed in order to manipulate beam propagation in desired manners. The metasurface is composed of patterned hybrid graphene-silicon nano-disks deposited on a low-index substrate, namely silica. It is shown that the proposed hybrid metasurface simultaneously benefits from the advantages of graphene-based metasurfaces and dielectric ones. Specially, we show that the proposed hybrid metasurface not only provides reconfigurability, just like previously proposed graphene-based metasurfaces, but also similar to dielectric metasurfaces, is of low loss and CMOS-compatible. Such exceptional features give the metasurface exceptional potentials to realize... 

The harmonic displacement response of a beam is utilized as the input signal function in wavelet analysis. Sudden changes in the spatial variation of transformed response identify the location of damages and defects. The damage incurred causes a change in the stiffness or mass of the beam. This causes a localized singularity which can be identified by a wavelet analysis of the displacement response. In this article, it is shown that using harmonic response is superior to the static deflection response and this approach is more effective in the presence of noise and more sensitive to the versatility of the applied harmonic loads. © 2007 SAGE Publications  

The response of a Timoshenko beam with uniform cross-section and infinite length supported by a generalized Pasternak-type viscoelastic foundation subjected to an arbitrary-distributed harmonic moving load is studied in this paper. Governing equations are solved using complex Fourier transformation in conjunction with the residue and convolution integral theorems. The solution is directed to compute the deflection, bending moment and shear force distribution along the beam length. A parametric study is carried out for an elliptical load distribution and influences of the load speed and frequency on the beam responses are investigated. © 2004 Elsevier Ltd. All rights reserved  

In this study, test results of four precast concrete beam-column connections and one monolithic concrete connection are presented. The tests constituted the second phase of an experimental program on a 2/5-scale model precast connection. The objective of the test program was to design a simple moment-resisting precast connection for regions of high seismicity. The connection transfers bending moment by a combination of lap-splicing and end anchorage of bars. The end portions of precast beams sit on the column bearing area at the beginning of subassemblage construction. The variables examined were the level of axial load on column, spacing of beam stirrups in the connection length region,... 

A new approach is presented that can be used to determine the kern of a general arbitrary section with any shape and conditions. The method is simple, practical and powerful, and is based on elementary calculus. Geometries containing curved boundaries and arbitrary shapes can be handled easily with the analytical equations presented, while the numerically specified shape of any other cross-section can also be analyzed by using a numerical form of the exact governing equations developed. The correctness of the results has been ascertained by comparison with analytical solutions, as well as with examples presented in the literature, and very good agreement has been achieved. © 2001 Elsevier... 

This article extends a procedure that has been used to discretize a continuous flexible beam into a system of rigid bars and joints, which resist relative rotation of the attached bars. The object of this article is to present and formulate a simple and practical approximate technique for determining the time response of beams with internal hinges and different boundary conditions, carrying a moving mass. The results are compared with a general-purpose nonlinear dynamic finite element program, and a good agreement is achieved. © 2000 Elsevier Science Ltd. All rights reserved  

In this paper, a continuous model for vibration analysis of a beam with an open edge crack including the effects of shear deformation and rotary inertia is presented. A displacement field is suggested for the beam and the strain, and stress fields are calculated. The governing equation of motion for the beam has been obtained using Hamilton's principle. The equation of motion is solved with a modified Galerkin method and the natural frequencies and mode shapes are obtained. A good agreement has been observed between the results of this research and the results of previous work done in this fiels. The results are also compared to results of a similar model with Euler-Bernoulli assumptions to... 

It is well known that shear strength of beams without stirrups shows a strong size effect. At present, several formulas of size effect are used by some codes and suggested by various researchers. Most of those formulas are not in agree with fracture mechanics. Recently, a simple formula based on modified compression field theory, MCFT, was proposed (Collins and Kuchma [1], Lubell et al. [2]), which shows a size effect stronger than the size effect formula based on fracture mechanics, proposed by Bazant (e.g. Bazant and Kazemi [3], Bazant and Yu [4]). In this paper it is shown that with some refined considerations, formulas are resulted in agree with Fracture Mechanics concept. In the derived...