轴向及弯曲荷载作用下薄壁梁柱构件的侧向屈曲

基于非线性稳定模型,推导出弯曲和轴向荷载作用下具有双向对称I型截面的简支梁柱构件的分析方案。设计中对一些具有代表性的荷载工况提供了一种独特紧凑的截面形式。分析中考虑了一阶弯曲分布,装载高度,预屈曲挠度效应和轴向荷载。通过采用壳单元的非线性有限元分析对建议的解决方案进行验证。所提议方法与非线性平衡方程计算结果能很好地吻合,证明古典线性稳定性的解决方案低估了这种构件在侧向屈曲稳定中的抵抗能力,尤其是大翼缘的I型截面。对轴力在超静定梁的抗侧向屈曲中所起作用进行数值研究,发现：当梁的轴向变形受到限制时会在梁中产生轴拉力作用,这导致了一些梁截面变形减小,梁呈现出无分叉的非线性性能。     

Linear and non-linear stability analyses of thin-walled beams with monosymmetric I sections

The paper investigates beam lateral buckling stability according to linear and non-linear models. First, the classical linear stability solutions are derived from the stability equation in the case of monosymmetric cross-sections. Bending distribution, load height parameter and Wagner's coefficient effects are taken into account. In the second step, they are extended to non-linear stability by considering pre-buckling deformation and improved solutions are then obtained. Based on a finite element model developed for large torsion of thin-walled beams with open sections, the stability of beams under gradient moments (M₀, ψM₀, ?1≤ψ≤1) is particularly investigated. It is then concluded that beam lateral buckling resistance depends not only on pre-buckling deformation but also on section shape and load distribution. For bisymmetric I beam, closed form solutions are possible and pre-buckling deformations have an incidence. In the case of beams with monosymmetric I and Tee sections, effects of pre-buckling deflections are important only when the largest flange is in compression under M₀ and positive gradient moment. Analytical solutions are possible. For negative gradient moments all available solutions fail and numerical solutions are more powerful. Effect of gradient moments on stability of redundant beams is investigated at the end. Under such boundary conditions, important axial forces are present due to non-linear beam deformation. These forces, omitted in literature, have an incidence on stability. The element is then concerned with beam-column behaviour rather than beam stability.     

RFID Authentication Protocols Based on Error-Correcting Codes: A Survey

Code-based cryptography is a very promising research area. It allows the construction of different cryptographic mechanisms (e.g. identification protocol, public-key cryptosystem, etc.). McEliece cryptosystem is the first code-based public-key cryptosystem; several variants of this cryptosystem were proposed to design various security protocols in different systems. In this paper, we present a survey on various and recent authentication protocols in radio frequency identification systems which use diverse variants of the McEliece cryptosystem. Moreover, we discuss the security and the performance of each presented protocol.

     

Phase formation and crystallization kinetics in cordierite ceramics prepared from kaolinite and magnesia

In this work, Algerian kaolinite, a naturally occurring clay mineral, was used as low-cost precursor for the synthesis of cordierite ceramics. The kaolinite was mixed with synthetic magnesia, and the mixture was ball milled and reaction sintered in the temperature range 900–1350 °C for 2 h. Thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, high temperature x-ray powder diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) complementary techniques were used to analyze sintering behavior, characterize phase transformations, and investigate crystallization kinetics. Milling the kaolinite and magnesia mixture for 10 h yielded a homogenous powder, decreased the average particle size, and improved the roundness of particles. Different crystalline phases were present in the samples sintered in the temperature range 900–1150 °C, the cordierite phase started to crystallize at 1200 °C, and the formation of highly dense cordierite (99%) was complete at 1250 °C. The activation energy values for cordierite formation calculated using Kissinger, Boswell, and Ozawa methods were found to be equal to 577, 589, and 573 kJ/mol, respectively. The kinetic parameters n and m had values close to 2. Bulk nucleation with a constant number of nuclei was the dominant mechanism in cordierite crystallization, followed by two-dimensional growth controlled by interface reaction.     

Lateral buckling of thin-walled beam-column elements under combined axial and bending loads

Based on a non-linear stability model, analytical solutions are derived for simply supported beam-column elements with bi-symmetric I sections under combined bending and axial forces. An unique compact closed-form is used for some representative load cases needed in design. It includes first-order bending distribution, load height level, pre-buckling deflection effects and presence of axial loads. The proposed solutions are validated by recourse to non-linear FEM software where shell elements are used in mesh process. The agreement of the proposed solutions with bifurcations observed on non-linear equilibrium paths is good. It is proved that classical linear stability solutions underestimate the real resistance of such element in lateral buckling stability especially for I section with large flanges. Numerical study of incidence of axial forces on lateral buckling resistance of redundant beams is carried out. When axial displacements of a beam are prevented important tension axial forces are generated in the beam. This results in important reduction of displacements and for some sections, the beam behaviour becomes non-linear without any bifurcation.