Experimental Study and Finite Element Analysis on Ultimate Strength of Dual-Angle Cross Combined Section Under Compression

This paper investigates Q420 dual-angle cross combined section columns under axial and eccentric compression by conducting experiments.The specimen parameters,experimental setup,and test results are presented.It showed that local buckling occurred apparently for single internode specimens(λ<35)under axial compression,while overall bending buckling appeared for others,and no torsional buckling occurred.The theoretical formulas on stability factor were derived by the energy approach.Non-linear finite element models considering residual stress were established using ANSYS which were verified by the corresponding experimental results.The parametric study was to evaluate the effects of slenderness ratio(λ),width to thickness ratio of angles(b/t),the number of filled plate(n),load relative eccentricity(e)and the lateral support stiffness on the ultimate strengths of dual-angle cross combined section columns.Based on above analysis,the design equations are proposed by using curve fitting technique.It is shown from comparison between test results,finite element analysis and related specifications that the ultimate strength from theoretical formulas,proposed equations and finite element models are consistent with experiments results.

High corrosion-resistant silver nanowire/poly(3,4-ethylene dioxythiophene)/poly(styrene sulfonate)@nickel electrode for transparent electromagnetic shielding film

Silver nanowire(AgNW)has become one of the best candidates for flexible transparent electromagnetic(EMI)shielding materials,while the low corrosion resistance of AgNW hinders its application in environments with high content of corrosive substances.Herein,an AgNW/poly(3,4-ethylene dioxythiophene)/poly(styrene sulfonate)(PEDOT:PSS)@nickel electrode was prepared through ultrasonic spray coating and electroplating methods.PEDOT:PSS is sprayed to improve the conductivity of the AgNW network,and a 9.8-16.5 nm Ni layer is deposited on the AgNW/PEDOT:PSS to protect the AgNWs from corrosion.The AgNW/PEDOT:PSS@Ni electrode shows a sheet resistance of 29 U·sq^(-1),a transmittance of 78.18%,an average EMI shielding efficiency of 19.64 dB and excellent corrosion resistance in Na2S solution.The resultant AgNW/PEDOT:PSS@Ni electrode is promisingly used in high corrosion resistance transparent EMI shielding film.

考虑节点半刚性的输电塔钢管构件稳定承载力分析

输电塔钢管构件的连接形式应是介于铰接与刚接之间的半刚性连接,故研究半刚性连接钢管构件的承载能力更贴合实际的受力情况。为此,研究了输电钢管塔K型节点的半刚性特性,并对考虑节点半刚性的轴心受压钢管构件承载能力进行了有限元分析。首先,以实际工程中的输电塔为原型建立K型节点的有限元模型,分析了主材规格、主材轴压比、主斜材夹角、节点板厚度、螺栓数量、插板厚度、插板宽度、斜材长度、斜材规格和钢材强度对节点半刚性特性的影响,总结了K型节点的大致初始转动刚度范围;然后,在节点半刚性特性的研究基础上,对考虑节点半刚性约束的轴心受压钢管构件承载能力进行了有限元分析,探究了转动刚度、端部连接形式和钢材强度在长细比变化时对轴心受压钢管构件承载能力的影响,并将分析结果与规范中的稳定系数-长细比关系曲线进行了对比。结果表明:K型节点的节点板受压区和受压斜材的插板首先达到屈服强度,随即发生破坏;K型节点中受压构件的弯矩-转角关系呈现非线性,节点板厚度、连接螺栓数量、插板厚度和宽度、斜材长度和规格以及钢材强度都对节点的半刚性特性有较大影响,主材规格、主材轴压比、主斜材夹角对节点的半刚性特性影响较小;K型节点的初始转动刚度范围为247.89~983.67 kN·m/rad;考虑节点半刚性的钢管构件的稳定承载力比铰接构件的稳定承载力要高,且两者间的差距随着长细比的增大而增大,当长细比大于80时,半刚接构件与铰接构件的差距均大于10%,当长细比大于140时,半刚接构件与铰接构件的差距均大于20%,这表明长细比越大,端部的约束作用越大;考虑节点半刚性的钢管构件的跨中位移均小于铰接构件的跨中位移,这表明半刚性约束可以降低钢管构件的变形;转动刚度、端部连接形式和钢材强度均会不同程度地影响半刚性节点钢管构件的稳定承载力。

Control mode selection for modal control of long-span arch bridge

For seismic control of arch bridge,a model reduction of long-span arch bridge was implemented based on modal analysis.As for the critical mode selection,an approach based on the maximum modal displacement was presented.This approach takes into consideration the effect of external seismic excitation and is more reasonable than only considering dynamic bridge characteristics based on a modal contribution ratio.The time domain and frequency domain analysis method were used to verify the simplified model of the Nimu arch bridge in Tibet as an example.The numerical results show that the method of maximal modal displacement better analyze long-span arch bridge when multisupport seismic excitation must be considered.The reduced-order system also is more in line with the performance of the original model.

Development of an analytical model to estimate the churning losses in high-speed axial piston pumps

The axial piston pumps in aerospace applications are often characterized by high-speed rotation to achieve great power density. However, their internal rotating parts are fully immersed in the casing oil during operation, leading to considerable churning losses (more than 10% of total power losses) at high rotational speeds. The churning losses deserve much attention at the design stage of high-speed axial piston pumps, but accurate analytical models are not available to estimate the drag torque associated with the churning losses. In this paper, we derive the analytical expressions of the drag torque acting on the key rotating parts immersed in oil, including the cylinder block and the multiple pistons in a circular array. The calculated drag torque agrees well with the experimental data over a wide range of rotational speeds from 1500 to 12000 r/min. The presented analytical model provides practical guidelines for reducing the churning losses in high-speed axial piston pumps or motors.