基于叠合式节点连接的弹性曲弯网壳绿色施工分析

弹性曲弯网壳是由平面网格变形而来,其节点形式采用了叠合式连接方式,这种特征导致其结构的建造与传统网壳施工有很大差别。文章对弹性曲弯网壳两种常用施工模式包括顶升法和沉降法的各自特点分别作了深入分析并与高空散装等传统网壳建造方法作了横向对比,同时揭示了弹性曲弯施工这种非常规空间结构建造方式中的生态可持续发展理念。

弹性曲弯单拱的极限承载力数值计算分析

文章针对弹性曲弯网壳的基本建造单元—弹性曲弯单拱的静力稳定性及其极限承载力问题,应用有限元软件ANSYS进行了计算分析,并探讨了其运用连续性整体和两阶段独立分析方法的各自特点和优势。

弹性曲弯网壳中建筑师的结构探索

弹性曲弯网壳的建造模式比较特殊,能适应相对复杂的网壳形态,是一种建筑师喜欢设计而结构工程师未必愿意配合的空间结构形式。分析了弹性曲弯网壳的建造特征,探讨了这种体系中建筑与结构相互关系的演变过程,在具体计算模式方面提出并验证了用SAP2000软件的施工模拟功能对弹性曲弯网壳进行从顶升到承载各阶段受力分析设计的可行性。

Unified Solution Method of Rectangular Plate Elastic Bending

The bending of rectangular plate is divided into the generalized statically determinate bending and the generalized statically indeterminate bending based on the analysis of the completeness of calculating condition at the corner point. The former can be solved directly by the equilibrium differential equation and the boundary conditions of four edges of the plate. The latter can be solved by using the superposition principle. Making use of the recommended method, the bending of the plate with all kinds of...

Analysis of plane strain bending of a strain hardening curved beam based on unified yield criterion

The analysis of plane strain elastic-plastic bending of a linear strain hardening curved beam with a narrow rectangular cross section subjected to couples at its end is conducted based on a unified yield criterion. The solutions for the mechanical properties of plane strain bending are derived, which are adapted for various kinds of non-strength differential materials and can be degenerated to those based on the Tresca, von Mises, and twin-shear yield criteria. The dependences of the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane on different yield criteria and Poisson’s ratios are discussed. The results show that the influences of different yield criteria and Poisson’s ratio on the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane of the curved beam are significant. Once the value of bis obtained by experiments, the yield criterion and the corresponding solution for the materials of interest are then determined.

Vibration characteristics of rotor system with tilting-pad journal bearing of elastic and damped pivots

In view of an entire dynamic model of tilting-pad journal bearing(TPJB) in which the pads swing and vibrate along geometric direction of preload, a TPJB of elastic and damped pivots was designed and manufactured. Vibration experiments were carried out under the conditions of different rotor bending stiffness and oil supply pressure to find out the relationship between the new bearing's vibration depression effect and other dynamic parameters of the rotor. The result shows that critical amplitudes can be efficaciously reduced while system's stability can be remarkably improved by this bearing. Besides, the bearing's effect of vibration depression weakens as the rotor bending stiffness increases, but heightens it as the oil supply pressure increases.

Research on spring-back behavior of high strength steel sheets

To investigate the spring-back behavior of dual-phase （DP） steel, V-shape spring-back experiments with different bending angles, relative bending radii and blank holding forces were carried out in this paper. It is concluded that with the increase of V-shape angle or blank holding force, the spring-back of DP steel sheets decreases; while raising fiIlet radius of punch, which has the most apparent effects on spring-back, advances spring-back angle. Among DP590, DP780 and DP980, higher strength yields more notable spring-back due to larger elastic deformation. The difference of spring-back among these materials is relevant with the microstructure and mechanical properties. The total elastic deformation approximately equals the ratio of the strength corresponding to the applied load to the modulus of elasticity.

BUCKLING OF SPATIAL CURVED RODS WITH CIRCULAR CROSS-SECTIONS

Formulae for determining Green strain of an initially curved and twisted rod with circular cross-sections are derived by using the natural (curvilinear) coordinate system. Finite element analyses are performed for the flexural buckling of initially curved and twisted thin rods under simultaneous action of axial force and torque. Numerical examples demonstrate that the given formulae are correcte. Some numerical results are compared with existing analytical solutions and data obtained by commercial FE software. The convergence of the proposed curved element is better than that of elements in the commercial FE software. It is shown that good accuracy and convergency are achieved by solving three-dimensional problems.

Experimental Investigation on Springback Performance of Transformation-induced Plasticity Steel Sheet during Cyclic Bending Process

In order to investigate the springback performance of a cold-rolled transformation-induced plasticity （TRIP） steel sheet during cyclic bending, three-points bending experiments were performed. The specimen was firstly forward bended and then reversed bended according to three basic punch strokes, 10 mm, 20 mm and 30 mm, respectively. The outlines of the deformed specimens, punch load and crosshead displacement were obtained. The experimental procedures and the method of determining the springback displacement were reported in detail. The contributi^m of the strain hardening and decrease of elastic modulus to the overall springback was explained. The results demonstrated that springback increases both with the cycles and with the punch stroke during the cyclic bending process. Furthermore, springback in forward bending is larger than that in the corresponding reverse bending. This may be helpful to understand the complex springback behavior of the complicated sheet metal pancls.

Innovative Proof for Elastic Flexure Formulas

The basic problem in teaching mechanics of materials is that some subjects discussed in the reference books are not easy to understand for most of the students. Using experience of many years teaching mechanics of materials, we have been continuously trying to find easier methods to help the students get a better understanding of fundamental concepts. This effort and investigation has led to innovative and simple approaches to prove the equations much easier than the existing ones and also to clarify complicated concept. In this paper, we are offering our innovative proof for elastic flexure formulas as well as an interesting model for the moment sign convention in the cross section of a beam. In this method, considering a portion of a beam under pure bending and obtaining the stress distribution in the cross section and applying the balance of the considered portion, we prove the Elastic Flexure Formulas much easier than the existing methods. Emphasizing on deeper understanding, some notes and a new model are offered during this proof.

Study on the Handle of Keratin Transgenic Cotton Fabric

Gene of animal keratin can be inoculated into cotton fiber and thus get the keratin transgenic cotton fiber through transgenic technology. Handle of two kinds of pure cotton poplin, one of which is made of the keratin transgenic cotton while the other is made of the ordinary cotton of the same breed as control group and both with absolutely identical spinning, weaving, and dyeing process, was objectively evaluated with KES system. The result of analysis indicates that the principal changes of keratin transgenic cotton fabric are that the bending and shearing property of the fabric are considerably enhanced, KOSHI (Stiffness) and HARI (Anti-drape stiffness) of the fabric are good, while SHINAYAKASA (Flexibility with soft feeling) and SHARI (Crispness) decline.

Linear Strain-Gradient Effect on the Energy Bandgap in Bent CdS Nanowires

Although possible non-homogeneous strain effects in semiconductors have been investigated for over a half century and the strain-gradient can be over 1% per micrometer in flexible nanostructures, we still lack an understanding of their influence on energy bands. Here we conduct a systematic cathodoluminescence spectroscopy study of the strain-gradient induced exciton energy shift in elastically curved CdS nanowires at low temperature, and find that the red-shift of the exciton energy in the curved nanowires is proportional to the strain-gradient, an index of lattice distortion. Density functional calculations show the same trend of band gap reduction in curved nanostructures and reveal the underlying mechanism. The significant linear straingradient effect on the band gap of semiconductors should shed new light on ways to tune optical-electronic properties in nanoelectronics.

A Study on Viscoelastic Fluid Flow in a Square-Section 90-Degrees Bend

It is well known that the drag-reducing effect is obtained in a surfactant solution flow in a straight pipe. We investigate about a viscoelastic fluid flow such as a surfactant solution flow in a square-section 90° bend. In the experimental study, drag-reducing effect and velocity field in a surfactant solution flow are investigated by measurements of wall pressure loss and LDV measurements. For the numerical method, LES with FENE-P model is used in the viscoelastic fluid flow in the bend. The flow characteristics of viscoelastic fluid are discussed compared with that of a Newtonian fluid.

Second-order two-scale method for bending behavior analysis of composite plate with 3-D periodic configuration and its approximation

This paper considers the bending behaviors of composite plate with 3-D periodic configuration.A second-order two-scale(SOTS)computational method is designed by means of construction way.First,by 3-D elastic composite plate model,the cell functions which are defined on the reference cell are constructed.Then the effective homogenization parameters of composites are calculated,and the homogenized plate problem on original domain is defined.Based on the Reissner-Mindlin deformation pattern,the homogenization solution is obtained.And then the SOTS’s approximate solution is obtained by the cell functions and the homogenization solution.Second,the approximation of the SOTS’s solution in energy norm is analyzed and the residual of SOTS’s solution for 3-D original in the pointwise sense is investigated.Finally,the procedure of SOTS’s method is given.A set of numerical results are demonstrated for predicting the effective parameters and the displacement and strains of composite plate.It shows that SOTS’s method can capture the 3-D local behaviors caused by3-D micro-structures well.

Study of TiO_2 thin films on Si substrate by the photoacoustic elastic bending method

The quantitative photoacoustic investigation of different TiO2 thin films on Si substrates is presented using the elastic bending method. Photoacoustic signal amplitude and phase spectra versus modulation frequency were measured and analyzed using different sample thicknesses. Within the proposed method particular attention is given to the analysis of optical, thermal, elastic and structural sample parameters. Considerable focus is devoted to the fitting procedure of experimental results using the two-layer sample theoretical model. Characteristics of previously developed photoacoustic apparatus are discussed, attempting to search the ideal experimental conditions which can provide a good signal-to-noise ratio and sensitivity.

Prediction of nonlocal scale parameter for carbon nanotubes

Based on the theory of nonlocal elasticity,a nonlocal shell model accounting for the small scale effect is developed for the bending characteristics of CNTs subjected to the concentrated load.With this nonlocal shell model,explicit expressions are derived for the bending solutions.To extract the proper values of nonlocal scale parameter,we have made molecular dynamics(MD) simulations for various radii and lengths of armchair and zigzag CNTs,the results of which are matched with those of nonlocal continuum model.It is found that the present nonlocal elastic shell model with its appropriate values of nonlocal scale parameter has the capability to predict the bending behavior of CNTs,which is comparable with the results of MD simulations.Moreover,exact closed form solutions for the nonlocal scale parameter for zigzag and armchair CNTs are obtained.The results show that nonlocal scale parameter is independent of the length of CNTs,and dependent on the radius of CNTs.

Extreme transmission of elastic metasurface for deep subwavelength focusing

In this paper,elastic metasurfaces composed of zigzag units are proposed to manipulate flexural waves at a deep subwavelength scale.Through the parameter optimization of the genetic algorithm,units with full transmission and full phase control can be found,while the width is only one-fifth of the wavelength.The outstanding capability of the units is explained by analyzing.their wave fields.The flat and the curved metasurfaces for focusing are designed and simulated,showing excellent performance.Experimental results of the flat metasurface show that the incident wave energy at the focal point is enhanced over 6 times,verifying the simulation results.The proposed metasurfaces could be useful in the design of.compact and efficient elastic devices.