圆板振子超谐分岔和混沌运动的实验研究

设计了非线性圆板混沌实验振动台,就轴对称圆板在简谐载荷作用下的非线性动力学行为进行了较为系统的实验研究,理论分析和数值计算,对基础作简谐运动,周边固支圆板,进行了实验。通过测量时间－中心挠度的加速度曲线,进行快速傅立叶变换（FFT）分析,实验发现了对称破缺,超谐分岔,调幅调相等复杂现象;对基础作简谐运动,周边固支,中心加质量块的圆板,进行了实验,通过测量时间－周边应变曲线,进行FFT分析,实验发现了混沌,对称破缺和恢复及超谐分岔等复杂动力学行为。     

A Simple Dual-Beam Time-Multiplexed Photon Doppler Velocimeter for Pressure-Shear Plate Impact Experiments

Experimental Mechanics - Pressure-shear plate impact experiments generate normal and transverse particle velocities during high strain rate deformations. Traditionally, freespace lenscoupled...     

Detwinning of High-Purity Zirconium: <Emphasis Type="Italic">In-Situ</Emphasis> Neutron Diffraction Experiments

Twinning is an important deformation mode in hexagonal metals to accommodate deformation along the c-axis. It differs from slip in that it accommodates shear by means of crystallographic reorientation of domains within the grain. Such reorientation has been shown to be reversible (detwinning) in magnesium alloy aggregates. In this paper we perform in-situ neutron diffraction reversal experiments on high-purity Zr at room temperature and liquid nitrogen temperature, and follow the evolution of twin fraction. The experiments were motivated by previous studies done on clock-rolled Zr, subjected to deformation history changes (direction and temperature), in the quasi-static regime, for temperatures ranging from 76 K to 450 K. We demonstrate here for the first time that detwinning of { 10[`1] 2 } á 10[`1][`1] ñ\left\{ {10\overline 1 2} \right\}\left\langle {10\overline 1 \overline 1 } \right\rangle tensile twins is favored over the activation of a different twin variant in grains of high-purity polycrystalline Zr. A visco-plastic self-consistent (VPSC) model developed previously, which includes combined slip and twin deformation, was used here to simulate the reversal behavior of the material and to interpret the experimental results in terms of slip and twinning activities.     

Plastic Flow Localization in Commercial Zirconium Alloys

The behavior of plastic flow curves and patterns of plastic strain localization were studied for tension of samples of Zr — 1% Nb (É110 alloy) and Zr — 1% Nb — 1.3% Sn — 0.4% Fe (É635 alloy) were studied. The relationship of the localization kinetics with the strain hardening law in plastic flow and transition to fracture is established. The dislocation microstructure of the alloys in strain localization and prefracture zones is examined.     

流动聚焦实验

介绍了一种制备微纳米量级颗粒的流动聚焦技术,它的最基本的特点是从毛细管流出的液体由高速运动气体驱动经小孔聚焦形成稳定的锥,锥顶端射出的微射流因不稳定性破碎成小颗粒.实验在自行设计的装置上完成.分析了流动聚焦技术中影响锥-射流以及颗粒形貌的因素,总结了过程中装置的结构参数以及气体压力降、液体流量和物性等参数对射流的直径的影响.结果显示该技术制备的颗粒单分散性好,直径达到微米和亚微米量级,在工业方面有重大应用前景.     

Spatiotemporal Thermal Inhomogeneities During Compression of Highly Textured Zirconium

Using a focal plane array infrared camera, the heat generated during large strain compression (at a rate of 1 s⁻¹) is used to study the characteristics of plastic flow for hcp zirconium. Heat generation during plastic flow in a reference material, copper, was seen to develop uniformly both at the lower (40 μm/pixel) and higher (8 μm/pixel) magnifications used in this study. The thermomechanical response of Zr, however, was seen to depend on the loading direction with respect to the specimen texture. Highly textured zirconium compressed along nonbasal oriented grains results in a homogeneous thermal response at both scales. However, compression along basal (0001) oriented grains shows evidence of inhomogeneous deformation at small strains that lead to macroscale localization and failure at large strains. The conversion of plastic work into heat is observed to be a dynamic process, both in the time-dependent nature of the energy conversion, but also in the passage of waves and ‘bursts’ of plastic heating. Basal compression also showed evidence of small scale localization at strains far below macroscale localization, even below 10%. These localizations at the lower strain levels eventually dominate the response, and form the shear band that is responsible for the softening of the macroscopic stress–strain curve.     

Deformation and Fracture of Zirconium Alloy at Low Temperatures

This paper describes the results of an experimental study on deformation and fracture of a Zr–1% Nb zirconium alloy in the case of multiple loads at low temperatures (?80°C). Samples cut out of pipes and applied as shells of nuclear fuel elements of fuel assemblies of nuclear reactors are used to conduct a series of experiments on low-cycle stretching and compression at low temperatures and study the effect of low temperature on stress relaxation in the material under different numbers of preliminary loads.     

Rosetta Stone Experiments

Dynamic failure events such as armor penetration and explosive fragmentation are too complex to be treated by classical single-crack continuum fracture mechanics. In such cases deformation and fracture result from multiple cracks, voids, and shear bands acting simultaneously and influencing one another’s evolution. An alternative “meso” fracture mechanics is needed that treats microfailure activity while permitting fast and inexpensive predictive computations. This paper discusses the approach and experiments that elucidate and quantify failure physics on the micron level. “Rosetta Stone” experiments that isolate a damage mode, produce statistical distributions of damage features, and “freeze in” damage at various stages of development are described and illustrated. The observations and data lead to equations describing nucleation and growth of cracks, voids, and shear bands. The resulting mesomechanical material failure models link the microworld with the macroworld and can be used in continuum hydrocodes for fast, efficient simulations of dynamic fracture scenarios.

LES Validation from Experiments

This paper addresses issues relating to the validation of LES from experiments. It highlights the differences between large eddy simulations (LES) and Reynolds averaged Navier–Stokes simulations (RANS) and how LES puts higher demands on the validation process than RANS. Some popular validation experiments are outlined, which are part of the Workshop on Turbulent Non-Premixed Flames. Important features of validation experiments are discussed to help modellers with the selection of suitable experiments, and experimentalists with the design. An LES validation using the typical approach is then presented, together with some unusual, more innovative approaches that deviate from common RANS practice. The final section considers experimental errors, with examples of their effects, and how LES can contribute to their analysis and compensation. This paper does not aim to provide a complete review of the field, but rather to communicate some ideas that were presented at an invited Workshop presentation.     

Experiments on unsteady cavitation

 The unsteady behaviour of cloud cavitation is obviously influenced by its internal flow pattern. The main purpose of this work is to investigate such a two phase flow during a cavitation cycle. The tests are carried out with a convergent divergent nozzle. Observations are made by using a classical video set in combination with a stroboscopic light sheet. The use of a double optical probe enables void fraction and velocity to be measured inside the two phase flow structure. Data acquisition is governed by a pressure signal measured near the cavity closures to follow their evolution during the shedding process. Special care has been taken in validating the experimental techniques because they have not been used in such flows. The measurements show an extended reversed flow occurring along the solid surface. It plays a significant function in the vapour cloud shedding process. Received: 11 September 1995 / Accepted: 28 June 1996     

Experiments with gas-filled triodes

Summary In this paper experiments are described showing the different types of electrical discharges in a gas-filled triode. The determining parameters are the following: the cathode emission, the spacing of cathode, grid and anode, the diameter of the meshes of the grid, the potentials of the grid and the anode, the gas pressure and the differential ionization function of the gas. The anode voltage may be concentrated in a space charge sheath. If this space charge sheath is located at the grid, the anode current may be modulated with moderate grid potentials. If not, much larger voltages are required for modulation.     

Experiments for Combustion-LES Validation

Designs of future combustors increasingly rely on numerical combustion simulations. Large-eddy simulation (LES) emerged as a method to better describe turbulence than Reynolds-averaged Navier–Stokes (RANS) approaches. Processes at the subgrid scale, however, need to be modelled. Validation using comprehensive and reliable experimental data sets is therefore a crucial part in the development of combustion-LES. Using well-defined benchmark flames and advanced laser diagnostics, different physical and chemical quantities can be precisely measured with high temporal and reasonable spatial resolution. In this contribution, quantities important to combustion-LES validation and the most frequently used laser diagnostic methods are briefly reviewed. New challenges in the field of diagnostics at high repetition rates and at walls are highlighted. In a closing chapter, some critical aspects on the comparison of experimental measurands and combustion-LES-predicted counterparts are discussed.     

Finite Element Analysis of Elasto-plastic Plate Bending Problems using Transition Rectangular Plate Elements

In this work, the finite element analysis of the elasto-plastic plate bending problems is carried out using transition rectangular plate elements. The shape functions of the transition plate elements are derived based on a practical rule. The transition plate elements are all quadrilateral and can be used to obtain efficient finite element models using minimum number of elements. The mesh convergence rates of the models including the transition elements are compared with the regular element models. To verify the developed elements, simple tests are demonstrated and various elasto-plastic problems are solved. Their results are compared with ANSYS results.The English text was polished by Keren Wang.     

薄板结构的安定性分析

本文关于薄板的分析采用样条函数插值及结构中的残余应力场用温度参数模拟，解决了薄板结构在交变载荷作用下的安定问题。由于温度参数的引用，使得研究的问题的自由度大幅度减少，文中还对薄板的Ｍｉｓｅｓ型屈服函数进行了线性化处理，它是安定定理的求解线性化的基础，算例表明本文所提出的方法及程序的可行和有效。     

Experiments on fall of open tori

Fall of open tori horizontally dropped in quiescent water is experimentally investigated. The fall is controlled by the Galileo number, the torus aspect ratio and the solid to fluid density ratio. The dependence of the descent velocity and of the drag coefficient on the control parameters is first analyzed. As the control parameters are varied, vertical translation, zigzagging and spiraling descent are observed. These different descent modes are characterized and a phase diagram of the falling tori are presented as function of the three control parameters.     

一种考虑剪切变形的平行四边形厚/薄板通用单元

根据Timoshenko二广义位移梁理论，构造了深梁位移场的插值函数。利用斜坐标系与直角坐标系的变换关系、有限条带思想和深梁位移插值函数，构造了一种考虑剪切变形的平行四边形厚／薄板弯曲通用单元的位移(曲率、剪应变、转角、横向位移)插值函数，导出了刚度矩阵和非结点荷载等效力。并对简支阍支方板、Razzaque斜板、四边简支斜交板弯曲进行了数值计算。算例表明此单元有较好的精度，对于薄板不出现剪切闭锁，可适应于目前桥梁建设中大量采用的斜交板桥结构分析。     

Experiments on underexpanded wall jets

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 2, pp. 76–81, March–April, 1992.