共面闭合断续节理岩体直剪强度特性研究

介绍了节理面和岩桥各自的抗剪强度机制,引入法向变形协调条件,基于Mohr-Coulomb理论,推导了共面闭合断续节理岩体的直剪强度公式。模型试验发现,剪切破坏面以拉剪复合破坏为主,同时岩块中伴随大量的拉张微裂隙。试样的强度和变形具有明显的阶段性,全应力应变曲线主要经历了线弹性增长、节理面错动、次生裂纹起裂稳态扩展、节理面贯通破坏和残余强度5个阶段。对比发现,理论计算结果与试验值吻合较好。     

光通量法在SHPSB剪切应变测量中的应用

利用光通量方法对分离式霍普金森压剪杆实验技术中的剪切应变测量进行了实验研究。实验装 置主要包括:准直激光器、光电接收器、光学挡板。由装置性能验证实验结果以及不确定度分析结果表明:利 用基于光通量法的剪切应变测量技术能够可靠地测量SHPSB(splitHopkinsonpressurebar)试样的剪切应 变。并对比了基于光通量法测量的剪切应变值与理论近似结果,结果显示前者小于后者,分析并讨论了原因。     

各向异性浮力紊流的显式代数应力模型及其验证

在Wallin & Johansson的显式代数雷诺应力模型(EARSM)基础上,引入浮力的紊动效应,使该模型能够反映浮力对紊流运动的影响.利用同位网格上的SIMPLEC算法,模拟了T-型连接管内的温度混合流动.与实验资料和DNS计算结果比较表明,提出的模型能够反映各向异性的浮力紊流特征,而且模型在计算进程中显示出良好的数值收敛性能,与涡粘性两方程模型的计算花费相当.     

Nonequilibrium Thermodynamics of Polymeric Liquids via Atomistic Simulation

The challenge of calculating nonequilibrium entropy in polymeric liquids undergoing flow was addressed from the perspective of extending equilibrium thermodynamics to include internal variables that quantify the internal microstructure of chain-like macromolecules and then applying these principles to nonequilibrium conditions under the presumption of an evolution of quasie equilibrium states in which the requisite internal variables relax on different time scales. The nonequilibrium entropy can be determined at various levels of coarse-graining of the polymer chains by statistical expressions involving nonequilibrium distribution functions that depend on the type of flow and the flow strength. Using nonequilibrium molecular dynamics simulations of a linear, monodisperse, entangled C₁₀₀₀H₂₀₀₂ polyethylene melt, nonequilibrium entropy was calculated directly from the nonequilibrium distribution functions, as well as from their second moments, and also using the radial distribution function at various levels of coarse-graining of the constituent macromolecular chains. Surprisingly, all these different methods of calculating the nonequilibrium entropy provide consistent values under both planar Couette and planar elongational flows. Combining the nonequilibrium entropy with the internal energy allows determination of the Helmholtz free energy, which is used as a generating function of flow dynamics in nonequilibrium thermodynamic theory.     

求解层间界面反平面剪切破坏的剪切梁模型(Ⅰ)——基本特性

在反平面剪切载荷及侧压力共同作用下引起的裂纹及裂纹扩展导致的层间界面失效,是岩土工程层间界面及砌体结构中界面层上典型的失效方式.运用弹性力学和断裂力学的理论原理,提出了能够反映上述层间界面断裂失效问题力学特性的剪切梁模型.文中采用具有应力软化特性的“粘性裂纹”(内聚力裂纹)模型来表述层间裂纹前方损伤过程区的本构行为.对通过粘性层结合在一起的两个弹性板,在反平面剪切载荷及侧压力共同作用下的力学行为作了解析分析计算,研究了层间界面裂纹扩展规律.     

基于剪切效应纤维梁单元的结构非线性有限元数值模拟

基于Euler-Bernoulli梁理论的经典纤维模型忽略了剪切变形给截面带来的影响,为了得到更加精确的梁单元模型,该文基于考虑剪切效应的纤维梁单元,根据Timoshenko梁理论,推导了该纤维梁单元的刚度矩阵,并结合弹塑性增量理论,同时考虑了几何非线性和材料非线性的双重影响,建立了压弯剪复杂应力状态下结构非线性有限元...     

压电弯曲元的夹层梁解析模型

压电弯曲元是一类传感和作动器件,已得到广泛的应用．基于一阶剪切变形理论发展了压电弯曲元夹层梁解析模型,对梁截面采用统一转角并将耦合电势沿厚度的分布假设为二次函数,进一步修正了横向剪应变对电位移的影响．以弯曲元简支梁自由振动为例进行数值分析,解析模型解与二维精确解相比具有良好的精度,为分析弯曲元动力机电响应提供了良好的解析模型．     

陶瓷材料在压剪联合冲击加载下动态响应的实验研究

 应用57 mm压剪炮和双磁场IMPS粒子测试系统对95%的Al₂O₃陶瓷材料在压剪联合加载条件下的力学行为进行了实验研究,测量得到了材料内部压缩波（P波）、剪切波（S波）的加载、卸载和传播规律。对剪切波的衰减随载荷的变化进行了研究,初步得到95% Al₂O₃陶瓷材料在压剪联合载荷冲击下发生损伤的纵向应力阀值是4.86 GPa。     

Investigation of Viscosity and Density Versus Temperature in Comparison with 1H Nmr Relaxation time Results for O,M-, P-Xylenes and α -,β-, γ - Picolines

The paper presents the results of density and viscosity measurements in liquid derivatives of benzene and pyridine, well purified, degassed or aerated, depending on temperature, in the whole liquidity range. Gaseous admixtures were found to affect the viscosity of liquids. From one to three Arrhenius regions were observed, depending on the structure and orientational freedom of the molecules. the results are discussed on the background of 1H NMR relaxation time studies with regard to the effect of dipole interactions on the structure of close packing.     

Numerical analysis of conservative unstructured discretisations for low Mach flows

Unstructured meshes allow easily representing complex geometries and to refine in regions of interest without adding control volumes in unnecessary regions. However, numerical schemes used on unstructured grids have to be properly defined in order to minimise numerical errors. An assessment of a low Mach algorithm for laminar and turbulent flows on unstructured meshes using collocated and staggered formulations is presented. For staggered formulations using cell‐centred velocity reconstructions, the standard first‐order method is shown to be inaccurate in low Mach flows on unstructured grids. A recently proposed least squares procedure for incompressible flows is extended to the low Mach regime and shown to significantly improve the behaviour of the algorithm. Regarding collocated discretisations, the odd–even pressure decoupling is handled through a kinetic energy conserving flux interpolation scheme. This approach is shown to efficiently handle variable‐density flows. Besides, different face interpolations schemes for unstructured meshes are analysed. A kinetic energy‐preserving scheme is applied to the momentum equations, namely, the symmetry‐preserving scheme. Furthermore, a new approach to define the far‐neighbouring nodes of the quadratic upstream interpolation for convective kinematics scheme is presented and analysed. The method is suitable for both structured and unstructured grids, either uniform or not. The proposed algorithm and the spatial schemes are assessed against a function reconstruction, a differentially heated cavity and a turbulent self‐igniting diffusion flame. It is shown that the proposed algorithm accurately represents unsteady variable‐density flows. Furthermore, the quadratic upstream interpolation for convective kinematics scheme shows close to second‐order behaviour on unstructured meshes, and the symmetry‐preserving is reliably used in all computations. Copyright © 2016 John Wiley & Sons, Ltd.