直剪状态下再生混凝土的变形性能及损伤分析

为研究再生混凝土直剪状态下的变形性能与损伤演变规律,以再生粗骨料取代率为变化参数,设计了33个再生混凝土试件进行直剪试验.试验观察了再生混凝土直剪荷载作用下的破坏形态,获取了再生混凝土直剪破坏全过程剪力-位移曲线,深入分析了精细化取代率对再生混凝土剪切模量、延性变形、能量耗散、损伤演变等性能的影响规律.结果表明:随着取代率的增加,再生混凝土的剪切模量减小,延性变形和能量耗散增加;取代率对损伤速率和损伤全过程曲线的影响不大,但对初始损伤时间有一定影响.基于抗剪强度试验结果,提出再生混凝土剪力-位移全曲线方程与再生混凝土损伤本构方程,所得计算结果与试验结果拟合较好.     

Dynamical Tension of a Hollow Cylindrical Specimen with Circular Crack

We propose a method for determining dynamic stress intensity factors for hollow cylindrical specimens with circular crack of finite length under impact tension. The solution of this problem is reduced to the numerical solution of an eigenvalue problem with the use of experimental loading–time diagrams. Simple formulas are obtained for determining dynamic stress intensity factors, depending on the history of loading of a specimen. The comparison of the values of dynamic stress intensity factors calculated by the formulas indicated and by the finite-element method testifies to the reliability of the results obtained.     

Flux Pinning-Induced Stress in a Long Hollow Cylindrical Superconductor Restricted by a Metal Tube

The tensile stress in a hollow cylindrical superconductor completely restricted by a metal tube in a parallel magnetic field is investigated. Using the plane strain approach, analytical expressions for the stress distribution of the superconductor and the contact stress between the metal tube and the superconductor are obtained and show that both the ratio of Young’s modulus and thickness ratio of the high-temperature superconductors and the metal tube significantly affect the stress distribution in the superconductor explicitly. In addition, the flux pinning-induced stress in the above-mentioned superconductor is systematically studied by the exponential critical state model during the field cooling process. The results indicate that the metal tube can reduce effectively the tensile stress in the hollow cylindrical superconductor during the magnetization process. The findings suggest that the appropriate selection of material parameters and size of the metal tube can improve superconductor performance efficiently.     

Superplasticity Extensibility and Deformation Mechanism of a Nanocrystalline Copper Sample

By means of the electrodeposition technique, a bulk sample of nanocrystalline (nc) copper was prepared with high purity and high density. An extreme extensibility (elongation > 5000 %) without a strain hardening effect was observed when the nc Cu sample was rolled at room temperature. A detailed study on the microstructure evolution of the nc Cu during the cold‐rolling process was examined by means of X‐ray diffraction (XRD) analysis, transmission electron microscopy (TEM), and thermal analysis. It was indicated that the deformation process in the nc Cu sample is dominated by the grain boundary activity rather than lattice dislocation. This phenomenon agrees well with the observed mechanical behavior of the nc Cu sample.     

Direct Evidence for Structural Transition Promoting Shear Thinning in Cylindrical Colloid Assemblies

In this paper, we describe stimuli‐responsive hydrogels prepared from a rigid rod‐like polyelectrolyte ‘imogolite’ and a dicarboxylic acid. The hydrogel exhibited thixotropy in response to mechanical shock within the order of seconds or sub‐seconds. Here, using the latest structural/rheological characterisation techniques, the relationship between the structural transition processes and the shear thinning was estimated. The evidence obtained by the experiments revealed for the first time the direct relationship between the microscopic structural change and the macroscopic thixotropic behavior that have been extensively discussed. The thixotropic hydrogel has the hierarchical architecture in the combination of imogolite and dicarboxylic acid, i.e., sheathed nanotubes/hydroclusters of cross‐bridged nanotubes/frameworks. The formation and disintegration of the network structure upon resting and agitating, respectively, were the origin of gel/sol transition (thixotropy), although the hydroclusters of cross‐bridged nanotubes were maintained throughout the transition.     

Weight Function for a Crack in a Two-dimensional Orthotropic Medium Under Impact Shear Loading

The paper examines the elastodynamic response of an infinite two-dimensional orthotr- opic medium containing a central crack under impact shear loading. Laplace and Fourier integral transforms are employed to reduce the problem to a pair of dual integral equations in the Laplace transformed plane. These equations are reduced to integral differential equations, which have been solved in the low frequency domain by iterations. To determine time dependence, these equations are inverted to yield the dynamic stress intensity factor (SIF) for shear point force loading that corresponds to the weight function for the crack under shear loading. It is used to derive SIF for polynomial loading.     

Exact Solutions of Finite Deformation for Everted Compressible Hyperelastic Cylindrical Tubes

The eversion problem for a class of compressible hyperelastic thinwalled cylindrical tubes is examined. The mathematical model is formulated as a second-order nonlinear ordinary differential equation based on the theory of nonlinear elasticity. The exact solution that describes the mechanism of the finite deformation of the everted cylindrical tube is obtained. Using numerical simulations, it is shown that the initial thickness of the tube plays a significant role in the eversion.     

A Layerwise Shear Deformation Theory for Two-Layered Cross-Ply Laminated Plates

A layerwise trigonometric shear deformation theory for flexural analysis of two-layered laminated plates, taking into account transverse shear deformation effects, is presented. The present theory has only three variables, that is, two variables less than those in the first-order shear deformation theory. The displacement field uses a sinusoidal function in terms of thickness coordinate to represent the shear deformation. The noteworthy feature of the theory is that the transverse shear stresses can be obtained directly from the use of constitutive relations with reasonable accuracy, satisfying the shear stress free surface conditions at the top and bottom surfaces of the plate and continuity conditions at interface between the layers. The transverse shear stresses can also be obtained, with better accuracy, by integrating equilibrium equations. The theory obviates the need for a shear correction factor. The governing equations and boundary conditions are obtained using the principle of virtual work. A two-layered cross-ply laminated plate is considered for the numerical study to demonstrate the efficacy of the theory. The results obtained using the present theory are discussed critically with those of other theories and are found to agree well with the exact elasticity results.     

Quintuple Band Antenna for Wireless Applications with Small Form Factor

A coplanar waveguide-fed quintuple band antenna with a slotted circular-shaped radiator for wireless applications with a high isolation between adjacent bands is presented in this paper. The proposed antenna resonates at multiple frequencies with corresponding center frequencies of 2.35, 4.92, 5.75, 6.52, and 8.46 GHz. The intended functionality is achieved by introducing a circular disc radiator with five slots and a U-shaped slot in the feed. The proposed antenna exhibits coverage of the maximum set of wireless applications, such as satellite communication, worldwide interoperability for microwave access, wireless local area network (WLAN), long-distance radio telecommunications, and X-band/Satcom wireless applications. The simulation and measurement results of the proposed fabricated antenna demonstrate the high isolation between adjacent bands. A stable realized gain with an advantageous radiation pattern is achieved at the operating frequency bands. The proposed simple design, compact structure, and simple feeding technique make this antenna suitable for integration in several wireless communication applications, where the portability of devices is a significant concern. The proposed antenna is anticipated to be an appropriate candidate for WLAN, long-term evolution, and fifth-generation mobile communication because of its multi-operational bands and compact size for handheld devices.     

Stress Concentration in a Pipeline with Surface Hollow in the Form of a Semiellipsoid of Revolution

For the analysis of stress concentration in the region of a local hollow in a pipeline in the form of a semiellipsoid of revolution, we use a computational model based on the three-dimensional problem of a layer subjected to biaxial tension. The numerical analysis of this problem is performed with the help of a semianalytic finite-element method by using bilinear quadrangular elements. We deduce an engineering formula for the evaluation of the maximum stress intensity factors.     

用于参数曲面自由变形的一种新的缩放因子

在《工程图学学报》2002年第1期论文"参数曲面自由变形新方法"的基础上,提出了一种用于参数曲面自由变形的新的缩放因子,该因子作用(缩放)于待变形曲面,能够使曲面发生形变.通过交互改变控制参数,可达到预期的变形效果.这种方法数学背景简单,易于操作和控制.大量实例证明,该方法可获得丰富的变形效果,适用于几何造型,计算机动画,CAD/CAM等领域.     

Specimen for the Determination of Fatigue Thresholds Under Cyclic Transverse Shear

Materials Science - We develop a basic element of the procedure of construction of the near-threshold part of the diagram of fatigue fracture for metallic materials under the conditions of...     

Deformation Localization and Shear Fracture of a Rapidly Solidified Al-Fe-V-Si Alloy at Elevated Temperature

The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy decrease significantly with increasing temperature and decreasing strain rate. Micro-structural examinations reveal that this change in mechanical behavior with increasing temperature is related to the mode of deformation of the alloy. Further observations show that localized shear deformation is responsible for the losses in both strength and ductility of the alloy at elevated temperature.     

圆柱型空腔电离室修正系数的Monte Carlo模拟与实验验证

采用标称体积为10 cm~3圆柱型空腔电离室对Cs-137空气比释动能进行绝对测量。使用Monte Carlo模拟计算和实验两种方法对电离室壁修正因子k_w和轴向不均匀修正因子k_(an)进行对比研究。结果显示,使用等效壁厚的实验外推法确定的k_w值比MC计算得到的值小0.1%,实验方法确定的k_(an)值比MC计算得到的值小0.63%。两种方法相互印证,给出的修正系数值之间的误差可以接受,由于重复实验不可避免将引入其他误差因素,且MC计算方法简便可重复性高,最终选取MC计算结果为k_w、k_(an)确定值。     

A Crack Emanating from a Wedge In Dissimilar Anisotropic Materials Under Antiplane Shear

A crack in a composite wedge consisting of two dissimilar anisotropic materials under concentrated antiplane loads is analyzed. The problem of a crack in an isotropic composite wedge is solved first by using the Mellin transform and the Wiener-Hopf method. Using a linear transformation of the original composite wedge into an isotropic composite wedge consisting of dissimilar isotropic materials, the antiplane displacement and stresses for the anisotropic composite wedge are obtained from the solution for the transformed wedge. The stress intensity factor for the crack in the original anisotropic composite wedge is obtained from the solution of the crack in the transformed wedge. Special attention is given to the asymptotic problem of a wedge crack in an anisotropic bimaterial. Numerical computations are carried out to obtain the energy release rate for various apex angles and anisotropic parameters as a function of crack angle.     

Harmonic Vibration and Resonance Effects in the Case of Longitudinal Shear of a Hollow Cylinder with Crack

Materials Science - We propose an efficient analytic-numerical method for the evaluation of dynamic stresses in a hollow cylindrical body of arbitrary cross section with a through crack under the...