圆中空夹层钢管混凝土柱扭转实验研究

以名义含钢率、外钢管强度和空心率为主要变化参数,设计了6根圆中空夹层钢管混凝土和1根双层空钢管试件,对其进行了扭转试验研究。试验结果表明:在加载过程中,钢管和混凝土变形协调,共同工作;试件表现出很好的塑性性能;试件名义含钢率和外钢管强度越大,试件抗扭承载力也越大;空心率越大,试件抗扭承载力也越大;圆中空夹层钢管混凝土比双层空钢管抗扭承载力有明显的提高。同时用有限元方法对试件扭矩-转角全过程曲线进行计算,计算结果与试验结果吻合良好。     

Elastic thermal stresses in a hollow circular overlay/substrate system

This paper investigates the thermal elastic fields in the hollow circular overlay fully bonded to a rigid substrate, which is subjected to a temperature change. Following our previous work for a solid circular overlay/substrate system (Yuan and Yin, Mech. Res. Commun. 38, 283–287, 2011), this paper presents a closed form approximate solution to the axisymmetric boundary value problem using the plane assumption, whose accuracy is verified by the finite element models. When the inner radius is reduced to zero, the present solution recovers the previous solution. When the outer radius approaches infinite, the solution provides the elastic fields for a tiny hole in the overlay. The effects of thickness and width of the overlay are investigated and discussed. When a circular crack initiates in a solid circular overlay, the fracture energy release rate is investigated. This solution is useful for thermal stress analysis of hollow circular thin film/substrate systems and for fracture analysis of spiral cracking in the similar structures.     

Plane-stress fracture testing of finite sheets under biaxial loads

A procedure which combines the Williams series-type stress- and displacement-field expressions at the crack-tip neighborhood with a suitable numerical scheme away from the crack-tip was employed in the determination of the plane-stress fracture properties of four finite 7076-T6 aluminum sheets containing cracks emanating from a circular hole under four biaxial loads. The compatibility of the analytical and numerical displacements at the nodal points along the boundary of the crack-tip neighborhood was utilized in formulating displacement-continuity expressions containing some undetermined constants which solution depends on the nature of the boundary loading conditions. By linear superposition of the displacement due to remote uniaxial load and the displacements due to remotely applied transverse load in the neighborhood of the crack-tip, biaxial-displacement-continuity expressions containing these important fracture properties—namely, the opening Mode I stress-intensity factorK, the nonsingular stress term associated with the stresses in the direction parallel to the plane of cracksA and the integration termB associated with the displacement in this direction—were evaluated. Because no known biaxial testing of this geometry had been reported prior to this research, the analytical procedure was used to select the optimum geometry required in a biaxial fracture test of a finite-sheet specimen containing cracks emanating from a circular hole. This geometric optimization of the specimen guaranteed uniformity of stress all over the volume of specimen and also made the alteration of the existing MTS test fixtures unnecessary. Four square sheets of 7075-T6 aluminum alloy containing a central hole with two collinear cracks emanating radially at the edge of the hole were then fabricated in accordance with the analytically determined geometric requirements. The biaxial fracture test was then conducted under four biaxial load factors (λ) of 0.0, 0.5, 1.0 and 1.5. The fracture toughness obtained in this research was compared with those reported for uniaxial loading of large panels. It was found that there is a good correlation between the reported fracture toughness and this work.     

One-dimensional deformations of nonlinearly elastic micropolar bodies

We find families of finite deformations of a Cosserat elastic continuum on which the system of equilibrium equations is reduced to a system of ordinary differential equations. These families can be used to describe the expansion, tension, and torsion of a hollow circular cylinder, cylindrical bending of a rectangular slab, straightening of a circular arch, reversing of a cylindrical tube, formation of screw and wedge dislocations in a hollow cylinder, and other types of deformations. In the case of a physically nonlinear material model, the above-listed families of deformations can be used to construct exact solutions of several problems of strong bending of micropolar bodies.     

Cylindrical interface crack in a hollow layered functionally graded cylinder under static torsion

A hollow functionally graded composite cylinder under static torsion, which consists of an inner and outer elastic circular tube with a cylindrical interface crack, is studied in this work. By utilizing Fourier integral transform method, the mixed boundary value problem is reduced to a Cauchy singular integral equation, from which the numerical results of the stress intensity factor are obtained by the Lobatto–Chebyshev quadrature technique. Numerical results demonstrate the coupled effects of geometrical, physical, and functionally graded parameters on the interfacial fracture behavior.     

Growth of an arc-crack in bonded dissimilar materials

The problem of growth of a crack lying along the interface of a circular inclusion embedded in an infinite plate is studied within the framework of linear elasticity. The plate is subjected to a uniform uniaxial stress at infinity at any angle of inclination relatively to the crack. The critical load for unstable crack growth, the angle of initial crack extension and the subsequent crack path are investigated using the strain energy density fracture criterion. The combined effect of crack length and orientation on the fracture stress is considered for the case of an aluminum-epoxy composite.     

Repeated impact on fatigue fracture of carbon spring En-42J steel

The influence of repeated impact loading on fatigue fracture of carbon spring En-42J steel is studied. A highly localized plastic deformation is observed at the time of impact. The circular disc specimen is failed by impact fatigue resulting in small chips and ordinary fatigue failure by slow crack growth. The crack growth behavior depends on specimen geometry, load spectra and material type. The resultant of applied and residual stress was highest at the edge of the circular disc where the crack initiated. The fractured surface showed typical cleavage facets and dimples indicating acicular martensite. A model is developed to explain fatigue crack initiation and propagation behavior under impact loading. Stress calculations are made to determine catastrophic failure. Crack initiation occupied the major part of impact fatigue life while crack growth was fast and led quickly to sudden fracture.     

A generalization of Prandtl’s and Spencer’s solutions on axisymmetric viscous flow

New analytical solutions for axisymmetric deformation of a viscous hollow circular cylinder on a rigid fibre are given. One of the solutions generalizes the famous Prandtl’s solution for compression of a rigid perfectly plastic layer between two rough, parallel plates and the other is a modification of Spencer’s solution for compression of an axisymmetric rigid perfectly plastic layer on a rigid fibre. All equations are satisfied exactly whereas some boundary conditions are approximated in a standard manner. Special attention is devoted to frictional interface conditions since these conditions result in additional limitations of the applicability of the solution when compared to that based on a rigid perfectly plastic models. In particular, difficulties with the convergence of numerical solutions under certain conditions can be explained with the use of results obtained. Therefore, the solutions can serve as benchmark problems for verifying numerical codes. The solutions are also adopted to predict the brittle fracture of fibres by means of an approach used in previous studies and confirmed by experiment.     

Some problems of linear elasticity for cylinders in micropolar orthotropic material

Some special problems for axisymmetric solids made of linearly elastic orthotropic micropolar material with central symmetry are dealt with. The first one is a hollow circular cylinder of unlimited length, subjected to internal and external uniform pressure. The second one is a hollow or solid circular cylinder of finite length, subjected to a relative rotation of the bases about its axis. In both cases, one of the axes of elastic symmetry is parallel to the cylinder axis; the other two are arbitrarily oriented in the plane of any cross-section of the solid. The elastic properties are invariant along the cylinder axis. It is shown that the two problems are governed by formally similar sets of ordinary differential equations in the kinematic fields (in-plane displacements and microrotations). In the general case, numerical solutions are derived. The solution for the cylinder subjected to radial pressure does not significantly differ from that obtained in classical elasticity, at least in terms of radial and hoop force stresses. In the case of a cylinder subjected to torsion the difference between the micropolar and the classical solutions is more pronounced. The torque induces twisting couple stresses about the cylinder axis of variable sign. Finally, size effects in terms of torsional inertia are pointed out.     

Using Semi Circular Bending Test to Evaluate Low Temperature Fracture Resistance for Asphalt Concrete

This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length.     

基于动力放大系数与等效单自由度体系的圆中空夹层钢管混凝土抗撞设计方法

中空夹层钢管混凝土（concrete-filled double-skin steel tubular,CFDST）构件作为超高输电塔、海上平台等重要结构的承重构件,其抗撞性能是设计阶段需考虑的关键问题。因此,在前期试验研究的基础上,采用ABAQUS有限元软件建立了200个圆CFDST柱力学模型,并进行了轴力与撞击耦合作用下的抗撞机理分析,研究了在0~0.7轴压比下不同名义含钢率、空心率、截面直径、材料强度对构件抗撞性能的影响规律;基于动力放大系数和等效单自由度方法提出了构件抗撞承载力计算公式,并预测了撞击作用下构件的跨中动力响应。结果表明:在0~0.7轴压比下,名义含钢率、外径、外钢管强度、撞击速度与撞击质量对构件跨中挠度峰值和撞击力平台值影响显著,空心率与混凝土强度影响较小;提出的简化计算方法能较好地预测圆CFDST构件的抗撞承载力和跨中位移响应。     

The symmetrical deformation of circular membrane under the action of uniformly distributed loads in its central portion

This paper presents the solution of symmetrical deformation of circular membrane under the action of uniformly distributed loads in its central portion. Its limiting case is the solution of circular membrane under concentrated load at the center. This solution is the third solution of the circular membrane problems after the well-known Hencky’s solution.     

Stress intensity factors of a crack in a composedcircular cylinder

A composed circular cylinder, formed by a core circular cylinder, containing a crackand enclosed by a layered hollow circular cylinder, is investigated in regard to the evaluation ofstress intensity factors. Analytic solutions to the problem are provided, with which the upper andlower bounds of stress intensity factors in a cracked circular cylinder, the stress distribution in alayered hollow circular cylinder, and the stress intensity factors for a crack in the composedcircular cylinder can precisely be determined. Numerical materials, demonstrating the discretevalues of the stress intensity factors, as well as the general pattern according to which the stressintensity factors vary with the material and geometric constants, are presented. The solutions aredeveloped based on a simplified and modified solution to the Hilbert problem, and the matrixpresentation and manipulation of functions and variables, used in the circuit theory.     

Magneto–thermo–electro–elastic transient response in a piezoelectric hollow cylinder subjected to complex loadings

The article presents an analytical solution for magneto–thermo–electro–elastic problems of a piezoelectric hollow cylinder placed in an axial magnetic field subjected to arbitrary thermal shock, mechanical load and transient electric excitation. Using an interpolation method solves the Volterra integral equation of the second kind caused by interaction among magnetic, thermal, electric and mechanical fields, the electric displacement is determined. Thus, the exact expressions for the transient responses of displacement, stresses, electric displacement, electric potential and perturbation of the magnetic field vector in the piezoelectric hollow cylinder are obtained by means of Hankel transforms, Laplace transforms, and inverse Laplace transforms. From sample numerical calculations, it is seen that the present method is suitable for a piezoelectric hollow cylinder subjected to arbitrary thermal shock, mechanical load and transient electric excitation, and the result carried out may be used as a reference to solve other transient coupled problems of magneto–thermo–electro–elasticity.     

Elastoplastic analysis of a bent circular plate with a central hole

A circular aluminum plate with a small concentric hole (1/10 the plate thickness) and supported on its outer edge by a ring was subjected to a concentrated load at its center, applied through a rigid ball of radius equal to the plate thickness. Strains were determined using grids, moiré, and electrical strain gages on the top and bottom surfaces of the plate for loads up to and including the one associated with the appearance of the first crack in the plate. The investigation is related to the development of specimens to be used to determine fracture characteristics of materials used in lightweight construction.     

多层平行裂隙型多孔介质通道内流体流动传热特性

基于Brinkman-extended Darcy模型和局部热平衡模型,对多层平行裂隙型多孔介质通道内的流动传热特性进行研究.获得了多层平行裂隙型多孔介质通道内各区域的速度场、温度场、摩擦系数及努塞尔数解析解,并分析了裂隙层数、达西数、空心率、有效热导率之比等对通道内流动传热特性的影响.结果表明:达西数较小时,通道多孔介质层内会出现不随高度变化的达西速度,此达西速度会随裂隙层数的增加而增大,但却不受各裂隙层下多孔介质层位置变化的影响.增加裂隙层数会减弱空心率对压降的影响,会使通道内流体压降升高,但升高程度会逐渐降低.增大热导率之比或减小空心率会使多裂隙通道内出现阶梯式温度分布,而在较小热导率之比或较大空心率时多裂隙情况下的温度分布曲线会趋于一致.此外,当热导率之比较小时,多层裂隙通道内的传热效果在任何空心率下都要优于单裂隙情况,当热导率之比较大时,存在临界空心率使各裂隙层数通道内的传热效果相同,且多裂隙通道内继续增加裂隙层数对传热强度影响不大.     

Optimal Forms of Shallow Arches with Respect to Vibration and Stability

Shallow, linearly elastic arches of unspecified form but with given uniform cross section and material are considered. For given span and length of the arch, two different optimization problems are formulated and solved. In the first, we determine the form of the arch which maximizes the fundamental vibration frequency. The corresponding vibration mode turns out to be either symmetric or antisymmetric. In the second, a static load with given spatial distribution is considered, and the critical value of the load magnitude for snap-through instability is maximized. This instability may occur at a limit point or a bifurcation point. Optimal forms are determined for sinusoidal loading, uniform loading, and a central concentrated load. In both types of problems, arches with simply supported or clamped ends are considered, and the maximum frequencies and critical loads obtained are compared to those for a circular arch with similar end conditions. In all the cases with simply supported ends, it is found that a circular arch is almost optimal. For clamped ends, however, it turns out that the optimal arches have zero slope at the ends and that they are much more efficient than a circular arch.     

Stresses in a long hollow cylindrically aeolotropic circular cylinder with plane ends subjected to surface forces

In this paper the stress distribution at a point in a long hollow cylindrically aeolotropic circular cylinder whose plane ends are subjected to systems of forces each of which is statically equivalent to a couple and a longitudinal force, and whose curved surface is subjected to a uniform normal pressure has been studied. The solution of this static mixed Saint-Venant type problem provides results from which the corresponding results of isotropic, transversely isotropic circular cylindrical bodies can be readily deduced. In the end a simple practical application has been made with regard to a similar problem of a long hollow wood pole made up of species walnut.     

Elastic behaviour of shrink-fitted forming die assemblies. Part I: Development of an analytical solution

Summary The paper deals with the elastic behaviour of the die assemblies obtained by shrinking a thick walled ring onto a finite hollow right circular cylinder in general of different length. Displacements and stresses in the two components of the assembly are evaluated by using the theoretical general solution on the finite thick-walled hollow elastic right circular cylinder with an axially symmetrical load system in terms of Airy's stress function. Radial and axial displacement influence coefficient technique is used to solve the integral equations governing the two extreme frictionless and slipless contact modes at the mating surface.

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Sommario L'articolo riferisce sul comportamento elastico di accoppiamenti realizzati per forzamento di un anello di grosso spessore su di un cilindro cavo circolare retto di lunghezza finita ed in generale diversa da quella dell'elemento forzante.La valutazione delle componenti di spostamento e di tensione presenti in ciascuno dei due elementi dell'accoppiamento è operata mediante una soluzione teorica, generale, relativa ad un cilindro cavo, circolare, retto, di lunghezza finita e sollecitato da un sistema di carichi distribuiti in modo assialsimmetrico e che è stata sviluppata in termini della funzione delle tensioni di Airy. Il metodo dei coefficienti di influenza applicato alle componenti radiale ed assiale degli spostamenti è utilizzato per la risoluzione delle equazioni, scritte in forma integrale, che governano le modalità di contatto relative alle due situazioni estreme di assenza di attrito e di adesione completa in corrispondenza delle superfici di accoppiamento.

     

基于细观建模的电子束预控弹体破裂机理数值研究

为研究电子束预控弹体的破裂机理。提出了基于电子束预控弹体细观几何特性的参数化建模方法,建立了含基体、熔融区、过渡区和空腔区弹体的三维有限元模型,采用LS-DYNA软件对典型弹体的爆炸驱动和破裂过程进行了数值模拟分析。结果表明:电子束预控弹体破裂过程可分为:弹体膨胀后的空腔区在环向拉应力作用下产生拉伸断裂、过渡区产生裂纹扩展和拉伸断裂以及空腔区底部基体在两侧拉应力和底部压应力作用下产生与弹体内壁法线呈45°的剪切破坏3个阶段。数值模拟结果与回收的破片截面形状和破坏模式吻合较好。研究结果对电子束预控弹体破片成型控制具有参考价值。