电流变夹层板控制系统的传感器优化布置

为了解决ER夹层板系统的模态控制的实用性问题,研究了悬臂板模态坐标估计和传感器定位问题。按照变刚度模态控制算法的要求,给出了离散坐标下模态坐标估计的方法;根据连续结构的振型分析,分析传感器定位计算,建立了数学优化模型;按照模态动能法初步筛选后,枚举得到传感器优化布置方案,并且从估计精度和控制效果两个角度进行了布置方案的算例验证。结果表明,优化的传感器布置能在较少的数目下,模态坐标估计满足模态控制算法的输入需求。     

Bending of curved sandwich beams

Curved sandwich beams in bending are analyzed with analytical elasticity methods and compared to simple analytical formulae and FEM calculations. Solutions to Airy's stress function in polar co-ordinates are used to obtain the stress distributions in the radial and circumferential directions. Plane stress and plane strain solutions are given with isotropic and orthotropic material models. It is shown that the properties of the core can have a significant influence on the circumferential stresses of the faces, but that the radial stress of the core is nearly constant with varying core properties. The radius of curvature can have a large influence on the circumferential stresses of the faces when the radius of curvature to sandwich thickness ratio is small to moderate. It is shown that simple analytical methods can be utilised to calculate the radial stresses in the core and the circumferential stresses of the faces for beams with large to moderate radii of curvature and thin to moderately thick faces.     

Indentation resistance of sandwich beams

High-order sandwich beam theory is used to model the local deformation under the central indentor for sandwich beams loaded under three-point bending. ‘High-order' refers to the non-linear variations of in-plane and vertical displacements through the height of the core which the model incorporates. The analysis is elastic, which is appropriate to describe the beam response up to peak load for the material combination of GFRP skins and Nomex honeycomb core which is the focus of this paper. Reasonable agreement is found between theoretical predictions of the displacement field under the indentor and experimental measurements using a beam with GFRP skins and Nomex honeycomb core. By using the model to consider the way in which different wavelengths of sinusoidal pressure loading on the top skin are transmitted to the core, a spreading length scale λ is introduced. λ, which is a function of the beam material and geometric properties, characterises the length over which a load on the top surface of a beam is spread out by the skin. Calculations of the effect of roller diameter on indentation behaviour illustrate the importance of this length scale. When λ is small compared with the roller radius R, corresponding to a flexible skin, the contact load at the roller-skin interface is transmitted relatively unchanged to the core. Conversely, when λ/R is greater than about 0.25, corresponding to a relatively rigid skin, the load from the roller is spread out by the skin and the pressure in the core is distributed over a length of the order of λ.     

Dynamic wrinkling in sandwich beams

Facings of sandwich structures employed in typical applications are often subject to parametric periodic loading. Such loading can cause local dynamic instability of the facings, i.e. large-amplitude small wavelength lateral vibrations. This phenomenon, called in the paper dynamic wrinkling, may result in fatigue damage or immediate failure. The problem of dynamic wrinkling of the facings is analyzed in the present paper for sandwich beams and for large aspect ratio wide panels that vibrate forming a cylindrical surface. The solution is obtained for the case of a relatively thick or compliant core where the Winkler elastic foundation model of the core is applicable. In addition, the problem is formulated as an extension of the Plantema core model that may be preferable for thinner and stiffer cores. In addition, a new simplified elasticity model is introduced in the paper that is based on the assumption that both facings experience simultaneous and interactive dynamic wrinkling instability. Numerical results shown for the elastic foundation model include the criterion for the onset of dynamic wrinkling and the critical value of the damping coefficient of the facing that is sufficient to prevent such wrinkling. As follows from these results, dynamic wrinkling is unlikely in most engineering applications, except for the case in which the maximum stresses in the facing approach the static wrinkling value.     

Bending response of web-core sandwich beams

This paper presents a new analytical solution for the bending response of a web-core sandwich beam. The beam is a transverse cut from the sandwich plate. The method is based on the plane frame analysis, where the response of the beam is divided into local and global components. The Clebsch’s method is used to calculate the deflection of the face plates. The validation of the plane frame method is carried out with FE-analyses based on the shell element formulation. Also a comparison is made with the method based on homogenized beam. Periodic stress distributions in the face plates are revealed with the plane frame analysis and are supported by the FE-analysis. The existing methods based on homogenized beam are not able to predict these stresses. The plane frame analysis can benefit the development of the theory related to web-core sandwich plate.     

Thermal buckling of bimodular sandwich beams

This paper presents a model that explores the thermal buckling of three-layer sandwich beams possessing thick facings and moderately stiff cores. Bimodular facings and core material are used. In contrast to conventional theory, the effects of transverse shear deformation in the facings as well as the effect of the stretching and bending action in the core on thermal buckling are considered. The governing equations are derived using the principle of minimum total potential energy and the fact that its second derivative is zero. The finite-element results are presented in order to investigate the effects of important parameters such as thickness, thermal expansion coefficients and moduli ratio on critical buckling temperatures.     

Fatigue analysis of honeycomb-composite sandwich beams

The fatigue behaviour of honeycomb sandwich beams is experimentally investigated through four-point bending tests. Two kinds of specimens, initially undamaged and damaged by interface debonding, have been tested. The fatigue tests results are presented in standard SN diagrams with a best curve fit of the experimental data, while the fatigue limit is evaluated through a stair-case procedure. Two different failure mechanisms were found: undamaged specimen failure is due to collapse of the compressed face, while damaged specimen failure occurs due to the collapse of the honeycomb cell walls at the tip of the debonded portion.     

复合材料面板对筒型基座整体抑振机制影响规律研究

提出一种新型复合材料筒型基座结构形式,其面板采用夹芯结构设计;通过系统阻抗特性分析理论预测面板结构及材料参数对基座减振性能的影响规律;针对夹芯面板开展静/动力学特性试验;以振级落差为减振效果评价指标,通过激振试验研究了面板结构参数对基座抑振机制的影响规律。研究结果表明：在频段 ,夹芯面板刚度能有效控制基座减振性能,随着频率的增加,面板刚度抑振机制减弱,阻尼高频损耗抑振机制增强;夹芯面板芯材厚度的增加对基座高频抑振性能优于表层厚度增加;面板对基座减振耗能贡献高于环壁间阻尼芯材。     

双钢板-混凝土组合结构在沉管隧道中的发展与应用

深中通道沉管管节采用钢壳-混凝土组合结构形式,通过向空钢壳浇筑混凝土预制而成。为评估沉管管节施工后的整体变形,建立了热-结构顺序耦合的分析框架,基于ANSYS APDL及UFPs二次开发模块,分别建立了考虑水化度、日照辐射、大气温度变化的精细温度场模型和考虑混凝土硬化及收缩特性的结构分析模型。通过对足尺管节的温度及应变模拟结果与监测数据的对比,验证了有限元模型的可靠性。在此基础上,分析了日照辐射、大气温度变化等对于管节温度场的影响,同时分析了管节的整体变形模式,以及温度效应、混凝土收缩及自重三种因素对管节整体横向、纵向及竖向变形的影响。结果表明：管节施工过程的温度场表现为时变和空间分布的特征,格仓边部温度受外界气温变化和日照辐射的影响存在周期性波动,而格仓中部温度峰值主要受混凝土自身水化放热特性的控制;管节最终表现为顶板横向及纵向内收,竖向下挠,底板横向及竖向变形不显著;太阳辐射对于结构温度场影响较日气温变化更显著,建议在混凝土温度峰值预测中予以考虑,而日气温变化可采用日平均气温值予以简化;温度效应及材料收缩对管节横向及纵向整体变形影响显著,自重因素导致的变形在横向及纵向的比例为44.3%、11.7%,而在竖向所占比例达92.5%,因而温度效应及材料收缩在管节横向及纵向变形分析中不可忽视;该分析方法可适用于大体积混凝土等结构的温度效应的预测和评估。

     

基于钢板屈曲分析的双钢板-混凝土组合剪力墙轴压承载力计算方法

双钢板混凝土组合结构结合了钢与混凝土两种材料的优势、力学性能以及耐久性优越,且施工快速便捷,正越来越广泛地应用于核电工程中。双钢板混凝土组合墙与钢筋混凝土筏板基础的锚固节点是其优越性能充分发挥的关键之一。插筋式节点相较于传统嵌入式节点和埋件式节点可以显著提高施工效率,从而得到更多青睐,但是目前关于该类节点锚固性能的研究较少。该文设计了4个1∶2缩尺的双钢板混凝土组合墙-钢筋混凝土基础插筋锚固节点,对其进行静力单调拉伸试验。通过对试件承载力、刚度、裂缝形态、钢筋及钢板应变等开展分析,探究了搭接钢筋布置方式以及对拉钢筋配置对于节点锚固性能的影响规律,并针对可能的破坏模式提出了相应的设计方法。试验结果表明：该类节点可以实现等强连接,且延性较好;对拉钢筋对控制裂缝发展,提高节点整体性具有重要作用,且沿长度方向对拉钢筋应变呈非线性分布;随着搭接钢筋与钢板距离的增大,钢筋与钢板间的不平衡力矩增加,导致对拉钢筋应变增大,但搭接钢筋的滑移有所降低。该文研究结果为插筋式节点的锚固设计提供了重要依据。     

Strength of sandwich beams with interface debondings

The adhesive joint bonding the faces to the core material in a sandwich structure ensures that the loads are transferred between the components. However, debondings may arise either during the manufacturing process or due to overloading. These will reduce both the stiffness and the load bearing capacity of the structure. In the present paper, debondings in foam core sandwich beams are investigated assuming that cracks in the interface between the face and core are present. Stress intensity factors are found from an analytical model and compared to solutions from several finite element calculations. Fracture toughness values, determined from simple specimens, are used to predict the fracture loads for beams with simulated debondings subjected to four-point bending.     

Fabrication and mechanical testing of glass fiber entangled sandwich beams: A comparison with honeycomb and foam sandwich beams

The aim of this paper is the fabrication and mechanical testing of entangled sandwich beam specimens and the comparison of their results with standard sandwich specimens with honeycomb and foam as core materials. The entangled sandwich specimens have glass fiber cores and glass woven fabric as skin materials. The tested glass fiber entangled sandwich beams possess low compressive and shear modulus as compared to honeycomb and foam sandwich beams of the same specifications. Although the entangled sandwich beams are heavier than the honeycomb and foam sandwich beams, the vibration tests show that the entangled sandwich beams possess higher damping ratios and low vibratory levels as compared to honeycomb and foam sandwich beams, making them suitable for vibro-acoustic applications where structural strength is of secondary importance, e.g., internal paneling of a helicopter.     

Flexural behaviour of glue-laminated fibre composite sandwich beams

This study involved experimental investigation onto the flexural behaviour of glue-laminated fibre composite sandwich beams with a view of using this material for structural beams. Composite sandwich beams with 1, 2, 3, and 4 composite sandwich panels glued together were subjected to 4-point static bending test in the flatwise and edgewise positions to evaluate their stiffness and strength properties. The results showed that the composite sandwich beams in the edgewise position failed with 25% higher bending strength but have 7% lower bending stiffness than beams in the flatwise position. The results however indicated that the bending stiffness of flatwise specimens converges to that of the edgewise specimens with increasing laminations. More importantly, the specimens in the edgewise position failed with greater ductility due to progressive failure of the fibre composite skins while the specimens in the flatwise position failed in a brittle manner due to debonding between the skin and core. Wrapping the glue-laminated sandwich beams with one layer of tri-axial glass fibres did not prove to be effective. Overall, it has been demonstrated that the glue-laminated sandwich beams exhibited better performance than the individual composite sandwich beams.     

电流变弹性体夹层结构梁的动力学仿真研究

对电流变弹性体夹层悬臂梁在不同电场控制下的振动响应特性和可控性进行研究。将电流变弹性体等效为一种具有电控力学性能的粘弹性阻尼材料,基于Hamilton原理建立了三层电流变弹性体夹层梁的有限元动力学方程,仿真分析了其在不同外加电场控制下的振动特性。分析结果显示,随着外加电场强度的增加,电流变弹性体夹层梁的固有频率不断增大,振动幅值却不断减小。表明电流变弹性体夹层梁具有与电流变液夹层梁相似的可控振动响应特性,能在外加电场作用下实现对结构振动的实时控制。     

Buckling and postbuckling behavior of delaminated sandwich beams

An investigation was performed to study the buckling and postbuckling behavior of sandwich beams containing lengthwise and depthwise through-the-width delaminations. An analytical beam model was developed to predict the buckling load of the beam and to describe its postbuckling response for arbitrarily situated delaminations and various combinations of boundary conditions. Griffith's energy release rate model was employed to predict the stability of delamination propagation under external loading and to determine the direction of delamination growth.

Parametric studies over a wide range of beam geometries, damage sizes and locations, composite facings and beam boundary conditions were carried out to study their effects on the overall behavior of the sandwich structure, as well as its damage tolerance. The results demonstrated that a sandwich construction is very ‘sensitive’ to the presence of delaminations situated at the core-faceplate interface. Premature buckling failure occurs at external loads which are significantly lower than the buckling load for a ‘perfect’ sandwich beam; in ‘imperfect’ beams with composite faceplates, the layup sequence affects significantly the load-carrying capacity of the beam; varying either the boundary conditions in a sandwich beam or the lengthwise location of a delamination has a small effect on the postbuckling behavior of the beam. Delaminations located within composite faceplates have less pronounced influence, and as the defect is moved outwards the limit load may reach the buckling load corresponding to that of the ‘perfect’ beam.

The proposed model is capable of analyzing the postbuckling behavior of both sandwich and composite laminated beams for arbitrary locations of the delamination, and various combinations of boundary conditions.     

Static indentation and unloading response of sandwich beams

This paper deals with analysis of foam core sandwich beams subject to static indentation and subsequent unloading (removal of load). Sandwich beams are assumed continuously supported by a rigid platen to eliminate global bending. An analytical model is presented assuming an elastic-perfectly plastic compressive behaviour of the foam core. An elastic part of indentation response is described using the Winkler foundation model. Upon removal of the load, an elastic unloading response of the foam core is assumed. Also, finite element (FE) analysis of static indentation and unloading of sandwich beams is performed using the FE code ABAQUS. The foam core is modelled using the crushable foam material model. To obtain input data for the analytical model and to calibrate the crushable foam model in FE analysis, the response of the foam core is experimentally characterized in uniaxial compression, up to densification, with subsequent unloading and tension until tensile fracture. Both models can predict load–displacement response of sandwich beams under static indentation and a residual dent magnitude in the face sheet after unloading along with residual strain levels in the foam core at the unloaded equilibrium state. The analytical and FE analyses are experimentally verified through static indentation tests of composite sandwich beams with two different foam cores. The load–displacement response, size of a crushed core zone and the depth of a residual dent are measured in the testing. A digital speckle photography technique is also used in the indentation tests in order to measure the strain levels in the crushed core zone. The experimental results are in good agreement with the analytical and FE analyses.     

电流变液力悬置可控高压电源的性能研究

为了将电流变技术用于汽车发动机液力悬置,必须有可控高压电源.介绍基于脉宽调制芯片TL494的高压电源的工作原理,其电压可由单片机控制的数字电位器进行调整.用数字示波器对电源性能进行了测试分析,获得电源性能曲线.该电源体积小,可靠性高,电压调整迅速准确,可以满足应用于电流变液力悬置的需要.     

基于剪切耗能假设的黏弹性夹芯梁的振动和阻尼特性

基于一阶剪切变形理论和哈密顿原理建立了三层粘弹性夹芯梁结构的有限元模型并对其振动和阻尼特性进行了研究。建模时认为粘弹材料层不可压缩,振动能量是依靠粘弹性层的剪切变形来耗散的。为验证本模型的正确性,将其与解析解作了对比。同时,为了证明本方法的优越性,将其与常用的“实特征模态”、“近似复特征模态”、“钻石法”和“近似法”四种数值方法做了比较。结果表明本方法的精度在这几种数值方法中是最好的。最后,讨论了粘弹性夹芯梁结构参数变化对系统固有频率和损耗因子的影响,得到了一些有工程实际意义的结论。     

Flow of electro-rheological materials

Summary An electro-rheological fluid is a material in which a particulate solid is suspended in an electrically non-conducting fluid such as oil. On the application of an electric field, the viscosity and other material properties undergo dramatic and significant changes. In this paper, the particulate imbedded fluid is considered as a homogeneous continuum. It is assumed that the Cauchy stress depends on the velocity gradient and the electric field vector. A representation for the constitutive equation is developed using standard methods of continuum mechanics. The stress components are calculated for a shear flow in which the electric field vector, is normal to the velocity vector. The model predicts (i) a viscosity which depends on the shear rate and electric field and (ii) normal stresses due to the interaction between the shear flow and the electric field. These expressions are used to study several fundamental shear flows: the flow between parallel plates, Couette flow, and flow in an eccentric rotating disc device. Detailed solutions are presented when the shear response is that of a Bingham fluid whose yield stress and viscosity depends on the electric field.     

Core compression in sandwich beams under contact loading

Failure of the core in sandwich structures under concentrated loading is of potential concern, and it is difficult to compute the core compressive stress by simple means. Contact loading adds additional complexity, as surface displacements are imposed and the contact zone size and pressure distribution is initially unknown. However contact loading is important as it is widely used in three or four point bend tests to determine failure properties, and is also typically involved in impact loading. The calculation of core compressive stress was addressed in the present work by utilizing an elasticity solution due to Pagano and Srinivas and Rao for transverse loading of layered orthotropic materials. Contact pressure distributions were obtained by systematically varying pressures and comparing the computed surface displacements with the indentor profile. The results show that the pressure distribution for an orthotropic half-space is applicable to sandwich beams over a wide range of variables. A beam-on-elastic-foundation model was found to be useful in correlating the analysis results for core compressive stress.