A new higher-order shear deformation theory and refined beam element of composite laminates

A new higher-order shear deformation theory based on global-local superposition technique is developed. The theory satisfies the free surface conditions and the geometric and stress continuity conditions at interfaces. The global displacement components are of the Reddy theory and local components are of the internal first to third-order terms in each layer. A two-node beam element based on this theory is proposed. The solutions are compared with 3D-elasticity solutions. Numerical results show that present beam element has higher computational efficiency and higher accuracy.

On well-posedness of two-phase nonlocal integral models for higher-order refined shear deformation beams

Due to the conflict between equilibrium and constitutive requirements,Eringen’s strain-driven nonlocal integral model is not applicable to nanostructures of engineering interest.As an alternative,the stress-driven model has been recently developed.In this paper,for higher-order shear deformation beams,the ill-posed issue(i.e.,excessive mandatory boundary conditions(BCs)cannot be met simultaneously)exists not only in strain-driven nonlocal models but also in stress-driven ones.The well-posedness of both the strain-and stress-driven two-phase nonlocal(TPN-Strain D and TPN-Stress D)models is pertinently evidenced by formulating the static bending of curved beams made of functionally graded(FG)materials.The two-phase nonlocal integral constitutive relation is equivalent to a differential law equipped with two restriction conditions.By using the generalized differential quadrature method(GDQM),the coupling governing equations are solved numerically.The results show that the two-phase models can predict consistent scale-effects under different supported and loading conditions.

Size-dependent thermomechanical vibration characteristics of rotating pre-twisted functionally graded shear deformable microbeams

A three-dimensional(3D)thermomechanical vibration model is developed for rotating pre-twisted functionally graded(FG)microbeams according to the refined shear deformation theory(RSDT)and the modified couple stress theory(MCST).The material properties are assumed to follow a power-law distribution along the chordwise direction.The model introduces one axial stretching variable and four transverse deflection variables including two pure bending components and two pure shear ones.The complex modal analysis and assumed mode methods are used to solve the governing equations of motion under different boundary conditions(BCs).Several examples are presented to verify the effectiveness of the developed model.By coupling the slenderness ratio,gradient index,rotation speed,and size effect with the pre-twisted angle,the effects of these factors on the thermomechanical vibration of the microbeam with different BCs are investigated.It is found that with the increase in the pre-twisted angle,the critical slenderness ratio and gradient index corresponding to the thermal instability of the microbeam increase,while the critical material length scale parameter(MLSP)and rotation speed decrease.The sensitivity of the fundamental frequency to temperature increases with the increasing slenderness ratio and gradient index,and decreases with the other increasing parameters.Moreover,the size effect can suppress the dynamic stiffening effect and enhance the Coriolis effect.Finally,the mode transition is quantitatively demonstrated by a modal assurance criterion(MAC).

A two variable refined plate theory for the bending analysis of functionally graded plates

Bending analysis of functionally graded plates using the two variable refined plate theory is presented in this paper.The number of unknown functions involved is reduced to merely four,as against five in other shear deformation theories. The variationally consistent theory presented here has, in many respects,strong similarity to the classical plate theory. It does not require shear correction factors,and gives rise to such transverse shear stress variation that the transverse shear stresses vary parabolically across the thickness and satisfy shear stress free surface conditions.Material properties of the plate are assumed to be graded in the thickness direction with their distributions following a simple power-law in terms of the volume fractions of the constituents.Governing equations are derived from the principle of virtual displacements, and a closed-form solution is found for a simply supported rectangular plate subjected to sinusoidal loading by using the Navier method.Numerical results obtained by the present theory are compared with available solutions,from which it can be concluded that the proposed theory is accurate and simple in analyzing the static bending behavior of functionally graded plates.

Exact solution for thermal vibration of multi-directional functionally graded porous plates submerged in fluid medium

An analytical method for analyzing the thermal vibration of multi-directional functionally graded porous rectangular plates in fluid media with novel porosity patterns is developed in this study.Mechanical properties of MFG porous plates change according to the length,width,and thickness directions for various materials and the porosity distribution which can be widely applied in many fields of engineering and defence technology.Especially,new porous rules that depend on spatial coordinates and grading indexes are proposed in the present work.Applying Hamilton's principle and the refined higher-order shear deformation plate theory,the governing equation of motion of an MFG porous rectangular plate in a fluid medium(the fluid-plate system)is obtained.The fluid velocity potential is derived from the boundary conditions of the fluid-plate system and is used to compute the extra mass.The GalerkinVlasov solution is used to solve and give natural frequencies of MFG porous plates with various boundary conditions in a fluid medium.The validity and reliability of the suggested method are confirmed by comparing numerical results of the present work with those from available works in the literature.The effects of different parameters on the thermal vibration response of MFG porous rectangular plates are studied in detail.These findings demonstrate that the behavior of the structure within a liquid medium differs significantly from that within a vacuum medium.Thereby,they offer appropriate operational approaches for the structure when employed in various mediums.

基于微分求积有限元法的双层微板系统振动特性研究

基于修正的偶应力理论和两变量精化的剪切变形理论,建立了由Winkler-Pasternak连续弹性夹层连接的双层微板系统的自由振动模型,着重推导了系统异步振动的运动微分方程和势能泛函。融合Gauss-Lobatto求积准则和微分求积准则构造了具有C~1连续性的微分求积有限元。通过与已有文献进行对比,验证了数值方法的有效性。详细讨论了各种因素对系统同步和异步振动特性的影响。结果表明,系统的自由振动特性对材料尺度参数、长宽比、长厚比以及边界条件呈现出依赖性;弹性夹层刚度仅对系统异步振动产生作用;随着模态阶次的增大,材料尺度参数和弹性夹层刚度对异步振动频率和模态的影响变得显著。

一种分析AGS结构的三角形加筋板壳单元

基于精细三角形Mindlin板单元构造了21个自由度三角形复合材料加筋板壳单元。在该单元构造过程中,考虑了肋骨弯曲、扭转、面内剪切和横向剪切变形的影响;由于肋骨和蒙皮的位移插值函数采用了相同的形函数,保证了两者变形的协调性,同时又放松了肋骨转动的约束,故与传统的板单元相比,能较好地反映了蒙皮和肋骨的变形特征。在此单元中,肋骨放置的数量、位置和角度可以任意,为结构的单元网格剖分带来了很大的便利。算例结果验证了单元的有效性,特别是在分析高肋结构时,显示出其比传统加筋板单元具有更高精度的优点。还以一典型的先进复合材料等格栅加筋板(AGS)为例,讨论了该结构弯曲变形的力学特性。

复合材料面层夹层扁壳非线性精化理论及应用

考虑面层横向剪切变形以及横向剪应力在面层和芯层粘结处连续，应用Hamilton原理建立了正交铺设复合材料面层夹层扁壳新的非线性精化理论。在静力问题情形，控制方程和边界条件化简为用四个基本未知函数表述。作为理论的应用，分析了简支边界条件下正交铺设复合材料面层夹层圆柱壳和夹层球壳的非线性弯曲，得到了其挠度响应和层间应力响应。

复合材料层合板精化高阶理论及其精化三角形板单元

提出一种新的精化高阶理论，该理论满足层间位移、应力连续条件，由此建立了三角形精化板单元。该单元满足单元间Ｃ１类弱连续条件，其收敛性得到保证，且具有简单、高效率的优点。

考虑横向正应力影响的高阶理论及其精化单元法

提出一种新的高阶理论 ,该理论满足层间位移、应力连续条件 ,其位移场只有 5个未知数 ,同一阶剪切变形理论中位移函数的未知数一样多 ,由此建立了三角形精化板单元。该单元满足单元间C1 类弱连续条件 ,其收敛性得到保证 ,且具有列式简单、计算效率和精度高的优点。

新型整体-局部高阶剪切变形理论及层合板精化三角形单元

基于整体-局部位移方法,建立了一种高阶剪切变形理论。整体位移部分采用的是R eddy理论的位移模式(1984),局部位移为L I X Y等(1997)建立的1,2-3理论的局部函数。这一理论使满足自由表面条件的R eddy理论进一步满足层间位移、应力连续,同时有效减少了1,2-3理论的未知数个数。基于此理论深入开展了有限元法研究,建立了满足C1连续条件的精化三节点三角形单元(每个节点参数为9个)。计算结果表明:建立的精化单元能准确计算整体位移和层间应力。

正交异性板的后屈曲和Karman型精化理论

基于Ｋａｒｍａｎ型正变异性板的精化理论，本文采用挠度型摄动技术研究了复合构造矩形板的屈曲与后屈曲性态．分析中应用了由该理论导出的广义大挠度Ｋａｒｍａｎ方程，不仅考虑横向剪切，而且包含因材料指向性引起的剪弯相互作用．用此摄动技术构造出了四边简支正交异性中厚板和夹层板的后屈曲路径高阶渐近展开式．通过比较可以看出，当前计算结果更接近相应的三维弹性理论精确解．

Vibration characteristics of piezoelectric functionally graded carbon nanotube-reinforced composite doubly-curved shells

This paper presents an analytical solution for the free vibration behavior of functionally graded carbon nanotube-reinforced composite(FG-CNTRC) doubly curved shallow shells with integrated piezoelectric layers. Here, the linear distribution of electric potential across the thickness of the piezoelectric layer and five different types of carbon nanotube(CNT) distributions through the thickness direction are considered. Based on the four-variable shear deformation refined shell theory, governing equations are obtained by applying Hamilton's principle. Navier's solution for the shell panels with the simply supported boundary condition at all four edges is derived. Several numerical examples validate the accuracy of the presented solution. New parametric studies regarding the effects of different material properties, shell geometric parameters, and electrical boundary conditions on the free vibration responses of the hybrid panels are investigated and discussed in detail.