复合材料对称层合板特征值问题的灵敏度分析

由于复合材料层合板的横向剪切模量较低,因此基于克希霍夫理论而计算的层合板特征值及其灵敏度与实际情况相差较大。本文采用层合板的一阶剪切变形理论,将纤维铺设角、材料参数和从层合板的中面到第K层板上表面的距离Z_K视为设计变量,研究了对称层合板特征值的灵敏度计算问题。     

CF/PEEK复合材料界面层结构与性能关系研究

本文根据聚醚醚酮(PEEK)在碳纤维表面形式的横晶层的结构特征分析,建立了CF/FEEK复合材料界面层微观力学性能的理论方程,计算了界面层的杨氏模量.通过超声浸渍法测量复合材料的力学性能验证了计算结果,证明所进行的分析合理.计算结果表明,PEEK界面横晶层在垂直于纤维方向的杨氏模量E_r随PEEK结晶度的增大,或随横晶中PEEK晶片长度的增大而增大,并随晶片厚度的增大而减小.该界面层的上述模量值始终高于界面层附近球晶的模量值E_s,两者之间的比值E_T/E_s;依赖于横晶及球晶中的晶片长度b、厚度c和宽度a.由于界面层的模量高于非界面层的模量,当复合材料中纤维表面形成横晶时,复合材料将有较高的刚性.     

环氧玻璃钢层合板冲击破坏及其断口微观特征的研究

S-GF/Ep648复合材料层合板[0₉°/θ]_s冲击抗力试验的结果表明其冲击抗力值与铺层角θ无关,只受浸水时间的影响;而另一种铺层形式[+θ₈/-θ₈]的复合材料层合板,在落重冲击试验中却发现:在相同的冲击能量下,θ越大,分层破坏越严重,损伤区面积也越大。利用SEM-505扫描电子显微镜对发生穿透性断裂、层间分层断裂或仅出现冲击损伤等破坏形式的断口表面进行了观察和分析,讨论了影响该复合材料冲击断裂和冲击损伤性能的因素。     

复合材料的Ⅰ型层间断裂韧性

本文采用铰链式双悬臂梁试件对碳/双马来酰亚胺复合材料的Ⅰ型层间断裂韧性进行了研究,分析比较了层间断裂韧性G_IC的表达方法,用三次多项式和幂函数拟合实验柔度的方法得到的结果比较满意,实验结果表明纤维桥连对单向层合板的G_IC的影响是显着的,用刀片切割桥连纤维后G_IC值下降百分之二十,分散性也有显着下降。另外发现G_IC值随试件厚度增加而增大。     

不同类型的基体对0-3型压电复合材料性能的影响

制备了PZT/环氧树脂和PZT/尼龙两种0-3型压电复合材料。研究表明,以尼龙-1010为基体的复合材料的饱和极化电场E_s和时间t_s均比环氧树脂E-20为基体的复合材料低,而压电系数d₃₃却比后者高。     

Modified sol-gel process for the preparation of BaTiO3 and PbTiO3 ferroelectric films

A modified method for preparing barium and lead titanate films is suggested, which combines precipitation from solution and elements of sol-gel processing. The ∼1-μm-thick BaTiO₃/Pt and PbTiO₃/Pt films deposited on Pt foil are transparent, show good adhesion, and have the 1 : 1 : 3 stoichiometry. The films are finegrained, with a mean grain size of 0.1–0.2 μm. The barium titanate films are characterized byt _C = 110-125°C, ε₂₀ = 167-500, tanδ₂₀ = 0.015-0.06, ε_max = 1050,P _s= 3.2 μC/cm²,E _c = 14 kV/cm, ρ = (5-7) × 10⁹ Ω cm, andV _br = 80-150 kV/cm. The lead titanate films are characterized byc/a = 1.056, ε₂₀ = 105-110, tanδ₂₀ = 0.11-0.16,P _s = 4.1 μC/cm²,E _c = 34 kV/cm, ρ = (0.8-3.0) × 10⁹ Ω cm, andV _br = 50-100 kV/cm.     

Kinetics of Reactions of Np and Pu Ions with Hydrazine Derivatives: XVIII. Reaction between Np(V) and Hydroxyethylhydrazine

The Np(V) reduction with hydroxyethylhydrazine is described by the equation −d[Np(V)]/dt = k ₁[Np(V)][HOC₂H₄N₂H ₄ ⁺ ] + k ₂[Np(V)][Np(IV][H⁺]^1.8, reflecting its main and autocatalytic pathways. The rate constants are k ₁ = 0.31±0.04 l mol⁻¹ min⁻¹ and k ₂ = 4.04±0.11 l^2.8 mol^−2.8 min⁻¹ at 80°C and ionic strength μ = 4. The activation energies are E ₁ = 90±6 and E ₂ = 116±4 kJ mol⁻¹, respectively. The autocatalytic pathway is limited by the reaction between hydroxyethyldiazenium ions, HOC₂H₄N₂H ₂ ⁺ and protonated Np(V) ions. __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 150–153. Original Russian Text Copyright ? 2005 by V. Koltunov, Baranov, G. Koltunov.     

500kV变电站厂界低频噪声控制指标适用性调查分析

随着电网设施的发展,变电站的低频噪声问题越来越受到关注。为分析500 kV变电站厂界低频噪声控制指标的适用性,基于实测数据对9座变电站厂界低频噪声进行了分析,并选取2座变电站分别对其实体围墙上下方和主变附近采取降噪措施前后的厂界噪声进行了比较。结果表明,变电站厂界低频噪声在中心频率为100 Hz的1/3倍频带上的峰值最为明显。厂界低频噪声样本低频段声能量比例θ_low和L_Ceq-L_Aeq平均值分别为87.2%和11.0 dB,并且呈现出L_Aeq较低的声样本的θ_low和L_Ceq-L_Aeq却较大的规律。围墙下方的厂界噪声L_Aeq和L_{100 Hz}通常小于围墙上方,但θ_low和L_Ceq-L_Aeq却可能更大。通过主变附近采取降噪措施使厂界噪声L_Aeq和L_{100 Hz}得到有效控制的情况下,θ_low和L_Ceq-L_Aeq也可能比原来更大。可见,直接引入θ_low和L_Ceq-L_Aeq指标来评价变电站厂界低频噪声存在一定缺陷。分析结果可为变电站厂界低频噪声排放控制指标选取和限值确定提供参考。     

碳纤维/环氧树脂复合材料动态拉伸试验研究与损伤分析

利用MTS试验机和分离式Hopkinson拉杆对2种碳纤维/环氧树脂(T300/epoxy)层合板试件[(45/-45)₄]_S和[(0/45/90/-45)₂]_S进行了准静态(应变率10-5~10-4 s-1)、中速(应变率10-1~101 s-1)和高速(应变率102~104 s-1)冲击拉伸试验。在热力学框架内建立了基于损伤能释放率的弹塑性动力损伤本构模型,用该损伤模型来分析试件的动态拉伸失效过程。模型中提出了3种基本损伤机制(纤维断裂、基体开裂及面内剪切)的演化规律,通过对损伤阈值黏性归一化的方法考虑了应变率对损伤演化的影响。编写了该模型有限元用户材料子程序,并模拟了拉伸试验过程,计算结果表明该模型能够较好地模拟碳纤维/环氧树脂层合板动态拉伸失效过程。     

复合材料夹层壳振动分析的高阶剪切变形理论

本文提出了计及复合材料面板横向剪切变形的夹层壳高阶位移模式,该模式满足夹层壳上、下表面剪应力为零的条件,并以此推导出夹层壳自由振动的有限元方程,讨论了夹层壳的夹芯及面板的阻尼特性,给出阻尼矩阵的形成方式,将数值计算与实验结果进行了对比,最后给出了阻尼比Ψ随夹芯厚度h_c、剪切模量G和阻尼损耗因子β的变化曲线.     

复合材料迭层板壳有限单元法现状分析

本文从剖析单元构成因素的角度出发,综合评述了目前用于复合材料板壳结构分析的各种有限单元,分析了这些单元的特点及其适用范围,并说明Mindlin类等参板壳单元广泛应用迭层板壳的原因以及存在问题、解决办法。还深入地讨论了杂交单元应用至迭层板壳计算的优点。     

Extended rotation‐free plate and beam elements with shear deformation effects

This paper describes a methodology for extending rotation‐free plate and beam elements to accounting for transverse shear deformation effects. The ingredients for the element formulation are a Hu–Washizu‐type mixed functional, a linear interpolation for the deflection and the shear angles over standard finite elements and a finite volume approach for computing the bending moments and the curvatures over a patch of elements. As a first application of the general procedure, we present an extension of the three‐noded rotation‐free basic plate triangle (BPT) originally developed for thin plate analysis to account for shear deformation effects of relevance for thick plates and composite‐laminated plates. The nodal deflection degrees of freedom (DOFs) of the original BPT element are enhanced with the two shear deformation angles. This allows to compute the bending and shear deformation energies leading to a simple triangular plate element with three DOFs per node (termed BPT+ element). For the thin plate case, the shear angles vanish and the element reproduces the good behaviour of the original thin BPT element. As a consequence the element is applicable to thick and thin plate situations without exhibiting shear locking effects. The numerical solution for the thick case can be found iteratively starting from the deflection values for the Kirchhoff theory using the original thin BPT element. A two‐noded rotation‐free beam element termed CCB+ applicable to slender and thick beams is derived as a particular case of the plate formulation. The examples presented show the robustness and accuracy of the BPT+ and the CCB+ elements for thick and thin plate and beam problems. Copyright © 2010 John Wiley & Sons, Ltd.     

On the validity of nonlinear shear deformation theories for laminated plates and shells

This paper addresses the validity of the recently introduced so-called nonlinear shear deformation theories for laminated composite plates and shells. The finite element method is used to determine the maximum stresses for a wide range of statically loaded plate and shell panels. Various thickness ratios are included. This paper concludes that for the vast majority of composite materials and for moderately thick plates and shells. stresses normally reach the maximum allowable stress before nonlinear terms can become important. This has been demonstrated by showing that for the limiting case of shear deformation theories (in which the minimum span length (or radius) to thickness ratio is 20), the material usually fails before the maximum deflection reaches the magnitude of the thickness (where nonlinear terms start to become significant). Therefore, the nonlinear shear deformation theories, which are considerably more complicated than linear ones, have limited applications.     

A co-rotational 8-node assumed strain shell element for postbuckling analysis of laminated composite plates and shells

 The formulation of a nonlinear composite shell element is presented for the solution of stability problems of composite plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thin and thick laminated plates and shells by incorporating bending moment and transverse shear resultant forces. The composite element is free of both membrane and shear locking behaviour by using the assumed natural strain method such that the element performs very well as thin shells. The transverse shear stiffness is defined by an equilibrium approach instead of using the shear correction factor. The proposed formulation is computationally efficient and the test results showed good agreement. In addition the effect of the viscoelastic material is investigated on the postbuckling behaviour of laminated composite shells. Received: 6 February 2002 / Accecpted: 6 January 2003 ID=" Present address: School of Civil Engineering, Asian Institute of Technology     

增补挠度场和剪应变场的厚薄板三角形广义协调元

本文提出将薄板三角形单元扩展为厚薄板通用单元的一般方法。对于薄板极限情况，这种厚薄板通用单元自动退化为原有的薄板单元，完全无剪切闭锁现象发生。应用此法构造的厚薄板通用三角形单元GCLLM-T9自由度少，推导简明并具有通用性，能够通过分片检验。数值算例表明单元GCLLM-T9对薄板和厚板都具有较高的精度，适用于实际工程计算。     

Finite element analysis of laminated composite plates using zeroth-order shear deformation theory

In this paper a generalized finite element model is developed for static and dynamic analyses of laminated composite plates using zeroth-order shear deformation theory (ZSDT). The theory ensures the parabolic distribution of transverse shear stresses across the plate thickness. A four-noded plate element is considered in this model and the generalized nodal variables are expressed using Lagrangian linear interpolation functions and Hermitian cubic interpolation functions. The solutions of the finite element model have been compared with the existing solutions for symmetric and antisymmetric laminated composite plates. The comparison confirms that the ZSDT can be efficiently used for finite element analysis of both thin and thick plates with high accuracy.     

A family of simple and robust finite elements for linear and geometrically nonlinear analysis of laminated composite plates

A family of simple, displacement-based and shear-flexible triangular and quadrilateral flat plate/shell elements for linear and geometrically nonlinear analysis of thin to moderately thick laminate composite plates are introduced and summarized in this paper.

The developed elements are based on the first-order shear deformation theory (FSDT) and von-Karman’s large deflection theory, and total Lagrangian approach is employed to formulate the element for geometrically nonlinear analysis. The deflection and rotation functions of the element boundary are obtained from Timoshenko’s laminated composite beam functions, thus convergence can be ensured theoretically for very thin laminates and shear-locking problem is avoided naturally.

The flat triangular plate/shell element is of 3-node, 18-degree-of-freedom, and the plane displacement interpolation functions of the Allman’s triangular membrane element with drilling degrees of freedom are taken as the in-plane displacements of the element. The flat quadrilateral plate/shell element is of 4-node, 24-degree-of-freedom, and the linear displacement interpolation functions of a quadrilateral plane element with drilling degrees of freedom are taken as the in-plane displacements.

The developed elements are simple in formulation, free from shear-locking, and include conventional engineering degrees of freedom. Numerical examples demonstrate that the elements are convergent, not sensitive to mesh distortion, accurate and efficient for linear and geometric nonlinear analysis of thin to moderately thick laminates.     

Analysis of thick orthotropic laminated composite plates based on higher order shear deformation theory

A two-dimensional finite element model is presented to perform the linear static analysis of laminated orthotropic composite plates based on a refined higher order shear deformation theory. The theory accounts for parabolic distributions of transverse shear stresses and requires no shear correction factors. A finite element program is developed using serendipity element with seven degrees of freedom per node. The present solutions are compared with those obtained using three-dimensional elasticity theory and those obtained by other researchers. The theory accurately predicts displacements and transverse shear stresses compared to previously developed theories for thick plates and are very close to three-dimensional elasticity solutions. The effects of transverse shear deformation, material anisotropy, aspect ratio, fiber orientation and lamination sequence on transverse shear stresses are investigated. The error in values of transverse shear stresses decreases as the number of lamina increases, for a plate of same thickness. An increase in degree of anisotropy results in lower values of deflection in the plate. For cross-ply plate an increase in anisotropy results in an increase in effective stress whereas for angle-ply plate the effect is almost negligible. Through thickness variation of transverse shear stresses are independent of anisotropy. The maximum effective stress increases exponentially at lower values of anisotropy and reaches to an asymptotic value at higher values. The stacking sequence has a significant effect on the transverse deflections and shear stress. Rectangular plates experience less effective, in-plane and transverse shear stresses compared to square plates.     

基于共旋三角形厚薄通用壳元的几何非线性分析

基于共旋列式方法发展了一种用于复合材料层合板结构几何非线性分析的简单高效的三结点三角形平板壳元。该壳元由具有面内转动自由度的广义协调膜元GT9与假设剪切应变场和假设单元转角场的广义协调厚薄通用板元TMT组合而成。为避免薄膜闭锁而采用单点积分计算与薄膜应变有关的项, 同时增加一个稳定化矩阵以消除单点积分导致的零能模式。基于层合板一阶剪切变形理论, 给出了考虑层合板具体铺层顺序的修正的横向剪切刚度, 使该壳元可用于中厚层合板结构的分析。由于共旋列式大转动小应变的假设, 共旋列式内核的几何线性的单元刚阵可仅计算一次而保存下来用于整个几何非线性求解的过程以提高计算效率。数值算例表明提出的壳元进行包括复合材料层合板结构的厚薄壳结构的几何非线性分析的精度高且效率高。     

Refined discrete quadrilateral degenerated shell element by using Timoshenko's beam function

A refined discrete degenerated 20‐DOF quadrilateral shell element RQS20 is proposed. The exact displacement function of the Timoshenko's beam is used as the displacement on the element boundary. The re‐constitute method for shear strain matrix is adopted. The proposed element can be used for the analysis of both moderately thick and thin plates/shells, and the convergence for the very thin case can be ensured theoretically. Numerical examples presented show that the new model indeed possesses higher accuracy in the analysis of thin and thick plates/shells, and that it can pass the patch test required for the Kirchhoff thin plate elements. Most important of all, it is free from the membrane and shear locking phenomena for extremely thin plates/shells, on the one hand, and it can also avoid the phenomenon of oscillatory solutions for thick plates/shells case on the other. Copyright © 2005 John Wiley & Sons, Ltd.