一种可适用于瞬态辐射换热问题的蜂窝夹芯壳体有限单元

提出一种三层32 结点温度壳单元, 对蜂窝夹芯复合材料壳体的瞬态温度场进行了有限元分析。分别假定上下面板与芯层沿厚度方向的温度分布规律, 事先近似满足上下表面的热边界条件及层间的温度连续条件, 以消减总的自由度数。壳体内外表面可以同时考虑热流、对流及辐射换热边界条件, 并通过温度的后处理使芯层温度场也满足层间的热流连续条件, 从而进一步提高温度场计算的准确性。两个实例分析验证了所提出单元的可靠性与有效性。     

圆柱形胞元蜂窝夹芯板梁理论的研究

为了研究蜂窝夹芯板梁受压塌陷的原因, 建立了圆柱形胞元蜂窝夹芯胞元壳的轴向受压理论分析模型, 推导了圆柱形胞元蜂窝夹芯板梁临界压应力的计算公式, 提出了一种全新的迭代优化设计方法, 给出了一套较完整的分析设计理论。通过用3D 有限元数值模拟技术, 对铝质圆柱形蜂窝胞元壳进行模拟, 结果与公式的计算值吻合较好。该研究对进一步完善蜂窝夹芯板梁理论提供依据。      

复合材料夹芯管胶接连接结构力学特性分析

针对在航空结构中广泛应用的复合材料蜂窝夹芯圆管中的接头这一最脆弱的部分,发展了一种分析复合材料蜂窝夹芯圆管胶粘接头力学特性的解析模型.该模型根据Gibson修正公式得到了蜂窝芯子的等效弹性参数,再运用经典的复合材料壳理论和线弹性理论得到管接头的控制方程,并通过状态空间法进行求解.运用本文模型,计算了管接头在扭矩和弯矩作用下胶层内的剪应力和剥离应力;同时采用有限元法对模型进行了数值模拟,并将模拟结果与模型计算结果进行了对比,最后分析了搭接长度对胶层内应力的影响.     

铝蜂窝填砂复合夹芯结构的低速冲击响应试验研究

以防护结构设计为背景,提出一种铝蜂窝填砂复合夹芯结构。从理论角度对填砂蜂窝模型进行力学分析,通过落锤冲击试验,对不同芯层规格的试件在梯度能级冲击下的响应进行了对比,根据荷载、位移和挠度的变化规律和破坏模式得到以下结论:在低能级冲击下,蜂窝芯层较软的试件填砂后对于其结构强度和刚度的提升作用较为明显,同时,在铝蜂窝质量相同的前提下,优先选择蜂窝胞元较小、高度较低的蜂窝作为填砂复合夹芯结构的芯层,可提高结构比强(刚)度;在高能级冲击下,当芯层高度达到一定值时,变形挠度减小,破坏范围缩小为局部贯穿破坏,芯层填砂对结构抗冲击性能产生较为积极的影响。研究结果为铝蜂窝填砂复合夹芯结构在防护结构中的应用奠定了基础。     

复合材料蜂窝夹芯结构低速冲击位置识别研究

进行了碳纤维增强复合材料蜂窝夹芯结构的低速冲击实验,采用一种基于应力波和免疫遗传算法的冲击载荷定位方法对蜂窝夹芯结构上的低速冲击载荷进行分析和定位。首先,通过一组事先确定冲击位置的低速冲击载荷产生的冲击应力波实验数据,使用小波变换方法对其在时频域进行分析,获得多个频率上冲击应力波在蜂窝夹芯结构中的传播速度;然后在此基础上,考虑蜂窝夹芯结构中应力波的各向异性特性,采用免疫遗传算法对未知的低速冲击载荷进行位置识别。实验研究结果表明了该方法的可行性和有效性     

安静型夹芯复合材料舵设计及其力学性能分析

通过对夹芯复合材料各层材料的选择，以及夹芯复合材料舵壳的结构设计，提出了夹芯复合材料舵的设计方案和制作工艺。并利用有限元方法计算了复合材料舵壳在流体压力作用下的应力和变形，以及在瞬态载荷作用下舵壳的振动响应。计算结果表明，夹芯复合材料舵壳满足结构的强度和刚度的要求，同时振动水平与钢舵比较有很大的改善。     

复合材料夹芯圆柱壳的声辐射性能

为了量化评估两种功能型材料的声振性能,基于结构有限元(FEM)法和声学边界元(BEM)法,计算出典型环肋圆柱壳的振动声辐射,结果与文献试验值的一致性较好。进行动态热力学实验并基于温频等效原理,得到了黏弹性吸声芯材的动态力学参数;采用流体有限元法模拟水和圆柱壳的耦合作用,最后采用间接边界元法计算了点激励作用下不同功能材料夹芯壳辐射声场。结果表明:周向模态对浮力材料夹芯壳和吸声材料夹芯壳模态阻尼比均有重要的影响,轴向模态仅对吸声材料的夹芯壳模态阻尼比有显著影响;与等质量的钢壳相比,浮体材料夹芯壳的最大声功率降低21.38 d B,吸声材料夹芯壳的最大声功率降低56.55 d B;将两种功能材料按比例组合作为夹芯材料,壳体的辐射声功率随着吸声材料占比的增加而降低,但是降低的幅度不断减小。     

纸蜂窝夹芯复合板材静态缓冲性能研究

目的为了新型纸蜂窝夹芯复合板材在运输包装中的推广应用,对新型泡状纸蜂窝夹芯复合板和纸蜂窝夹芯复合平板的缓冲性能和吸能特性进行研究。方法主要通过静态压缩实验,研究不同芯高的纸蜂窝结构类板材的应力-应变曲线、总能量吸收图、单位体积能量吸收图和缓冲系数-应变曲线,分析结构和芯高对板材静态压缩性能的影响。结果数据表明同种芯高的板材,纸蜂窝夹芯复合平板的应力峰值稍高;纸蜂窝夹芯复合平板的能量吸收、单位体积能量吸收最好;泡状纸蜂窝夹芯板由于泡结构的作用,缓冲性能大大增强。结论纸蜂窝夹芯复合平板的平压强度最好,而泡状纸蜂窝夹芯复合板的缓冲性能优于同等结构的蜂窝纸板,2种板材都有很好的应用前景。     

船舶宏观负泊松比蜂窝夹芯隔振器优化设计

对新型宏观负泊松比蜂窝夹芯船舶隔振器形状及尺寸设计方法进行研究,探讨蜂窝形状参数及壁厚对整体隔振性能影响。建立负泊松比蜂窝夹芯隔振器动力学分析有限元模型,给出蜂窝胞元壁厚、胞元宽度尺寸、胞元高度尺寸对隔振器结构应力、固有频率、底部振级及振级落差影响曲线;建立以蜂窝胞元壁厚、胞元宽度尺寸、胞元高度尺寸为设计变量的蜂窝夹芯隔振器动力学优化模型。结果证明了形状参数影响曲线的有效性,可为负泊松比蜂窝隔振器设计提供指导。     

四边简支新型类方形蜂窝夹层结构振动特性研究

新型类方形蜂窝是六边形蜂窝的一种过渡形式,对其等效弹性参数和振动特性的研究具有重要意义。采用改进的Gibson公式对比分析了双壁厚与等壁厚类方形蜂窝夹芯的面内等效弹性参数的差异,并应用经典层合板理论分析了不同等效弹性参数下2种壁厚类型的四边简支类方形蜂窝夹层结构的振动特性,基于有限元仿真技术分析了不同壁厚类方形蜂窝夹层结构的振动特性,并与理论分析结果进行对比。结果表明等效弹性参数的数值模拟结果与理论值基本吻合。在蜂窝基本结构参数相同的条件下,双壁厚类方形蜂窝夹芯的面内等效剪切模量、面外刚度和等效密度均比等壁厚类方形蜂窝夹芯大;在低阶振动模态下,双壁厚类方形蜂窝夹层结构的固有频率比等壁厚类方形蜂窝夹层结构的低,在高阶振动模态下,双壁厚类方形蜂窝夹层结构的固有频率比等壁厚类方形蜂窝夹层结构的高;影响夹层结构固有频率的3个主要因素所占权重由大到小依次为蜂窝夹芯yoz面等效剪切模量、蜂窝夹芯等效密度,蜂窝夹芯壁厚。研究结果表明采用经典层结构理论计算得到类方形蜂窝夹层结构的固有频率与数值仿真结果的一致性较好,这进一步证明了采用改进Gibson公式得到的类方形蜂窝夹芯等效弹性参数的正确性,同时证明了将该振动理论运用到一般蜂窝夹层结构研究的可行性,为扩展研究其他类型蜂窝夹层结构振动特性奠定了基础。     

热载荷下轴对称回转复合材料层合壳体的边界效应

本文采用有限单元法研究轴对称回转复合材料层合壳体在热荷载作用下壳体内的温度场和热应力场的分布, 并以算例讨论了温度场的分布、铺层次序、壳厚对层合壳体热应力(包括层间应力)的影响。      

Static and Dynamic Analysis of Laminated Thick and Thin Plates and Shells by a Very Simple Displacement-based 3-D Hexahedral Element with Over-Integration

A very simple displacement-based hexahedral 32-node element (denoted as DPH32), with over-integration in the thickness direction, is developed in this paper for static and dynamic analyses of laminated composite plates and shells. In contrast to higher-order or layer-wise higher-order plate and shell theories which are widely popularized in the current literature, the proposed method does not develop specific theories of plates and shells with postulated kinematic assumptions, but simply uses the theory of 3-D solid mechanics and the widely-available solid elements. Over-integration is used to evaluate the element stiffness matrices of laminated structures with an arbitrary number of laminae, while only one element is used in the thickness direction without increasing the number of degrees of freedom. A stress-recovery approach is used to compute the distribution of transverse stresses by considering the equations of 3D elasticity. Comprehensive numerical results are presented for static, free vibration, and transient analyses of different laminated plates and shells, which agree well with existing solutions in the published literature, or solutions of very-expensive 3D models by commercial FEM codes. It is clearly shown that the proposed methodology can accurately and efficiently predict the structural and dynamical behavior of laminated composite plates and shells in a very simple and cost-effective manner.     

A mixed solid‐shell element for the analysis of laminated composites

This paper presents a versatile low order locking‐free mixed solid‐shell element that can be readily employed for a wide range of linear elastic structural analyses, that is, from thick isotropic structures to multilayer anisotropic composites. This solid‐shell element has eight nodes with only displacement degrees of freedom and few assumed stress parameters that provide very accurate interlaminar stress calculations through the element thickness. These elements can be stacked on top of each other to model multilayer structures, fulfilling the interlaminar stress continuity at the interlayer surfaces and zero traction conditions on the top and bottom surfaces of the laminate. The element formulation is based on the well‐known Fraeijs de Veubeke–Hu–Washizu mixed variational principle with enhanced assumed strains formulation and assumed natural strains formulation to alleviate the different types of locking phenomena in solid‐shell elements. The distinct feature of the present formulation is its ability to accurately calculate the interlaminar stress field in multilayer structures, which is achieved by the introduction of a constraint equation on the interlaminar stresses in the Fraeijs de Veubeke–Hu–Washizu principle‐based enhanced assumed strains formulation. The intelligent computer coding of the present formulation makes the present element appropriate for a wide range of structural analyses. To assess the present formulation's accuracy, a variety of popular numerical benchmark examples related to element convergence, mesh distortion, and shell and laminated composite analyses are investigated and the results are compared with those available in the literature. These benchmark examples reveal that the proposed formulation provides very good results for the structural analysis of shells and multilayer composites. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of nonlinear exact geometry sampling surfaces solid-shell elements and ANSYS solid elements for 3D stress analysis of piezoelectric shell structures

In this work, the finite rotation exact geometry four-node solid-shell element using the sampling surfaces (SaS) method is developed for the analysis of the second Piola-Kirchhoff stresses in laminated piezoelectric shells. The SaS method is based on choosing inside the layers the arbitrary number of SaS parallel to the middle surface and located at Chebyshev polynomial nodes in order to introduce the displacements and electric potentials of these surfaces as fundamental shell unknowns. The outer surfaces and interfaces are also included into a set of SaS. To circumvent shear and membrane locking, the hybrid-mixed solid-shell element on the basis of the Hu-Washizu variational principle is proposed. The tangent stiffness matrix is evaluated by 3D analytical integration throughout the finite element. This novelty provides a superior performance in the case of coarse meshes. A comparison with the SOLID226 element showed that the developed exact geometry SaS solid-shell element allows the use of load increments, which are much larger than possible with existing displacement-based finite elements. Thus, it can be recommended for the 3D stress analysis of doubly-curved laminated piezoelectric shells because the SaS formulation gives the opportunity to obtain the 3D solutions of electroelasticity with a prescribed accuracy.     

A micro-to-meso sublaminate model for the viscoelastic analysis of thick-section multi-layered FRP composite structures

Classical ply-by-ply analysis of multi-layered thick-section composite structures with tens of layers through the cross-section is often impractical, especially when material nonlinearity and time-dependent effects are included. This study introduces an integrated micromechanical-sublaminate modeling approach for the nonlinear viscoelastic analysis of thick-section and multi-layered composite structures. The sublaminate model is used to generate three-dimensional (3D) effective nonlinear responses at through-thickness material integration points with given spatial variations of strains determined from the trial strain increments of the standard displacement-based finite-element (FE). The number of material integration points is determined by the resolution of the FE discretization of the composite structure. The sublaminate model at a selected material point represents the effective nonlinear continuum behavior in its neighborhood using the 3D lamination theory with uniform in-plane strain and out-of-plane stress patterns through the representative layers. Therefore, the sublaminate has first-order stress and strain paths and cannot recognize the local sequence of the layers. While this approach is very effective approximation especially in the case of a very large number of repeating layers using relatively few elements (integration points) through the thickness, it cannot be used to represent the interlaminar stresses or bending/extension/twisting coupling effects within a sublaminate. A previously developed micromechanical model by the authors for a nonlinear viscoelastic unidirectional lamina is used for each layer in the sublaminate. The proposed modeling approach is first calibrated and verified against creep tests on off-axis glass/epoxy performed by Lou and Schapery (J. Compos. Mater. 5:208–271, 1971). Analyses for different thick-section laminated structures are presented using the integrated sublaminate with both shell and 3D continuum elements. The proposed 3D nonlinear time-dependent sublaminate model is computationally efficient and robust in analyzing multi-layered composite structures having large number of plies.     

Finite Element Simulation of Low Velocity Impact Damage on an Aeronautical Carbon Composite Structure

Low velocity barely visible impact damage (BVID) in laminated carbon composite structures has a major importance for aeronautical industries. This contribution leads with the development of finite element models to simulate the initiation and the propagation of internal damage inside a carbon composite structure due by a low velocity impact. Composite plates made from liquid resin infusion process (LRI) have been subjected to low energy impacts (around 25 J) using a drop weight machine. In the experimental procedure, the internal damage is evaluated using an infrared thermographic camera while the indentation depth of the face is measured by optical measurement technique. In a first time we developed a robust model using homogenised shells based on degenerated tri-dimensional brick elements and in a second time we decided to modelize the whole stacking sequence of homogeneous layers and cohesive interlaminar interfaces in order to compare and validate the obtained results. Both layer and interface damage initiation and propagation models based on the Hashin and the Benzeggagh-Kenane criteria have been used for the numerical simulations. Comparison of numerical results and experiments has shown the accuracy of the proposed models.     

复合材料加筋结构界面层间应力分析建模

通过采用将复合材料加筋结构在界面附近按照单层、在界面附近以外的区域处理为均质各向异性材料,建立了一种复合材料加筋结构界面层间应力分析的新模型。采用该模型大大减少了加筋结构分析时需要的单元数目,同时又能得出界面上的层间应力。算例表明这种建模方法是切实可行的。算例揭示出了界面上层间应力的分布规律,得出了一些重要结论。     

A hybrid equilibrium element for folded plate and shell structures

This paper extends hybrid equilibrium formulation concepts, previously used with success for planar problems, to the analysis of folded plates and curved shells. A 2D hybrid equilibrium flat shell quadrilateral element is formulated for linear analysis, where detailed consideration is given to the implication of slope discontinuity when the element is used for non‐planar domains. Benchmark plate bending, folded plate and curved shell problems are modelled using equilibrium and conforming elements for comparison. In models of the latter two problems, torsional moments may be released along lines of slope discontinuity, and the effects of this assumption for the folded plate are studied by analysing a third type of model composed of 3D solid brick elements. The comparisons demonstrate an excellent performance from the new hybrid equilibrium analysis method for folded plates and curved shells. Copyright © 2013 John Wiley & Sons, Ltd.     

Three-dimensional piezoelasticity solution for dynamics of cross-ply cylindrical shells integrated with piezoelectric fiber reinforced composite actuators and sensors

A benchmark three-dimensional (3D) exact piezoelasticity solution is presented for free vibration and steady state forced response of simply supported smart cross-ply circular cylindrical shells of revolutions and panels integrated with surface-bonded or embedded monolithic piezoelectric or piezoelectric fiber reinforced composite (PFRC) layers. The effective properties of PFRC laminas for the 3D case are obtained based on a fully coupled iso-field model. The governing partial differential equations are reduced to ordinary differential equations in the thickness coordinate by expanding all entities for each layer in double Fourier series in span coordinates, which identically satisfy the boundary conditions at the simply-supported ends. These equations with variable coefficients are solved using the modified Frobenius method, wherein the solution is constructed as a product of an exponential function and a power series. The unknown constants of the general solution are finally obtained by employing the transfer matrix method across the layers. Results for natural frequencies and the forced response are presented for single layer piezoelectric and multilayered hybrid composite and sandwich shells of revolution and shell panels integrated with monolithic piezoelectric and PFRC actuator/sensor layers. The present benchmark solution would help assess 2D shell theories for dynamic response of hybrid cylindrical shells.     

2D and 3D calculations of micromagnetic wall structures using finite elements

To compute wall structures in a uniaxial magnetic garnet, static micromagnetic equations are solved using the finite-element method. After setting up the physical and the mathematical context, the discretized equations are presented and discretized by standard first-order brick finite elements. A descent method, solving the nonlinear problem, is discussed, and some simulation results are given. This method is found to be time-consuming in 3-D, and a general framework for an adapted mesh algorithm that will speed up the computations is proposed.<>