含不同形状分层缺陷蜂窝夹层板的压缩性能

对含面板/夹芯界面中央分层缺陷复合材料蜂窝夹层板的压缩性能进行了试验研究和理论分析,考察了一种圆形分层和2种矩形分层缺陷对其压缩强度的影响,并采用子层局部屈曲模型对压缩强度进行了计算。结果表明：无缺陷夹层板表现为总体失稳破坏,而对于含分层缺陷的夹层板,则视分层形状及其大小的不同而表现出不同的破坏机制。对于矩形缺陷的长边与载荷方向垂直的夹层板,一般情况下面板子层局部屈曲对夹层板的最终破坏不起控制作用;对于矩形缺陷的长边与载荷方向平行的夹层板,表现为总体失稳破坏。压缩破坏过程中,面板子层屈曲起控制作用的夹层板,子层局部屈曲模型能够比较精确地预测其压缩强度。     

复合材料蜂窝夹层板结构的多工况优化设计研究

以复合材料蜂窝夹层板结构作为研究对象,建立了多工况优化模型,对众多的材料设计变量进行必要的取舍,通过优化分析确定复合材料蜂窝夹层板面板各分层的厚度以及蜂窝芯层的厚度等,使结构满足相应的频率约束、屈曲约束,以及强度约束、位移约束和尺寸限制等,同时达到结构的重量最轻。采用序列二次规划法对某卫星的承力筒结构进行了优化设计,优化结果表明:在满足其振动特性以及静力学特性的条件下,复合材料蜂窝承力筒的各面板层厚度以及蜂窝芯层的厚度均有所减小,减重效果显著,较好地实现了复合材料蜂窝夹层板结构的多工况优化设计。     

基于多尺度方法的蜂窝夹层复合材料结构轴向压缩稳定性

为有效预测蜂窝夹层复合材料结构压缩失稳载荷和破坏模式,本文基于层压板宏细观多尺度数值分析模型,研究蜂窝夹层复合材料结构在轴向压缩载荷下的屈曲稳定性。基于改进的通用单胞理论模型,并结合ABAQUS用户自定义子程序接口,建立蜂窝夹层复合材料结构宏细观数值模型,预报蜂窝夹层复合材料结构失效载荷和破坏模式,并与试验结果对照,验证了模型的有效性。结果表明:通过本文建立的数值模型可以有效预测蜂窝夹层复合材料结构在压缩载荷下的失稳载荷和破坏模式,其一阶失稳载荷为128.12 kN,与试验结果误差为4.58%,蜂窝夹层复合材料结构破坏模式为先发生屈曲失稳,然后迅速破坏。      

铝蜂窝夹层板低速冲击响应及损伤模式的参数化影响

以铝蜂窝夹层板为对象，通过低速落锤试验及包含面板、胶层及蜂窝的细节仿真模型，探究了蜂窝胞元直径、蜂窝壁厚、面板厚度及冲头半径参数影响下低速冲击响应曲线及损伤模式的变化情况，确定在试验工况下的3种损伤模式：芯层屈曲、芯层剪切及夹层板穿透，其中芯层剪切模式具有更好的吸能分布。结果表明：蜂窝胞元直径与蜂窝壁厚对冲击响应与损伤模式具有类似的影响，面板厚度增加可以较大程度地提升抗冲击性能，冲头半径的大小会显著影响损伤模式。在此基础上建立与上述参数相关的损伤模式极限载荷公式，绘制相应的损伤模式图，为铝蜂窝夹层板的抗冲击设计提供参考。     

结构参数对CFRP蒙皮-铝蜂窝夹层板低速冲击性能的影响

针对碳纤维增强树脂复合材料（CFRP）蒙皮-铝蜂窝夹层结构,使用半球头式落锤冲击试验平台进行了低速冲击载荷下蜂窝芯单元尺寸对夹层板冲击性能影响的试验探究,并基于渐进损伤模型、内聚力模型和三维Hashin失效准则,在有限元仿真软件ABAQUS中建立了含蒙皮、蜂窝芯、胶层的CFRP蒙皮-铝蜂窝夹层板精细化低速冲击仿真模型,仿真结果与试验结果吻合较好。利用该数值模型进一步探究了蜂窝芯高度、蒙皮厚度和蜂窝芯壁厚等结构参数对于蜂窝夹层板低速冲击吸能效果的影响。结果表明:增大铝蜂窝芯的单元边长,会减小蜂窝夹层板的刚度,提升夹层板的吸能效果;芯层高度对夹层板的刚度及抗低速冲击性能影响较小;增大蜂窝夹层板的蒙皮厚度,可以提高夹层板的刚度,但会降低夹层板的吸能效果;增大蜂窝芯的壁厚,可以提高夹层板的刚度和抗低速冲击性能。      

蜂窝夹层复合材料不确定性参数识别方法

提出蜂窝夹层复合材料不确定性参数识别方法。采用三明治夹芯板理论建立铝蜂窝夹层结构的初始有限元模型,其中芯层等效弹性参数由均匀化方法计算。据芯层结构及相对灵敏度分析选存在不确定性且对动态特性敏感性较大的面外剪切模量及面板厚度为待识别参数。对6块铝蜂窝复合材料板进行自由-自由边界条件下动态试验,获得试验模态参数的均值及标准差。据试验结果采用所提方法识别铝蜂窝夹层板不确定性参数。结果表明,对存在不确定性参数的铝蜂窝夹层复合材料用该方法能准确识别铝蜂窝夹层板不确定参数的均值及标准差。并建立具有准确统计意义的动力学模型。     

纸蜂窝夹层板主共振频率的影响因素

目的 研究芯层结构因素和静应力因素对纸蜂窝夹层板-质量系统主共振频率的影响。方法 采用正弦振动试验测试纸蜂窝夹层板-质量系统的振动传递特性,分析不同静应力作用下不同蜂窝芯的纸蜂窝夹层板-质量系统的主共振频率变化规律。结果 纸蜂窝夹层板-质量系统的主共振频率在150~350 Hz之间;蜂窝芯结构及芯层材料影响纸蜂窝夹层板的刚性,从而影响系统的主共振频率;载荷质量变化引起静应力的变化,也会影响系统的主共振频率。主共振频率均随蜂窝胞元边长、纸板厚度、芯纸定量及静应力的增大而降低。结论 可为纸蜂窝夹层板的振动传递特性研究提供基础,有助于不同材质蜂窝夹层板的优化设计。     

基于Virtual.Lab Acoustics的蜂窝夹层板结构传声特性分析

针对蜂窝夹层板进行传声特性仿真计算分析。基于声学间接边界元理论,利用有限元软件Patran进行夹层板的三维实体建模和模态分析,采用声学软件Virtual.Lab Acoustics计算结构的传声性能,得到场点声压分布、构件两侧声压级差和结构隔声量曲线。在此基础上系统地探讨面板厚度和密度以及芯层高度、壁厚及壁长五个设计参量对蜂窝夹层板传声性能的影响。结果显示,面板厚度与芯层高度对结构在低频段尤其是刚度控制区域的隔声性能影响显著。     

复合材料夹层板屈曲强度的分散性分析

将面板单层及芯层厚度、 面板纤维方向角和材料参数作为随机变量, 通过编制基于高阶剪切理论的随机有限元程序, 对复合材料夹层板的屈曲强度分散性进行了分析, 得到了不同铺层方式下夹层板屈曲强度分散系数随纤维方向角及夹层板长厚比的变化规律。并通过对屈曲强度的分散系数进行灵敏度分析, 确定了影响分散系数大小的主要因素, 从而为材料设计、 制造工艺改进和夹层板结构可靠度的提高提供了理论依据。      

蜂窝金属夹芯板重复冲击动态响应研究

蜂窝金属及其夹芯结构是一种物理功能与结构一体化的新型轻质高强结构,广泛应用于结构轻量化与碰撞冲击防护领域。采用ABAQUS非线性有限元软件建立了蜂窝金属夹芯板(honeycomb sandwich panel,HSP)结构动态冲击数值仿真模型,数值仿真计算结果与文献实验结果吻合较好,验证了数值仿真模型的正确性。在此基础上,开展了重复冲击载荷作用下蜂窝金属夹芯板结构动态响应研究,得到了重复冲击力时程曲线、动态变形时程曲线、冲击力位移曲线以及最终挠度,分析了冲击能量、蜂窝壁厚以及上、下面板厚度分配对蜂窝金属夹芯板结构重复冲击动态响应的影响规律。研究结果表明,重复冲击载荷作用下蜂窝金属夹芯板结构上、下面板弯曲变形以及蜂窝芯层压缩变形逐渐积累,蜂窝芯层薄壁结构逐渐达到密实化,结构抗弯刚度逐渐上升,变形增量逐渐减小,结构整体能量吸收率下降。通过调节蜂窝壁厚和上、下面板厚度分配可以显著调节蜂窝金属夹芯板结构重复冲击动态响应与能量吸收性能。     

飞机典型薄壁复合材料夹层结构整体屈曲

为了研究飞机机身无筋无框复合材料典型薄壁夹层结构在型号上应用的可行性,本文采用解析方法、有限元方法和试验方法对蜂窝夹层复合材料结构的面内压缩和剪切整体屈曲开展系统研究。基于经典层合板理论和工程解析方法推导蜂窝夹层复合材料的压缩和剪切屈曲载荷随试验件尺寸的变化规律。依据某型飞机机身典型结构分别设计压缩和剪切试验件尺寸大小、边界条件和加载方式。利用有限元商用软件ABAQUS对试验设计建立虚拟试验分析,对比验证解析方法和有限元方法的一致性。最后通过真实试验方法确定解析方法和有限元方法的有效性,并验证典型薄壁夹层结构的承载能力和破坏模式。结果显示,压缩试验结果失效模式与理论预测一致,故3种方法得到的结构整体失稳载荷相近,验证了理论方法的有效性;剪切试验结果发生局部破坏,故试验结果偏低,但有限元方法与解析方法所得结果一致,解析方法相对保守。     

Failure analysis of adhesive surface damage in sandwich plates under compressed loads

Abstract

Failures of honeycomb sandwich plates are analyzed using experiments and three-dimensional (3D) finite element simulations to understand the failure mechanism. Meanwhile, correlations of the critical load and various physical parameters (e.g., height and thickness of the core) are investigated. The results demonstrated that the core height and skin thickness have significant effects on the compressed load buckling of the honeycomb sandwich plates, the core density is a sub-critical sensitive factor, while wall thickness and spacing of the cell, and the sandwich modulus have negligible effects. Cracking on the adhesive surface is the dominant factor to reduce the buckling critical load of the laminated plate, which leads to failures of sandwich plates. The ultimate failure of the sandwich panel is attributed to severe deformations that lead to local cracking of the entire cemented adhesive surface. Due to the bonding of the adhesive surface defects, the actual loads related to the core height are large enough to cause compressions with local buckling. Hence, the actual loads cannot reflect the performance of the sandwich panels. It is recommended to use panels with appropriate thicknesses below the sandwich and moderate grid density in the design.     

Mechanical behaviour of cellular core for structural sandwich panels

This paper deals with the analysis of the mechanical properties of the core materials for sandwich panels. In this work, the core is firstly a honeycomb and secondly tubular structure. This kind of core materials are extensively used, notably in automotive construction (structural components, load floors...). For this study, three approaches are developed: a finite element analysis, an analytical study and experimental tests. Structural members made up of two stiffs, strong skins separated by a lightweight core (foam, honeycomb, tube...) are known as sandwich panels. The separation of the skins by the core increases the inertia of the sandwich panel, the flexure and shear stiffness. This increase is obtained with a little increase in weight, producing an efficient structure to resist bending and buckling loads. A new analytical method to analyse sandwich panels core will be presented. These approaches (theoretical and experimental) are used to determine elastic properties and ultimate stress. A parameter study is carried out to determine elastic properties as a function of geometrical and mechanical characteristics of basic material. Both theoretical and experimental results are discussed and a good correlation between them is obtained.     

缝纫泡沫夹芯复合材料板的稳定性分析

整体屈曲是缝纫复合材料夹芯板的一种重要失效模式。考虑到缝纫夹芯复合材料板一般较厚且面板与芯层厚度相差较大, 缝纫工艺对夹芯板刚度影响较大的特点, 基于高阶剪切理论, 编制了缝纫泡沫夹芯复合材料板稳定性分析的有限元程序。利用该程序对多个算例进行了计算, 所得临界屈曲应力与文献及试验结果吻合很好。同时, 讨论了不同边界条件下缝纫泡沫夹芯复合材料板稳定性随缝纫参数(包括针距、 行距和缝纫针半径)以及结构参数(包括面板铺层角、 芯层厚度和缝纫夹芯板边长)的变化规律。      

Mechanical behaviors of carbon fiber composite sandwich columns with three dimensional honeycomb cores under in-plane compression

Mechanical properties and failure modes of carbon fiber composite egg and pyramidal honeycombs cores under in plane compression were studied in the present paper. An interlocking method was developed for both kinds of three-dimensional honeycombs. Euler or core shear macro-buckling, face wrinkling, face inter-cell buckling, core member crushing and face sheet crushing were considered and theoretical relationships for predicting the failure load associated with each mode were presented. Failure mechanism maps were constructed to predict the failure of these composite sandwich panels subjected to in-plane compression. The response of the sandwich panels under axial compression was measured up to failure. The measured peak loads obtained in the experiments showed a good agreement with the analytical predictions. The finite element method was used to investigate the Euler buckling of sandwich beams made with two different honeycomb cores and the comparisons between two kinds of honeycomb cores were conducted.     

Crush dynamics of square honeycomb sandwich cores

Square honeycombs are effective as cores for all‐metal sandwich plates in that they combine excellent crushing strength and energy absorption with good stiffness and strength in out‐of‐plane shear and in‐plane stretch. In applications where sandwich plates must absorb significant energy in crushing under intense impulsive loads, dynamic effects play a significant role in the behaviour of the core. Three distinct dynamic effects can be identified: (i) inertial resistance, (ii) inertial stabilization of webs against buckling, and (iii) material strain‐rate dependence. Each contributes to dynamic strengthening of the core. These effects are illustrated and quantified with the aid of detailed numerical calculations for rates of deformation characteristic of shock loads in air and water. A continuum model for high rate deformation of square honeycomb cores is introduced that can be used to simulate core behaviour in large structural calculations when it is not feasible to mesh the detailed core geometry. The performance of the continuum model is demonstrated for crushing deformations. Copyright © 2005 John Wiley & Sons, Ltd.     

Testing and modeling of Nomex™ honeycomb sandwich Panels with bolt insert

Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled. The objective was to predict the honeycomb local buckling load and to identify a Nomex™ honeycomb constituent material model. Sandwich specimens were subjected to bolt pull-out load tests. The same sandwich structure was also tested in flat-wise tension with strain gages installed on the honeycomb walls. Finite element models of the flat-wise tension and bolt pull-out tests were built. The honeycomb geometry and strain gages were modeled with shell elements. An orthotropic honeycomb material model was identified by comparing the two test models to the experimental data. The material parameters identified are in the mid-range of previously published values. The pull-out test model was used to predict honeycomb wall buckling with a nodal rotation vector sum criterion. The buckling loads predictions closely corresponded to the start of the experimental load/displacement slope transition zone.     

Mechanical response of metallic honeycomb sandwich panel structures to high-intensity dynamic loading

Explosive tests were performed in air to study the dynamic mechanical response of square honeycomb core sandwich panels made from a super-austenitic stainless steel alloy. Tests were conducted at three levels of impulse load on the sandwich panels and solid plates with the same areal density. Impulse was varied by changing the charge weight of the explosive at a constant standoff distance. At the lowest intensity load, significant front face bending and progressive cell wall buckling were observed at the center of the panel closest to the explosion source. Cell wall buckling and core densification increased as the impulse increased. An air blast simulation code was used to determine the blast loads at the front surfaces of the test panels, and these were used as inputs to finite element calculations of the dynamic response of the sandwich structure. Very good agreement was observed between the finite element model predictions of the sandwich panel front and back face displacements and the experimental observations. The model also captured many of the phenomenological details of the core deformation behavior. The honeycomb sandwich panels suffered significantly smaller back face deflections than solid plates of identical mass even though their design was far from optimal for such an application.     

Investigation of elastic moduli of Kraft paper honeycomb core sandwich panels

In order to understand the influence of the thicknesses of Kraft paper honeycomb core and medium density fiberboard skins on the stiffness of the sandwich panel, the corresponding finite element models for the resulting sandwich panels were developed. The material properties for the core and skin components of these finite element models were determined using the published data and specifications. It was found that a decrease in the thickness ratio of the core to skin layer (shelling ratio) resulted in an increase in the modulus of elasticity and shear modulus of the sandwich panels. The increase was significant when the shelling ratio was smaller than six. Cell size only affected the modulus of elasticity of the sandwich panels under the flat-wise compression and panel’s inter-laminar shear modulus. Regression equations relating the stiffness of the sandwich panels to the shelling ratio and core cell size were obtained using the finite element model simulated results and were found to compare well with the existing models for layered wood composites.