基于DFM/FEM铝蜂窝夹层结构耦合损耗因子预测

在使用统计能量分析对复杂的蜂窝夹层结构进行高频动力学响应预示的关键环节之一在于准确估算耦合损耗因子。本文研究应用对偶模态/有限元法（DFM/FEM）估算铝蜂窝夹层结构之间的耦合损耗因子,通过算例对该方法进行仿真验证,结果表明,该方法可行且高效准确。最后对L型耦合铝蜂窝夹层板结构进行振动实验,并使用功率输入法辨识试件间的耦合损耗因子,比较功率输入和和对偶模态/有限元法结果,两者一致性好,进一步验证了对偶模态/有限元法估算铝蜂窝夹层板系统耦合损耗因子的可行性,扩展了统计能量分析在复杂结构上的应用。     

Deformation and impact energy absorption of cellular sandwich panels

The response and energy absorption capacity of cellular sandwich panels that comprises of silk-cotton wood skins and aluminum honeycomb core are studied under quasi-static and low velocity impact loading. Two types of sandwich panels were constructed. The Type-I sandwich panel contains the silk-cotton wood plates (face plates) with their grains oriented to the direction of loading axis and in the case of Type-II sandwich panel, the wood grains were oriented transverse to the loading axis. In both of the above cases, aluminum honeycomb core had its cell axis parallel to the loading direction. The macro-deformation behavior of these panels is studied under quasi-static loading and their energy absorption capacity quantified. A series of low velocity impact tests were conducted and the dynamic data are discussed. The results are then compared with those of quasi-static experiments. It is observed that the energy absorption capacity of cellular sandwich panels increases under dynamic loading when compared with the quasi-static loading conditions. The Type-I sandwich panels tested in this study are found to be the better impact energy absorbers for low velocity impact applications.     

梯度铝蜂窝夹芯板的力学行为

梯度分层铝合金蜂窝板是一种有效的吸能结构,本工作在梯度铝蜂窝结构的基础上根据梯度率的概念,通过改变蜂窝芯层的胞壁长度,设计了4种质量相同、梯度率不同的铝蜂窝夹芯结构。通过准静态压缩实验,并结合非线性有限元模拟准静态及冲击态下梯度铝蜂窝夹芯结构的变形情况及其力学性能,分析对比了相同质量下梯度铝蜂窝夹芯结构在准静态下的变形模式以及冲击载荷下分层均质蜂窝结构和不同梯度率的分层梯度蜂窝结构的动态响应和能量吸收特性。结果表明:在准静态压缩过程中,铝蜂窝梯度夹芯板的变形具有明显的局部化特征,蜂窝芯的变形为低密度优先变形直至密实,层级之间的密实化应变差随芯层密度的增大而逐渐减小;在高速冲击下,梯度蜂窝板并非严格按照准静态过程中逐级变形直至密实,而是在锤头冲击惯性及芯层密度的相互作用下整体发生的线弹性变形、弹性屈曲、塑性坍塌及密实化;另外,在本工作所设计的梯度率中,当梯度率为γ₁=0.0276时,梯度蜂窝夹芯板的吸能性达到最好,相较于同等质量下的均质蜂窝夹芯板,能量吸收提高了10.63%。     

Dynamic response of aluminum honeycomb sandwich panels under foam projectile impact

The dynamic response of honeycomb sandwich panels under aluminum foam projectile impact was investigated. The different configurations of panels were tested, and deformation/failure modes were obtained. Corresponding numerical simulations were also presented to investigate the energy absorption and deformation mechanism of sandwich panels. Results showed that the deformation/failure modes of sandwich panels were sensitive to the impact velocity and density of aluminum foam. When the panel was impacted by the aluminum foam projectile with the back mass of nylon, the “accelerating impact” stage can be produced and may lead to further compression and damage of the sandwich structures.     

Generation of transient vibrations on aluminum honeycomb sandwich panels subjected to hypervelocity impacts

This paper presents the results of a set of experiments aimed at discovering the main features of impact-induced vibrations on all-aluminum honeycomb sandwich panels, representative of the GOCE satellite's top floor, which is exposed to the orbital debris environment. The activity focused on the characterization of the vibrations induced in the vicinity of internal payloads by hypervelocity impacts occurring on the vehicle's external shell. More than 30 tests were realized by launching 0.8–2.3 mm aluminum projectiles in the velocity range 4–5.5 km/s on targets with tri-axial accelerometer assemblies mounted on both the front and rear face of the panel, at a nominal distance of 150 mm from the impact point. It was found that a hypervelocity impact produces in both the front and rear side of the sandwich panel a vibration environment which can be described through the shock response spectrum (SRS) of three different types of waves that can be distinguished on the basis of the acceleration direction: out-of-plane, in-plane longitudinal and in-plane shear. The influence of projectile mass and velocity on SRS appeared to vary with frequency, with the most significant difference in the range between ∼10³ and ∼10⁴ Hz. The results of whole experimental set were used to derive an interpolation law through standard techniques of nonlinear fit. The empirical equation obtained makes it possible to predict the near-field vibration environment produced by hypervelocity impacts with debris having given size and velocity, reproducing all the test data with an average uncertainty of ±6 dB.     

An analytical model for composite sandwich panels with honeycomb core subjected to high-velocity impact

In this paper, an analytical model for perforation of composite sandwich panels with honeycomb core subjected to high-velocity impact has been developed. The sandwich panel consists of a aluminium honeycomb core sandwiched between two thin composite skins. The solution involves a three-stage, perforation process including perforation of the front composite skin, honeycomb core, and bottom composite skin. The strain and kinetic energy of the front and back-up composite skins and the absorbed energy of honeycomb core has been estimated. In addition, based on the energy balance and equation of motion the absorbed energy of sandwich panel, residual velocity of projectile, perforation time and projectile velocity have been obtained and compared with the available experimental tests and numerical model. Furthermore, effects of composite skins and aluminium honeycomb core on perforation resistance and ballistic performance of sandwich panels has been investigated.     

碳纤维铝蜂窝夹芯复合结构隔声性能研究

铝蜂窝夹芯复合结构在航空工业、高速列车及汽车车体中得到越来越多的应用,其隔声性能对车内及机舱噪声有重要影响。建立了碳纤维铝蜂窝夹芯复合结构有限单元模型,用有限单元法计算了结构在声载荷激励下的响应,并计算分析了复合结构的隔声性能,分析了碳纤维复合面板厚度、面板层数、铺设角度、铝蜂窝芯层的厚度、铝蜂窝壁厚对隔声性能的影响。研究结果表明,面板采用碳纤维复合结构时,在小于1 000 Hz的低频段,相同面板厚度的铝蜂窝复合结构隔声性能比全铝合金材料的铝蜂窝夹芯复合结构有所降低,而且在高频段会出现隔声量更低的隔声低谷;相较于铝合金面板,复合结构的面板采用碳纤维复合材料时,能够实现整体结构轻量化也提高复合结构的隔声性能;各层之间按相对90°铺设时复合结构隔声性能最好;随着面板厚度的增加复合结构隔声性能增加,面板层总厚度不变的情况下,单层面板或者过多的层数都会使复合结构隔声性能降低。     

Behaviour of sandwich panels subject to intense air blasts – Part 2: Numerical simulation

Finite element simulation is employed to analyse the behaviour of clamped sandwich panels comprising equal thicknesses mild steel plates sandwiching an aluminium honeycomb core when subject to blast loadings. Pressure-time histories representative of blast loadings are applied to the front plate of the sandwich panel. The FE model is verified using the experimental test results for uniform and localised blast loading in the presence of a honeycomb core and with only an air gap between the sandwich plates. It is observed that for the particular core material, the load transfer to the back plate of the panel depends on the load intensity, core thickness and flexibility of the sandwich panels.     

Composite robot end effector for manipulating large LCD glass panels

Recently, the design and the manufacture of light robot end effectors with high stiffness have become important in order to reduce the deflection due to the self-weight and weight of glass panel, a part of LCD, as the size of glass panels as well as robot end effectors increases. The best way to reduce the deflection and vibration of end effectors without sacrificing the stiffness of end effectors is to employ fiber reinforced composite materials for main structural materials because composite materials have high specific stiffness and high damping. In this work, the end effector for loading and unloading large glass panels were designed and manufactured using carbon fiber epoxy composite honeycomb sandwich structures. Finite element analysis was used along with an optimization routine to design the composite end effector. A box type sandwich structure was employed to reduce the shear effect arising from the low modulus of honeycomb structure. The carbon fiber epoxy prepreg was hand-laid up on the honeycomb structure and cured in an autoclave. A special process was used to reinforce the two sidewalls of the box type sandwich structure. The weight reduction of the composite end effector was more than 50% compared to the weight of a comparable aluminum end effector. From the experiments, it was also found that the static and dynamic characteristics of the composite end effector were much improved compared to those of the aluminum end effector.     

明胶鸟弹撞击复合材料蜂窝夹芯板试验

开展明胶鸟弹撞击复合材料蜂窝夹芯板试验,研究夹芯结构在软体高速冲击下的损伤形式,分析相关因素对结构动态响应结果的影响。通过CT扫描对复合材料蜂窝夹芯板内部进行检测可知,面板出现分层、基体开裂、纤维断裂、凹陷、向胞内屈曲等损伤形式,蜂窝芯出现芯材压溃、与面板脱粘的损伤形式;分析复合材料蜂窝夹芯板后面板的动态变形过程及撞击中心处位移-时间数据可知,复合材料蜂窝夹芯板在撞击过程中出现由全局弯曲变形主导和局部变形主导的两种变形模式;通过对比不同工况下的复合材料蜂窝夹芯板损伤程度可知,复合材料蜂窝夹芯板损伤程度随鸟弹撞击速度的增加而增大;蜂窝芯高度为10 mm的复合材料蜂窝夹芯板较蜂窝芯高度为5 mm的复合材料蜂窝夹芯板的损伤程度大;初始动能较大的球形鸟弹较圆柱形鸟弹对复合材料蜂窝夹芯板造成的冲击损伤程度更大。      

Compression after impact test (CAI) on NOMEX™ honeycomb sandwich panels with thin aluminum skins

Sandwich panels are used in industrial fields where lightness and energy absorption capabilities are required. In order to increase their exploitation, a wide knowledge of their mechanical behavior also in severe loading conditions is crucial. Light structures such as the one studied in the present work, sandwich panels with aluminum skins and Nomex^™ honeycomb core, are exposed to a possible decrease of their structural integrity, resulting from a low velocity impact. In order to quantitatively describe the decrease of the sandwich mechanical performance after an impact, an experimental program of compression after impact tests (CAI) has been performed. Sandwich panel specimens have been damaged during a low velocity impact test phase, using an experimental apparatus based on a free fall mass tower. Different experimental impact energies have been tested. Damaged and undamaged specimens have been consequently tested adopting a compression after impact procedure. The relation between the residual strength of the panel and the possible relevant parameters has been statistically investigated. The results show a clear reduction of the residual strength of the damaged panels compared with undamaged ones. Nevertheless, a reduced dependency between the impact energy and the residual strength is found above a certain impact energy threshold.     

Impact analysis of fiber reinforced polymer honeycomb composite sandwich beams

Large scale fiber reinforced polymer (FRP) composite structures have been used in highway bridge and building construction. Recent applications have demonstrated that FRP honeycomb sandwich panels can be effectively and economically applied for both new construction and rehabilitation and replacement of existing structures. This paper is concerned with impact analysis of an as-manufactured FRP honeycomb sandwich system with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components including: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, and (3) equivalent core material properties, are first introduced, and these properties for the face laminates and equivalent core are later used in dynamic analysis of sandwich beams. A higher-order impact sandwich beam theory by the authors [Yang MJ, Qiao P. Higher-order impact modeling of sandwich beams with flexible core. Int J Solids Struct 2005;42(20):5460–90] is adopted to carry out the free vibration and impact analyses of the FRP honeycomb sandwich system, from which the full elastic field (e.g., deformation and stress) under impact is predicted. The higher order vibration analysis of the FRP sandwich beams is conducted, and its accuracy is validated with the finite element Eigenvalue analysis using ABAQUS; while the predicted impact responses (e.g., contact force and central deflection) are compared with the finite element simulations by LS-DYNA. A parametric study with respect to projectile mass and velocity is performed, and the similar prediction trends with the linear solution are observed. Furthermore, the predicted stress fields are compared with the available strength data to predict the impact damage in the FRP sandwich system. The present impact analysis demonstrates the accuracy and capability of the higher order impact sandwich beam theory, and it can be used effectively in analysis, design applications and optimization of efficient FRP honeycomb composite sandwich structures for impact protection and mitigation.     

Finite Element Analysis of Dynamic Mechanical Responses of Aluminum Honeycomb Sandwich Structures Under Low-Velocity Impact

Honeycomb sandwich structures, composed of many regularly arranged hexagonal cores and two skins, often show excellent impact performance due to strong energy absorption ability under impact loads. This paper studies dynamic mechanical responses of aluminum honeycomb sandwich structures. Parametric geometry modeling using UG software and finite element analysis using ANSYS explicit dynamics module are performed. Finite difference algorithm based on time-stepping integration is used to get the impact displacement, and stress and strain with time. Effects of different impact velocities, core length and wall thickness on the distributions of plastic stress and strain are also explored. Results show that thinner honeycomb side length and thicker wall thickness lead to stronger impact resistance. This research provides theoretical support for promoting optimal design of lightweight structures against impact loads.     

高速冲击载荷作用下钎焊蜂窝夹层板动态响应

目的 以钎焊高温合金蜂窝夹层板为研究对象,分析其在弹丸高速冲击作用下的力学性能。方法 采用轻气炮冲击加载试验结合有限元模拟,对蜂窝夹层板开展不同冲击强度下的动态响应和失效研究。开展含高速冲击损伤的蜂窝夹层板侧压试验,研究损伤模式对剩余强度的影响。结果 冲击强度对夹层板的失效过程和失效模式有着明显的影响,当冲击条件不足以使得迎弹面发生侵彻时,夹层板失效为表面压痕损伤;随着冲击强度的提高,出现不同程度的局部芯层压缩;当冲击强度大于临界值时,迎/背弹面陆续被侵彻,夹层板出现侵入损伤及贯穿损伤。结论 高速冲击损伤使得蜂窝夹层板的侧压失效模式,由理想塑性屈曲转变为局部失稳,侧压极限载荷大幅降低。     

泡沫铝夹层结构复合材料低速冲击性能

以泡沫铝为夹芯材料,玄武岩纤维(BF)和超高分子量聚乙烯纤维(UHMWPE)复合材料为面板,制备夹层结构复合材料。研究纤维类型、铺层结构和芯材厚度对泡沫铝夹层结构复合材料冲击性能和损伤模式的影响规律,并与铝蜂窝夹层结构复合材料性能进行对比分析。结果表明:BF/泡沫铝夹层结构比UHMWPE/泡沫铝夹层结构具有更大的冲击破坏载荷,但冲击位移和吸收能量较小。BF和UHMWPE两种纤维的分层混杂设计比叠加混杂具有更高的冲击破坏载荷和吸收能量。随着泡沫铝厚度的增加,夹层结构复合材料的冲击破坏载荷降低,破坏吸收能量增大。泡沫铝夹层结构比铝蜂窝夹层结构具有更高的冲击破坏载荷,但冲击破坏吸收能量较小;泡沫铝芯材以冲击部位的碎裂为主要失效形式,铝蜂窝芯材整体压缩破坏明显。     

散布式扬声器音板材料振动特性的研究

利用激光干涉器检测矩形夹心板(芯层为厚度不等的PU泡沫和孔径不等的蜂窝纸芯,皮层为环氧树脂层压板或铜版纸)在受迫振动时的幅值,通过比较不同结构夹心板的幅频曲线以及加速度-频率曲线,从微观结构的角度出发,讨论了音板材料的结构变化对其振动特性的影响.实验结果表明,随着PU泡沫芯或蜂窝纸芯的孔径减小,夹心板的第一阶共振频率不变,共振振幅呈下降趋势,非共振振幅无变化,材料的阻尼特性是制约夹心板中高频段的内在因素;当皮层和芯层的模量相近时皮层不能对芯层形成刚性约束,共振频率和振幅会发生很大的变化.     

复合材料蜂窝夹芯板低速冲击损伤研究

本文对蜂窝夹芯板试件进行了低速冲击试验, 然后用X 光技术、热揭层技术、断面显微技术和外观检测等对冲击后板的损伤进行了较为全面的研究, 讨论了表面布的作用, 分析了外观损伤、面板损伤、蜂窝损伤等与冲击能量的关系。     

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。      

高速列车夹芯地板结构隔声特性研究

采用传递矩阵法,建立高速列车内地板的声学特性分析模型,探索不同三明治夹芯板材料和结构对高速列车内地板隔声特性的影响,并根据内地板结构的传递损失评价具有不同参数的三明治夹芯板的隔声性能。通过不同的表层材质（木材、铝材、钢材）、厚度和蜂窝夹层密度,进行了内地板隔声量变化规律的分析和比较。探寻拟定隔声性能优越的三明治夹芯板材料类型和结构型式。结果表明,（1）表层夹板厚度一定,钢材作为表层材料,内地板隔声量最好,其次是铝材,最后是木材;（2）表层厚度影响,木材夹层板,厚度每增加1 mm,各个频段隔声量增加1 dB ～1.5 dB。铝材夹层板,厚度每增加1 mm,各个频段隔声量增加1 dB ～3 dB。钢材夹层板,厚度每增加1 mm,各个频段隔声量增加1 dB ～5 dB;（3）蜂窝板密度降低一半,内地板隔声量有增加趋势,但影响较小。     

Transverse shear stiffness of thickness gradient honeycombs

This paper describes the transverse shear stiffness of a novel topology of gradient honeycomb structures. Opposite to classical honeycomb configurations, gradient honeycombs feature elements of their unit cells with a regular geometry variation across the whole honeycomb panel. The tessellation of the cells is not periodic, but is dictated by geometric constraints between adjacent units. Gradient honeycombs with wall thickness linearly increasing along the panel are described using experimental data and Finite Element models. The gradient behaviour of the cellular structure provides additional complexity, and the possibility of tailoring design properties, such as the stiffness per unit of weight. We observe a good agreement between the Finite Element and the experimental results, with maximum percentage errors <7% for the shear moduli of the honeycombs.