Transverse honeycomb composite transducers

Composites with 3-1 connectivity were fabricated by impregnating an extruded, sintered honeycomb configuration of PZT with epoxy. The composites had lower density (≈ 3000 Kg/m³) and lower dielectric constant (≈ 400) than that of solid PZT. The maximum piezoelectric d?₃₃ coefficient of the composites was 350 pC/N, and the maximum hydrostatic d?_h 220 pC/N. ?_h and d?_h?_h of the composites were an order of magnitude higher than that of solid PZT. Considering the symmetry and phase connectivity of the individual phases in the composite, an explanation is given for the improved piezoelectric properties of the composites.     

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.     

A novel centresymmetric honeycomb composite structure

In this paper analytical and finite element (FE) simulations are carried out to calculate the in-plane Poisson’s ratio and Young’s moduli of a new centresymmetric honeycomb configuration under uniaxial loading. Opposite to similar re-entrant honeycomb structures studied in the past, the new re-entrant unit cell topology takes into account possible manufacturing constraints typical of production routes like Resin Transfer Moulding (RTM) or Rapid Prototyping (RP). The results obtained through the analytical and FE analysis show a significant decrease of the Poisson’s ratio for the internal cell angle between −20° and +20° compared to the classical re-entrant configurations exhibited in literature. The results also show that the presence of edge corners in the unit cell honeycomb configuration gives rise to a cellular structure with enhanced flexibility compared to the classical centresymmetric one. The results obtained by the analytical model show good agreement with the Gibson and Ashby rib-bending model when the honeycomb configuration reduces to the theoretical layout without modifications due to manufacturing constraints.     

多级复合材料蜂窝结构的力学性能

根据多级结构设计思想,把高性能聚甲基丙烯酰亚胺（PMI）泡沫加入到单向碳纤维增强树脂复合材料之间,制备多级复合材料蜂窝结构。对多级复合材料蜂窝结构的平压性能进行了研究,包括多级复合材料蜂窝结构平压性能的理论预报和试验验证。研究了多级复合材料蜂窝结构平压性能随结构等效密度变化的关系。并对多级复合材料蜂窝结构的三点弯曲性能进行了研究,主要包括理论预报和试验验证。通过理论研究对结构的失效模式进行了预报,绘制了失效模式机制图,并通过三点弯曲试验对理论预报结果进行了验证。      

Ballistic impact response of laminated composite panels

Laminated ballistic composite panels are an important part of hard-plate protective body armour and may be subjected to a wide variety of impact conditions depending on the projectile, impact velocity and armour construction, to name a few.     

Neutron imaging inspections of composite honeycomb adhesive bonds

Numerous commercial and military aircraft, including the Canadian Forces CF188 Hornet, use composite honeycomb structures in the design of their flight control surfaces (FCS). These structures provide excellent strength to weight ratios, but are often susceptible to degradation from moisture ingress. Once inside the honeycomb structure moisture causes the structural adhesive bonds to weaken, which can lead to complete failure of the FCS in flight. There are two critical structural adhesive bonds: the node bond and the filet bond. The node bond is integral to the honeycomb portion of the composite core and is located between the honeycomb cells. The filet bond is the adhesive bond located between the skin and the core. In order to asses overall structural degradation and develop repair procedures, it is important to determine the degree of degradation in each type of bond. Neutron radiography and tomography of the adhesive bonds was conducted at the Royal Military College (RMC) and FRM-II. Honeycomb samples were manufactured from FCS with in-service water ingress. The radiographs and tomograms provided important information about the degree of degradation in the core as well as about which adhesive bonds are more susceptible. The information obtained from this study will help to develop repair techniques and assess the flight worthiness of FCS.     

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。     

On the dynamic behavior of honeycomb based composite solids

Summary The aim of this contribution is twofold. First, a dispersive model of periodic composite solids made of an isotropic matrix reinforced by a hexagonal system of slender fibres or by a honeycomb-like slender skeleton is formulated. Second, this model is applied to the analysis of vibration and wave propagation problems in the above honeycomb based composites. Contrary to the known homogenized models the main feature of the proposed model is that it describes the effect of cell size on the overall dynamic behavior of a composite solid. It is shown that on the macro-level the response of honeycomb based composites is isotropic. It is also proved that there exist dispersive dilatational-type and shear-type waves, which can propagate in these composites. Simple formulae for lower and higher free vibration frequencies are derived, and the existence of certain restrictons imposed on the physically allowable wave propagation speeds is shown.     

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     

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.     

湿热环境对复合材料蜂窝板振动特性的影响

为了研究复合材料蜂窝板在湿热环境下的振动特性,针对由碳纤维/双马来酰亚胺复合材料层合板和Nomex芯层复合而成的蜂窝板进行了不同温湿度下固有频率的数值分析。基于分段剪切变形理论,分别考虑复合材料蜂窝薄板和厚板两种情况,利用湿度与温度的等效性,求解了复合材料蜂窝板的振动特征方程。利用有限元软件ABAQUS,建立了四端固支的复合材料蜂窝板精细化模型。分别讨论了温度、湿度、温湿度联合作用对复合材料蜂窝薄板和厚板固有频率的影响。结果表明:相比于温度的升高,复合材料蜂窝板固有频率对吸湿量的增加更为敏感;相同的湿热环境下,复合材料蜂窝厚板结构的固有频率比薄板结构大,且阶次越高,固有频率上升的幅度越大;温湿度的联合作用比它们单独作用的叠加对复合材料蜂窝板固有频率的影响更大,且在复合材料蜂窝薄板中更加明显。      

A theoretical approach to the deformation of honeycomb based composite materials

Honeycomb sheet is already widely used as a core in aeronautical sandwich construction. An alternative application is to use it as the reinforcing element for composites in which the cells of the honeycomb are filled with various materials. This paper presents the results of a study of such a composite, in which a low modulus infill is used. The work covers, in simple terms, the elastic properties of the unfilled sheet and the composite under in-plane direct loading and out-of-plane bending. The plastic deformation characteristics under in-plane direct loading are also considered. Specimen experimental results are presented, which show that the simple analytical approach used is clearly justifiable.     

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。      

Comparative study on pulsed thermography and modulated thermography of composite honeycomb panels

为了探索适合复合材料蜂窝板缺陷检测的红外热像检测法及热像信号处理方法,对蜂窝板的脉冲热像检测（PT）、调制热像检测（MT）及几种热像信号处理方法的缺陷检测能力进行了比较。在脉冲热像检测中,用脉冲相位法进行热像序列处理,并与最佳原始热像进行比较。在调制热像检测中,提出用离散傅里叶级数法和相关系数法进行热像序列处理,并与经典的四点法进行比较。研究结果表明,在蜂窝板脱粘缺陷的检测中,调制热像法的检测效果好于脉冲热像法。在调制热像法的信号处理中,离散傅里叶级数法和相关系数法的应用效果均好于四点法。在最佳调制频率下,以＂调制热像-离散傅里叶级数＂法进行蜂窝板脱粘缺陷的检测具有最大的缺陷探测能力。     

Modelling of composite sandwich structures with honeycomb core subjected to high-velocity impact

In this study the perforation of composite sandwich structures subjected to high-velocity impact was analysed. Sandwich panels with carbon/epoxy skins and an aluminium honeycomb core were modelled by a three-dimensional finite element model implemented in ABAQUS/Explicit. The model was validated with experimental tests by comparing numerical and experimental residual velocity, ballistic limit, and contact time. By this model the influence of the components on the behaviour of the sandwich panel under impact load was evaluated; also, the contribution of the failure mechanisms to the energy-absorption of the projectile kinetic energy was determined.     

Effective elastic characteristics of honeycomb sandwich composite shells made of generally orthotropic materials

This paper works on the analytical development of the method of two-scale asymptotic homogenization. The technique is used to determine the effective elastic stiffnesses of hexagonal honeycomb-cored structural sandwich composite shells made of generally orthotropic materials. Orthotropy of the constituent materials leads to much more complex unit-cell problems and is considered in the present paper for the first time. At first, a 3D-to-2D general shell model based on a set of unit-cell problems is derived. This is followed by the exploitation of the model to the derivation of analytical estimate formulae; used to calculate the force and moment resultants present in the sandwich shell structure. The implication of the general shell model is further indicated by calculating similar design characteristics for a three-layered composite sandwich panel reinforced with hexagonal and triangular shaped cellular core made from the generally orthotropic material.     

Tension-tension and compression-compression fatigue behavior of an injection-molded short-glass-fiber/poly(ethylene terephthalate) composite

Injection-molded plaques of glass-fiber-filled thermoplastic poly(ethylene terephthalate) (PET) were cut into strips either parallel to (L-specimens) or transverse to (T-specimens) the mold-fill direction. The through-thickness microstructure of the specimens consisted of three layers: for an L-specimen, outer layers with fibers oriented preferentially in the loading direction (the mold-fill direction) and a core with fibers preferentially normal to the loading direction. The fiber orientation of the layers with respect to loading direction is reversed for T-specimens. Tensile specimens from each strip were tested and the influence of specific strip microstructure on the tensile behavior assessed. Tension-tension and compression-compression fatigue lives were characterized for each strip position. Failure surfaces for each loading condition were examined. For tensile and tension-tension fatigue testing, failure always initiated in Compression-compression fatigue failures initiated in layers with fibers aligned parallel to the loading direction, and were thermally induced.     

复合材料蜂窝板脉冲热像检测和调制热像检测的比较研究

为了探索适合复合材料蜂窝板缺陷检测的红外热像检测法及热像信号处理方法, 对蜂窝板的脉冲热像检测(PT)、调制热像检测(MT)及几种热像信号处理方法的缺陷检测能力进行了比较。在脉冲热像检测中, 用脉冲相位法进行热像序列处理, 并与最佳原始热像进行比较。在调制热像检测中, 提出用离散傅里叶级数法和相关系数法进行热像序列处理, 并与经典的四点法进行比较。研究结果表明, 在蜂窝板脱粘缺陷的检测中, 调制热像法的检测效果好于脉冲热像法。在调制热像法的信号处理中, 离散傅里叶级数法和相关系数法的应用效果均好于四点法。在最佳调制频率下, 以"调制热像-离散傅里叶级数"法进行蜂窝板脱粘缺陷的检测具有最大的缺陷探测能力。     

薄面板复合材料蜂窝夹层结构冲击试验

为研究薄面板复合材料蜂窝夹层结构在冲击载荷下的接触力响应和损伤情况,用两种不同质量的冲头对不同面板厚度的复合材料夹层结构进行了多种能量的落锤式冲击试验,并对冲击后的试验件进行了损伤测量。结果表明：冲击能量相对较低时,最大接触力较小,随着冲击能量的增加,最大接触力在增大过程中会出现门槛值,即达到某一值后不再上升。低能量下,冲击损伤表现为面板凹坑和冲击点周围的少量分层,随着冲击能量变大,面板逐渐出现纤维断裂进而被穿透。面板未穿透时,冲头会反弹,接触力-时间曲线的下降段没有台阶,分层区域直径约为冲头直径的1.2倍;面板穿透时,冲头不反弹,接触力-时间曲线下降段出现台阶,分层区域直径约为冲头直径的1.8倍。当最大接触力达到门槛值后,相同冲击能量下,冲头质量越大,冲击持续时间越长,凹坑越深。