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.     

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.     

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.     

An experimental study of the insert joint strength of composite sandwich structures

This paper addresses an experimental study of the pull-out and shear failure loads of composite sandwich insert joints. For specimen fabrication, a Nomex honeycomb core and a carbon–epoxy composite were used. The film-type adhesive FM73 was used for core and face co-cured bonding. Specimen sizes are 120 × 120 mm² for the pull-out test and 60 × 120 mm² for the shear loading test. About 80 specimens of 16 different types depending on the core height and density, face thickness, insert clearance, and loading direction were tested. The results show that while the insert joint failure loads for pull-out loading are affected by the core height and density, they are also greatly influenced by the face thickness. The joints with 0.11 mm clearance between the insert flange and the composite face, which is filled with potting material, showed larger failure loads compared to tightly fitted insert joints. In the shear loading, the failure loads of joints were dominated by the face thickness, while core properties such as the core height and direction had little effect on the failure load.     

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。      

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.     

等腰梯形蜂窝芯玻璃钢夹芯板的面内压缩性能

为研究等腰梯形蜂窝芯玻璃钢夹芯板面内压缩破坏机制, 利用材料试验机对夹芯板面内压缩性能进行了试验测试, 并开展了模拟研究。结果表明: 夹芯板的面内压缩破坏方式主要有面板折断、夹芯板屈曲失稳和夹芯板中面板与蜂窝芯脱粘3种类型。面板为夹芯板面内压缩的主要承载构件, 蜂窝芯对面板起到固支作用。面板结构参数与材料参数为影响夹芯板面内压缩抗压强度与抗压刚度主要因素, 多数蜂窝芯的结构参数与材料参数对夹芯板面内压缩抗压强度的影响微弱, 而个别蜂窝芯的结构参数对夹芯板面内压缩抗压刚度的影响比较显著。夹芯板体积一定时, 随着蜂窝芯胞体单元数量的增加, 夹芯板面内压缩的抗压强度与抗压刚度逐渐增大。      

The influence of core height and face plate thickness on the response of honeycomb sandwich panels subjected to blast loading

This paper reports on an investigation into the behaviour of circular sandwich panels with aluminium honeycomb cores subjected to air blast loading. Explosive tests were performed on sandwich panels consisting of mild steel face plates and aluminium honeycomb cores. The loading was generated by detonating plastic explosives at a pre-determined stand-off distance. Core height and face plate thickness were varied and the results are compared with previous experiments. It was observed that the panels exhibited permanent face plate deflection and tearing, and the honeycomb core exhibited crushing and densification. It was found that increasing the core thickness delayed the onset of core densification and decreased back plate deflection. Increasing the plate thickness was also found to decrease back plate deflection, although the panels then had a substantially higher overall mass.     

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。      

Investigation on the square cell honeycomb structures under axial loading

To investigate into the collapse of a sandwich panel or beam with a square cell honeycomb, the novel plate model and beam model are developed according to the cross-sectional symmetry of the cell. The treble series solution of buckling mode is presented, and the formulas of critical compressive stress on skins are derived. The honeycomb sandwich panels are classified as thin, medium and thick plates based on their failure forms. It is found that the different kinds of cells have different buckling modes and different parameter governing equations. A new iterative optimization design method for a square honeycomb sandwich panel is developed and the curves of critical compressive stresses with geometrical parameters are provided in details. Finally, the 3D finite element numeric simulations have validated the formulas presented by this paper. Our study reveals some mechanical characteristics of the square honeycomb sandwich structures.     

Failure mode maps for honeycomb sandwich panels

Failure modes for sandwich beams of GFRP laminate skins and Nomex honeycomb core are investigated. Theoretical models using honeycomb mechanics and classical beam theory are described. A failure mode map for loading under 3-point bending is constructed, showing the dependence of failure mode and load on the ratio of skin thickness to span length and honeycomb relative density. Beam specimens are tested in 3-point bending. The experimental data agree satisfactorily with the theoretical predictions. The effect of honeycomb direction is also examined. The concept of a failure mode map is extended to give a useful design tool for sandwich panels manufacturers and their customers.     

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.     

Static strength tests of steel plate strengthened concrete beams

The behaviour of damaged concrete beams strengthened by externally bonded steel plates is experimentally investigated. The study includes an investigation of the mode of failure, including flexural failure and the interface separation of the steel plate. Simply supported beams under monotonically increasing loads are considered exclusively. A total of five plain concrete beams externally reinforced with bonded steel plates were tested under static loads to determine their strength and behaviour. The variables tested were the thickness of the external steel plate, length and location of the interfacial crack, and the degree of surface preparation of the steel plate. In all five beams the thickness of adhesive was kept constant. The results indicate that (i) the behaviour of a damaged open sandwich beam is similar to that of a singly reinforced concrete beam when no debonding occurs between the concrete and the adherent steel plate; (ii) when debonding occurs, the failure is sudden and at loads smaller than for a case where failure is either by yielding of steel or crushing of concrete; (iii) the case with an interfacial crack between the steel and the adhesive is more critical than the case when the interfacial crack is between the adhesive and the concrete; and (iv) the failure load and the mode of failure are dependent on the degree of surface preparation of the steel plate. Analytical investigation to predict the interfacial debonding is summarized, and the results suggest that linear elastic fracture mechanics is suited for predicting the failure load for open sandwich beams which fail by interface debonding.     

水下冲击波作用的铝合金蜂窝夹层板动力学响应研究

为研究铝合金蜂窝夹层板水下爆炸冲击波载荷作用的动态响应及抗冲击性能,利用非药式水下爆炸冲击波加载装置对气背固支5A06铝合金夹层板及具有相同面密度的单层板进行水下冲击波加载试验。利用高速相机结合三维数字散斑技术(DIC)对夹层板后面板动态响应进行实时测量,获得夹层板气背面受水下冲击波作用的动态响应历程及变形毁伤模式,比较分析铝合金蜂窝夹层板抗冲击防护性能。结果表明,较相同面密度的单层板,蜂窝夹层板受水下冲击波载荷作用的芯层压缩能有效减少气背面板的塑性变形,提高夹层结构整体抗冲击性能。     

Quasi-static indentation tests on aluminium foam sandwich panels

Mechanical response and energy absorption of aluminium foam sandwich panels subjected to quasi-static indentation loads were investigated experimentally. These sandwich panels consisted of two aluminium face-sheets and a closed cell aluminium foam core (ALPORAS®). Quasi-static indentation tests were conducted using an MTS universal testing machine, with sandwich panels either simply supported or fully fixed. Force–displacement curves were recorded and the total energy absorbed by sandwich panels was calculated accordingly. Videos and photographs were taken to capture the deformation of top face-sheets, foam cores and bottom face-sheets. Effects of face-sheet thickness, core thickness, boundary conditions, adhesive and surface condition of face-sheets on the mechanical response and energy absorption of sandwich panels were discussed.     

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。     

Optimization of shear-deformable laminated plates under buckling and strength criteria

A shear deformable laminated theory is used to study the optimal design of rectangular plates under biaxial compressive loads. Such loads lead to plate failure by buckling or material failure which corresponds to the violation of the selected strength criterion. The minimum of the two loads (buckling load or material failure load) determines the critical failure load for a given set of problem parameters. At the optimum values of the ply angles, buckling or both failure criteria may be operational depending on the laminate thickness. The present study investigates the effect of laminate thickness on the optimal design and gives numerical results for symmetrically laminated angle-ply plates.     

Characterisation and Assessment of Load Response, Failure and Fatigue Phenomena in Sandwich Structures Induced by Localised Effects: A Review

Abstract:  The objective of the paper is to provide an overview of the mechanical effects, which determine the occurrence and severity of localised bending effects in sandwich structures, and to provide a survey of the available structural sandwich models, with special emphasis on their ability to describe local bending effects. The presentation includes a brief survey of the various structural models, including classical, 'first-order shear', 'high-order' and continuum mechanics-based models. Moreover, the paper focuses on and addresses the experimental characterisation and assessment of local effects in sandwich structures based on realistic engineering practice, examples including sandwich panels with core materials of different stiffness (core junctions), sandwich plates with inserts and junctions between sandwich panels of different curvature. The issues of general load response (global and local) as well as failure and fatigue of such sandwich structures subjected to out-of-plane and in-plane loads are discussed in some detail, with the inclusion of recent theoretical and experimental results.     

Light-weight honeycomb core sandwich panels containing biofiber-reinforced thermoset polymer composite skins: Fabrication and evaluation

The application of biofiber based paper-reinforced polymer (PRP) composites as skin materials for light-weight sandwich panel constructions was explored. Various sandwich panels with PRP composite skins and a commercial resin-impregnated aramid paper honeycomb core of different cell sizes and core heights were fabricated in the laboratory. The effects of honeycomb core height and cell size on the flexural properties of the lab-made sandwich panels were evaluated. The flexural moduli and strengths of the lab-made panels were compared to the reported values for three existing commercial products used for automotive load floor applications. The lab-made PRP composite/honeycomb core sandwich panels had comparable bending rigidity and flexural load bearing capability but lower areal weights when compared to the commercial products suggesting that PRP composites have the potential to be used as an alternative to glass fiber-reinforced polymer composites as skin materials in sandwich panel fabrication.