Simulation of hyper-velocity impact on double honeycomb sandwich panel and its staggered improvement with internal-structure model

The double honeycomb sandwich panel, which was formed by inserting an intermediate facesheet into single honeycomb core, showed better capability than single honeycomb panel in shielding hyper-velocity impact from space debris. Shielding structures with double honeycomb cores are thoroughly investigated with material point method and point-based internal-structure model. The front honeycomb core and the rear honeycomb core are staggered to obtain better shielding effect. It is found that staggered double honeycomb cores can fragment the debris and lessen impact threats much more than original double honeycomb cores. The sizes of the holes on the rear facesheet are greatly reduced, and the panels are not perforated for some impact velocities. Staggered double honeycomb panels can be adopted as novel effective shielding structures for hyper-velocity impacts.     

Large inelastic response of unbonded metallic foam and honeycomb core sandwich panels to blast loading

Sandwich panels constructed from metallic face sheets with the core composed of an energy absorbing material, have shown potential as an effective blast resistant structure. In the present study, air-blast tests are conducted on sandwich panels composed steel face sheets with unbonded aluminium foam (Alporas, Cymat) or hexagonal honeycomb cores. Honeycomb cores with small and large aspect ratios are investigated. For all core materials, tests are conducted using two different face sheet thicknesses. The results show that face sheet thickness has a significant effect on the performance of the panels relative to an equivalent monolithic plate. The Alporas and honeycomb cores are found to give higher relative performance with a thicker face sheet. Under the majority of the loading conditions investigated, the thick core honeycomb panels show the greatest increase in blast resistance of the core materials. The Cymat core panels do not show any significant increase in performance over monolithic plates.     

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.     

Vacuum-bag-only co-bonding prepreg skins to aramid honeycomb core. Part II. In-situ core pressure response using embedded sensors

Miniature pressure sensors were embedded into the honeycomb core of sandwich panels featuring both tool-side and bag-side skins. The pressure response was measured throughout the vacuum hold and elevated temperature processing stages of both oven and autoclave manufacturing. The elevated temperature processing measurements validated the honeycomb core pressure model presented in Part I, confirming that gas flow primarily occurs through the bag-side skin in semi-infinite panels. Aramid core panels showed much higher honeycomb core pressures than aluminum cores during elevated temperature processing. Higher core pressures during processing led to more gas flow and as a result, cured skins with interconnected porosity. The best sealed aramid core honeycomb skins were processed under one atmosphere of positive pressure with a vented vacuum bag, avoiding the continuous extraction of gas through the skins by the vacuum pump while the resin was highly mobile.     

Response of flexible sandwich-type panels to blast loading

This paper reports on experimental and numerical investigations into the response of flexible sandwich-type panels when subjected to blast loading. The response of sandwich-type panels with steel plates and polystyrene cores are compared to panels with steel face plates and aluminium honeycomb cores. Panels are loaded by detonating plastic explosive discs in close proximity to the front face of the panel. The numerical model is used to explain the stress attenuation and enhancement of the panels with different cores when subjected to blast induced dynamic loading. The permanent deflection of the back plate is determined by the velocity attenuation properties (and hence the transmitted stress pulse) of the core. Core efficiency in terms of energy absorption is an important factor for thicker cores. For panels of comparable mass, those with aluminium honeycomb cores perform “better” than those with polystyrene cores.     

Numerical and experimental analysis of a triangular auxetic core made of CFR-PEEK using the Directionally Reinforced Integrated Single-yarn (DIRIS) architecture

The Directionally Reinforced Integrated Single-yarn (DIRIS) architecture is a novel, patented concept of creating directionally reinforced high-strength cores for sandwich panels developed at the Institute of Mechanics of Materials and Geostructures S.A. This technology using glass or carbon fibre-reinforced PEEK has been so far implemented on high-strength honeycomb cores of triangular isogrid geometry with impressive results in all constitutive parameters both in-plane and out-of-plane. In this paper the application of the DIRIS technology on creating high-strength auxetic triangular cores is presented. The mechanical behaviour of the resulting core and panel was numerically investigated using FEA and testing on manufactured prototypes confirmed the high strength of the proposed design. In fact the shear modulus of the DIRIS auxetic cores was found superior to that of existing mass-produced honeycomb cores despite the inherent complexity of the geometrical configuration and the non-standardized manufacturing method.     

高精度碳纤维增强树脂复合材料夹层天线面板热变形影响参数仿真与实验

为满足亚毫米波、太赫兹波段等高频天线反射面的应用需求,采用附加树脂修型技术制得1米级、面形精度优于10 μm均方差(RMS)的碳纤维增强树脂(CFRP)复合材料天线面板。主要开展了针对高精度CFRP复合材料面板在极端低温环境下的热变形机制研究。根据基础材料性能测试数据,建立面板的有限元仿真模型,预测大温差工况下多结构参数面板的热变形残差,分析了影响面板热变形特性的主要因素。比较了铝蜂窝和碳管阵列夹芯两种面板结构热变形特性的差异。结果表明,碳管夹芯结构面板具备更高的比刚度和热稳定性。通过仿真结构优化给出了面板的结构设计参数,并重新试制了原型面板。采用基于高精度数字摄影测量的实验方法,对铝蜂窝和碳管阵列两种夹芯结构原型面板在低温环境下的热变形误差进行了测量,通过分析实验与仿真结果的误差来源,讨论了有限元预测方法的可行性,给出了针对高精度CFRP复合材料面板设计及工艺方法的指导意见。      

Finite element analysis of sandwich panels with stepwise graded aluminum honeycomb cores under blast loading

This paper presents details and brief results of an experimental investigation on the response of metallic sandwich panels with stepwise graded aluminum honeycomb cores under blast loading. Based on the experiments, corresponding finite element simulations have been undertaken using the LS-DYNA software. It is observed that the core compression stage was coupled with the fluid–structure interaction stage, and the compression of the core layer decreased from the central to the peripheral zone. The blast resistance capability of sandwich panels was moderately sensitive to the core relative density and graded distribution. For the graded panels with relative density descending core arrangement, the core plastic energy dissipation and the transmitted force attenuation were larger than that of the ungraded ones under the same loading condition. The graded sandwich panels, especially for relative density descending core arrangement, would display a better blast resistance than the ungraded ones at a specific loading region.     

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.     

Evaluation of the mechanisms of water migration through honeycomb core

Thirteen commerical wing panels were fabricated and flown on a commercial aircraft to investigate the mechanisms of water migration through various honeycomb cores. A 12.2 J impact damage was not observed to cause damage propagation in aluminum and Korex® honeycomb materials. This was attributed to the ability of the cores to localize the impact damage. In Nomex® and glass fiber cores a different damage propagation mechanism was observed. In these cores, the damage was not confined to the localized area around the impact. Instead, core damage was seen as far as 2.0 cm from the point of impact. This increased core damage allowed the core to retain water. The retained water helped propagate the impact damage through a freeze thaw mechanism. Speed-tape repairs were only found to be statistically significant when water migrated through the core. Filling the honeycomb core with foam was shown to be an effective method for minimizing the damaging effects of water ingression. Slotting and draining the core also offered some relief from water accumulation in the core, but foaming damaged core was established as the most effective technique.     

Static and Fatigue Behaviour of Hexagonal Honeycomb Cores under In-plane Shear Loads

Due to their high specific strength and high specific stiffness properties the use of honeycomb panels is particularly attractive in spacecraft structures. However, the harsh environment produced during the launch of a satellite can subject the honeycomb cores of these sandwich structures to severe quasi-static and dynamic loads, potentially leading to static or early fatigue failures. Knowledge of the static and fatigue behavior of these honeycomb cores is thus a key requirement when considering their use in spacecraft structural applications. This paper presents the findings of an experimental test campaign carried out to investigate the static and fatigue behaviors of aluminum hexagonal honeycomb cores subject to in-plane shear loads. The investigation involved carrying out both static and fatigue tests using the single block shear test method. These results are also discussed in relation to the observed damage and failure modes which have been reported for the statically tested specimens and for the fatigue tested specimens at various stages of fatigue life. As well as conducting tests for the more conventional principal cell orientations (L and W), results are also presented for tests carried out at intermediate orientations to investigate the variation of core shear strength with loading orientation. The results are further investigated using explicit non-linear finite element analysis to model the buckling failure mechanisms of the tested cores.     

镁合金蜂窝板隔声性能分析

采用AZ31镁合金板材、AZ31镁合金蜂窝芯、铝合金蜂窝芯制备了镁合金蜂窝板和镁-铝蜂窝板,并测定具有不同结构参数的蜂窝板的隔声性能。预期高隔声镁合金蜂窝板应用于交通运输装备上,将可提高地板或壁板的减振降噪能力,极大改善乘坐的舒适性,提高能源效率。     

Effective properties for sandwich plates with aluminium foil honeycomb core and polymer foam filling – Static and dynamic response

The estimation of static and eigenvibration properties of honeycomb sandwich reinforced by polymeric foam were investigated in the paper. A new “real microstructure” numerical 3D FEM model was proposed for the analysis in which the face materials and the honeycomb were modelled by shell elements, whereas filling foam was modelled by solid elements. Two variants of the honeycomb sandwich panel were considered: with and without polymer foam filling. Static and modal analyses have been performed in both, filled and hollow cases, to observe the effect of core stabilization with foam, particularly for higher natural frequencies. The effective properties of the honeycomb sandwich panels were estimated for both considered cases. Similar calculations have been made for the core materials without top and bottom faces and for the sandwich plate without honeycomb core structure (only polymer foam). One can observe: (1) the substantial increase of the effective elastic properties of the plate; (2) that the eigenvibration properties depend strongly on: the face material, honeycomb core and filling materials properties. The above conclusions are important for design process of structural parts.     

Nomex蜂窝夹层结构真空袋共固化过程蜂窝变形

针对蜂窝夹层板的共固化工艺,以玻璃纤维120斜纹织物/环氧5224体系为面板,以Nomex蜂窝为夹芯材料,研究了蜂窝侧向抗压刚度的影响因素,并通过自行建立的成型过程气压测试装置,分析了芯材内压的影响因素及蜂窝的变形情况。结果表明：对于孔格边长和芯材高度较大的情况,蜂窝侧向抗压能力较小,在真空压力的作用下容易发生变形;芯材内压与芯材内气体的膨胀和预浸料铺层的渗透性直接相关,因此芯材内压受温度制度、预浸料层数和胶膜影响较大;芯材内压对抵抗蜂窝变形起到重要作用,预浸料凝胶前较大的芯材内压有利于抑制蜂窝变形的发生。     

蜂窝夹芯板的热学与力学特性分析

采用细观力学的分析方法, 从蜂窝夹芯复合材料板中选取代表性的细观胞元, 应用周期性条件、三维有限元方法分析了细观胞元的温度场和应力场, 计算得到宏观热学与力学参数, 还考虑了蜂窝芯内部的辐射换热, 讨论了蜂窝芯对夹芯板宏观导热系数、刚度及热膨胀系数的影响。结果表明: 沿厚度方向导热系数与传统算法比较有较大差异, 刚度参数除D₁₂外都可以由传统公式近似, 而计算热膨胀系数时不能忽略芯层热膨胀的影响。      

Fracture test for double cantilever beam of honeycomb sandwich panels

A modified double cantilever beam (DCB) test geometry is designed to investigate the fracture behavior of honeycomb sandwich panels containing embedded artificial pre-crack, and measure the strain energy release rate of the laminate facesheet/honeycomb cores interface. However, in terms of our DCB fracture test, owing to that the pre-crack does not propagate expectedly along the interface of facesheet/honeycomb core, a new fracture mode, namely IKP (initiation of interlaminar delamination, kinking into facesheet and propagation of interlaminar delamination), has been found.     

Fabrication of lightweight structural panels through ultrasonic consolidation

A fundamental investigation of the feasibility of producing lightweight structural panels using ultrasonic consolidation (UC) was undertaken. As a novel solid freeform fabrication technology, UC utilizes both additive ultrasonic joining and subtractive CNC milling to enable the creation of complex aluminum structures with internal geometry at or near room temperature. A series of experiments were performed to understand the issues associated with sandwich structure fabrication using UC, including peel test experiments which evaluated the bond strength for various geometric configurations. The honeycomb lattice was found to offer the best core configuration due to its ability to resist vibration from the sonotrode and provide adequate support for pressure induced by the sonotrode. UC was found to be capable of producing lightweight and stiff structures, including honeycomb and other sandwich panels, without the use of adhesives. An effective manufacturing process plan for fabricating structural panels was developed. A case study was performed on a deck built for the TOROID small satellite spacecraft. The fabricated deck was tested for mechanical integrity. Finally, the cost and benefits of utilizing UC for lightweight structural panels versus traditional fabrication methods are discussed.     

Fabrication of lightweight structural panels through ultrasonic consolidation

A fundamental investigation of the feasibility of producing lightweight structural panels using ultrasonic consolidation (UC) was undertaken. As a novel solid freeform fabrication technology, UC utilizes both additive ultrasonic joining and subtractive CNC milling to enable the creation of complex aluminum structures with internal geometry at or near room temperature. A series of experiments were performed to understand the issues associated with sandwich structure fabrication using UC, including peel test experiments which evaluated the bond strength for various geometric configurations. The honeycomb lattice was found to offer the best core configuration due to its ability to resist vibration from the sonotrode and provide adequate support for pressure induced by the sonotrode. UC was found to be capable of producing lightweight and stiff structures, including honeycomb and other sandwich panels, without the use of adhesives. An effective manufacturing process plan for fabricating structural panels was developed. A case study was performed on a deck built for the TOROID small satellite spacecraft. The fabricated deck was tested for mechanical integrity. Finally, the cost and benefits of utilizing UC for lightweight structural panels versus traditional fabrication methods are discussed.     

Finite element modelling of low velocity impact of composite sandwich panels

This paper outlines a finite element procedure for predicting the behaviour under low velocity impact of sandwich panels consisting of brittle composite skins supported by a ductile core. The modelling of the impact requires a dynamic analysis that can also handle non-linearities caused by large deflections, plastic deformation of the core and in-plane degradation of the composite skins. Metal honeycomb, frequently used as a core material, is anisotropic and requires a non-standard approach in the elasto-plastic part of the analysis. A suitable yield criteria based on experimental observations is proposed. Comparisons of experimental and finite element responses are shown for sandwich panels with carbon fibre skins and aluminium honeycomb cores.     

Kevlar短纤维增韧碳纤维/铝蜂窝夹芯板三点弯曲与面内压缩性能

介绍了碳纤维/铝蜂窝夹芯结构的Kevlar短纤维界面增韧方法。通过三点弯曲实验和面内压缩实验,对比增韧试件与未增韧试件的载荷位移曲线、破坏模式等特征,发现未增韧试件往往先发生界面分层破坏,继而面板和芯体分别发生局部破坏;而增韧试件通常发生整体破坏。实验数据显示,Kevlar短纤维界面增韧可以使碳纤维/铝蜂窝夹芯板的抗弯强度、压缩强度、能量吸收等力学性能分别至少提高14.06%、55.80%和61.53%。对破坏后界面的SEM观测发现:增韧试件并未发生界面脱粘,而是由于芯体撕裂造成面/芯剥离,揭示了Kevlar短纤维的界面增韧机制。对具有Kevlar短纤维界面增韧的碳纤维/铝蜂窝夹芯结构进行有限元建模,并分别对其在三点弯曲和面内压缩载荷下的力学行为进行数值分析,以指导该类夹芯结构的分析与设计。