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.     

含面芯界面缺陷的蜂窝夹芯板侧向压缩破坏模式

为了对含面芯层间脱胶缺陷的蜂窝夹芯板在侧向压缩载荷作用下的典型破坏模式进行数值预报, 建立了基于蔡-希尔破坏准则和粘结模型的计算模型。该计算模型是建立在对蜂窝夹芯板的双悬臂梁(DCB)和单臂梁(SLB) 试验中所发现的一种新的破坏模式的分析基础之上的。对蜂窝夹芯板的侧向压缩破坏行为的数值预报中, 发现一种新的破坏模式: 位于脱胶区域的面板首先发生局部屈曲失稳, 随后面板内部靠近芯子的45°/0°层间出现分层, 与此同时最靠近芯子的45°铺层发生断裂, 伴随着45°/0°层间分层的扩展, 面板发展成为对称性整体屈曲失稳。与侧向压缩试验测试结果对比发现, 计算模型模拟中所预报的破坏模式在实验测试中也得到了很好的验证。      

Shock loading response of sandwich panels with 3-D woven E-glass composite skins and stitched foam core

Sandwich composite are used in numerous structural applications, with demonstrated weight savings over conventional metals and solid composite materials. The increasing use of sandwich composites in defense structures, particularly those which may be exposed to shock loading, demands for a thorough understanding of their response to suc highly transient loadings. In order to fully utilize their potential in such extreme conditions, design optimization of the skin and core materials are desirable. The present study is performed for a novel type of sandwich material, TRANSONITE^® made by pultrusion of 3-D woven 3WEAVE^® E-glass fiber composites skin preforms integrally stitched to polyisocyanurate TRYMER^TM 200L foam core. The effect of core stitching density on the transient response of three simply supported sandwich panels loaded in a shock tube is experimentally studied in this work. The experimental program is focused on recording dynamic transient response by high-speed camera and post-mortem evaluation of imparted damage. The obtained experimental results reveal new important features of the transient deformation, damage initiation and progression and final failure of sandwich composites with unstitched and stitched foam cores. The theoretical study includes full 3-D dynamic transient analysis of displacement, strain and stress fields under experimentally recorded surface shock pressure, performed with the use of 3-D MOSAIC analysis approach. The obtained theoretical and experimental results for the transient central deflections in unstitched and two stitched foam core sandwiches are mutually compared. The comparison results reveal large discrepancies in the case of unstitched sandwich, much smaller discrepancies in the case of intermediate stitching density, and excellent agreement between theoretical and experimental results for the sandwich with the highest stitching density. The general conclusion is that further comprehensive experimental and theoretical studies are required in order to get a thorough understanding of a very complex behavior of composite sandwiches under shock wave loading.     

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.     

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。      

Impact response of integrated hollow core sandwich composite panels

This paper deals with an innovative integrated hollow (space) E-glass/epoxy core sandwich composite construction that possesses several multi-functional benefits in addition to the providing lightweight and bending stiffness advantages. In comparison with traditional foam and honeycomb cores, the integrated space core provides a means to route wires/rods, embed electronic assemblies, and store fuel and fire-retardant foam, among other conceivable benefits. In the current work, the low-velocity impact (LVI) response of innovative integrated sandwich core composites was investigated. Three thicknesses of integrated and functionality-embedded E-glass/epoxy sandwich cores were considered in this study—including 6, 9 and 17 mm. The low-velocity impact results indicated that the hollow and functionality-embedded integrated core suffered a localized damage state limited to a system of core members in the vicinity of the impact. The peak forces attained under static compression and LVI were in accordance with Euler's column buckling equation. Stacking of the core was an effective way of improving functionality and limiting the LVI damage in the sandwich plate. The functionality-embedded cores provided enhanced LVI resistance due to energy additional energy absorption mechanisms.     

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.     

Flexural performance of sandwich panels comprising polyurethane core and GFRP skins and ribs of various configurations

This study explored the feasibility of fabrication and flexural performance of panels composed of low-density polyurethane foam core sandwiched between two GFRP skins. A comprehensive material testing program was first carried out on the constituents. Large scale panels with nominal dimensions of 2500 × 660 × 80 mm were then tested in one-way bending under a simulated uniform load. Various configurations of internal and exterior GFRP ribs connecting the two skins were explored and compared to a panel without ribs. The study showed that, by integrating the ribs, strength and stiffness of the panels increased substantially, by 44–140%, depending on the configuration of the ribs. The maximum gain in strength was equivalent to the effect of doubling the core density in a panel without ribs. Shear deformation of the core contributed over 50% of mid-span deflection in the panel without ribs. By adding ribs, flexure became more dominant and shear deformations of the ribs contributed only 15–20% of the total deflection. Simple analytical expressions have been proposed, and captured these effects reasonably accurately. It was shown that ultimate strengths of the panels were equivalent to those of similar size reinforced concrete panels with moderate to heavy steel reinforcement ratios of 0.6–2.0%, but sandwich panels were 9–14 times lighter in weight.     

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。     

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.     

Fabrication and mechanical properties of lightweight ZrO2 ceramic corrugated core sandwich panels

ZrO₂ ceramic corrugated core sandwich panels were fabricated using gelcasting technique and pressureless sintering. The nominal density of the as-prepared ZrO₂ ceramic corrugated panel was only 2.4 g/cm³ (42.9% of bulk ceramic). Lightweight was realized through this sandwich structured design. The three-point bending strength was measured to be 298.4 MPa. And the specific bending strength was as high as 124.3 (114% higher than bulk ceramic). The compressive strength was 20.2 MPa. High strength was also realized through this sandwich structured design. The stress distribution during three-point bending and compression testing was finally simulated using finite element analysis (FEA) method.     

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.     

Insight into the shear behaviour of composite sandwich panels with foam core

While sandwich construction offers well-known advantages for high stiffness with light weight, the problem of designing the sandwich structure to withstand shear loading remains an important problem. This problem is more difficult with lower stiffness foam cores under high shear loading because the core is typically the weakest component of the structure and is the first one to fail in shear under the assuming of perfect contact between the skin and the foam core. In the present study, the shear response of the composite sandwich panels with Polyvinylchloride (PVC) foam core was investigated. The PVC H100 foam core is sandwiched between Glass Fiber Reinforced Polymer (GFRP) skins using epoxy resin to build a high performance sandwich panel to be investigated. Experiments have been carried out to characterise the mechanical response of the constituent materials under tension, compression and shear loading. Static shear tests for the sandwich panel reveal that the main failure mode is the delamination between the skin and the core rather than shearing the core itself due to the considerable value of the shear strength of the PVC foam. The Finite Element Analysis (FEA) of the sandwich structure shows that shear response and failure mode can be predicted, but that accurate predictions require a consideration of the non-linear response of the foam core. The results have a direct application in predicting the ability of the sandwich structure to withstand the shear loading.     

Impact behavior and energy absorption of paper honeycomb sandwich panels

Dynamic cushioning tests were conducted by free drop and shock absorption principle. The effect of paper honeycomb structure factors on the impact behavior was analyzed. Results of many experiments show that the dynamic impact curve of paper honeycomb sandwich panel is concave and upward; the thickness and length of honeycomb cell-wall have a great effect on its cushioning properties; increasing the relative density of paper honeycomb can improve the energy absorption ability of the sandwich panels; the thickness of paper honeycomb core has an up and down fluctuant effect on the cushioning properties; with the increase of the thickness of paper honeycomb core, the effect dies down; flexible corrugated paperboard as liners can improve the compression resistance and cushioning properties of paper honeycombs. The research results can be used to optimize the structure design of paper honeycomb sandwich panel and material selection for packaging design.     

Impact response of fiber metal laminate sandwich composite structure with polypropylene honeycomb core

Fiber metal laminates (FMLs) were used as skin on polypropylene honeycomb core to form a sandwich structure. Impact response was measured by conducting a series of low-velocity impact test. Impact force and the force time history were recorded and analyzed. It was found that the maximum impact load increased up to a threshold value at which it plateaus while the energy absorption in the structure increased with increasing impact energy. Post-impact optical image showed a change in damage area with increasing impact energy. The impact damage threshold energy for the sandwich structure was clearly shown in the range of impact energy between 7.84 J and 11.76 J where damages including delamination of the skins and global bending of the structure were observed.     

嵌锁式碳纤维/树脂基复合材料方形蜂窝夹芯结构的力学性能及损伤失效

设计并采用嵌锁组装工艺制备了碳纤维/树脂基复合材料方形蜂窝夹芯结构,开展了面外平压性能和三点弯曲性能试验研究,获得了夹芯结构在平压载荷作用下的破坏模式,分析了其损伤失效机制及吸能特性,讨论了在三点弯曲载荷作用下面板质量非对称性和槽口方向对夹芯梁的破坏模式及承载能力的影响.研究结果表明嵌锁式碳纤维/树脂基复合材料方形蜂窝...     

Prediction of inter-laminar stresses in composite honeycomb sandwich panels under mechanical loading using Variational Asymptotic Method

This work focuses on the formulation of an asymptotically correct theory for symmetric composite honeycomb sandwich plate structures. In these panels, transverse stresses tremendously influence design. The conventional 2-D finite elements cannot predict the thickness-wise distributions of transverse shear or normal stresses and 3-D displacements. Unfortunately, the use of the more accurate three-dimensional finite elements is computationally prohibitive. The development of the present theory is based on the Variational Asymptotic Method (VAM). Its unique features are the identification and utilization of additional small parameters associated with the anisotropy and non-homogeneity of composite sandwich plate structures. These parameters are ratios of smallness of the thickness of both facial layers to that of the core and smallness of 3-D stiffness coefficients of the core to that of the face sheets. Finally, anisotropy in the core and face sheets is addressed by the small parameters within the 3-D stiffness matrices. Numerical results are illustrated for several sample problems. The 3-D responses recovered using VAM-based model are obtained in a much more computationally efficient manner than, and are in agreement with, those of available 3-D elasticity solutions and 3-D FE solutions of MSC NASTRAN.     

Impact tolerant and healable aluminum millitube reinforced shape memory polymer composite sandwich core

In order to improve impact tolerance and energy absorption of sandwich panel under impact loading, a new aluminum hollow tube reinforced shape memory polymer (AHTR-SMP) composite sandwich core is designed and fabricated. Physical/mechanical properties were examined through a variety of tests, including axial compression, three-point bending, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and shape recovery tests. In order to characterize its dynamic performances, low velocity impact test was conducted. According to the tests results, this new AHTR-SMP core demonstrated considerable impact tolerance and damage healing functionality, and may be considered as a promising option for critical structural applications featured by tolerating repeated impacts.     

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.