Mechanical behavior of carbon fiber reinforced polymer composite sandwich panels with 2-D lattice truss cores

Composite sandwich structures with lattice truss cores are attracting more and more attention due to their superior specific strength/stiffness and multi-functional applications. In the present study, the carbon fiber reinforced polymer (CFRP) composite sandwich panels with 2-D lattice truss core are manufactured based on the hot-pressing method using unidirectional carbon/epoxy prepregs. The facesheets are interconnected with lattice truss members by means of that both ends of the lattice truss members are embedded into the facesheets, without the bonding procedure commonly adopted by sandwich panels. The mechanical properties of the 2-D lattice truss sandwich panels are investigated under out-of-plane compression, shear and three-point bending tests. Delamination of the facesheets is observed in shear and bending tests while node failure mode does not occur. The tests demonstrate that delamination of the facesheet is the primary failure mode of this sandwich structure other than the debonding between the facesheets and core for conventional sandwiches.     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.     

Mechanical Response of All-composite Pyramidal Lattice Truss Core Sandwich Structures

The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally.Sandwich structures were fabricated with a hot compression molding method using carbon fiber reinforced composite T700/3234.The out-of-plane compression and shear tests were conducted.Experimental results showed that the all-composite pyramidal lattice truss core sandwich structures were more weight efficient than other metallic lattice truss core sandwich structures.Failure modes revealed that node rupture dominated the mechanical behavior of sandwich structures.     

碳纤维增强金字塔点阵夹芯结构的抗压缩性能

提出了一种碳纤维增强复合材料点阵夹芯结构的一体化成型工艺方法。该方法克服了传统夹芯结构面板与芯子之间因需要二次粘接或焊接的方法所带来弱界面的缺点。将纤维杆两端埋入面板内,使面板与芯子成为一体而不存在明显的界面。对用该方法制备的碳纤维增强金字塔点阵夹芯板进行平压试验,研究发现随着载荷的增加,纤维杆发生弹性屈曲并在中间部位出现断裂。理论分析了点阵夹芯结构平压载荷下的弹性模量和纤维杆极限屈曲载荷。通过与传统夹芯材料相比较发现,这种新型复合材料点阵夹芯结构具有密度低、比强度和比刚度高等优点。      

复合材料点阵夹芯结构平压性能不确定分析与优化

考虑一体化成型工艺制备的复合材料点阵夹芯结构及其不确定性, 采用区间向量实现不确定参数定量化, 建立复合材料点阵夹芯结构平压性能区间分析模型。考虑结构功能状态判断的模糊性, 分别在不考虑设计容差与考虑设计容差情形下, 建立了不确定平压载荷作用下含区间参数模糊可靠性分析与优化模型。研究结果表明: 材料参数及结构参数不确定性, 特别是设计容差对复合材料点阵夹芯结构平压性能影响明显, 因此在工程优化中不仅需要充分考虑材料参数与外部载荷等不确定性, 而且需要充分重视传统不确定设计方法中未计及的设计容差的影响。本研究实现了理论成果与工程应用的有机结合, 为工程领域复合材料点阵夹芯结构平压性能分析与优化提供有效理论方法。     

Hybrid truss concepts for carbon fiber composite pyramidal lattice structures

A novel hybrid truss construction concept is presented that incorporates a second-phase core material into trusses of carbon fiber (CF) composite pyramidal lattice (CPL) structures. Embedded core materials of wood and silicone rubber are selected for trial structures. Hybrid CPL structures were fabricated using a hot press molding approach and out-of-plane compression tests were performed to investigate properties. For prototype wood–core truss CPL, structural efficiencies increased comparing with solid truss CPL, while energy absorption capability was enhanced for rubber–core truss CPL. Employing the hybrid truss construction, the density-specific performance space of CF composite lattice structures can be expanded, and desired functional potential can be realized by judicious selection of core materials while simultaneously retaining structural properties.     

Mechanical Behavior of CFRP Lattice Core Sandwich Bolted Corner Joints

The lattice core sandwich structures have drawn more attention for the integration of load capacity and multifunctional applications. However, the connection of carbon fibers reinforced polymer composite (CFRP) lattice core sandwich structure hinders its application. In this paper, a typical connection of two lattice core sandwich panels, named as corner joint or L-joint, was investigated by experiment and finite element method (FEM). The mechanical behavior and failure mode of the corner joints were discussed. The results showed that the main deformation pattern and failure mode of the lattice core sandwich bolted corner joints structure were the deformation of metal connector and indentation of the face sheet in the bolt holes. The metal connectors played an important role in bolted corner joints structure. In order to save the calculation resource, a continuum model of pyramid lattice core was used to replace the exact structure. The computation results were consistent with experiment, and the maximum error was 19%. The FEM demonstrated the deflection process of the bolted corner joints structure visually. So the simplified FEM can be used for further analysis of the bolted corner joints structure in engineering.     

Improving bending characteristics of FRP sandwich structures with reinforcement webs

Sandwich-structure materials consist of a high-strength skin material and a lightweight core material. The advantages of sandwich structures are known to include excellent mechanical properties and low weight. Sandwich structures are lightweight because of their lightweight core; meanwhile, the skin structure provides mechanical strength and bears bending stress. Carbon-fiber-reinforced plastic (CFRP) is a high-specific-strength and high-specific-rigidity material. In recent years, CFRP sandwich structures have been used in aerospace applications due to their lightweight properties. However, soft-core members such as plastic foam materials have low rigidity and therefore may not exhibit adequate function as a sandwich structure. Webs can make up for the lack of rigidity of soft core members. Consequently, sandwich structures with reinforcement webs offer higher strength than sandwich structures without reinforcement webs. This study focused on reinforcement webs suitable for use in CFRP sandwich structures by evaluating the bending characteristics of CFRP sandwich structures with reinforcement webs. Experimental results demonstrated that CFRP sandwich structures with reinforcement webs had improved bending strength. The effects of the spacing interval of reinforcement webs and the number of layers of carbon fiber fabric on the bending characteristics of CFRP sandwich structures were also examined. Finally, an optimal condition model was created for CFRP sandwich structures with reinforcement webs.     

Pyramidal lattice sandwich structures with hollow composite trusses

Pyramidal lattice sandwich structures with hollow composite trusses were fabricated using a thermal expansion molding approach. Composite lattice structures with three relative densities were fabricated with two fiber architectures and the out-of-plane compression properties were measured and compared. Lattice cores with a fraction of carbon fibers circumferentially wound around the hollow trusses (Variant 2) exhibited superior mechanical properties compared with similar structures comprised of unidirectional fibers (Variant 1). The out-of-plane compressive properties of composite pyramidal lattice structures in Variant 2 were well-matched by analytical predictions. Unusual strain hardening behavior was observed in the plateau region for Variant 2, and the energy absorption capabilities were measured and compared with the similarly constructed silicone rubber–core truss pyramidal lattice structures (Variant 3). The energy absorption per unit mass of selected hollow truss composite lattice structures reported here surpassed that of both hybrid truss counterparts (Variant 3) and hollow truss metallic lattice structures.     

Mechanical behavior of the sandwich structures with carbon fiber-reinforced pyramidal lattice truss core

Sandwich panel construction with carbon fiber-reinforced pyramidal lattice truss is attracting more and more attention due to its superior mechanical properties and multi-functional applications. Pyramidal lattice truss sandwich panels made from carbon fiber reinforced composites materials are manufactured by hot-pressing. The facesheets are interconnected with truss cores, the facesheets and truss cores are manufactured in one manufacturing process without bonding. The buckling and splitting of truss member is observed in the compressive and shear tests and no nodal failure is observed. The predicted results show that the mechanical behavior of the pyramidal lattice truss core sandwich panels depends on the relative density of core and the material properties of truss members.     

High Velocity Impact Response of Composite Lattice Core Sandwich Structures

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.     

Lightweight carbon fibre rods and truss structures

Lightweight carbon fibre rods and truss structures are of growing importance for modern transportation technologies. The struts of such frameworks are commonly designed as fibre-wound CFRP tubes. Here CFRP sandwich rods are an advantageous alternative. They have a lightweight foam core covered by a relative thin layer of composite material. In many real applications, however, the superior mechanical properties of such struts can only be utilized with appropriate load transfer elements. Two types of load transfer elements designed for high tensile and compressive loads with a simple screw connection will be described. The framework structures discussed in this paper refer to framework beams which have, in their simple version, cross-sections of an equilateral triangle. To realise a single point support at the ends of the beam-like truss, the rail struts must converge into a conical structure. The presented structures are connection designs without any metallic elements. An outstanding application of CFRP-trusses, rod connectors, and the mentioned formlocking load transfer elements can be found in the advanced lightweight structure of a recently developed semi-rigid airship, the Zeppelin NT.     

陶瓷棒填充点阵金属夹层结构的制备及抗侵彻实验

为提高轻量化复合装甲的抗侵彻能力,提出了内部填充陶瓷棒并由混杂短切玻璃纤维的环氧树脂封装的点阵金属夹层防护结构。首先,通过弹道冲击实验研究了陶瓷棒填充点阵金属夹层防护结构的抗弹丸侵彻能力;然后,结合失效模式和吸能效率,综合分析了该夹层防护结构的抗侵彻机制。结果表明:陶瓷棒填充点阵金属夹层防护结构的主要失效模式包括点阵金属结构和混杂填充材料的拉伸断裂、陶瓷棒的破裂、面板和背板的局部剪切破坏以及背板的总体弯曲变形。在球形弹丸侵彻过程中,由于点阵金属结构的塑性大变形和剪切扩孔、陶瓷棒和环氧树脂的断裂破坏以及面板的宏观弯曲变形,防护结构的抗侵彻能力得到大幅提高。研究结果可为新型轻质复合装甲的防护设计提供一定参考。      

Cellular Metal Truss Core Sandwich Structures

Closed cell honeycomb core structures are widely used for sandwich panel construction. Periodic open cell tetrahedral truss core structures have recently been shown to possess weight specific properties that compete with those of honeycomb core designs. In contrast to honeycomb, the open cell topologies provide many opportunities for multifunctionality. Past approaches to miniature tetrahedral truss fabrication from metals have utilized investment casting routes. Material choices are then constrained by the need for high fluidity during casting. Strength knockdown due to casting defects has been observed. Here, we utilize a comparatively simple wrought metal based approach. The truss cores are made by deformation shaping hexagonal perforated metal sheets. They are then bonded between thin facesheets using a transient liquid phase approach. When designed to minimize bending of members within the core, a linear dependence of core modulus and strength upon relative density is anticipated. Core relative densities of less than two percent have been obtained. With this approach, low cost truss core structures can be made from a wide variety of heat‐treatable wrought alloys.     

Vibration and Buckling of Truss Core Sandwich Plates on An Elastic Foundation Subjected to Biaxial In-plane Loads

Truss-core sandwich plates are thin-walled structures comprising a truss core and two thin flat sheets. Since no direct analytical solution for the dynamic response of such structures exists, the complex three dimensional (3D) systems are idealized as equivalent 2D homogeneous continuous plates. The macroscopic effective bending and transverse shear stiffness are derived. Two representative core topologies are considered: pyramidal truss core and tetrahedral truss core. The first order shear deformation theory is used to study the flexural vibration of a simply supported sandwich plate. The buckling of the truss core plate on an elastic foundation subjected to biaxial in-plane compressive loads is also investigated. It's found that the lowest buckling loads and modes are dependent on the foundation stiffness as well as bending and transverse shear stiffness of the plate. The geometric parameters of a sandwich plate are optimized to obtain strongest buckling resistance per unit weight. To verify the accuracy of analytical solutions, 3D finite element (FE) models are established, and good agreement is observed between them. It's obvious that the homogenization procedure leads to great savings in computational effort.     

Ultra-light asymmetric photovoltaic sandwich structures

This work evaluated the possibility of using silicon solar cells as load-carrying elements in composite sandwich structures. Such an ultra-light multifunctional structure is a new concept enabling weight, and thus energy, to be saved in high-tech applications such as solar cars, solar planes or satellites. Composite sandwich structures with a weight of ～800 g/m² were developed, based on one 140 μm thick skin made of 0/90° carbon fiber-reinforced plastic (CFRP), one skin made of 130 μm thick mono-crystalline silicon solar cells, thin stress transfer ribbons between the cells, and a 29 kg/m³ honeycomb core. Particular attention was paid to investigating the strength of the solar cells under bending and tensile loads, and studying the influence of sandwich processing on their failure statistics. Two prototype multi-cell modules were produced to validate the concept. The asymmetric sandwich structure showed balanced mechanical strength; i.e. the solar cells, reinforcing ribbons, and 0/90° CFRP skin were each of comparable strength, thus confirming the potential of this concept for producing stiff and ultra-lightweight solar panels.     

面外载荷下含孔复合材料点阵夹层结构弯曲强度数值计算方法

通过实验手段和有限元方法针对含孔碳纤维增强树脂基复合材料(Carbon Fiber Reinforced Polymer,CFRP)点阵夹层结构在面外载荷作用下的失效模式及其影响因素进行了研究。首先通过实验获得了含孔CFRP点阵夹层结构的失效模式,其次建立了其有限元渐进损伤失效分析模型,基于该模型对开孔形状、开孔率及开孔位置对结构弯曲强度的影响进行了探讨。结果表明,当面板较厚时,含孔CFRP点阵夹层结构的主要失效模式为节点脱粘和面板皱曲;有限元计算结果和实验结果吻合较好,极限承载力的误差约为9.1%;当开孔率φ1.3%时,CFRP点阵夹层结构的弯曲承载能力与开孔形状基本无关;当开孔率1.3%≤φ8.5%时,含圆形孔夹层结构的弯曲承载能力较大;当开孔率φ8.5%时,含方孔夹层结构的弯曲承载能力较大;当开孔位于点阵夹层结构的几何中心或边缘时,对弯曲承载能力影响较大。     

碳纤维增强聚合物复合材料方形蜂窝夹层结构水下爆炸动态响应数值模拟

基于ABAQUS有限元仿真软件,建立了不同夹芯相对密度的碳纤维增强聚合物（Carbon Fiber Reinforced Polymer,CFRP）复合材料方形蜂窝夹层结构在水中爆炸冲击波载荷作用下的仿真模型,分析了结构的变形过程、夹芯的压缩特性及结构的失效及破坏情况。数值模拟结果表明,CFRP复合材料蜂窝夹芯压缩量在前面板速度降至与后面板相同时达到最大; CFRP复合材料蜂窝夹芯的最大压缩量随着初始压力的增大呈先缓慢增大后快速增大的趋势,其增大趋势在夹芯接近完全压缩时又趋于缓慢; CFRP复合材料夹层结构失效随夹芯相对密度和初始压力的变化呈现不同的模式,且其防护性能优于等重的层合结构。研究结果可以为复合材料夹层结构在水中冲击波载荷防护中的应用提供参考。      

Fabrication and Testing of Carbon Fiber Reinforced Truss Core Sandwich Panels

Truss core sandwich panels reinforced by carbon fibers were assembled with bonded laminate facesheets and carbon fiber reinforced truss cores.The top and bottom facesheets were interconnected with truss cores.Both ends of the truss cores were embedded into four layers of top and bottom facesheets.The mechanical properties of truss core sandwich panels were then investigated under out-of-plane and in-plane compression loadings to reveal the failure mechanisms of sandwich panels.Experimental results indicated...     

Designing and compression behaviors of ductile hierarchical pyramidal lattice composites

To improve the ductility of lightweight cellular material, hierarchical pyramidal lattice truss composites were designed and manufactured. Rib of the hierarchical pyramidal lattice truss composite is made of glass fiber reinforced woven textile sandwich structure and designed weft-loaded. Flat-wise compression experiments were carried out to explore the strength and deformation mode of the hierarchical pyramidal lattice truss composite. Progressive crushing of the sandwich rib enables the hierarchical lattice composite to have a long stable deformation plateau. Stress of the deformation plateau of the hierarchical lattice composite is rather close to its strength, indicating that the hierarchical lattice composite would have excellent specific energy absorption, even better than aluminum lattice structures. The experiments reveal that the hierarchical structure makes the fiber reinforced lattice composite much more ductile and weight efficient in energy absorption.