Development of Spaceborne Antenna for Circularly Polarized SAR Using Kevlar Honeycomb Core

This paper presents the development of circularly polarized microstrip antenna using Kevlar honeycomb core as the substrates for application of CP-SAR （circularly polarized synthetic aperture radar） which signal propagation is not affected by Faraday rotation effect in the ionosphere, as compared to linearly polarized systems especially at the L-band. The reason why Kevlar honeycomb core is used is because it is suitable for space environment in terms of lightweight and resistant to heat and shock. Measurements of the fabricated antenna were performed to confirm the simulation results. The results show good characteristics of the antennas except the axial ratio. The reason of insufficient axial ratio is assumed as fabrication error of the radiator and microstrip line.

Postprocessor development for ultrasonic cutting of honeycomb core curved surface with a straight blade

When ultrasonically cutting honeycomb core curved parts,the tool face of the straight blade must be along the curved surface’s tangent direction at all times to ensure high-quality machining of the curved surface.However,given that the straight blade is a nonstandard tool,the existing computer-aided manufacturing technology cannot directly realize the above action requirement.To solve this problem,this paper proposed an algorithm for extracting a straight blade real-time tool face vector from a 5-axis milling automatically programmed tool location file,which can realize the tool location point and tool axis vector conversion from the flat end mill to the straight blade.At the same time,for the multi-solution problem of the rotation axis,the dependent axis rotation minimization algorithm was introduced,and the spindle rotation algorithm was proposed for the tool edge orientation problem when the straight blade is used to machine the curved part.Finally,on the basis of the MATLAB platform,the dependent axis rotation minimization algorithm and spindle rotation algorithm were integrated and compiled,and the straight blade ultrasonic cutting honeycomb core postprocessor was then developed.The model of the machine tool and the definition of the straight blade were conducted in the VERICUT simulation software,and the simulation machining of the equivalent entity of the honeycomb core can then be realized.The correctness of the numerical control program generated by the postprocessor was verified by machining and accuracy testing of the two designed features.Observation and analysis of the simulation and experiment indicate that the tool pose is the same under each working condition,and the workpieces obtained by machining also meet the corresponding accuracy requirements.Therefore,the postprocessor developed in this paper can be well adapted to the honeycomb core ultrasonic cutting machine tool and realize high-quality and high-efficient machining of honeycomb core composites.

Effects of inclination angles of disc cutter on machining quality of Nomex honeycomb core in ultrasonic cutting

Ultrasonic cutting with a disc cutter is an advanced machining method for the high-quality processing of Nomex honeycomb core.The machining quality is influenced by ultrasonic cutting parameters,as well as tool orientations,which are determined by the multi-axis machining requirements and the angle control of the cutting system.However,in existing research,the effect of the disc cutter orientation on the machining quality has not been studied in depth,and practical guidance for the use of disc cutters is lacking.In this work,the inclined ultrasonic cutting process with a disc cutter was analyzed,and cutting experiments with different inclination angles were conducted.The theoretical residual height models of the honeycomb core,as a result of the lead and tilt angles,were established and verified with the results obtained by a linear laser displacement sensor.Research shows that the residual height of the honeycomb core,as a result of the tilt angle,is much larger than that as a result of the lead angle.Furthermore,the tearing of the cell wall on the machined surface was observed,and the effects of the ultrasonic vibration,lead angle,and tilt angle on the tear rate and tear length of the cell wall were studied.Experimental results revealed that ultrasonic vibration can effectively decrease the tearing of the cell wall and improve the machining quality.Changes in the tilt angle have less effect than changes in the lead angle on the tearing of the cell wall.The determination of inclination angles should consider the actual processing requirements for the residual height and the machining quality of the cell wall.This study investigates the influence of the inclination angles of a disc cutter on the machining quality of Nomex honeycomb core in ultrasonic cutting and provides guidelines for machining.

Analytical modeling and vibration analysis of fiber reinforced composite hexagon honeycomb sandwich cylindrical-spherical combined shells

This study analyzes and predicts the vibration characteristics of fiberreinforced composite sandwich(FRCS)cylindrical-spherical(CS)combined shells with hexagon honeycomb core(HHC)for the first time based on an analytical model developed,which makes good use of the advantage of the first-order shear deformation theory(FSDT),the multi-segment decomposition technique,the virtual spring technology,the Jacobi-Ritz approach,and the transfer function method.The equivalent material properties of HHC are firstly determined by the modified Gibson’s formula,and the related energy equations are derived for the HHC-FRCS-CS combined shells,from which the fundamental frequencies,the mode shapes,and the forced vibration responses are solved.The current model is verified through the discussion of convergence and comparative analysis with the associated published literature and finite element(FE)results.The effects of geometric parameters of HHC on the dynamic property of the structure are further investigated with the verified model.It reveals that the vibration suppression capability can be greatly enhanced by reducing the ratio of HHC thickness to total thickness and the ratio of wall thickness of honeycomb cell to overall radius,and by increasing the ratio of length of honeycomb cell to overall radius and honeycomb characteristic angle of HHC.

A Study on Transmission Loss Characteristics of Honeycomb Panel for Offshore Structures

Honeycomb panel is consisted of 3 layers that are double-faced sheets and honeycomb-shaped core. It is highly desirable for ship, railway, and aerospace industry. The reason is that honeycomb panel excels in strength and in its weight. However in terms of insulation, it is a little bit insufficient to commonly use sandwich-panel. In this paper, Moor’s theory is used to predict sound transmission loss (STL). The theory is assumed that core layer is homogeneous orthotropic. And to calculate STL, it is evaluated in terms of the symmetric and anti-symmetric panel impedances, and the characteristic impedance of air. After that predicted data are compared with experiment data.

Anti-explosion performance and dynamic response of an innovative multi-layer composite explosion containment vessel

An innovative multi-layer composite explosion containment vessel(CECV)utilizing a sliding steel platealuminum honeycomb-fiber cloth sandwich is put forward to improve the anti-explosion capacity of a conventional single-layer explosion containment vessel(SECV).Firstly,a series of experiments and finite element(FE)simulations of internal explosions are implemented to understand the basic anti-explosion characteristics of a SECV and the rationality of the computational models and methods is verified by the comparison between the experimental results and simulation results.Based on this,the CECV is designed in detail and a variety of FE simulations are carried out to investigate effects of the sandwich structure,the explosive quantity and the laying mode of the fiber cloth on anti-explosion performance and dynamic response of the CECV under internal explosions.Simulation results indicate that the end cover is the critical position for both the SECV and CECV.The maximum pressure of the explosion shock wave and the maximum strain of the CECV can be extremely declined compared to those of the SECV.As a result,the explosive quantity the CECV can sustain is up to 20 times of that the SECV can sustain.Besides,as the explosive quantity increases,the internal pressure of the CECV keeps growing and the plastic deformation and failure of the sandwich structure become more and more severe,yielding plastic strain of the CECV in addition to elastic strain.The results also reveal that the laying angles of the fiber cloth's five layers have an impact on the anti-explosion performance of the CECV.For example,the CECV with fiber cloth layered in 0°/45°/90°/45°/0°mode has the optimal anti-capacity,compared to 0°/0°/0°/0°/0°and 0°/30°/60°/30°/0°modes.Overall,owing to remarkable anti-explosion capacity,this CECV can be regarded as a promising candidate for explosion resistance.

基于静态凝聚法的蜂窝芯轴向变胞元非均匀排布优化

为了有效改善蜂窝结构的强度与刚度,提出利用静态凝聚法实现变胞元的几何参数和非均匀排布同时优化的方法。根据卡氏定理,推导胞元的等效弹性模量和泊松比;沿轴向均匀划分蜂窝芯为若干列子结构,利用有限元法得到子结构的刚度矩阵;采用静态凝聚法建立超单元刚度矩阵,依据超单元节点编号装配获得蜂窝芯的整体刚度矩阵;计算蜂窝芯在剪切载荷作用下的结构变形,并与ANSYS结果比较分析。以子结构的个数以及胞元的夹角、夹板宽与斜壁长之比为设计变量,胞元的等效弹性模量最大和蜂窝芯的变形最小为设计目标,利用改进的粒子群算法进行优化并研究蜂窝芯优化前后的静、动态特性变化规律。结果表明:变胞元非均匀排布优化后,最大的位移、应力、应变均明显减小,且激励频率等于第二阶固有频率时振动最为强烈。研究结论可为蜂窝结构变胞元排布的优化设计提供指导。

复合材料油箱口盖零件的成型工艺研究

文章以某飞机油箱口盖为研究对象,通过材料设计、密封设计、耐火设计、雷电防火设计,对油箱口盖的复合材料成型工艺进行分析。通过工艺试验,合理选用油箱口盖零件原材料,设计铺层结构,优化工艺参数,采用热压罐成型工艺包括下料、铺贴、封装、固化、脱模、修整等具体过程完成复合材料油箱口盖的成型。

高温合金蜂窝芯加工振动分析与试验研究

高温合金蜂窝芯具有薄壁、多孔、面内弱刚性等特点,加工过程中易出现毛刺、撕裂、塌边等缺陷,采用冰固持加工后改善了加工质量,但仍然存在振动幅值较大的问题。针对高温合金蜂窝芯冰固持加工的振动问题,分析并确定冰固持条件下的高温合金蜂窝芯加工振动的主要形式是非谐波非周期性激励下的强迫振动,求解切入角变化导致的强迫振动激励间隔时间的变化规律。通过试验获得切削用量对高温合金蜂窝芯冰固持加工振动的影响规律,试验结果表明,当主轴转速为7000r/min、进给速度为4000mm/min、切削深度为0.5~1.5mm、切削宽度为0.5mm时,振动幅值较小,加工状态稳定,加工质量较好。

固化循环热历程对芳纶纸蜂窝芯材尺寸收缩的影响

在芳纶纸蜂窝夹芯结构的修理过程中,需对蜂窝零件进行多次加热固化,这可能会导致蜂窝芯材的尺寸收缩,从而导致零部件产生凹陷。因此,有必要研究固化循环热历程对芳纶纸蜂窝芯材尺寸收缩的影响规律,为飞机复合材料芳纶纸蜂窝夹芯结构的修理填补方案提供参考依据。研究了不同修理固化温度及固化循环次数对国产及国外几种芳纶纸蜂窝芯材尺寸收缩的影响。通过对每次固化后的蜂窝芯材尺寸进行测试,探究蜂窝芯材的收缩规律。结果表明,经中高温(121℃)和高温(177℃)下修理固化循环多次后,国产与国外的蜂窝芯材的尺寸收缩程度均明显高于经中低温(93℃)和低温(66℃)固化加热循环后的收缩程度;经5次修理加热循环后,几种蜂窝芯材的尺寸收缩程度均明显高于第1次修理固化后的收缩程度;对于相同厚度的国产和国外蜂窝芯材,经多次固化循环后,国产蜂窝芯材的收缩程度更低。总体而言,芳纶纸蜂窝芯材在常见修理温度下多次热历程循环后,蜂窝芯材加热后的收缩程度较小,具有良好的尺寸稳定性,能够较好地满足蜂窝夹芯结构多次修理填补的需求。

超轻型微球介电吸波材料性能及应用研究

为了实现吸波材料轻量化,本文通过设计材料微观结构及合成方法,将碳材料的介电特性与空心结构的低密度特性相结合,开发出一种超轻型材料,制备的碳空心球(C@air)材料具有优良的吸波性能。基于该材料分别制备吸波板材及可用于隐身飞机机翼前缘的吸波蜂窝芯,并对其进行电磁仿真及雷达反射截面积(RCS)测试,吸波蜂窝芯在同向水平极化下达到-32.3 dB,同向垂直极化下达到-27.2 dB。验证了该材料具有优秀的吸波性能及应用效果,为吸波材料的设计与应用提供思路。

地下车库蜂巢芯空心楼盖施工技术

结合泊里镇驻地改造施工现场情况,论述了蜂巢芯空心楼盖技术在地下车库施工过程中的应用。通过对蜂巢芯空心楼盖的施工技术要点描述,从降低工程造价;方便施工、减少模板;有效缩短施工工期;有效减少混凝土收缩裂缝;加强防水、防火性能及保温、隔声性能和抗震性能;相比一次性膜壳,蜂巢芯无脱落风险等方面分析地下车库顶板采用蜂巢芯空心楼盖的优势。

蜂巢芯空心楼盖的有限元分析

运用ABAQUS有限元软件,分别建立承受相同竖向均布荷载作用且跨度相同的蜂巢芯空心楼盖、井字楼盖、密肋楼盖三种有限元模型,并进行受力分析,得到三种不同类型楼盖在相同状态下的应力云图和挠度云图。结果表明,当楼盖跨度较大时,在竖向均布荷载和结构自重条件基本相同的条件下,相对于常见的井字楼盖和密肋楼盖,蜂巢芯空心楼盖受力更加均匀合理;相对于密肋楼盖,蜂巢芯空心楼盖具有更大的抗弯刚度;相对于井字楼盖,在建筑层高相同的情况下,蜂巢芯空心楼盖可以提供更大的使用空间,在楼层净高相同的情况下,蜂巢芯空心楼盖可以使层高降低,从而节约工程造价。

基于五轴高速铣削数控机床的航空用芳纶纸蜂窝加工工艺及试验研究

芳纶纸蜂窝是航空航天领域常用的减重复合材料,由韧性较大的芳纶纤维和含量较高的脆性树脂固化而成,固化成型后较难加工。为了满足某型号加工精度要求,根据该材料的组成成分和结构特点,结合需加工零件的形状尺寸,用五轴高速铣削数控机床进行加工工艺试验,通过单因素试验法,研究磨削速度、进给速度和刀具前倾角对其表面质量及形面精度的影响。试验结果表明:不同工艺参数对该型号芳纶纸蜂窝表面质量及形面精度差异较大。该型号蜂窝零件加工切削角速度最优参数为12000 rpm,参数可选区间为11000 rpm~13000 rpm之间;加工进给速度最优参数为1000 mm/min,为保证加工质量,参数可选区间为1000 mm/min~1200 mm/min之间;前倾角可选参数区间为10~30之间。

夹层结构斜削区蜂窝滑移机理及改善研究

基于蜂窝夹层结构固化原理分析和蜂窝在180℃高温下的力学性能分析,构建了蜂窝滑移受力模型,确定了影响蜂窝滑移的4个关键因素,分别为蜂窝侧向抗压能力、层间摩擦系数、蜂窝芯边缘倒角和固化压差。针对关键因素进一步分析,表明分别影响4个关键因素的子因素及其影响作用。同时提出了抑制蜂窝滑移的有效措施:1)最靠近蜂窝芯的铺层(推荐0/90°织物)延伸至零件边缘以便进行外力(防滑带、玻璃纤维等)拴系;2)工艺手段(浸胶法、胶膜法、隔膜法等稳定化方法)提高蜂窝侧向抗压能力。

卫星承力筒复合材料结构的优化设计

应用 JIFEX软件对大型通信卫星主承力结构——中心承力筒的复合材料结构进行优化设计。在优化设计中考虑了固有频率和屈曲稳定性的约束条件 ,使用了多种类型的设计变量 ,对蜂窝夹芯材料采用了一种离散材料变量连续化处理方法。进行了多种方案的优化设计和比较 。

复合材料蜂窝夹芯板低速冲击损伤研究

本文对蜂窝夹芯板试件进行了低速冲击试验，然后用Ｘ光技术、热揭层技术、断面显微技术和外观检测等对冲击后板的损伤进行了较为全面的研究，讨论了表面布的作用，分析了外观损伤、面板损伤、蜂窝损伤等与冲击能量的关系。

蜂窝芯层等效参数研究综述

蜂窝芯层等效参数的相关研究是蜂窝夹层结构设计和计算的重要基础,深入研究蜂窝芯层的力学特性具有重要的应用意义。对蜂窝芯层等效参数的研究进行了综述,首先介绍蜂窝芯层面内等效参数的研究进展,主要基于经典梁理论和均匀化理论,从线性和非线性两方面展开综述。然后介绍芯层面外等效参数研究,围绕各种计算方法、等效力学模型、线性和非线性等效,以及各自的优缺点等问题进行总结和评述。此外还对一些解析公式的精度和适用范围进行了比较,以方便工程应用。最后,指出了这一领域需要进一步研究的若干问题。

直刃尖刀超声辅助切割Nomex蜂窝芯切削力分析

以直刃尖刀超声辅助切割Nomex蜂窝芯的简化模型为基础,建立基于脆性断裂力学理论的超声辅助切削动态力模型,并分情况讨论了刀具与材料间的相对运动关系。分析指出在不同振幅条件下,材料的切割破坏存在断续和连续两种形式,进而推导了切割过程中的切削力的理论公式。其中超声振幅、刀具前倾角、进给速度和超声频率等参数对材料切削力大小均有影响。在理论分析的基础上,开展了超声辅助切割Nomex蜂窝芯复合材料实验。试验结果表明,进给方向的超声振幅和刀具前倾角对切削力的影响较大:当进给方向的超声振幅从0到15μm变化、刀具前倾角从15°到45°变化时,切削力均可降低70%~80%;进给速度和超声频率对于切削力影响较小:当进给速度从500到6000 mm/min变化12倍时,切削力仅变为1.5倍;超声频率35 k Hz与15 k Hz相比,切削力降低10%~30%。试验结果与理论分析结论一致。

六边形蜂窝芯异面类静态压缩力学行为的仿真分析

目的研究六边形蜂窝芯材异面类静态压缩载荷的数值模拟方法及相关力学行为。方法基于蜂窝单元阵列的方法,构筑了单双壁厚六边形蜂窝芯材异面类静态压缩有限元数值计算模型和分析方法。结果借助于该模拟方法,分析计算了不同结构参数条件下单双壁厚六边形蜂窝芯材的异面变形模式、变形曲线和类静态峰应力值,并绘制了相应的图、压缩力位移曲线和数据表格。结论将计算结果与现有的实验和理论计算结果作对比分析可知,计算结果与已有结果吻合较好,证明了所提出的有限元分析方法的可靠性。