Stress and buckling analysis of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets

In this paper,the stresses and buckling behaviors of a thick-walled mi-cro sandwich panel with a flexible foam core and carbon nanotube reinforced composite(CNTRC)face sheets are considered based on the high-order shear deformation theory(HSDT)and the modified couple stress theory(MCST).The governing equations of equi-librium are obtained based on the total potential energy principle.The effects of various parameters such as the aspect ratio,elastic foundation,temperature changes,and volume fraction of the canbon nanotubes(CNTs)on the critical buckling loads,normal stress,shear stress,and deflection of the thick-walled micro cylindrical sandwich panel consider-ing different distributions of CNTs are examined.The results are compared and validated with other studies,and showing an excellent compatibility.CNTs have become very use-ful and common candidates in sandwich structures,and they have been extensively used in many applications including nanotechnology,aerospace,and micro-structures.This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

Experimental study of partially-cured Z-pins reinforced foam core composites:K-Cor sandwich structures

This paper presents an experimental study of a novel K-Cor sandwich structure rein- forced with partially-cured Z-pins. The influence of pultrusion processing parameters on Z-pins characteristics was studied and the effect of Z-pins on mechanical properties was disclosed. Differential scanning calorimetry （DSC） and optical microscopy （OM） methods were employed to determine the curing degree of as-prepared Z-pins and observe the implanted Z-pins in the K-Cor structure. These partially-cured Z-pins were treated with a stronger bonding link between face sheets and the foam core by means of a hot-press process, thereby decreasing burrs and cracking defects when the Z-pins were implanted into the Rohacell foam core. The results of the out-of-plane tensile tests and the climbing drum peel （CDP） tests showed that K-Cor structures exhibited superior mechanical performance as compared to X-Cor and blank foam core. The observed results of failure modes revealed that an effective bonding link between the foam core and face sheets that was provided from partially-cured Z-pins contributed to the enhanced mechan- ical performances of K-Cor sandwich structures.

Fabrication of Open-cell Al Foam Core Sandwich by Vibration Aided Liquid Phase Bonding Method and Its Mechanical Properties

The open-cell Al foam core sandwiches（AFCSs） were successfully fabricated by using a specially designed Zn-Al-Cu based filler alloy via vibration aided liquid phase bonding method.The effects of the vibration on the bonding seam were investigated and the bonding strength between Al foam core and solid Al alloy face sheet was tested by shearing tests.The results show that vibration can significantly improve the quality of the bonding and the shearing strength of the bonding seam,which implies that this joining method has a good potential in practical applications.

Vibration and Buckling Analyses of Sandwich Plates Containing Functionally Graded Metal Foam Core

In the present work,free vibration and buckling analyses of sandwich plates with various functionally graded foam cores are carried out.Foam cores are assumed to be made of metal,and three different configurations of the porous distribution in the core layer are taken into consideration.To carry out a comparative study between the distributions of pores in the core foam,the mass of foam in all three cases is kept the same.The vibration and buckling behaviors of skew plates are also analyzed as a part of the current investigation.The principle of minimization of potential energy and Hamilton’s principle are used for the derivation of the governing equations,while a C-0 finite element-based higher-order zigzag formulation is developed to solve the free vibration and buckling problems.The influences of gradation laws,boundary conditions,skew angle and geometry of plates are studied in detail for the dynamic and stability characteristics.It is found that both the non-dimensional natural frequency and buckling load decrease with the increase in the thickness of the metal foam cores,while they show an increasing trend as the skew angle of the plate increases.

In Situ Growth of 3D Hierarchical ZnO@Ni_xCo_(1-x)(OH)_y Core/Shell Nanowire/Nanosheet Arrays on Ni Foam for High-Performance Aqueous Hybrid Supercapacitors

In this study, we designed and synthesized a novel battery-type electrode featuring three-dimensional(3D) hierarchical ZnO@Ni_xCo_(1-x)(OH)_y core/shell nanowire/nanosheet arrays arranged on Nifoam substrate via a two-step protocol including a wet chemical process followed by electro-deposition. We then characterized its composition, structure and surface morphology by X-ray diff raction, energy-dispersive X-ray spectrometry(EDS), X-ray photoelectron spectroscopy, scanning electron microscopy(SEM), transmission electron microscopy, EDS elemental mapping. Our electrochemical measurements show that the ZnO@Ni_(0.67)Co_(0.33)(OH)_y electrode material exhibited a noticeably high specific capacity of as much as 255(mA ·h)/g at 1 A/g. Additionally, it demonstrated a superior rate capability, as well as an excellent cycling stability with 81.6% capacity retention over 2000 cycles at 5 A/g. This sample delivered a high energy density of 64 W·h/kg and a power density of 250 W/kg at a current density of 1 A/g. With such remarkable electrochemical properties, we expect the 3D hierarchical hybrid electrode material presented in this work to have promising applications for the next generation of energy storage systems.

Porous Cobalt Oxide@Layered Double Hydroxide Core-Shell Architectures on Nickel Foam as Electrode for Supercapacitor

The high performance of an electrode relies largely on a scrupulous design of nanoarchitectures and smart hybridization of electroactive materials.A porous core-shell architecture in which one-dimensional cobalt oxide(Co_3O_4)nanowire cores are grown on nickel foam prior to the growth of layered double hydroxide(LDH)shells is fabricated.Hydrothermal precipitation and thermal treatment result in homogeneous forests of 70-nm diameter Co_3O_4 nanowire,which are wrapped in LDH-nanosheet-built porous covers through a liquid phase deposition method.Due to the unique core-shell architecture and the synergetic effects of Co_3O_4and NiAl-LDH,the obtained Co_3O_4@LDH electrode exhibits a capacitance of 1 133.3F/g at a current density of 2A/g and 688.8F/g at 20A/g(5.3F/cm^(2 )at 9.4mA/cm^(2 )and 3.2F/cm^(2 )at 94mA/cm^2),which are better than those of the individual Co_3O_4nanowire.Moreover,the electrode shows excellent cycling performance with a retention rate of 90.4%after 3 000cycles at a current density of 20A/g.

Mathematical modeling for dynamic stability of sandwich beam with variable mechanical properties of core

The paper is devoted to mathematical modelling of static and dynamic stability of a simply supported three-layered beam with a metal foam core. Mechanical properties of the core vary along the vertical direction. The field of displacements is for- mulated using the classical broken line hypothesis and the proposed nonlinear hypothesis that generalizes the classical one. Using both hypotheses, the strains are determined as well as the stresses of each layer. The kinetic energy, the elastic strain energy, and the work of load are also determined. The system of equations of motion is derived using Hamilton＇s principle. Finally, the system of three equations is reduced to one equation of motion, in particular, the Mathieu equation. The Bubnov-Galerkin method is used to solve the system of equations of motion, and the Runge-Kutta method is used to solve the second-order differential equation. Numerical calculations are done for the chosen family of beams. The critical loads, unstable regions, angular frequencies of the beam, and the static and dynamic equilibrium paths are calculated analytically and verified numerically. The results of this study are presented in the forms of figures and tables.

泡沫芯材开槽打孔方式对风电叶片轻量化的影响

风电叶片的大型化对叶片质量及成本提出更高的要求,在保证叶片质量的同时降低叶片重量,成为近年来叶片行业降本增效的重要方向。对腹板平板及壳体轮廓板泡沫芯材采用不同的开槽打孔方式,并对其灌注固化后吸胶量、密度及剪切性能进行计算测试。研究发现,增大十字开槽、打孔的间距及采用一字开槽、打孔方式可有效降低芯材吸胶量及密度,G13方向芯材剪切性能均满足要求,G23方向一字槽轮廓板剪切性能较弱;腹板平板主要受到点阵增强柱的影响,40 mm×40 mm双面十字浅槽及打孔试样吸胶后密度最低,减重最多,壳体轮廓板受到点阵增强及板格结构的交互作用,40 mm×40 mm十字深槽间距、20 mm×20 mm孔间距试样剪切性能符合要求,减重效果较好。

芯材双向开槽工艺对PET泡沫三明治结构弯曲性能的影响

借助实验结合仿真分析的研究方法,深入探究了芯材表面双向开槽对PET泡沫三明治结构弯曲性能的影响,采用熵权法-优劣解距离法对16种开槽工况进行了详细分析。结果表明,在三点弯曲实验中,PET泡沫芯材的压缩应变主要集中在中间压头附近,永久塑性变形出现在铝合金面板和胶层处,未在各组分材料中发现明显的失效行为。随着芯材开槽体积的增大,结构的刚度、峰值载荷和总能量吸收均增大,结构的比吸能减小;开槽深度、宽度、间距会对这些性能指标产生显著影响;胶粘剂在连接芯材和面板的同时,增强了结构的抗弯曲性能。最后,基于熵权法-优劣解距离法,确定了芯材表面最优的开槽方案。

穿孔泡沫夹层复合材料低速冲击性能试验研究

针对普通泡沫夹层复合材料层间性能较弱的问题,提出在泡沫上预先打孔的方法,在泡沫芯材中形成胶钉从而提高泡沫夹层材料的力学性能,并对穿孔泡沫夹层复合材料的低速冲击性能进行了研究。通过手糊和真空辅助成形工艺制备穿孔泡沫夹层复合材料试验件,对其进行不同能量的低速冲击试验,记录接触力、冲头位移和能量吸收率等力学响应,并采用目视检测和超声C扫无损检测两种方法确定冲击损伤的范围,探究胶钉密度、打孔深度和泡沫槽宽等变量对穿孔泡沫夹层复合材料低速冲击阻抗性能的影响。试验结果表明,随着冲击能量的增加,最大接触力、最大冲头位移和残余变形均增加,凹坑深度和内部损伤面积也增大,同时结构的能量吸收率也有所提高;适当地增加胶钉密度和泡沫槽宽能提高穿孔泡沫夹层材料的低速冲击阻抗性能,而泡沫孔深度对其冲击性能的影响较小。

高速冲击载荷下梯度金属泡沫夹芯梁的动态响应与失效

采用泡沫弹冲击加载实验对梯度金属泡沫夹芯梁结构开展了不同冲击强度下的动态响应和失效研究,分析了由三种不同密度泡沫铝组成的等面密度的五种不同梯度的夹芯结构在夹支边界条件下的抗高速冲击性能,结合三点弯曲实验,研究梯度效应对夹芯结构抗冲击性能的影响。研究表明:密度梯度对结构的失效过程和失效模式有着明显的影响,且夹芯梁结构的初始失效模式对结构整体响应和主要的能量吸收机制起着主导作用;当冲击条件不足以使得均质芯材发生压缩时,均质及负梯度夹芯结构初始失效模式为整体弯曲变形,低强度芯层位于前两层的梯度结构随着冲击强度的变化出现不同程度的局部芯层压缩;当冲击强度较低时,梯度结构通过丰富的局部失效表现出明显优于均质结构的抗冲击变形能力;当冲击强度大于临界值时,均质结构具有更好的抗冲击变形能力。通过合理地设计密度梯度实现逐层压缩吸能,能够有效的提升防护结构的抗冲击性能。

内嵌聚甲基丙烯酰亚胺泡沫的碳纤维增强复合材料蜂窝夹层结构水中抗爆试验研究

为了分析新型内嵌聚甲基丙烯酰亚胺(Polymethacrylimide,PMI)泡沫的碳纤维增强复合材料蜂窝夹层结构的水中抗爆性能,开展了水中爆炸作用下结构抗爆性能试验研究,对比了均质钢板、纯蜂窝夹芯夹层结构以及内嵌两种不同密度PMI泡沫蜂窝夹芯夹层结构的水中抗爆性能,分析了结构变形与破坏模式、结构表面压力特性以及结构后面板变形情况。结果表明,内嵌泡沫能够有效提升夹层结构的水中抗爆性能。研究结果可以为水中抗爆防护结构的轻量化设计及优化提供参考。

双曲率泡沫夹层复合材料异形件成型工艺研究

一体化结构的PMI泡沫夹层结构异形蒙皮组件是飞机轻量化设计和复合材料可设计性的创新应用,具有比强度高、比模量高、结构效率高的特点。以PMI泡沫夹层结构双曲率异形件为研究对象,介绍了其结构特征及选材方案,分析了不同模具方案的特点。针对制件成型后的脱模方案、泡沫芯拼接质量、闭角区域传压及成型质量等问题,制定了一套高效、高可靠性的成型方案。结果表明:分块芯模的设计方案,可有效解决异形零件的成型与脱模问题;热压工艺可以提高预浸料层间压实效果,避免泡沫芯架桥;发泡胶拼接工艺可解决闭角区域泡沫芯成形难题;硅橡胶芯模可保证压力均匀传递,避免辅助材料架桥,提高成型质量。

全高度PMI泡沫夹芯复合材料组件制造技术研究

某型民用支线飞机舵面尖部选用全高度泡沫夹层,以实现舵面结构和操纵功能,提出了PMI泡沫芯材不同铣切方法,验证了无铣切夹具加工双曲面全高度PMI泡沫芯材的铣切技术,探讨了共胶接和共固化制造技术特点,使用共胶接成型增加了骨架组件修整操作,实现了制造过程可视化。以组件角分线为分模面,采用“软硬合模”工装,确定了“预浸料+airpad+预浸料+airpad”的“软模”压力垫形式,实现固化压力有效传递。

灌注无机保温芯材的烧结复合保温砌块制备关键技术研究

文中研究了一种灌注保温芯材的城市污泥烧结复合保温砌块。混合料的塑性指数和热值是制备烧结保温砌块两个重要技术指标,按照城市污泥︰页岩︰煤矸石为10︰70︰20的比例制得的混合料塑性指数为12.1,干燥敏感性系数为0.6,烧制的保温砌块表面平整,无过烧、欠火等质量问题。掺入适量的速凝剂(SQ)或SAC可制备出稳定不塌模的保温芯材,其干密度为197kg/m^(3)、抗压强度为0.35MPa、导热系数为0.0703W/(m·K)。经孔型孔结构设计,综合利用孔洞内空气与保温芯材对热流的阻隔作用,提高复合保温砌块的保温性能。制备的城市污泥烧结复合保温砌块的干密度为1089kg/m^(3)、抗压强度为5.9MPa、传热系数K值为1.27W/(m^(2)·K),可应用于建筑外墙自保温围护结构体系。

核壳乳胶的制备及其对阻尼涂料性能的影响研究

本研究采用预乳化半连续滴加的方式,以甲基丙烯酸甲酯、丙烯酸丁酯、苯乙烯为主要单体,聚合出性能优异的核壳结构水性丙烯酸乳胶。探究了乳胶结构、交联剂及链转移剂对乳胶及水性阻尼涂料性能的影响。根据实际应用结果,进行乳胶配方优化,得出水性阻尼涂料用耐高温烘烤高阻尼乳胶优化配方。最终结果表明:当核壳比为3∶7,玻璃化转变温度分别为20℃与-10℃时,可以形成稳定的核壳结构。相比于普通结构乳胶,以该乳胶为主要原料制备的水性阻尼涂料,高温烘烤表面平整,有不起泡、无裂纹的特点,且阻尼值高。

钢边框发泡水泥复合屋面板承载力影响因素研究

为了解钢边框发泡水泥复合屋面板承载能力影响因素,对工业厂房既有钢边框发泡水泥复合屋面板的构造、性能等进行了检测试验,分析了多种因素与板材承载能力的关系。结果表明:芯材的厚度、干密度及强度与板材承载力相关性较大。可为后续发泡水泥复合屋面板检测应用提供一定参考依据。

全厚度缝合复合材料泡沫芯夹层结构力学性能研究与损伤容限评定

探索了全厚度缝合复合材料闭孔泡沫芯夹层结构低成本制造的工艺可行性及其潜在的结构效益。选用3种夹层结构形式,即相同材料和工艺制造的未缝合泡沫芯夹层和缝合泡沫芯夹层结构及密度相近的Nomex蜂窝夹层结构,完成了密度测定、三点弯曲、平面拉伸和压缩、夹层剪切、结构侧压和损伤阻抗/损伤容限等7项实验研究。结果表明,泡沫芯夹层结构缝合后,显著提高了弯曲强度/质量比、弯曲刚度/质量比、面外拉伸和压缩强度、剪切强度和模量、侧压强度和模量、冲击后压缩(CAI)强度和破坏应变。这种新型结构形式承载能力强、结构效率高、制造维护成本低,可以在飞机轻质机体结构设计中采用。

泡沫夹芯型吸波隐身结构复合材料的发展趋势

介绍了吸波隐身材料的发展趋势、泡沫型吸波材料的优势及新型聚甲基丙烯酰亚胺(PMI)泡沫的优异性能,展望了以PMI泡沫为芯材制备泡沫隐身复合材料的应用前景。

整体成型复合材料模型机翼设计、制造与验证

根据给定的外形设计了四种不同结构形式的复合材料模型机翼,通过对所采用树脂基体的化学流变特性的研究,确定其最佳固化工艺条件。采用整体成型技术制备了四种全复合材料模型机翼,并进行了三点弯曲试验。结果表明,工字梁结构形式的模型机翼具有最高的载荷重量比,其次为C型梁机翼,而蒙皮-夹芯机翼的载荷重量比最小。其中,蒙皮-夹芯模型机翼在测试中表现为加载点上蒙皮压缩破坏;蒙皮-加筋机翼则表现为支点处的剪切破坏;梁式结构机翼均表现为支点与加载点中间的前缘剪切破坏。采用有限元分析模型机翼的强度与破坏过程,其结果与试验结果吻合良好。