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.

Elaboration and Characterization of Composite Materials Reinforced by Papaya Trunk Fibers (<i>Carica papaya</i>) and Particles of the Hulls of the Kernels of the Winged Fruits (<i>Canarium schweinfurthii</i>) with Polyester Matrix

In this work we determine the physical and mechanical properties of local composites reinforced with papaya trunk fibers (FTP) on one hand and particles of the hulls of the kernels of the garlic (PCNFA) in the other hand. The samples are produced according to BSI 2782 standards;by combining fibers and untreated to polyester matrix following the contact molding method. We notice that the long fibers of papaya trunks improve the tensile/compression characteristics of composites by 45.44% compared to pure polyester;while the short fibers improve the flexural strength of composites by 62.30% compared to pure polyester. Furthermore, adding fibers decreases the density of the final composite material and the rate of water absorption increases with the size of the fibers. As regards composite materials with particle reinforcement from the cores of the winged fruits, the particle size (fine ≤ 800 μm and large ≤ 1.6 mm) has no influence on the Young’s modulus and on the rate of water absorption. On the other hand, fine particles improve the flexural strength of composite materials by 53.08% compared to pure polyester;fine particles increase the density by 19% compared to the density of pure polyester.

Steam Exploded Peanut Shell Fiber as the Filler in the Rigid Polyurethane Foams

In this study,steam exploded peanut shell fibers(SE-PSFs)were utilized to fabricate with rigid polyurethane foam(RPUF)in order to improve sound absorption performance and hydrothermal weather resistance.Optimized method of SE treatment,RPUF preparation and flame retardant treatment were selected to prepare SE-PSF/RPUF composites in this experiment.Physical and mechanical properties including density,water absorption capacity,thickness swelling rate,compressive strength,thermal conductivity and average sound absorption coefficient of SE-PSF/RPUF were investigated and compared with the control(PRUF).The results showed that the density,water absorption capacity,thickness swelling rate and thermal conductivity showed an increasing trend with the increase of SE-PSFs content.The strength of the composite material showed a downward trend with the increase of the SE-PSFs content.The average sound absorption coefficient of the SE-PSFs/RPUF compared with PRUF significant increased,and the average sound absorption coefficient of the SE-PSFs/RPUF with SE-PSFs 40%was 0.47.The study getted the best ratio of flame retardants for 10%EG and 3%DMMP.The oxygen index was 35.56 vol%.

Predicting buckling of carbon fiber composite cylindrical shells based on backpropagation neural network improved by sparrow search algorithm

The buckling load of carbon fiber composite cylindrical shells(CF-CCSs)was predicted using a backpropagation neural network improved by the sparrow search algorithm(SSA-BPNN).Firstly,two CF-CCSs,each with an inner diameter of 100 mm,were manufactured and tested.The buckling behavior of CF-CCSs was analyzed by finite element and experiment.Subsequently,the effects of ply angle and length–diameter ratio on buckling load of CF-CCSs were analyzed,and the dataset of the neural network was generated using the finite element method.On this basis,the SSA-BPNN model for predicting buckling load of CF-CCS was established.The results show that the maximum and average errors of the SSA-BPNN to the test data are 6.88%and 2.24%,respectively.The buckling load prediction for CF-CCSs based on SSA-BPNN has satisfactory generalizability and can be used to analyze buckling loads on cylindrical shells of carbon fiber composites.

Effect of Groundnut Shell Powder on the Mechanical Properties of Recycled Polyethylene and Its Biodegradability

Natural fiber reinforced composites have gained considerable attention particularly in the manufacturing industry owing to their light weight, corrosion resistance, abundance, and biodegradability. In this work, alkaline treated and untreated groundnut shell powder (GSP) was used to reinforce recycled polyethylene to produce GSP-recycled polyethylene composites with improved mechanical properties and biodegradability. GSP with particle sizes of 0 - 300 μm and 300 - 600 μm was used in different proportions: 5%, 10%, 15%, 20%, 25%, and 30% wt. The fiber was immersed for 5 hours in a 10 wt% NaOH solution. Tensile and hardness test data showed an improvement in mechanical properties of the treated fiber composites. Results of water absorption test also showed that treated GSP-recycled polyethylene composites had a lower rate of water absorption than the untreated GSP-recycled polyethylene composites. Through Fourier transform infrared spectroscopy, disappearance of characteristics peaks of hemicellulose and lignin was observed. Growth of fungi on the fiber-reinforced composites was observed, which was evidence that GSP-recycled polyethylene composite was biodegradable. Finally, SEM micrographs showed uniform distribution of treated fibers in the polymer matrix;this explained the observed improvement in the mechanical properties of treated GSP-recycled polyethylene composites.

玻纤增强PA6焊机外壳性能的影响因素数值模拟

深入探讨了玻璃纤维增强聚酰胺6在焊机外壳应用中的性能表现,并基于ANSYS软件平台,进行了静力学仿真和落球冲击仿真分析,旨在揭示玻纤含量、玻纤长径比以及玻纤取向等关键参数对焊机外壳性能的影响。静力学分析显示,当外壳承受2500 N的拉力时,玻纤含量的增加对焊机外壳应力强度的影响较小,但能够降低了外壳变形程度。当玻纤质量分数超过25%时,等效应力趋于稳定(约51 MPa)。此外,玻纤的取向对焊机外壳性能具有显著影响。当纤维沿X轴和Z轴取向且各占50%时(方向向量为a2),外壳的等效应力达54.6 MPa,同时变形量最小,仅为0.5 mm,这一性能与玻纤质量分数为40%的外壳相当。而玻纤长径比的增加对等效应力的影响并不显著,但有助于减少变形。进一步,通过落球冲击分析发现,随着玻纤含量的增加,外壳的等效应力逐渐增大,变形逐渐减小,这一趋势与静力学分析结果高度一致。当玻纤质量分数低于20%时,焊机外壳在冲击下易出现破裂;然而,当玻纤质量分数为20%~35%时,外壳表现出了优异的冲击性能,未出现开裂现象。

引发方式、铺层对纤维增强复合材料圆柱壳吸能特性影响的冲击试验研究

对作为吸能元件的纤维增强复合材料圆柱壳的吸能特性进行了试验研究。制备了不同铺层角度和不同引发方式的玻璃纤维/聚酯树脂基圆柱壳,通过对该圆柱壳进行动态试验,探求铺层方式和引发方式对该吸能元件吸能效果的影响,以及该复合材料层合壳体压溃过程的破坏机理。

仿贝壳结构制备纤维增强的复合材料

模仿贝壳的层状结构,以环氧树脂作为基体,在树脂中添加了竹纤维和麻纤维,并对其力学性能进行了测试。结果表明:与环氧树脂材料相比,添加了竹纤维和麻纤维的环氧树脂复合材料的力学性能有所改善;竹纤维和麻纤维的增韧机制主要有裂纹滞止、微裂纹、界面剥离、纤维拔出、塑性桥连等,与具有弱界面的脆/塑复合材料增韧机制相似。

纤维缠绕复合材料壳体原位成型工艺研究

热固型缠绕复合材料壳体以其优异的性能在航空、军事和工业等领域得到了广泛应用.目前,制约其应用和发展的主要瓶颈是壳体的成本和性能,而壳体成型工艺直接决定了其最终性能和成本.由于缠绕壳体为中空结构,因此可以采用加热壳体内部金属芯模或内衬的方法实现缠绕后的或正在缠绕的复合材料的固化成型,即原位成型.本文介绍复合材料壳体原位成型新工艺,建立筒型壳体内加热固化过程的数学模型,利用有限元法对筒体固化过程中的温度和固化度进行了数值模拟分析.该研究为实现壳体高效、优质且低成本成型提供新思路,为原位成型工艺设计、模拟和参数优化提供分析模型和方法.

复合纤维含量对精铸硅溶胶型壳强度及透气性的影响

采用陶瓷和尼龙复合纤维增强熔模精铸硅溶胶型壳,通过测试与分析复合纤维增强硅溶胶型壳的常温及焙烧后强度和透气性,研究复合纤维含量对硅溶胶型壳强度和透气性的影响规律,确定复合纤维含量与焙烧温度和型壳强度的关系,并通过SEM对型壳试样断口形貌进行观察和分析。结果表明:复合纤维对硅溶胶型壳强度和透气性的影响显著,当复合纤维含量小于0.6%(质量分数)时,硅溶胶型壳强度和透气性同时增大;当复合纤维含量大于0.6%时,型壳常温及焙烧后强度开始减小,焙烧后基体中孔隙率增加,型壳透气性继续增大;当复合纤维含量为0.6%、焙烧温度为1050℃时,型壳焙烧后强度达到最大值。

混杂纤维缠绕圆柱壳外压稳定性与缠绕参数

本文在文献的基础上，以加权因子和铺设角为参量给出了混杂纤维缠绕正交各向异性圆柱壳外压失稳最佳缠绕参数的理论计算公式。讨论了该公式的使用条件，并提出混杂纤维缠绕结构是否具有极值意义最佳参数的判别式。文中算例表明，本文公式不仅可以确定混杂纤维缠绕外压圆柱壳的最佳参数，也可以确定纤维增强各向同性外压圆柱壳的最佳纤维含量及纤维缠绕方向。

凹回转曲面纤维缠绕架空分析及应用

针对诸如带喷管固体火箭发动机的凹曲面过渡段等负高斯曲率面的缠绕,应用微分几何曲面理论推导出了凹回转曲面的纤维缠绕架空条件及判据,并对不同的过渡段曲线进行了分析,分别给出了判别公式。通过缠绕实验验证了架空判据的正确性和实用性,表明采用单叶双曲面比采用凹圆曲线回转曲面具有更好的缠绕工艺性,且其直纹线的缠绕角恰好为不架空的临界缠绕角;缠绕时,为了保证运动的平稳性,需要剔除奇异点,进行平滑处理。

层状纤维圆柱壳轴向压缩破损实验研究

通过对端部引发缺陷层状纤维复合材料圆柱壳在轴向准静态和冲击压缩下的实验研究，分析其渐进压缩破损模式和破坏模式的形成机理．研究此类结构的缓冲性能．实验研究表明随着纤维铺设角度的改变其破损模式的主导形式与分层扩展强度、环向断裂强度和纤维与基体脱胶裂纹相关．

基于分层壳单元与纤维梁单元组合剪力墙滞回性能分析

为系统研究带边框组合柱剪力墙组合结构的抗震性能,基于分层壳单元与非线性纤维梁单元,在ABAQUS软件中进行用户材料模型子程序二次开发。用分层壳单元模拟剪力墙,纤维梁单元模拟外围组合框架,分别对钢管混凝土组合框架、带钢管混凝土边框柱及型钢混凝土边框柱的组合剪力墙进行低周往复加载试验数值模拟。计算、试验结果总体吻合较好。在此基础上,对比分析该类组合剪力墙滞回性能、受力特征及破坏特征,数值模拟获得墙板在典型时刻的裂缝分布等与实测结果接近。研究表明,采用分层壳单元与纤维梁单元能较准确、有效模拟带边框柱组合剪力墙体系的滞回性能,亦能较好描述剪力墙裂缝发展情况。该方法可为实现高层建筑钢与混凝土混合结构体系抗震性能有效、准确的数值模拟分析提供参考。

生物质在制动摩擦材料中的应用

通过分析现有制动摩擦材料存在的环境问题,提出应用生物质开发环境友好型制动摩擦材料,即全部采用无毒、无环境污染、可生物降解的原材料如天然植物纤维、天然坚果壳粉和农业或林业废弃物(蔗渣、木屑等),天然矿物纤维和填料、从生物质合成可取代酚醛的树脂。生物质在制动摩擦材料中的主要作用有轻量、降低摩擦系数和改善耐磨性。在制动摩擦材料中引入生物质的关键是采用化学和物理处理方法提高热稳定性和合成木质素树脂。

压电纤维复合材料层合壳的非线性动力学研究

本文对横向激励作用下的1-3型压电纤维复合材料层合壳进行了非线性动力学分析,并研究了压电特性对结构振动响应的影响.首先建立了压电纤维复合材料层合壳的非线性动力学方程,并且在已知的几何结构和材料特性基础上考虑了电场属性.然后根据位移边界条件,选择合适的振型函数,通过Galerkin方法将运动控制方程转化成两自由度的非线性常微分方程.通过数值模拟方法分析了横向激励和压电系数对压电纤维复合材料层合壳非线性振动特性的影响.通过波形图、三维相图、庞加莱图和分叉图等来研究壳体不同类型的周期和混沌运动.结果表明,外激励作用下结构存在复杂的非线性振动响应,同时压电参数对层合壳结构振动响应具有很强的调节作用.

X射线分层层析成像技术及在航空航天领域的应用

X射线分层层析成像(Computed Laminography,CL)是一种先进的非接触式无损三维检测技术,能以高分辨率图像的形式直观地三维可视化板、壳产品内部结构与缺陷,弥补了传统计算机层析成像(Computed Tomography,CT)技术的不足。航空航天领域存在较多的诸如太阳能帆板、水平尾翼、发动机涡轮盘、叶片以及微电子芯片等板、壳类零部件。对其内部损伤与缺陷进行有效的无损检测与评价,是航空航天器飞行安全的重要保障。以航空航天板壳结构CL无损检测应用和笔者在此方面的工程实践为背景,简述了CL技术原理和特点,总结了其研究现状,分析了其关键技术和难点,并展望了其应用前景。

静电纺丝制备PLA-PCL核-壳结构复合纤维

采用同轴静电纺丝技术制备聚乳酸(PLA)-聚己内酯(PCL)核-壳结构复合纤维.利用扫描电子显微镜(SEM)观察纺丝电压、收集距离和核层-壳层溶液推进速度对PLA-PCL核-壳结构复合纤维形貌的影响.通过透射扫描电子显微镜(TEM)分析核层-壳层溶液推进速度对PLA-PCL核-壳结构形成的影响.研究结果表明:当核-壳溶液推进速度为0.1-0.2和0.1-0.3 m L/h时形成了清晰的核-壳结构;随着壳层溶液推进速度加快,PLA-PCL复合纤维核层含量降低,增加纺丝电压能够有效地降低复合纤维平均直径,而增大收集距离使复合纤维平均直径先降低后增加.

基于Kriging近似模型的碳纤维增强复合材料疲劳性能预测及其应用

以平纹机织碳纤维增强树脂基(CFRP)复合材料为研究对象,通过力学试验测试材料的静态力学和疲劳力学性能,结合Kriging插值方法和Basquin疲劳方程建立预测任意载荷下疲劳应力-循环寿命(S-N)曲线的恒幅寿命图模型,并以此作为复合材料结构优化设计的性能约束;同时,利用最优拉丁超立方试验设计方法和Kriging近似模型构建优化目标和约束响应的近似模型,采用遗传算法优化得到CFRP复合材料电动汽车电池箱壳体的厚度,并通过台架实验加以验证.结果表明,优化后,电池箱壳体结构的减重率达到34.39%.

纤维复合壳板与金属构件连接的对比分析

为了提高纤维复合壳板与金属构件的连接强度,拓展材料应用范围,优化材料组合结构,提出了一种采用纤维复合榫头与金属构件凹槽连接的新型连接技术,这种新型连接技术工艺简单,可采用相同的材料,在糊制纤维复合壳板时,同步成型,同步固化,连接牢固,质量可靠,使连接处的强度等同母材,组成的结构受力均匀,承载能力大大提高,综合技术性能更加优越,可作为承载主结构。