复合材料波纹夹层圆柱壳设计及轴压性能

结构轻量化是航空航天发展的永恒主题, 波纹夹层圆柱壳作为常见的轻质结构形式, 在航空航天领域具有很大的发展空间。采用模具热压法, 制备出纵向和环向碳纤维复合材料波纹夹层圆柱壳, 其中芯子整体成型, 面板分瓣制备。采用经典板壳屈曲理论, 分析纵向和环向波纹夹层圆柱壳的轴压力学性能, 得到了欧拉屈曲、整体屈曲、局部屈曲和面板压溃4种失效模式下的极限载荷理论公式。绘制出结构的失效机制图, 直观显示出了失效模式与试件尺寸之间的关系。通过对纵向和环向波纹夹层圆柱壳的轴向压缩试验, 获得了结构的载荷-位移曲线及局部屈曲和面板压溃2种失效模式。结果表明:纵向波纹夹层圆柱壳的轴向承载能力及载荷/质量效率优于环向波纹夹层圆柱壳, 在一定范围内增加圆柱壳面板的厚度、减小圆柱壳的高度可提高结构的载荷/质量效率。      

复合材料褶皱夹芯结构的制备及压缩性能研究

目的 探究复合材料褶皱芯子的一次性成型工艺,并研究浸胶量对褶皱夹芯结构压缩性能的影响。方法 以V型褶皱夹芯结构为研究对象,首先采用真空吸附成型工艺制备V型复合材料褶皱芯子,然后通过黏接工艺将碳纤维复合材料层合板与褶皱芯子进行复合,得到复合材料褶皱夹芯结构,最后通过实验测试,研究该结构在压缩载荷作用下的力学性能和失效模式,以及不同浸胶量对其压缩性能的影响。结果 采用真空吸附成型工艺能够一次性制备出褶皱芯子,其成型精度有待提高;由压缩实验可知,褶皱夹芯结构先从壁面开始失效,后逐步扩散至棱线处,最终导致芯子的整体失效;由压缩实验测试结果可知,浸胶量(质量分数)为11%、17%、22%的褶皱夹芯结构的破坏载荷分别为362.853、420.521、471.389 N。结论 采用真空吸附成型工艺可一次性成型出褶皱芯子,其制备效率较高,但存在成型尺寸精度不高问题,后续需要进一步改进;在一定范围内,复合材料褶皱夹芯结构的压缩破坏载荷与芯子的浸胶量近似成正比例线性关系。     

曲面碳纤维增强树脂复合材料点阵夹芯结构的弯曲和振动特性

采用热压一次成型的工艺制备了曲面碳纤维增强树脂复合材料点阵夹芯结构,进行了三点弯试验探究了结构的弯曲破坏载荷与破坏模式。结果显示：结构的载荷位移曲线分为4个阶段,分别为线性阶段、损伤起始阶段、损伤演化阶段和失效阶段;破坏模式主要为面板压溃与节点失效。通过ABAQUS显示求解器建立了有效的弯曲和模态振动模型,得到弯曲破坏过程的失效模式、载荷位移曲线及结构振动模态与固有频率。讨论了不同参数(几何参数和材料性能)对弯曲和振动性能的影响,比较了不同边界条件对固有频率的影响。结果显示：相对密度(面板厚度、芯子直径)的增加会使结构的弯曲破坏载荷和固有频率增大,而芯子倾角ω的增大会使弯曲破坏载荷与固有频率的减小;材料的比刚度越大,固有频率越高。     

超高模量聚乙烯纤维复合材料的制备与性能研究

研制了用于UHMPE纤维表面处理的连续化学处理装置.将经过处理的UHMPE纤维与环氧树脂体系制备成复合材料.用复合材料的短梁剪切强度评价纤维处理效果.测定了复合材料的压缩性能、弯曲性能和冲击性能(包括平面冲击、缺口与非缺口冲击).结果表明,UHMPE纤维复合材料的韧性极好,虽然其刚度较低,压缩强度与弯曲强度较差.这种复合材料的失效模式主要是纤维与基体的脱粘、分层、纤维屈曲和大变形,而不是纤维的断裂.     

碳/芳纶混杂纤维增强波纹夹芯结构低速冲击性能

采用碳纤维和芳纶纤维增强复合材料对波纹夹芯结构的面板进行层间混杂铺层设计,通过真空辅助树脂灌注(VARI)成型工艺制备混杂波纹夹芯结构。在60 J、80 J和100 J三种不同冲击能量下,研究了面板混杂铺层方式对波纹夹芯结构低速冲击性能及冲击后压缩强度的影响,并利用超声C扫和工业CT断层成像两种无损检测技术对波纹夹芯结构的冲击损伤机制进行了分析。结果表明：冲击能量较低时,波纹夹芯结构的吸收能量基本不受面板的混杂铺层方式影响,而凹坑深度随表层碳纤维层数增加而减少。冲击能量较高时,面板为分层式混杂(碳/芳纶纤维单层交替铺层)的波纹夹芯结构的抗冲击性能最好,纤维断裂损伤和层间分层主要发生在试样表层,但损伤面积较大;面板为夹层式混杂(以碳纤维为蒙皮、芳纶纤维为芯材)的波纹夹芯结构具有较高的吸收能量,整个上面板的纤维都发生了断裂破坏,但损伤面积较小。碳/芳纶混杂波纹夹芯结构的面板采用分层式和夹层式的混杂铺层设计时,具有较高的冲击后压缩强度。     

玻璃纤维立体织物增强环氧树脂泡沫夹层复合材料的制备及力学性能

为了进一步提高泡沫夹层复合材料的承载能力和综合性能,实现其在轨道交通及汽车等工业领域的应用,开展了玻璃纤维立体织物增强环氧树脂泡沫(GF-Fabric/EP)复合材料的制备及其力学性能的研究。制备GF-Fabric/EP复合材料及其夹层结构,探索了GF-Fabric/EP复合材料及其夹层结构的失效行为,以揭示立体织物的增强机制。结果表明：立体织物的引入可显著改善GF-Fabric/EP复合材料的强度、刚度及破坏应变;但在不同承载条件下,各纱线发挥承载作用和效果不同。面板、芯材各自的性能、尺寸及面/芯界面性能均是影响GF-Fabric/EP夹层复合材料力学性能及失效特征的重要因素。以三点加载下的弯曲性能为例,针对不同的GF-Fabric/EP夹层复合材料,需调整跨厚比和试样尺寸并获得理想的失效特征,方可对其弯曲性能或层间剪切性能进行有效、合理的评价。     

缝合参数对泡沫夹层结构复合材料力学性能的影响

采用真空辅助树脂注射(VARI)成型工艺制备不同缝合方式和缝合密度的缝合泡沫夹层复合材料, 研究缝合参数对平面拉伸、三点弯曲、芯子剪切以及滚筒剥离性能的影响。结果表明: 缝合使泡沫夹层复合材料的平面拉伸强度和芯子剪切强度明显降低, 可以改善弯曲性能并大幅提高滚筒剥离性能, 改进锁式缝合方式优于临缝式缝合方式; 适当地增加缝合行距对力学性能有一定的积极作用, 但不利于滚筒剥离性能的提高; 与未缝合泡沫夹层复合材料相比, 当缝合密度为30 mm×10 mm时, 改进锁式缝合泡沫夹层复合材料的平拉强度和芯子剪切强度分别降低了14.75%和24.79%, 弯曲强度和平均剥离强度分别提高了7.96%和80.78%。     

橡胶改性对硼纤维/环氧单向复合材料力学性能的影响

对环氧树脂进行液体丁腈橡胶改性, 并采用缠绕无纬布层压成型工艺制备了硼纤维/环氧单向复合材料。测试了环氧树脂液体丁腈橡胶改性前后硼纤维/环氧单向复合材料的力学性能, 研究了硼纤维/环氧单向复合材料的纵向拉伸破坏模式。结果表明, 基体中的10%液体丁腈橡胶使硼纤维/环氧单向复合材料的拉伸强度、 弯曲强度、 层间剪切强度和断裂延伸率分别提高了18.42%、 13.39%、 28.45%和43.40%, 但其拉伸和弯曲模量稍有下降。基体中含10%液体丁腈橡胶的硼纤维/环氧单向复合材料的纵向拉伸破坏模式为界面层的内聚破坏和脱黏破坏共存的混合破坏。      

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。      

GFRP复合材料-轻木夹芯梁弯曲疲劳性能试验

为研究真空导入成型的玻璃纤维增强树脂基复合材料-Balsa轻木（GFRP-Balsa）夹芯梁弯曲疲劳性能,进行了普通无格构、单格构增强、双格构增强三种类型共42根试件在不同荷载等级下的四点弯曲疲劳试验,得到夹芯梁的弯曲疲劳破坏模式、疲劳寿命和损伤演化规律,分析了三种类型夹芯梁在弯曲疲劳载荷下不同的损伤机制。研究结果发现,无格构夹芯梁的失效模式统一为芯材剪切和面板脱粘,格构增强夹芯梁的失效模式随格构设置及载荷等级变化,主要有上面板屈曲或压坏、下面板拉断等;采用指数经验模型拟合夹芯梁的疲劳荷载-寿命（S-N）曲线,得到三种类型夹芯梁的寿命预测公式;夹芯梁的位移演化历经"位移瞬降-平稳演化-损伤萌生至破坏"三个阶段,相对于无格构试件,格构增强试件在疲劳失效前有较明显预兆。     

齿板-玻璃纤维混合夹层结构弯曲性能试验

提出了一种齿板-玻璃纤维混合面板和泡沫芯材组成的新型混合夹层结构,齿板通过齿钉与泡沫芯材相连。该结构采用真空导入成型工艺制备,通过三点弯曲试验研究该结构在不同跨度以及不同芯材密度情况下的破坏模式和弯曲性能,并与普通泡沫夹层结构进行对比分析,同时探究了齿板对该结构界面性能的影响。结果表明:在泡沫芯材密度为35kg/m~3、80kg/m~3和150kg/m~3情况下,齿板-玻璃纤维混合泡沫夹层梁弯曲承载能力与普通泡沫夹层梁相比分别提高了168%、211%和258%,其界面剪切强度依次为0.09 MPa、0.21 MPa和0.45 MPa;随着芯材密度和跨度的变化,该结构主要产生芯材剪切和芯材凹陷两种破坏形态,齿板的嵌入有效抑制界面的剪切失效。另外,利用理论公式估算了试件受弯极限承载能力,理论值与实测值吻合较好。     

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.     

Compression and bending performances of carbon fiber reinforced lattice-core sandwich composites

To restrict debonding, carbon fiber reinforced lattice-core sandwich composites with compliant skins were designed and manufactured. Compression behaviors of the lattice composites and sandwich columns with different skin thicknesses were tested. Bending performances of the sandwich panels were explored by three-point bending experiments. Two typical failure mechanisms of the lattice-core sandwich structures, delaminating and local buckling were revealed by the experiments. Failure criteria were suggested and gave consistent analytical predictions. For panels with stiff skins, delamination is the dominant failure style. Cell dimensions, fracture toughness of the adhesives and the strength of the sandwich skin decide the critical load capacity of the lattice-core sandwich structure. The mono-cell buckling and the succeeding local buckling are dominant for the sandwich structures with more compliant skin sheets. Debonding is restricted within one cell in bending and two cells in compression for lattice-core sandwich panels with compliant face sheets and softer lattice cores.     

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.     

泡沫铝夹层结构复合材料低速冲击性能

以泡沫铝为夹芯材料,玄武岩纤维(BF)和超高分子量聚乙烯纤维(UHMWPE)复合材料为面板,制备夹层结构复合材料。研究纤维类型、铺层结构和芯材厚度对泡沫铝夹层结构复合材料冲击性能和损伤模式的影响规律,并与铝蜂窝夹层结构复合材料性能进行对比分析。结果表明:BF/泡沫铝夹层结构比UHMWPE/泡沫铝夹层结构具有更大的冲击破坏载荷,但冲击位移和吸收能量较小。BF和UHMWPE两种纤维的分层混杂设计比叠加混杂具有更高的冲击破坏载荷和吸收能量。随着泡沫铝厚度的增加,夹层结构复合材料的冲击破坏载荷降低,破坏吸收能量增大。泡沫铝夹层结构比铝蜂窝夹层结构具有更高的冲击破坏载荷,但冲击破坏吸收能量较小;泡沫铝芯材以冲击部位的碎裂为主要失效形式,铝蜂窝芯材整体压缩破坏明显。     

Mechanical behavior of sandwich panels with hollow Al–Si tubes core construction

A new type of lightweight sandwich panels consisting of vertically aligned hollow Al–Si alloy tubes as core construction and carbon fiber composite face sheets was designed. The hollow Al–Si alloy tubes were fabricated using precision casting and were bonded to the face sheets using an epoxy adhesive. The out-of-plane compression (i.e. core crushing), in-plane compression, and three-point bending response of the panels were tested until failure. The hollow Ai–Si alloy tubes core configuration show superior specific strength under crushing compared to common metallic and stochastic foam cores. Under in-plane compression and three-point bending, the buckling of face sheets and debonding of hollow cores from the face sheets were observed. Simple analytical relationships based on the concepts of mechanics of materials were provided for the compression tests, which estimate the sandwich panels’ strength with high fidelity. For three-point bending, detailed finite element analysis was used to model the response and initial failure of the sandwich panels.     

液态扩散焊制备泡沫铝夹芯板及其疲劳行为

采用超声辅助液态扩散焊接的方法制备冶金复合泡沫铝夹芯板,利用光学显微镜（OM）和SEM观察冶金复合样品的界面组织和结构,发现连接界面发生了侵蚀作用,接头均匀连续;EDS线扫结果表明,连接界面处焊接合金（Zn-10Al）和铝基体间的元素扩散现象明显,表明在超声作用下,基体材料表面氧化膜被破坏,枝晶在界面附着生长,形成良好的冶金连接。将制备的冶金复合样品和胶黏泡沫铝夹芯板样品进行三点弯曲疲劳对比试验,结果显示,冶金复合样品和胶黏样品的疲劳极限分别达到3 058 N和2 829 N。在相同载荷下,冶金复合样品的疲劳寿命（S-N）远远长于胶黏样品。两种样品的疲劳破坏方式完全不同,胶黏样品表现为面板和芯层黏接面的脱黏剪切破坏,冶金复合样品的疲劳剪切破坏出现在泡沫铝芯层,没有出现面板脱离现象。     

Design of sandwich structures for concentrated loading

While sandwich construction offers well-known advantages for high stiffness with light weight, the problem of designing the sandwich structure to withstand localized loading, such as from accidental impact, remains an important problem. This problem is more difficult with lower stiffness cores, such as expanded foam. In the present study, experiments have been carried out on foam core sandwich beams with carbon/epoxy faces, under conditions of concentrated loading. The variables considered were the density of the foam and the relative thickness of the core. The common failure modes of sandwich structures were observed, including core failure in compression and shear, delamination, and fiber failure in the faces. These failure modes were systematically related to the test variables by means of a detailed stress analysis of the specimen, and a consideration of the failure properties of the constituent materials. The loading is characterized by localized high stress and strain concentrations that are not predicted in first-order shear deformation sandwich beam theory. The three-dimensional elasticity solution of Pagano was used to obtain the stress distributions. The strength prediction requires a detailed consideration of the localized nature of the loading, including the effects of strain gradients in the faces. The results show that failure modes and load levels can be predicted for sandwich structures under concentrated loading, but that accurate predictions require a consideration of the details of the concentrated loading. The results have a direct application in predicting the ability of sandwich structures to withstand localized loading such as from accidental impact.     

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。