Z-pins对层合复合材料非对称分层增韧作用参数分析——Ⅰ型层间韧性

假设纤维Z-pins的桥联力与嵌入厚度成正比,建立适于非对称分层(分层位于层合板厚度方向上的任意位置)的Z-pin细观力学模型并构造相应的Z-pin单元,结合考虑一阶剪切变形的梁单元,建立了用于分析含浅部分层采用Z-pins增韧的双悬臂梁(Double cantilever beam,DCB)有限元模型,并在分层裂纹面上引入接触单元以防止分析过程中2个分层子梁在分层前缘处的相互嵌入。通过数值算例分析了Z-pins对含非对称分层的DCB试件Ⅰ型层间韧性的增强作用。参数分析表明,当分层位置靠近层合板的表面时,Z-pins的增韧作用明显下降,其较薄分层子层的厚度是决定Z-pins对Ⅰ型层间韧性增强效果的关键参数。     

织物增强复合材料层合板Ⅰ型层间断裂特性

采用双悬臂梁(DCB)试验测试和研究了织物增强复合材料层合板的层间断裂韧性与断裂行为。为了评价测试温度和试样几何尺寸的变化对层间断裂韧性的影响，分别在室温(RT)和液氮温度(77K)条件下对不同尺寸的试样进行了双悬臂梁试验。采用扫描电镜对分层断裂面进行了观察，分析和验证了层间断裂特性。     

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

Z—pins几何分布对其增强复合材料双悬臂梁I型层间韧性的影响

复合材料z—pinning增强技术通过在层合板内嵌人体分比小于5％的z—pins，能大幅度提高层合板的层间断裂韧性，减少因低能量冲击所产生的分层损伤。本文作者基于细观力学模型，构造了相应的z—pin单元；结合梁单元，建立了用于分析含z—pins的双悬臂梁（Double　cantilever　beam，DCB）的有限元模型；在分层裂纹面上引人接触单元以防止分析过程中2个分层子梁在分层前缘处的相互嵌人。通过数值算例分析了z—pins对层间韧性增强效果的影响及其原因。数值计算结果表明，z—pins的几何分布对其增强层间韧性的影响相对较小。     

织物增强复合材料层合板I型层间断裂特性

采用双悬臂梁(DCB)试验测试和研究了织物增强复合材料层合板的层间断裂韧性与断裂行为。为了评价测试温度和试样几何尺寸的变化对层间断裂韧性的影响,分别在室温(RT)和液氮温度(77K)条件下对不同尺寸的试样进行了双悬臂梁试验。采用扫描电镜对分层断裂面进行了观察,分析和验证了层间断裂特性。      

Z-pins几何分布对其增强复合材料双悬臂梁Ⅰ型层间韧性的影响

复合材料Z-pinning 增强技术通过在层合板内嵌入体分比小于5 %的Z-pins , 能大幅度提高层合板的层间断裂韧性, 减少因低能量冲击所产生的分层损伤。本文作者基于细观力学模型, 构造了相应的Z-pin 单元; 结合梁单元, 建立了用于分析含Z-pins 的双悬臂梁(Double cantilever beam , DCB) 的有限元模型; 在分层裂纹面上引入接触单元以防止分析过程中2 个分层子梁在分层前缘处的相互嵌入。通过数值算例分析了Z-pins 对层间韧性增强效果的影响及其原因。数值计算结果表明, Z-pins 的几何分布对其增强层间韧性的影响相对较小。      

缝合层合板的Ⅰ型层间断裂韧性研究

通过缝合的方法改善织物增强复合材料层合板的层间断裂韧性.采用双悬臂梁(DCB)试验测试和研究了缝合层合板的层间断裂韧性与断裂行为.为了评价缝合工艺参数(缝合密度)对层间断裂韧性的影响,用改进的插入型夹具在实测不同缝合工艺层合板的Ⅰ型层间断裂韧性值(G_IC)的基础上,分析和阐明了缝合工艺参数(缝合密度)与G_IC间的关系;以提高层合板的平均层间断裂韧性值为目标,以拉伸和弯曲强度为约束条件优化了缝合工艺;采用摄影显微镜对分层断裂面进行了观察,分析和考察了缝合对其它性能的影响.结果表明:改进的插入型夹具可方便地完成缝合层合板的Ⅰ型层间断裂韧性测试;缝合后裂纹不连续扩展,缝合密度对裂纹扩展行为有较大影响;随着缝合密度的增大,层间断裂韧性值增大,但拉伸和弯曲强度降低,缝合密度存在最佳值.     

低温环境下测试复合材料Ⅰ型层间断裂韧性的简易方法

目前ASTM复合材料Ⅰ型层间断裂韧性测试标准需不断观测裂纹扩展长度。然而在低温环境下,裂纹扩展长度不易测量且过程繁琐。为克服这一缺陷,本文采用双柔度法测试复合材料低温环境下Ⅰ型层间断裂韧性,该方法的步骤与ASTM标准基本相同,但不需观测裂纹扩展长度便能获得低温下Ⅰ型层间断裂韧性。为了验证该方法的可靠性和精度,采用5件碳纤维增强环氧树脂基复合材料双悬臂梁（DCB）试样在-10℃环境下进行Ⅰ型层间裂纹扩展实验,应用ASTM标准所推荐的三种方法及本文的双柔度法进行数据处理获得复合材料Ⅰ型层间断裂韧性。结果表明:ASTM标准的三种方法与双柔度法得到的Ⅰ型层间断裂韧性结果一致,相对差别小于5%,而本文的双柔度法不需测量裂纹扩展长度,因此更简单,为测试低温环境下Ⅰ型层间断裂韧性提供了一种准确、简单的新方法。      

碳纤维与玻-碳层间混杂2.5维机织复合材料的力学性能对比研究

2.5D机织复合材料由于具有特殊的层间联锁结构和相对成熟的织造、制备技术,在很多领域得到了广泛关注和应用。本工作制备了一种碳纤维2.5D机织复合材料和一种碳纤维-玻璃纤维混杂的2.5D机织复合材料。对两种复合材料经向和纬向的压缩、弯曲及剪切性能进行研究,并分析结构与性能间的关系。结果显示：2.5D织物经向压缩强度高于纬向,也优于2.5D混杂织物复合材料,而2.5D织物与2.5D混杂织物复合材料纬向压缩强度十分接近;2.5D织物与2.5D混杂织物复合材料经向弯曲强度差别不大,2.5D织物纬向弯曲强度则明显高于2.5D混杂织物复合材料;2.5D织物纬向最大层间剪切强度大于经向层间剪切强度,2.5D织物与2.5D混杂织物复合材料经向剪切强度差别不大,而2.5D混杂织物复合材料纬向剪切强度远低于2.5D织物复合材料。     

Investigation of mechanical properties of auxetic woven polymer composite material

Contrary to normal materials, the auxetic/meta‐materials expand transversally as well as longitudinally when subjected to longitudinal load and contract in both directions on compression. In this work, auxeticity is obtained in composites reinforced with carbon woven fabrics placed at certain angles. The auxetic effect on the mechanical properties of the prepared carbon/epoxy composites was investigated. The mechanical properties include the tensile, flexural and impact properties. It is found that the tensile properties are not affected by the auxetic effect; however, the flexural and impact properties are significantly enhanced by the auxetic effect.     

二维平纹机织复合材料弹性性能预测的域分解方法

为了预测二维平纹机织复合材料的弹性性能, 提出了基于有限元重合网格法的域分解方法。域分解方法与传统代表体元法的有限元建模不同, 前者不再建立精细的纤维与基体模型, 而是分别建立二维平纹机织复合材料单胞的整体域与纤维域, 整体域是真实基体体积与纤维体积的叠加, 两区域网格独立剖分, 互不影响。采用MSC. Nastran中的多节点约束在纤维节点与基体节点之间建立位移协调来模拟纤维和基体单元的位移函数关系, 实现了纤维域和基体域的耦合计算。研究表明, 域分解方法大大简化了机织复合材料细观力学建模的复杂性, 降低了建模时间, 采用域分解方法预测的二维平纹机织复合材料弹性常数与试验值吻合较好, 充分说明了该预测模型与方法的正确性。研究了不同纤维体积分数下, 域分解方法预测二维平纹机织复合材料的弹性常数的变化趋势, 结果表明, 随纤维体积分数增加, 模量呈上升趋势, 泊松比呈降低趋势。     

基于组合单元的层压复合材料三维应力分析

为了分析层压复合材料层间特性,推导了将刚性元-弹簧元相结合的离散型界面单元的刚度矩阵。建立了层压板的准三维模型,即将Mindlin板单元应用于层压板的各子层,层间作用则利用上述界面单元来模拟。通过弯曲板元计算子层面内应力,通过界面单元的弹簧力确定层间应力。对受面内拉伸的多向层压板条进行了应力分析,与使用商业软件三维实体模型计算得到的层间和面内应力对比,结果表明准三维模型的计算结果合理。这种新型界面单元的优点是可用来表征层间损伤,并且能通过对弹簧刚度的消减来模拟分层损伤的演变。     

Modeling and analyses of thermo-elastic properties of radially grown carbon nanotubes-based woven fabric hybrid composite materials

Carbon nanotubes (CNTs) may be useful due to their sound thermo-mechanical properties. The present work deals with the evaluation and analysis of elastic properties and coefficient of thermal expansions (CTEs) of a CNTs-based 2D plane woven fabric composite material system where the CNTs are radially grown on the surface of the carbon fiber. Detailed constructional features of the proposed trans-scale composite material system is explained in detail. The mathematical modeling for the material properties of each constituent or building block of the hybrid composite is developed. The mathematical model for the thermo-elastic properties of yarns is also formulated based on strength of material method whereas the thermo-elastic properties of representative unit cell is based on the unit cell method. Various numerical results have been obtained by varying the CNTs content, carbon fiber contents, and temperatures. Effects of different geometrical parameters (such as yarn thickness, yarn width, and the ratio of gap length to yarn width of the yarn) on the elastic properties as well as the CTEs are also investigated.     

织物形式对苎麻纤维渗透率及其复合材料力学性能的影响

采用树脂传递模塑工艺(RTM)研究了三种典型苎麻纤维织物结构(平纹、 斜纹和缎纹)对树脂流动性的影响, 并研究了三种苎麻纤维织物结构对其增强酚醛树脂复合材料的拉伸性能和层间剪切性能的影响。结果表明, 苎麻纤维织物树脂渗透率主要受纤维屈曲和流道面积的影响。斜纹和缎纹苎麻织物的纤维屈曲较小且流道面积较大, 其织物的树脂渗透率较大, 同时, 较小的纤维屈曲使其增强的复合材料拉伸性能也较优。然而, 不同织物形式对苎麻纤维织物/树脂复合材料的层间性能影响不大。     

添加剂对电沉积Al2O3/Ni-Co复合材料力学性能的影响

通过脉冲电沉积技术制备出含1,4-丁炔二醇或糖精为添加剂的Al2O3/Ni-Co复合材料,采用TEM、EDS等方法分析了含2种添加剂的Al2O3/Ni-Co复合材料的微观组织结构,比较了添加剂对材料光洁度、显微硬度、室温塑性以及高温塑性的影响,并通过SEM对变形后材料的显微结构进行了表征.以糖精为添加剂所制备的AlO3...     

喷丸处理对TiB_2/Al复合材料表面基体力学性能的影响

通过X射线衍射线形分析表征了喷丸表面的组织结构,利用原位拉伸X射线衍射应力分析研究了TiB2/6351Al复合材料喷丸表面基体的力学行为.结果表明,喷丸后复合材料表面基体的屈服强度提高了26%,整体强度提高约28%,显微硬度提高50%以上.喷丸前、后复合材料基体承载系数分别为81%和83%,喷丸后的基体承载系数略有提高.喷丸表面基体的晶块尺寸及位错密度分别约51 nm和3.05×1014 m-2,晶块细化及位错密度增高是导致表面基体力学性能提高的主要原因.     

Effect of Remote Ply Orientation on the Perceived Mode I and Mode II Toughness of θ/θ and θ/−θ interfaces

Results are presented from an investigation of the effect of remote ply orientation on the perceived mode I and mode II toughness of a laminated graphite/epoxy. Experimental and numerical studies were conducted on four commonly used stacking sequences. Each sequence contained a midplane delamination and was subjected to bending loads that produced either predominantly mode I or predominately mode II conditions. Of the four sequences, two contained delaminations at 30/30 interfaces, and two contained delamination at 30/-30 interfaces. For each interface type, one stacking sequence exhibited a relatively small transverse curvature under the applied loadings but a relatively large twisting curvature, whereas the other sequence exhibited a small twisting curvature but a large transverse curvature. For the two types of loadings (mode I and mode II), each of the four sequences was analyzed by three dimensional finite element analyses and tested in precracked and non-precracked configurations. Using appropriate nondimensional parameters, the results of this study are combined with the results of companion numerical investigations to make recommendations regarding the choice of stacking sequences for the determination of the toughness of arbitrary interfaces.     

Effects of osteoblast-like cell seeding on the mechanical properties of porous composite scaffolds

In tissue engineering technology, polymer–ceramics or polymer–polymer composites have been considered as advanced scaffolds having mechanical stability, biocompatibility, cell proliferation, and easy processability. However, the relationship between the mechanical properties and the cell proliferation behavior of such composite scaffolds has not been clarified yet. In this study, two types of composite scaffolds, poly(ethylene terephthalate) (PET) fiber/collagen and β-tricalcium phosphate (β-TCP)/gelatin scaffolds, were investigated. MC3T3-E1 cells were cultured in these scaffolds under appropriate conditions. Compression tests were then periodically conducted to evaluate the compressive elastic modulus. It was found that the modulus of the scaffolds containing cells increased with the cell culture period. It is noted that the modulus of the β-TCP/gelatin with cells was approximately seven times larger than that of the PET fiber/collagen with cells.