Characteristics of continuous unidirectional kenaf fiber reinforced epoxy composites

Kenaf fibers generally has some advantages such as eco-friendly, biodegradability, renewable nature and lighter than synthetic fibers. The aims of the study are to characterize and evaluate the physical and mechanical properties of continuous unidirectional kenaf fiber epoxy composites with various fiber volume fractions. The composites materials and sampling were prepared in the laboratory by using the hand lay-up method with a proper fabricating procedure and quality control. Samples were prepared based on ASTM: D3039-08 for tensile test and the scanning electron microscopy (SEM) was employed for microstructure analysis to observe the failure mechanisms in the fracture planes. A total of 40 samples were tested for the study. Results from the study showed that the rule of mixture (ROM) analytical model has a close agreement to predict the physical and tensile properties of unidirectional kenaf fiber reinforced epoxy composites. It was also observed that the tensile strength, tensile modulus, ultimate strain and Poisson’s ratio of 40% fiber volume content of unidirectional kenaf fiber epoxy composite were 164 MPa, 18150 MPa, 0.9% and 0.32, respectively. Due to the test results, increasing the fiber volume fraction in the composite caused the increment in the tensile modulus and reduction in the ultimate tensile strain of composite.     

基于失效机制的单向纤维增强树脂复合材料退化模型基于失效机制的单向纤维增强树脂复合材料退化模型

基于复合材料力学理论和失效机制,建立了一种新的适用于单向纤维增强树脂基复合材料的突降退化模型,用于描述复合材料基本材料性能在不同模式失效发生后的衰减行为。在模型中不仅考虑了复合材料拉伸和压缩弹性模量的差别,还考虑了损伤后材料拉伸和压缩性能退化的不同,以及裂纹闭合效应和侧向约束对压缩失效后性能的影响。另外,该模型只需要基本材料参数作为输入,便于应用。为了验证所提出的模型,建立了T800碳纤维增强X850环氧树脂基复合材料的退化模型,并对典型复合材料螺栓连接结构的拉伸失效行为进行渐进损伤分析。数值模拟获得的结构破坏载荷、破坏形式及载荷位移曲线与试验结果有较好的一致性,验证了所提出模型的计算精度和有效性。      

Stress transfer analysis of unidirectional composites with randomly distributed fibers using finite element method

A three-dimensional representative volume element (RVE) of unidirectional composites with both randomly distributed fibers and periodic geometry was generated using DIGIMAT-FE software. Finite element analysis of the stress transfer mechanisms around a fiber break in the RVE was performed via ABAQUS/Standard. The influences of distance to the broken fiber, fiber/matrix stiffness ratio and fiber volume fraction on the stress transfer process of intact fibers were discussed for the case of perfect fiber/matrix adhesion. The study shows that the nearest fibers and the second nearest fibers share the stress released from the broken fiber. The stress transfer coefficient and the ineffective stress transfer length of the nearest fibers was found to increase with the increasing distance to the broken fiber and the stiffness ratio, while decrease with the increasing fiber volume fraction. However, the trends in the two stress transfer parameters of the second nearest fibers are slightly different from those of the nearest fibers due to the random distribution of other intact fibers.     

Micromechanics based ply level material degradation model for unidirectional composites

The damaged response of a composite lamina depends on various mechanisms that take place at the microlevel, i.e., at the level of the fiber and matrix. The present work focuses on developing a ply level continuum damage model for point-wise stiffness degradation through simplified representation of the microlevel damage. A three dimensional micromechanical analysis of a single cell representative volume element is carried out for various volume fraction, and levels of damage. The model brings out the coupled effect of damage on the effective point-wise ply level stiffness. Further, the numerical results are employed to develop a functional continuum representation of stiffness degradation as a function of the damage parameters and fiber volume fraction perturbations. The micromechanics model is consistent with experimentally observed stiffness degradation, i.e., a strong influence of fiber breakage and fiber matrix debond, and a weak influence of normal cracking of matrix. The proposed model can be considered as an improved version of the widely accepted diffused (meso) damage models, i.e., DML. The study also gives a generalized and consistent definition for the free energy, which can be used for modeling growth of damage.     

甘蔗渣纤维增强聚丙烯复合材料的制备和力学性能

利用注射成型制备了甘蔗渣纤维增强聚丙烯复合材料, 分析了纤维质量分数、 注射成型条件以及添加物对复合材料力学性能的影响。结果表明, 随着纤维质量分数的增加, 材料的弯曲模量呈递增趋势。由于甘蔗渣纤维热降解的发生, 材料的力学性能随筒体温度的增加呈下降趋势。在模具温度90℃、 注射间隔时间30s、 不同的筒体温度185℃和165℃的成型条件下, 材料的弯曲性能和冲击强度分别呈现最大值。添加了马来酸酐改性聚丙烯后, 材料的弯曲强度和冲击强度得到了提高。      

Micromechanics modeling of viscoelastic properties of hybrid composites with shunted and arbitrarily oriented piezoelectric inclusions

A comprehensive micromechanics model is developed to estimate the effective viscoelastic properties of hybrid composites containing polymer matrix, conductive inclusions and shunted piezoelectric inclusions. The model is derived using the viscoelastic correspondence principle in conjunction with the Mori-Tanaka approach and the orientation averaging scheme. Three dimensional complex moduli are explicitly presented for hybrid composites with any orientation distribution. The model is first validated by comparison with available experimental results. Then, the loss factors are examined for hybrid composites with inclusions of various volume fractions and of shapes ranging from thin disks to long fibers. It is seen that hybrid composites with randomly oriented inclusions exhibit shear loss factors which are not possible with monolithic piezoelectric plate. Furthermore, the numerical results indicate that composites with long spheroid inclusions provide the best damping performance. The results recommend that aligned inclusion composites are good for alleviating longitudinal oscillations. If oscillation energy needs to be dissipated in all directions and for all modes, three dimensional random composites should be used. It is also observed that spherical inclusion composites cannot improve shear damping irrespective of the orientation and the volume fraction. In general, to achieve a pronounced damping piezoelectric inclusions that lie in aspect ratio range 0.1?α?2 should be avoided.     

纤维增强复合材料黏弹性行为的预测模型

根据标准线性固体模型构造了一种预测纤维增强复合材料黏弹性行为的模型, 推导出该模型的本构方程与松弛模量和蠕变柔量表达式, 该模型经有限元仿真验证具有较高的精度。利用该模型研究了纤维几何特性对蠕变柔量和松弛模量的影响。结果表明, 复合材料蠕变柔量与纤维比长度呈线性关系, 而当纤维比半径增大到临界值后, 其变化对材料的松弛模量和蠕变柔量影响减小, 该临界值随纤维弹性模量的增大而减小; 当纤维模量与基体模量相差较大时, 复合材料的增强系数和减柔系数几乎不受时间变化的影响。      

碱处理对竹纤维及竹纤维增强聚丙烯复合材料性能的影响

为探究竹纤维表面能对纤维与树脂的粘附功及复合材料界面的影响,采用碱处理对竹纤维进行表面改性,通过模压工艺制备了竹纤维增强聚丙烯(PP)复合材料。研究了碱处理对竹纤维性能、竹纤维与PP间的粘附功及对竹纤维/PP复合材料力学性能的影响,采用SEM研究了不同浓度碱处理后竹纤维表面形貌的变化。结果表明:随着碱浓度的增加,竹纤维断裂强度呈现一定波动,当碱浓度为1wt%时竹纤维断裂强度达到最大值;竹纤维与PP的粘附功与竹纤维极性比密切相关,竹纤维极性比越小,粘附功越大;随着碱浓度增大,竹纤维与PP间粘附功与竹纤维/PP复合材料剪切性能呈现相同的趋势,并且都在碱浓度为20wt%时达到最大值,此时竹纤维与PP的粘附功较未处理时提高了67.18%;竹纤维/PP复合材料剪切性能较未处理时提高了23.29%;复合材料弯曲强度在碱浓度为5wt%时达到最大值,相比未处理时提高了23.13%。     

碳纤维-玻璃纤维层内混杂单向增强环氧树脂复合材料拉伸性能

采用不同混杂比的碳纤维-玻璃纤维层内经向混编单轴向织物制备了混杂纤维增强环氧树脂复合材料, 研究了不同混杂结构和不同混杂比的碳纤维-玻璃纤维/环氧树脂复合材料拉伸性能的变化及破坏形式。0°拉伸结果表明:同种混杂织物的不同混杂结构中, 碳纤维相对集中的完全对齐结构强度最高, 不同混杂比织物的完全对齐结构强度相当;碳纤维-玻璃纤维/环氧树脂复合材料的模量遵循混合定律。90°拉伸结果表明:纤维与树脂间的界面结合强度为碳纤维/树脂>玻璃纤维/树脂, 碳纤维-玻璃纤维/环氧树脂复合材料的强度、模量与材料厚度方向上界面的不同形式(单一或交替界面、碳纤维或玻璃纤维的分布位置等)有关, 与碳纤维的含量基本无关。      

基于深度学习的短纤维增强聚氨酯复合材料性能预测基于深度学习的短纤维增强聚氨酯复合材料性能预测

结合深度学习在图像识别领域的优势,将卷积神经网络（CNN）应用于有限元代理模型,预测了平面随机分布短纤维增强聚氨酯复合材料的有效弹性参数,并针对训练过程出现的过拟合,提出了一种数据增强的方法。为验证该代理模型的有效性,比较了其与传统代理模型在预测有效杨氏模量和剪切模量上的精度差异。在此基础上结合蒙特卡洛法利用卷积神经网络代理模型研究了材料微几何参数不确定性的误差正向传递。结果表明:相对于传统代理模型,卷积神经网络模型能更好地学习图像样本的内部特征,得到更加精确的预测结果,并在训练样本空间外的一定范围内可以保持较好的鲁棒性;随着纤维长宽比的增大,微几何参数的不确定性对材料有效性能预测结果会传递较大的误差。      

纳米改性连续纤维增强热塑性树脂复合材料及其力学性能研究进展

连续纤维增强热塑性树脂复合材料（CFRTP）具有易加工、可回收、力学性能优异等特点,在航空航天、汽车等领域的应用前景良好。随着纳米技术的发展,研究者发现利用纳米材料改性CFRTP可显著提升其性能。本文对纳米材料改性CFRTP领域的最新研究进展进行了综述,首先对CFRTP改性中常用的纳米材料（如碳纳米管、石墨烯以及无机纳米颗粒）和主要的改性方法（包括树脂基体中直接添加纳米填料和利用纳米材料对增强相纤维表面进行修饰）进行了介绍,在此基础上总结并讨论了纳米改性对CFRTP力学性能（包括界面结合性能、拉伸性能、动态力学性能以及冲击性能）的影响,最后对纳米材料改性CFRTP的发展方向进行了展望。      

陶瓷纤维增强氧化硅气凝胶复合材料力学性能试验

氧化硅气凝胶具有极低的热导率和密度,可作为很好的隔热材料,而脆弱的力学性能限制了其在隔热领域的应用。在不影响隔热效果的前提下,通过复合陶瓷纤维可增加氧化硅气凝胶的强度及韧性。试验探索了陶瓷纤维增强氧化硅气凝胶在室温下的拉伸、压缩和剪切等基本力学性能,分别研究了300℃、600℃和900℃下复合材料纤维铺层面方向的压缩性能,并采用扫描电子显微镜对高温试样微观结构进行了观察分析。结果表明：陶瓷纤维增强氧化硅气凝胶的性能表现出方向性,弹性模量在铺层面内方向与厚度方向的数值最大相差约28倍,强度极限亦然;在室温条件下,复合材料的拉伸和压缩弹性模量不同,X 、Y 和 Z 方向拉伸模量与对应的压缩模量之比分别为1.60、1.83和0.56;高温下复合材料沿厚度方向收缩,收缩量随温度升高而增大,900℃下的最大收缩量可达10.8%;高温下复合材料铺层面内方向压缩性能随温度升高而增强。     

激光改性纤维对其增强环氧树脂复合材料力学性能的影响

利用激光对玻璃纤维、玄武岩纤维和碳纤维进行表面改性后,以环氧树脂为基体,分别制备三种纤维增强环氧树脂复合材料。利用SEM和万能试验机对表面改性前后的碳纤维形态、力学性能及三种纤维/环氧树脂复合材料的力学性能和断面形貌进行表征,研究了纤维激光表面改性对三种纤维及其增强环氧树脂复合材料力学性能的影响。结果表明:激光表面改性对碳纤维/环氧树脂复合材料的力学性能提升最高,其拉伸强度最大提高了77.06%,冲击强度最大提高了31.25%,玄武岩纤维/环氧树脂复合材料的力学性能提升次之,而玻璃纤维/环氧树脂复合材料的力学性能有所下降。因此,激光进行表面改性适用于碳纤维和玄武岩纤维。     

单向连续碳纤维-玻璃纤维层间混杂增强环氧树脂基复合材料的力学性能

为了研究连续单向纤维的层间混杂方式对复合材料力学性能及破坏方式的影响,采用碳纤维-玻璃纤维体积比为1∶1,以拉-挤成型法制备了具有不同层间混杂结构的连续单向纤维增强环氧树脂基复合材料,并研究了不同层间混杂结构的连续单向碳纤维-玻璃纤维增强环氧树脂基复合材料的力学性能及破坏形式。结果表明：具有层间混杂结构的复合材料抗拉强度处于纯碳纤维/环氧树脂复合材料和纯玻璃纤维/环氧树脂复合材料之间,复合材料的拉伸断裂方式为劈裂;具有层间混杂结构的复合材料的层间剪切强度均优于纯碳纤维/环氧树脂复合材料和纯玻璃纤维/环氧树脂复合材料,复合材料的剪切断裂方式为层间断裂。     

Effect of fiber arrangement on mechanical properties of short fiber reinforced composites

The present paper developed a three-dimensional (3D) “tension–shear chain” theoretical model to predict the mechanical properties of unidirectional short fiber reinforced composites, and especially to investigate the distribution effect of short fibers. The accuracy of its predictions on effective modulus, strength, failure strain and energy storage capacity of composites with different distributions of fibers are validated by simulations of finite element method (FEM). It is found that besides the volume fraction, shape, and orientation of the reinforcements, the distribution of fibers also plays a significant role in the mechanical properties of unidirectional composites. Two stiffness distribution factors and two strength distribution factors are identified to completely characterize this influence. It is also noted that stairwise staggering (including regular staggering), which is adopted by the nature, could achieve overall excellent performance. The proposed 3D tension–shear chain model may provide guidance to the design of short fiber reinforced composites.     

氧化石墨烯改性玄武岩纤维及其增强环氧树脂复合材料性能

为了改善玄武岩纤维/环氧树脂复合材料的界面性能,通过偶联剂对氧化石墨烯进行改性,并将改性后的氧化石墨烯引入到上浆剂中对玄武岩纤维进行表面涂覆改性,同时制备了氧化石墨烯-玄武岩纤维/环氧树脂复合材料.采用FTIR表征了氧化石墨烯的改性效果;运用SEM分析了改性上浆剂处理对玄武岩纤维表面及复合材料断口形貌的影响和作用机制.结果表明:偶联剂成功接枝到氧化石墨烯表面;玄武岩纤维经氧化石墨烯改性的上浆剂处理后,表面粗糙度及活性官能团含量增加,氧化石墨烯-玄武岩纤维/环氧树脂界面处的机械齿合作用及化学键合作用增强,界面黏结强度得到改善,玄武岩纤维的断裂强力提高了30.8%,氧化石墨烯-玄武岩纤维/环氧树脂复合材料的层间剪切强度提高了10.6%.     

碳纤维增强油井水泥石的力学性能

油井水泥石在井下易脆裂,造成油井层间封隔失效,进而影响油井开采。为了解决这一问题,需要对水泥石进行降脆增韧。首先,考察了甲基纤维素和羧甲基纤维素对碳纤维的分散效果;然后,研究了碳纤维对油井水泥石抗压强度、抗折强度和劈裂抗拉强度的影响,并模拟井下环境测试了水泥石单轴和三轴应力-应变曲线;最后,使用扫描电子显微镜对碳纤维增强水泥石的微观形貌进行观察,探讨碳纤维对水泥石的增韧机制。结果表明:0.2wt%的羧甲基纤维素溶液可有效分散碳纤维;养护28d后,0.3wt%碳纤维增强水泥石的抗压强度、抗折强度和劈裂抗拉强度较纯水泥石的分别提高8.6%、31.5%和52.4%,三轴直接加载条件下,其弹性模量较纯水泥石的低49.5%;经过分散的碳纤维在水泥石中乱向分布,形成三维网络结构,通过桥联、剥离及拔出耗能作用增强水泥石。研究结果为解决油井水泥石易脆裂的问题提供了理论参考。     

长玻璃纤维增强聚丙烯复合材料的研究

选用无碱玻璃纤维 ,采用特殊方法使长纤维与基体聚丙烯树脂有序复合 ,制备了一系列不同纤维长度、含量以及采用不同表面处理的玻纤 /PP复合材料 ,并测定了材料的力学性能 ,通过SEM观察了复合体系的界面 ,从微观上验证了材料力学性能的变化规律。实验表明 ,所采用的复合材料制备方法可使纤维的排布更加有序 ,并可改进材料的力学性能。     

碳纤维增强铜基复合材料制备方法研究进展

综述了碳纤维增强铜基复合材料的主要制备方法及其发展现状,重点讨论了粉末冶金法、热压扩散烧结法、熔渗法、PVD法、CVD法及电镀法等常用制备工艺的原理及特性,分析了不同制备方法的优缺点及适用领域,提出了现有方法中存在的问题,并展望了碳纤维增强铜基复合材料的发展趋势及在输变电领域的应用前景。     

混杂纤维增强水泥基复合材料的力学性能

研究了化学改性聚丙烯（PP）纤维以及掺加聚丙烯纤维和芳纶纤维混杂比例和混杂效应对水泥基复合材料力学性能的影响,并构建了纤维增强水泥砂浆界面层的物理模型,描述了纤维对水泥砂浆的增强机制。实验表明,聚丙烯纤维经改性后使水泥砂浆前期抗折强度明显提高,聚丙烯纤维和芳纶纤维的混杂使水泥砂浆的后期抗折强度显著提高。改性聚丙烯纤维掺加体积分数为0.56%,芳纶纤维的体积分数为0.24%时,混杂纤维增强水泥砂浆试样较空白试样,3天、28天抗折强度分别提高了18.48%、31.17%,3天、28天抗压强度分别提高了7.16%、5.19%。