平纹编织碳纤维/Kevlar纤维增强混杂复合材料微-宏观切削去除机理研究

由于碳纤维和Kevlar纤维力学性能相差迥异,在C-K纤维混杂增强复合材料(Carbon-Kevlar fiber hybrid composite,CKFH)加工中易产生加工缺陷,比单种纤维复合材料的加工缺陷更难控制。由此,从微观和宏观角度,构建CKFH三维有限元切削模型,分析CKFH的切削去除机理及平纹编织结构对切削过程的影响机制。结果表明,在不同纤维取向下,Kevlar纤维均易产生抽丝拉毛现象,尤其当纤维取向θ=0°/180°时最为明显;纤维取向θ=0°/180°时,切屑多为卷曲片状切屑,纤维取向θ=45°、90°、135°时,两种纤维的断裂相互影响,切削表面、切屑形态均与切削方向存在密切关系,当纤维取向θ=45°时,多为细小片状切屑,纤维取向θ=90°时,切屑多为絮状块状切屑,纤维取向θ=135°时,切屑多为成块状切屑;从碳纤维切向Kevlar纤维时,Kevlar纤维出现松散、抽丝拉毛现象明显,从Kevlar纤维切向碳纤维时,在Kevlar纤维的韧性弯曲区碳纤维发生弯曲脆断、碎裂,易出现凹坑;平纹编织结构对切削应力的传递具有明显的阻断作用,有限元仿真结果与试验观测结果基本吻合。     

碳纤维复合材料层合板三点弯曲损伤仿真研究

研究碳纤维复合材料在弯曲载荷作用下的失效形式与损伤过程,以预测材料抗外力损伤性能,指导碳纤维复合材料车身结构设计。进行碳纤维复合材料性能试验和三点弯曲试验,获得材料力学性能参数。建立基于Tiebreak算法的碳纤维复合材料层合板三点弯曲有限元模型,与试验对比验证模型的有效性。研究单元划分方式和Tiebreak接触层设置方式对仿真结果的影响规律,实现碳纤维复合材料分层破坏和纤维断裂的复杂失效及弯曲大变形损伤过程模拟。研究结果表明,计算精度与Tiebreak接触层设置相关,层合板弯曲变形的层间裂纹和层内裂纹扩展速度不同且相互影响。     

固化方式和纤维表面处理对碳纤维-树脂界面化学组成的影响

对碳纤维进行低温等离子法表面处理,分别在室温和微波固化条件下将碳纤维与环氧树脂复合成型,制备出碳纤维复合材料.采用原子力显微镜、拉曼光谱对碳纤维表面形貌和微观结构进行表征,采用扫描电镜和能量散射光谱对碳纤维-树脂界面区形貌和元素分布进行表征.结果表明,碳纤维经处理后,表面无序结构比例增大,有利于提高纤维的微波吸收能力,使微波固化复合材料的界面结合比室温固化复合材料更牢固.经过表面处理的碳纤维与树脂形成良好的化学键合,S i元素在复合材料界面区发生偏聚.     

碳纤维增强树脂基复合材料的热膨胀行为

采用光纤法对碳纤维增强树脂基复合材料沿纤维方向的热膨胀应变进行测试,然后分别用传统的片状模型和改进模型对复合材料沿纤维方向的热膨胀应变进行了理论计算,将计算结果与测试结果进行对比分析;之后利用改进模型和ABAQUS有限元软件分别计算得到了复合材料沿垂直于纤维方向的热应力,并利用有限元模拟了纤维排布对热应力的影响,得到了热应力的分布。结果表明:随着温度升高,复合材料的热膨胀应变基本呈线性增加,纤维分布集中区域的热应力可达到一般区域的1.5倍以上,应力集中现象产生于纤维与基体的接触处;与片状模型相比,改进模型计算得到的热应变与试验结果更吻合,误差小于10%,证明了改进模型的正确性和所建有限元模型的合理性。     

CFRP纤维方向对切削过程影响规律的仿真研究

碳纤维增强复合材料是一种典型弹脆性材料,其纤维铺层方向与材料加工性能、破坏机理和切削质量有着密切的关系。针对复合材料各向异性的特点,利用Abaqus/Explicit有限元仿真软件,基于Hashin失效准则,建立碳纤维复合材料单向纤维铺层二维正交切削宏观模型。研究不同铺层方向条件下纤维和基体的破坏机理,开展复合材料平面铣削试验,并将试验加工得到的铣削表面与仿真结果进行了比较,验证了模型的合理性。     

注塑成型短玻纤增强复合材料各向异性弹性常数预测方法

针对注塑成型短玻纤增强复合材料,研究二阶纤维取向张量与纤维取向角度之间的连续函数关系,建立纤维均质化RVE模型。基于Taguchi正交试验设计方法,利用DIGIMAT软件对短玻纤增强复合材料RVE模型进行仿真试验,定量分析纤维质量分数（A）、纤维长径比（B）和纤维取向张量（C）对短玻纤增强复合材料力学性能的影响规律。考虑注塑成型过程中的纤维分层效应,提出了夹芯分层模型并进行铺层设计。基于灰箱理论和反求工程,选取纤维长径比、表层厚度比和芯层厚度比、表层纤维取向张量、纤维取向矢量旋转角四个影响因素,反演预测短玻纤增强复合材料PA66（GF50）正交各向异性弹性常数,与材料拉伸弹性模量E₃₃、泊松比u₃₁和泊松比u₃₂的试验结果对比,相对误差分别为0.80%、0.29%和1.35%。     

碳纤维复合材料低速冲击特性及损伤分析研究

针对碳纤维复合材料汽车保险杠的低速耐冲击性能问题,利用真空辅助树脂扩散成型工艺制备了不同铺层比例与铺层顺序的碳纤维复合材料试样,对其进行了简支梁低速冲击性能试验,根据低速冲击响应特性曲线及损伤模式探究了复合材料能量吸收机理;同时基于ABAQUS/Explicit对典型铺层试样建立了简支梁冲击仿真模型,利用Hashin失效准则进行失效判断,研究了低速冲击响应应力变化及损伤过程并将模拟结果与实验值进行了比较。研究结果表明:碳纤维复合材料简支梁低速冲击主要损伤模式为纤维断裂,通过增加(0,90)铺层能够提高接触力载荷与冲击韧性强度,通过在试样冲击表面铺设(±45)铺层能够缓解结构剧烈破坏。峰值载荷误差为5.1%,峰值位移误差为3.2%,证明了模型的有效性,为碳纤维复合材料保险杠提供了设计基础。     

碳纤维表面处理对单向C/C复合材料强度的影响

通过对碳纤维表面进行适当的氧化处理 ,改善纤维 /基体之间的界面结合 ,能在复合材料中得到较好的纤维强度利用率 ,提高材料性能。本文在不同条件下对碳纤维进行液相氧化和空气氧化处理 ,并测定了所制备的单向 C/C复合材料的强度 ,研究了不同氧化工艺条件对复合材料拉伸强度的影响 ,对采用氧化后纤维制备材料断裂机制的改变进行了讨论 ;研究发现液相氧化处理对 C/C复合材料的性能影响较为显著。     

铺丝成形复合材料格栅筋条的纤维形态与弯曲性能评价

为进一步提高复合材料格栅筋条结构承载效率,提出了基于“剪断-续铺”的格栅节点纤维形态调控方法,采用显微观察、有限元仿真、试验验证的手段,研究了不同剪断续铺层含量和分布位置对复合材料格栅节点处纤维形态和格栅筋条弯曲性能的影响。结果表明,复合材料格栅筋条铺丝成形过程中,合理的非连续铺层在提高筋条极限弯曲载荷的同时,还会在其内部引入伪韧性弯曲行为。仿真结果与试验结果误差小于8%,具有良好的一致性。利用建立的有限元模型分析了含非连续铺层的格栅结构失效机理。综合分析非连续铺层对格栅节点纤维形态、格栅结构弯曲载荷承载能力和力学行为的影响,对于常见格栅筋条,其最优的格栅筋条节点非连续层含量为25%且在节点顶部集中分布。     

涂层刀具高速铣削碳纤维复合材料的铣削力研究

由于碳纤维复合材料(CFRP)的各向异性,纤维的铺层方向对其整体性能有重要的影响。本文采用斜角自由切削方法对具有12种不同纤维方向的T800、T700和T300碳纤维复合材料的切削力进行了试验研究,得出了CFRP单向层合板在不同基体类型和不同纤维方向下切削力的变化规律,并分析了纤维结构对切削力的影响机理。结果表明:基体类型对切削力的影响均匀稳定,无方向性;纤维方向对切削力的影响具有显著的方向性,对切削力影响的强弱关系为F_XF_ZF_Y。     

Effect of fiber orientation on friction and wear of fiber reinforced polymeric composites

The friction and wear behavior of composites (i.e. uniaxially oriented graphite fiber-epoxy, Kevlar fiber-epoxy and biaxially oriented glass fiber-MoS₂-polytetrafluoroethylene (PTFE)) was investigated as a function of varying fiber orientations with respect to the sliding direction. In graphite fiber-epoxy composites, both wear and friction coefficients were minimum when the orientation of the fibers was normal to the sliding surface. In Kevlar-epoxy composites when the fibers were oriented normal to the surface and the sliding direction, the wear rate was also minimum but the friction coefficient was the highest. In glass fiber-MoS₂-PTFE composites wear was minimum when the largest fraction of fibers was oriented normal to the sliding surface.     

热机械循环载荷下短纤维增强金属基复合材料性能分析

从复合材料内部组分的细观力学关系人手,选取代表体积元,基于Eshelby椭圆夹杂理论和瞬时体积平均的概念,通过集中张量描述纤维与基体以及纤维与纤维间的相互作用,并把在弹性范围内得到的各集中张量推广到弹塑性范围内,建立能够在弹塑性范围内分析热机械循环载荷作用下短纤维增强金属基复合材料的性质的模型。为了接近工程实际,假设纤维始终保持线弹性,对基体材料采用能反映bauschinger效应的混合硬化模型,依据基体的弹塑性状态决定复合材料整体的弹塑性状态。在塑性范围内,从各向异性的角度出发,采用增量法迭代得出每个加载步结束时复合材料整体以及各相的应力应变增量。编写控制应变和温度加载条件下,计算复合材料应力应变响应的程序,着重讨论纤维的外形、空间分布、体积百分比以及温度载荷对复合材料宏观性质的影响,并与相关的实验结果和数值结果进行比较。     

Sample preparation and image acquisition using optical-reflective microscopy in the measurement of fiber orientation in thermoplastic composites

A complete sample preparation procedure used to determine three-dimensional fiber orientation from optical micrographs of glass fiber-reinforced thermoplastic composites is presented. Considerations for elimination of irregularities in the elliptical footprints, contrast enhancement between fibers and surrounding polymer matrix, controlled-etching that allows the identification of small shadows where fiber recedes into the matrix, and topographical reconstruction of the elliptical footprint are described in the procedure. This procedure has produced high-quality optical micrographs employed to obtain accurate fiber orientation data for thermoplastic composites using the method of ellipses. The optimal definition of the nonelliptical footprints' borders allows an accurate measurement of orientation in small sampling areas.     

Tribological Characteristics of Sustainable Fiber-Reinforced Thermoplastic Composites under Wet Adhesive Wear

The friction and specific wear rate of sustainable kenaf fiber–reinforced polyurethane composites were investigated against stainless steel counterface and under wet contact conditions. The new composites were evaluated at different applied loads (50–80 N), sliding distances (up to 2.7 km), and fiber mat orientations. Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. The results revealed that sustainable kenaf fibers assisted in enhancing the wear and frictional performance of the polyurethane thermoplastic composite by about 59 and 90%, respectively. Operating parameters and mat orientation controlled the wear and the frictional behavior of the composite. Better wear performance was exhibited at high loads and when the fiber mats were oriented perpendicularly to the sliding direction. Observations of the worn surfaces revealed different features of damage such as microcracks, fiber tearing, fiber detachment, and delamination. However, there was no trace of fiber pull-out in any of the tested conditions.     

纤维改性聚四氟乙烯密封材料的制备及性能研究

以碳纤粉、短玻纤为主要增强纤维,采用冷压成型和自由烧结工艺制备改性聚四氟乙烯(PTFE)密封复合材料.分析了增强纤维含量以及不同纤维表面处理工艺对材料抗拉强度和压缩回弹率、应力松弛率等密封性能的影响.结果表明:增强纤维含量对材料密封性能具有显著影响,而表面处理工艺的影响则不甚明显;碳纤粉对PTFE的改性效果明显好于短玻纤;具有适当填充量的PTFE密封复合材料可满足200 ℃下长期使用的要求.     

Visualization of microfibrillar elements in cross‐section of polyacrylonitrile fiber along the fiber spinning line

The microfibrils served as the structural elements in polyacrylonitrile (PAN) fiber, which played an important role in the quality of the PAN precursor fibers. Their morphologies were examined by the scanning electron microscopy (SEM), atomic force microscopy (AFM) and high‐resolution transmission electron microscope (HRTEM). The microfibrils existed in all of PAN fibers and arranged evenly in the cross‐sections. Furthermore, the pores existed between the microfibrils. The unoriented microfibrillar network was already formed in nascent fiber during coagulated process. Although the microfibrillar network was elongated and the microfibrils oriented along the fiber longitudinal direction during the spinning process, the interconnected microfibrillar network was still existed in the fiber transverse section. Furthermore, the transverse connection of the microfibrils was reinforced and the small microfibrils were tended to aggregate into the large fibrils. For mechanical performance of PAN fibers, their tensile strength increased to 708 MPa and the elongation at break decreased to 15.5%. PAN fibers exhibited ductile rupture during the mechanical test and the microfibrils served as reinforcing elements.     

Evaluation of cellulose electro-active paper made by tape casting and zone stretching methods

Cellulose has been discovered as a smart material that can be used as sensor and actuator material. In this paper, cellulose smart material termed as electro-active paper (EAPap) is prepared by an automated process that includes tape casting and zone stretching. To evaluate characteristics of the EAPap, its Young’s modulus and piezoelectric charge constant are measured depending on the orientation angle, in comparison with the manually fabricated EAPap results. The zone stretching method can effectively align the cellulose fibers in the EAPap so as to improve its Young’s modulus as well as piezoelectric charge constant. The 0 degree oriented sample shows its maximum Young’s modulus and the 45 degree oriented sample exhibits the maximum piezoelectric charge constant. This 45 degree is associated with its shear piezoelectricity. The actuator performance of EAPap is evaluated by measuring its bending displacement depending on the orientation angle and the excitation voltage. The 45 degree oriented sample exhibits the maximum bending displacement. Details of the material preparation, the automation process, characterization and the actuator performance are addressed. This automated process that includes tape casting and zone stretching is suitable for mass production of the EAPap.     

基于短纤维增韧的复合材料制孔毛刺和分层抑制研究

由于复合材料的各向异性、树脂导热性差和层间韧性低,在二次机械加工特别是钻削制孔过程中,复合材料易产生毛刺、分层等缺陷和损伤,将短纤维层间增韧方法用于钻削损伤的抑制研究。制备低密度芳纶短纤维薄膜,采用低压接触成型工艺制备了含短纤维增韧与未增韧的复合材料层合板,进而在加工试验台上进行钻削试验。通过对试件加工孔的红外无损检测和显微观测,研究转速和短纤维增韧对复合材料制孔损伤的影响,结果表明提高转速和短纤维界面增韧可改善制孔质量。基于短纤维与基体间相互作用,揭示其增韧机理是由于短纤维在层间形成的丰富桥联抑制了分层扩展,同时短纤维与层间树脂复杂的破坏机制而产生额外的能量耗散,并讨论短纤维参数对增韧效果的影响。该方法为复合材料高质量加工提供借鉴意义。