不同拉伸条件下基于Weibull模型的粘胶基碳纤维强度分布研究

从粘胶基碳纤维的拉伸实验得到其 S-S曲线和强度、模量、断裂伸长等力学性能数据 ,表明该材料是典型的脆性断裂 ,且断裂分散性较大。采用 VB编程软件设计了 Weibull程序 ,该模型能计算出碳纤维的平均强度、Weibull模数、尺度参数 ,并能模拟碳纤维强度的累积概率分布和概率密度曲线。不同氧化拉伸条件下强度的实验数据基本上落在程序模拟出的累积概率分布直线上 ,证明了该数学模型适用于分析碳纤维强度分布。在氧化完全松弛的条件下 ,粘胶基碳纤维的平均强度较高 ,但 Weibull模型分析的结果表明氧化拉伸比为 -5 %时 ,Weibull模数最大 ,不匀率最小 ,而氧化拉伸对粘胶基碳纤维模量没有显著影响。     

基于DSC法的混杂纤维增强树脂基复合材料拉挤工艺研究

为提高碳纤维/玻璃纤维混杂增强树脂基复合材料(以下简称混杂纤维复合材料)拉挤型材的固化质量和力学性能,通过差示扫描量热分析(DSC)法,得出了相同配方条件下复合材料的4种不同升温速率下的固化DSC曲线,运用T–β外推法初步确定了三段式加热拉挤成型方法的温度工艺参数范围。在此基础上,选择直径为10 mm的混杂纤维棒材作为研究对象,变化不同的拉挤温度和速度制备型材,并对其分别进行力学性能试验,研究拉挤工艺参数对复合材料力学性能的影响,从而根据力学性能表征进一步明确适合于本配方的生产工艺参数。结果表明,通过以上方法所得到的混杂纤维复合材料拉挤工艺参数能够满足制备混杂纤维复合材料型材的要求;与传统的经验方法相比,采用该方法更为高效和准确。     

预浸料软硬度定量表征测试方法研究

软硬度是复合材料预浸料的重要工艺性能之一,国内外一直缺乏预浸料软硬度的定量表征方法。本文自行研制了软硬度设备,通过将预浸料在固定直径芯轴上悬垂距离来定量表征预浸料的软硬度,研究了芯轴直径、试样长度、放置时间等因素对软硬度的影响,确定了最佳参数并建立测试方法。通过对同规格不同批次预浸料、不同规格预浸料以及不同外置时间预浸料的软硬度测试进一步对测试方法进行了验证。结果表明:对不同批次间预浸料软硬度数据度差异较小,该方法测试状态稳定;对不同规格下预浸料的软硬度,该测试方法能够有效区分;对同一材料软硬度测试方法能够定量表征出不同外置时间下软硬度的变化趋势;说明该测试方法是合理可行的。     

阳极氧化处理对碳纤维强度离散性的影响及表征

采用阳极氧化法对碳纤维进行了表面处理,并探讨了表面处理后碳纤维接触角、强度的变化和碳纤维强度离散性的表征方法。研究发现:碳纤维在阳极氧化表面处理后,接触角变小,说明浸润性增强,强度略有下降,离散性略有增大;表面处理后随放置时间延长,接触角有一定程度增大,强度继续下降,离散性继续增大。用强度CV值和韦伯分布拟合强度所得的韦伯模数两种不同指标表征了表面处理后碳纤维的强度离散性,经验证,两种表征方法的一致性好。     

碳纤维及其复合材料性能测试方法和评价指标

从宏观和微观两个角度综述了碳纤维及其复合材料性能的常用测试方法。表明浸润性是表征树脂浸入纤维的重要参数,接触角、表面能、粘附功是表征浸润性常用的指标;纤维表面性能如粗糙度、化学特性等都影响着复合材料界面粘结性能,常用SEM、AFM、XPS等手段测试;复合材料界面结合强度的大小反应了复合材料力学性能的好坏。     

溶液喷射法制备聚丙烯腈基纳米碳纤维的研究

采用溶液喷射法制备了聚丙烯腈(PAN)纳米纤维,探讨了纺丝工艺参数对纤维形貌和直径的影响,优化了纺丝工艺,制得了直径分布为160～380 nm的PAN纳米纤维;经260℃空气氛围预氧化,900℃氮气氛围碳化,对得到的纤维的结构和形貌进行了表征,结果表明得到了平均直径为170 nm的纳米碳纤维。     

基于尖锐四棱锥压头的陶瓷材料断裂韧性测试方法

根据量纲分析建立陶瓷材料断裂韧性与压入响应参数以及裂纹开裂长度之间的无量纲函数关系,采用虚拟裂纹闭合法和有限元数值分析法实现HPC裂纹、RC裂纹以及过渡裂纹的裂纹尖端等KI开裂面几何的设计,通过对仿真数据的回归分析得到无量纲函数关系的通解,进而建立基于尖锐四棱锥压头的陶瓷材料断裂韧性压入测试方法.对三种陶瓷试样压入实验表明,测试方法精度较高,可以在较小载荷条件下产生裂纹,测试结果几乎不受压入载荷的影响.     

聚双环戊二烯/碳纤维复合材料的制备和力学性质

采用扫描电镜(SEM)对分别经刻蚀、氧化及氧化后再刻蚀的碳纤维表面进行表征;用不同方法处理的碳纤维通过反应注射成型(RIM)技术制备出了聚双环戊二烯(PDCPD)/碳纤维复合材料,对材料的断面形貌和力学性能进行了表征.结果表明,在实验范围内,经过氧化后再刻蚀的碳纤维其复合材料力学性能提高较大,随着碳纤维含量的增加,复合...     

PAN原丝直径对碳纤维收率的影响

对不同预氧化条件下两种直径PAN原丝的碳纤维收率进行了分析,并利用TG、XPS、NMR、Raman等测试表征方法,深入讨论了原丝直径对其碳纤维收率的影响。结果表明:预氧化温度越高,PAN原丝的碳纤维收率越高,相同工艺条件下粗直径PAN原丝的碳纤维收率高于细直径原丝的碳纤维收率,粗直径PAN原丝的热失重一直低于细直径原丝的热失重,细直径PAN预氧丝的预氧化程度高于粗直径PAN原丝的预氧化程度,而不同直径预氧丝表面元素及碳纤维表面微晶结构无差异。     

一种表征聚丙烯腈纤维预氧化程度的新方法

在工业化连续碳纤维生产线上,对干喷湿纺和湿纺的聚丙烯腈(PAN)原丝进行对比实验,跟踪了这两类原丝在预氧化和碳化过程中力学性能的变化规律。采用密度仪、纤维单丝断裂强力仪等测试分析了不同预氧化条件下预氧化纤维的力学性能与相应碳纤维力学性能之间的内在联系。结果表明,碳纤维的力学性能与预氧化纤维的断裂强力密切相关。通过与不同的预氧化程度表征方法相比较,提出了以预氧化纤维的强力损失率作为表征PAN纤维预氧化程度的新方法。     

Mechanical and structural characterization of electrospun PAN-derived carbon nanofibers

The mechanical and structural properties of individual electrospun PAN-derived carbon nanofibers are presented. EELS spectra of the carbonized nanofibers shows the C atoms to be partitioned into ∼80% sp² bonds and ∼20% sp³ bonds which agrees with the observed structural disorder in the fibers. TEM images show a skin-core structure for the fiber cross-section. The skin region contains layered planes oriented predominantly parallel to the surface, but there are some crystallites in the skin region misoriented with respect to the fiber long axis. Microcombustion analysis showed 89.5% carbon, 3.9% nitrogen, 3.08% oxygen and 0.33% hydrogen. Mechanical testing was performed on individual carbonized nanofibers a few microns in length and hundreds of nanometers in diameter. The bending modulus was measured by a mechanical resonance method and the average modulus was 63 GPa. The measured fracture strengths were analyzed using a Weibull statistical distribution. The Weibull fracture stress fit to this statistical distribution was 0.64 GPa with a failure probability of 63%.     

Simultaneous effects of silanized coal fly ash and nano/micro glass fiber on fracture toughness and mechanical properties of carbon fiber‐reinforced vinyl ester resin composites

In this study, the simultaneous effects of both silanized coal fly ash (S‐CFA) and nano/micro glass fiber (nGF) on fracture toughness and mechanical properties of vinyl ester (VE) resin filled with carbon fiber‐based composite materials were investigated. The CFA was treated with (3‐trimethoxysilyl) propyl methacrylate to introduce the methacryloxy groups into the surface of CFA, and was confirmed by using FTIR technique. The nGF and S‐CFA with different weight ratios were well mixed with VE resin by using of high‐speed mechanical stirrer, and ultrasonic technique before using as matrices for fabrication of carbon fiber‐based composite materials via sheet molding compound (SMC) method and hot curing processing. Many characteristics of both cured VE resin composites and carbon fiber‐based composite were examined such as mechanical properties, fracture toughness, and morphology. The results showed that by adding of both 0.1 wt% nGF and 1 wt% S‐CFA into VE resin the tensile strength, tensile modulus, flexural strength, K_IC, impact strength as well as the Mode I interlaminar fracture toughness (G_IC) of VE composites and carbon fiber based composites get optimum values and increased about 61.39%; 39.83%; 36.21%; 103.1%; 81.79%; 48.61%, respectively when compared with pristine materials. POLYM. ENG. SCI., 59:584–591, 2019. © 2018 Society of Plastics Engineers     

Mechanical properties of vapor grown carbon nanofibers

Individual as-fabricated, high temperature heat-treated and graphitized/surface oxidized vapor grown carbon nanofibers (VGCNFs), with average diameter of 150 nm were tested for their elastic modulus and their tensile strength by a MEMS-based mechanical testing platform. The elastic modulus increased from 180 GPa for as-fabricated, to 245 GPa for high temperature heat-treated nanofibers. The nominal fiber strengths followed Weibull distributions with characteristic strengths between 2.74 and 3.34 GPa, which correlated well with the expected effects of heat treatment and oxidative post-processing. As-fabricated VGCNFs had small Weibull modulus indicating a broad flaw population, which was condensed upon heat treatment. For all VGCNF grades, the nanofiber fracture surface included the stacked truncated cup structure of the oblique graphene layers comprising its backbone and cleavage of the outer turbostratic or thermally graphitized layer.     

碳纤维对C_f-HA/PMMA复合材料力学性能的影响

采用原位合成和溶液共混相结合的方法,制备了短切碳纤维(Cf)增强纳米羟基磷灰石(hydroxyapatite,HA)/聚甲基丙烯酸甲酯[poly(methyl methacrylate),PMMA]生物复合材料(Cf-HA/PMMA).重点研究了短切碳纤维对Cf-HA/PMMA复合材料的微观结构和力学性能的影响.采用万能材料试验机测试了Cf-HA/PMMA复合材料的力学性能,使用扫描电子显微镜对材料微观形貌进行了测试和表征.结果表明:采用浓硝酸和二甲基亚砜处理后的碳纤维与PMMA基体的界面结合性得到有效改善,显著提高了Cf-HA/PMMA复合材料的力学性能;碳纤维和HA的质量分数分别为4%和8%,复合材料的弯曲强度、弯曲模量、拉伸强度和压缩强度均达到最佳值.     

Processing and properties of solution impregnated carbon fiber reinforced polyethersulfone composites

Carbon fiber reinforced polymer composites are attractive because of their high stiffness and strength‐to‐weight ratios. In order to fully utilize the stiffness and strength of the reinforcement fiber, it is necessary to bring the polymer matrix and the reinforcement fiber together with homogeneous wetting. In this paper, a solution processing technique and the mechanical properties of carbon fiber reinforced polyethersulfone composites were investigated. The polymer was dissolved in cyclopentanone and fed onto a continuous carbon fiber tow using a drum winder. The solution‐processed composite prepregs were then layed up and compression molded into unidirectional composite panels for evaluation. The composite samples showed uniform fiber distribution and reasonably good wetting. The longitudinal flexural modulus was as high as 137 GPa, and longitudinal flexural strength 1400 MPa. In addition, the effects of polymer grade and processing conditions on the mechanical properties of the composites were discussed. It is suggested that the transverse properties and interlaminar fracture toughness could benefit from higher polymer matrix molecular weight. A careful design in the spatial distribution of the molecular weight would be necessary for practical applications.     

Interfacial toughness and its effect on compression strength in polycarbonate/carbon fiber composites

Processing Polycarbonate/carbon fiber composites for long times at high temperatures significantly improved adhesion between the matrix and the fibers. The interfacial properties were studied by measuring transverse fracture toughness, observing fracture specimens by scanning electron microscopy, and by monitoring composite cross-sections using atomic force microscopy. The processing treatment provided an ideal method for varying the properties of the interface without changing any other properties. We used this method to study the effect of interfacial properties on the axial compression properties of unidirectional composites. Both the compression strength and compression modulus increased significantly as the fiber/matrix adhesion improved. We concluded that improving interfacial adhesion increased compression properties by inhibiting fiber microbuckling.     

Mechanical behavior and fracture toughness characterization of high strength fiber reinforced polymer textile composites

The mechanical and fracture behavior of polymer composites are the subject of great interest from many years and still interesting among the researchers. Composites are extremely used for their superior mechanical, thermal and fracture toughness properties in various sectors such as automobile, aerospace and defense applications. In this article, unidirectional and woven high strength glass, carbon and Kevlar fiber reinforced polymer textile composites are taken into consideration for the comprehensive review of mechanical behavior and fracture toughness characterization. Current review work began with the introduction to polymer textile composites with its manufacturing stages, processing techniques and factors affecting the performance under mechanical loading. The mechanical behavior of high strength fiber reinforced polymer (HSFRP) textile composites was discussed in tension, compression, flexural, low velocity and high velocity impact loading with the recent numerical and experimental characterization studies. Textile geometrical modeling and CAE tools are also described for numerical characterization. Under the influence of mechanical loading on composites, failure occurs actually due to the crack initiation and propagation, so it is also required to characterize. Significant elements of fracture mechanics are well described for the better understanding of fracture toughness characterization. Mode-I, Mode-II, Mode-III interlaminar and Mode-I intralaminar fracture toughness characterization are widely explained by considering the effect of filler content, fiber orientation and fiber volume fraction. Fracture toughness characterization techniques and research summery are uniquely presented by considering various factors under one umbrella for better understanding of fracture behavior. Statistical Weibull distribution is also presented for the failure prediction of composites.

     

Estimate of carbon fiber’s fracture toughness based on the small angle X-ray diffraction

According to the Weibull theory, the micropore sizes were used to analyze the stress intensity factor of carbon fiber monofilament crack tip stress field. Based on the analysis of carbon fiber monofilament and multifilament tensile strength, diameter and micropore size get the relationship between carbon fiber monofilament tensile strength and the pore radius by the Guinier principle and Griffith fracture theory, thus to estimate carbon fiber fracture toughness. The results show that this method can implement the estimation of fracture toughness on the basis without destroying the structure of the carbon fibers; the fracture toughness of T300 estimated by the average pore size was 1.34 MPa·m^1/2, in accordance with data 1.25 and 1.32 MPa·m^1/2 by producing defects, errors are 7.2 and 1.5%, respectively.     

Influence of multiwalled carbon nanotubes on the processing behavior of epoxy powder compositions and on the mechanical properties of their fiber reinforced composites

This study reports the preparation of advanced carbon fiber composites with a nanocomposite matrix prepared by dispersing multiwall carbon nanotubes (CNTs) in a powder type epoxy oligomer with two different processing techniques (1) master batch dilution technique and (2) direct mixing (with the help of twin‐screw extruder in both cases). The master batch technique shows a better efficiency for the dispersion of the CNTs aggregates. The rheological results demonstrate that the incorporation of the CNTs into the epoxy oligomer leads, as expected, to a marked increase in the viscosity and of the presence of a yield stress point that also depends on the processing technique adopted. Carbon fiber (CFRP) and glass fiber (GFRP) composite materials were produced by electrostatic spraying of the epoxy matrix formulations on the carbon and glass fabric, respectively, followed by calendering and mold pressing. The mechanical properties of the obtained epoxy/CNT‐matrix composite materials, such as interlaminar fracture toughness, flexural strength, shear storage and loss moduli are discussed in terms of the processing techniques and fabric material. The incorporation of 1 wt% CNTs in the epoxy matrix results in a relevant increase of the fracture toughness, flexural strength and modulus of both CFRP and GFRP. POLYM. COMPOS., 37:2377–2383, 2016. © 2015 Society of Plastics Engineers     

碳纤维改性HA/PMMA生物复合材料力学性能的研究

采用原位合成与溶液共混相结合的方法,制备了短切碳纤维增强纳米羟基磷灰石(HA)/聚甲基丙烯酸甲酯(PMMA)生物复合材料。研究了碳纤维的含量和长度对HA/PMMA复合材料结构和力学性能的影响。采用万能材料试验机和扫描电子显微镜对复合材料的力学性能及断面的微观形貌进行了测试和表征。结果表明:碳纤维在HA/PMMA复合材料中分布均匀,有效提高了复合材料的力学性能;碳纤维含量为4%时,复合材料的拉伸强度、弯曲强度、压缩强度和弹性模量等均达到最大值;复合材料的断裂伸长率随碳纤维含量的增加而减小;当碳纤维含量一定时,随其长度的增加,复合材料的拉伸强度、弯曲强度和弹性模量均增加,但断裂伸长率降低。