超高分子量聚丙烯冻胶纤维的力学性能研究EI北大核心

采用冻胶纺丝法制备超高分子量聚丙烯纤维(UHMWPP),并在不同的拉伸温度下对其进行拉伸。研究了在不同拉伸倍率下,拉伸温度对UHMWPP纤维力学性能的影响。结果表面:UHMWPP纤维在室温低拉伸倍率下表现为结晶高聚物的拉伸行为,高温时则为硬弹性材料的拉伸行为。纤维的断裂强度与杨氏模量主要由拉伸倍率决定,断裂伸长率则由拉伸倍率和拉伸温度决定。     

超高分子量聚丙烯冻胶纤维的力学性能研究

采用冻胶纺丝法制备超高分子量聚丙烯纤维(UHMWPP),并在不同的拉伸温度下对其进行拉伸.研究了在不同拉伸倍率下,拉伸温度对UHMWPP纤维力学性能的影响.结果表面:UHMWPP纤维在室温低拉伸倍率下表现为结晶高聚物的拉伸行为,高温时则为硬弹性材料的拉伸行为.纤维的断裂强度与杨氏模量主要由拉伸倍率决定,断裂伸长率则由拉伸倍率和拉伸温度决定.     

熔纺UHMWPE纤维在拉伸过程中的结构与力学性能

采用高流动性的超高分子量聚乙烯(UHMWPE)树脂颗粒,以熔融纺丝法制备出了拉伸强度为1.6GPa的UHMWPE纤维。利用热分析(DSC)、广角X射线衍射(WAXD)、小角X射线散射(SAXS)、拉伸试验研究了UHMWPE纤维在拉伸过程中结构和力学性能的变化。研究显示,随着拉伸倍数的增加,UHMWPE纤维的结晶度增加,晶粒尺寸下降,纤维的缺陷度逐渐下降,取向度逐渐增大,拉伸强度逐渐增加;其结构和力学性能变化规律与凝胶法相似;有效拉伸倍率低可能是导致熔纺UHMWPE纤维的拉伸性能不如凝胶纺丝纤维的主要原因。     

竹纤维/不饱和聚酯复合材料拉伸强度及断面图像特征

研究纤维形态和表面处理对竹纤维/不饱和聚酯复合材料拉伸强度的影响及断面图像差分刺激特征。结果表明,纤维形态对复合材料拉伸强度有显著影响。化学浆纤维和竹原纤维增强复合材料的拉伸强度显著高于竹粉与机械浆纤维增强的复合材料。竹纤维经1,6-己二异氰酸酯与2-羟乙基丙烯酸酯改性后,复合材料拉伸强度显著提高。纤维处理前复合材料拉伸断面图像差分刺激角度值的直方图高度明显高于处理后的,拉伸断面电镜图像差分刺激角度值反映了复合材料拉伸强度的差异。     

化学处理和吸湿水对剑麻纤维及其与树脂界面性能的影响

使用KMnO₄、NaOH、阻燃剂、硅烷对剑麻纤维进行表面处理。采用单丝拉伸和微脱粘方法分别测试了剑麻纤维的拉伸性能及其与改性丙烯酸酯、环氧树脂的界面性能,考察了吸湿水对剑麻纤维表面形貌、拉伸性能及其与树脂界面粘结的影响,分析了相应的破坏模式。结果表明,经过表面化学处理后剑麻纤维的拉伸强度和模量均有不同程度的下降,其中经KMnO₄和硅烷处理后,纤维拉伸强度下降了44%,经NaOH处理后其拉伸强度降低了27%,阻燃剂处理对剑麻性能的影响不明显。表面化学处理还会降低剑麻纤维与改性丙烯酸酯的界面粘结强度,其下降的幅度与纤维拉伸强度下降程度不一致,阻燃剂处理的剑麻/改性丙烯酸酯的界面强度最低,仅为2.0 MPa,较未处理剑麻纤维复合体系下降了80%。经硅烷处理后,剑麻纤维的吸水率下降,吸水后其拉伸性能保留率高于未处理剑麻纤维。湿态条件下未处理剑麻纤维与环氧树脂的界面强度为6.6 MPa,高于硅烷处理剑麻/环氧树脂的界面强度,其断口形貌表明硅烷处理可导致微纤之间的弱粘结,从而降低了剑麻纤维自身及其与树脂的界面性能。     

聚己酸内酯纳米纤维的拉伸试验及表面表征

文中采用静电纺丝法制备了纳米聚己酸内酯纤维,对单根纤维进行了单向拉伸试验,研究了单根纤维在纳米尺度的基本力学性能;并通过原子力显微镜研究了纤维表面结构特征对纤维力学性能的影响。结果表明,在拉伸载荷作用下,随着纤维直径的减小,纤维的杨氏模量没有显著的变化;纤维表面特征对纤维的拉伸强度有重要影响,但对纤维的杨氏模量影响不大。     

PET和PAN纤维的拉伸形变和断裂过程

在扫描电子显微镜样品室中拉伸PET和PAN纤维,动态观察了纤维的形变和断裂行为,用照片记录了裂缝发生、发展和纤维最终断裂的过程。剪切带的出现和由此引起微裂缝的发生是PET纤维拉伸形变的主要特征,而个别大分子束的断裂形成裂缝的广泛出现则是PAN纤维的主要特征。研究得出纤维的结晶状况是拉伸下纤维形变和断裂行为的决定性因素。     

聚酰亚胺纤维复丝拉伸性能测试影响因素的研究

采用TG、DSC和万能材料试验机对聚酰亚胺纤维浸胶复丝拉伸性测试方法进行了研究。考察了不同测试条件下,聚酰亚胺纤维拉伸强度、表观拉伸弹性模量和断裂伸长率的变化规律。研究结果表明,聚酰亚胺纤维的拉伸性能样品制备条件有很大关系,影响因素包括含胶量、固化张力和胶液种类。含胶量低于40%时,纤维力学性能比正常值低。制样时施加适当的固化张力可得到较高的拉伸性能。对比环氧E51和E44两种树脂两种固化体系,采用E51的拉伸强度和断裂伸长率更大。加载速率低于80mm/min时,其对拉伸性能几乎没有影响。     

Weibull分布理论在硼纤维及B/Al复合材料中的应用

本文采用单一Weibull统计分布函数来描述硼纤维拉伸强度的分散性,发现具有不同断裂机制的缺陷所引发的断裂其拉伸强度分布分别符合Weibull分布,并具有各自独特的形态和参数;对热压复合前后的硼纤维的拉伸强度分布特征进行分析比较,结果表明热压复合过程对纤维的性能及拉伸强度分布特征有一定的影响,这主要是因为热压改变了纤维内部缺陷的类型和分布.本文还就以上研究结论在硼纤维的生产及其产品的性能表征方法、B/Al复合材料性能的非破坏性评估方法上的应用进行了讨论.     

考虑纤维缠绕形态的复合材料结构拉伸承载行为

纤维缠绕复合材料的纤维束具有交叉起伏形态特征,该形态对复合材料结构的力学行为有显著的影响。本文采用数值仿真和实验手段研究了纤维缠绕复合材料平板结构的拉伸力学行为。实验方面,开展纤维缠绕复合材料平板的准静态拉伸实验,通过数字图像相关技术(DIC)监测其表面应变场的演化过程,研究交叉起伏特征对载荷-位移曲线和应变分布特征的影响;数值分析方面,构建包含纤维缠绕形态的介观有限元模型,基于3D Hashin失效准则开展渐进损伤过程模拟,并引入了复合材料的剪切非线性行为。选取层合板结构为参照组,同时开展实验和数值分析。实验结果表明:对于层合结构,缠绕结构的整体刚度更低,失效位移更大,失效载荷基本相同,且缠绕结构菱形特征单元中部纤维交叉起伏区域存在明显的应变集中现象。所构建的有限元模型和实验结果吻合较好,呈现出纤维起伏区域的应变集中、失效起始和扩展行为。      

玻璃纤维增强PBT／PET共混复合体系的力学性能

ＰＢＴ／ＰＥＴ共混物经玻纤维增强后，冲击强度、拉伸强度、弯曲强度、热变形温度以及玻纤含量均大幅度提高。但玻纤之间玻纤与树脂之间的磨耗易引起ＰＢＴ、ＰＥＴ分子链断裂，特性粘度下降。作增强用玻纤含量一般控制在４５％以内。玻纤起增强作用的关键是其表面偶联剂与树脂ＰＢＴ、ＰＥＴ的偶联作用。树脂基体将吸收的外来冲击能通过树脂与玻纤的偶联传递到玻纤上，再经玻纤分散在较大体积范围内，表现为其力学性能影响。     

Tensile and creep behaviour of polyethylene terephthalate and polyethylene naphthalate fibres

Ropes made of twisted polyester (PET) yarns have been replacing traditional steel ropes and chains as mooring lines for offshore platforms in deep-sea environments. In order to optimise rope manufacture and the design of mooring systems, a thorough understanding of the material’s mechanical behaviour is necessary. Besides PET, other materials can also be considered such as PEN, as it also a polyester similar to PET but stiffer. This paper presents a study and comparison of PET and PEN fibres’ mechanical behaviour, based on experiments carried out on single filaments. Both fibres show similar non-linear tensile behaviour, with an evolution of modulus in four steps. The same microstructural model is proposed for both fibres, based on microfibrils aligned along the fibre axis and composed of an alternation of amorphous, mesamorphous and crystalline phases. The shape of the tensile loading curve is explained by the successive loading of these phases. Creep behaviour is also evaluated by considering the evolution of creep rate with applied load. This evolution is again similar for PET and PEN, both from a qualitative and quantitative point of view. The similarity in creep rate values for both fibres indicates that the microstructural mechanisms involved in creep may differ from those involved in short term tension loading.     

碳纤维涂覆SiC新工艺及涂层纤维的力学特性

用气相SiO和CO反应形成SiC的方法成功地在碳纤维上涂覆SiC.SiC涂层是由β-SiC团粒从碳纤维表面向外生长形成,并具有玉米棒子状的表面形貌。SiC层厚度增加到≥0.2μm,涂层纤维的拉伸强度随SiC层厚度增加而下降,此结果与Ochiai的理论模型相吻合。SiC层厚度达到1μm的涂层纤维,其拉伸时的力学行为与具有弱界面结合的1维脆性纤维-脆性基质复合材料相似,并显示SiC层的多次断裂。对碳纤维芯因涂层处理而引起的性能退化进行了讨论。      

Influence of the Physical Structure of Flax Fibres on the Mechanical Properties of Flax Fibre Reinforced Polypropylene Composites

This study investigates the influence of the physical structure of flax fibres on the mechanical properties of polypropylene (PP) composites. Due to their composite-like structure, flax fibres have relatively weak lateral bonds which are in particular present in flax fibres that are often used in natural fibre mat reinforced thermoplastics (NMT). These weak bonds can be partly removed by combing the fibres. In order to study the influence of the physical structure of flax fibres on NMT tensile and flexural properties, uncombed and combed flax fibre reinforced PP composites were manufactured via a wet laid process. The influence of improved fibre-matrix adhesion was studied using maleic-anhydride grafted PP. Results indicated that the flax physical structure has a significant effect on flax-PP composite properties and that the flax fibre reinforced PP properties are similar to values predicted with existing micromechanical models. The tensile modulus of flax-PP composites can fairly compete with commercial glass mat reinforced thermoplastic (GMT) modulus, the strength, however, both tensile and flexural, can not. In order to rise the strength of flax fibre reinforced PP composites to the level of GMT strength, the flax fibres have to be further isolated to elementary flax fibres.     

Micro-Raman study of the fatigue and fracture behaviour of single PA66 fibres: Comparison with single PET and PP fibres

The micro/nano-structural evolution before and after tensile loading, fatigue and ultimately, failure has been studied by Raman microspectroscopy for PA66, PP, PBO and PET single fibres and precursors, using two probes: low wavenumber collective modes at <150 cm⁻¹ as representative of the crystalline and amorphous chains and stretching and bending modes, as representative of the C-C bond local behaviour. Wavenumber and bandwidth distributions across fibre/precursors diameters reveal different types of skin/core heterogeneity. The in situ analysis at different strain levels shows that amorphous chains in the fibre accommodate the stress differently. Slight tensile straining is observed for crystalline PA 66 chains, and compression for PP and PET chains indicating different local chain architectures. The post mortem analysis of a series of fibres failed in fatigue tests shows that amorphous domains are highly stressed during the failure and a remnant stress can be measured.     

Predicting the tensile strength of natural fibre reinforced thermoplastics

The tensile strength of short natural fibre reinforced thermoplastics (NFRT) was modeled using a modified rule of mixtures (ROM) strength equation. A clustering parameter, requiring the maximum composite fibre volume fraction, forms the basis of the modification. The clustering parameter highlights that as fibre loading increases, the available fibre stress transfer area is decreased. Consequently, at high volume fractions this decrease in stress transfer area increases the brittleness of the short fibre composite and decreases the tensile strength of the material. A key parameter, the interfacial shear strength, was determined by fitting the micromechanical strength model to tensile strength data at low fibre loading (10 wt%) where there is minimal fibre clustering.To test the modified ROM strength model, compression molded specimens of high-density polyethylene (HDPE) reinforced with hemp fibres, hardwood fibres, rice hulls, and E-glass fibres were created with fibre mass fractions of 10–60 wt%. The modified ROM strength model was found to adequately predict the tensile strength of the various composite specimens.     

Effects of fluctuation of fibre orientation on tensile properties of flax sliver-reinforced green composites

Plant-based natural fibres are often used as a reinforcing material for environmentally friendly green composites. Especially, the form of slivers of natural fibres is anticipated for increasing their stiffness and strength. However, the sliver structure has fluctuations in fibre orientation, which decreases their mechanical properties. This paper describes the effects of such fibre orientation fluctuation on tensile properties of fibre-reinforced fully green composites. The composites were reinforced with slivers of high-strength flax fibres, for which a fabrication method called ‘direct method’ was applied. To quantify the morphology of the fibre orientation, fibre orientation angles were measured on fine segments, which were divided into 1 mm × 1 mm squares on a photograph of the whole composite surface. Although it is well-known that tensile strength of unidirectional composites decreases with increasing fibre orientation angle, the tensile strength obtained here did not show any appreciable relation to the statistical properties of measured fibre orientation angles such as average and standard deviation. The concept of two-dimensional (2D) autocorrelation was used in the present study to express the degree of similarity between fibre orientation angles in two different local areas. Results show that, if high 2D autocorrelation coefficients occupy more area on a composite surface, then this composite possesses more regular fibre orientation and tends to exhibit higher tensile strength. This tendency is stronger in the composites close to on-axis alignment, whereas it became weak in the off-axis composites angled more than 15° because of shear fracture.     

Determination of single fibre strength distribution from fibre bundle testings

The strength of fibres used as reinforcement materials for advanced composites is often assumed to follow the two-parameter Weibull distribution function. However, the experimental process widely used for obtaining the two parameters is tedious and prone to error. In this paper, two simple methods for determining the parameters of the Weibull distribution function are developed based upon the analysis of the tensile curves of fibre bundles. The first method focuses on the relation between the shape of a fibre bundle tensile curve and the survivability of fibres; the second method makes use of the relation between the maximum load point of a fibre bundle tensile curve and the shape parameter of the Weibull distribution of fibre strength. These two methods, in particular the second one, have greatly simplified the fibre testing process. Experimental results on Thornel-300 carbon fibres further demonstrate the validity of these techniques.On leave from Northwestern Polytechnical University, Xian, Shaanxi, China.On leave from Yantze Valley Planning Office, Wuhan, China.     

Statistical fracture of E-glass fibres using a bundle tensile test and acoustic emission monitoring

Mechanical strength studies have been carried out on fibre bundles used in composite manufacturing. The variability in mechanical properties of glass fibres has been studied using bundles of about 2000 filaments. The fibre strength distributions were analysed using the survival probability-applied strain (S–ε) curve, in relation with various experimental conditions. We also examine the effect of lubricant’s viscosity on the fracture behaviour of E-glass fibre bundles. Acoustic emission (AE) was monitored during the bundle tensile tests in order to verify that individual filament failures are statistically independent. On tensile tests with lubricated bundles of E-glass fibres, it is shown that each individual fibre break can be detected using AE. Hence, AE monitoring of a lubricated bundle of E-glass fibres provides a convenient and relatively quick method to obtain the Weibull parameters of strength distribution.     

Tensile properties of heat-treated Nicalon and Hi-Nicalon fibres

In this study we compare the tensile properties of two types of Nicalon fibres, one with high oxygen content and the other with low oxygen content. Both types of fibre were coated with a carbon layer during manufacture. The fibres were tested at room temperature in the as-received and desized conditions and after heat treatment at 800 and 1200°C in flowing air and argon. Nicalon-607 and Hi-Nicalon fibres exhibited brittle behaviour and a decrease in tensile strength after heat treatment at 1200°C. It was found that Hi-Nicalon fibres had generally higher tensile properties than Nicalon-607 fibres. It was also observed that the high-oxygen-content fibres had more surface defects than the fibres with low oxygen content.