短纤维增强弹性体复合材料的强度预测

探讨了纤维的取向、长度和含量对短纤维增强弹性体复合材料强度的影响,在Fukuda预测模型的基础上,考虑了末端纤维的脱粘、纤维临界长度和高纤维体积含量等因素,建立了三维随机分布短纤维弹性体复合材料强度预测模型,并对预测结果与现有理论计算得到的结果进行了分析比较.     

2D-C/SiC复合材料面内剪切性能统计及强度B基准值

针对2D-C/SiC复合材料进行大子样面内剪切实验,研究材料面内剪切模量和强度的分布规律及强度B基准值。运用线性回归结合假设检验的方法,确定2D-C/SiC复合材料面内剪切力学性能的分布规律及参数,对比两种不同经验失效概率得到统计结果;通过观察试样最窄净截面微CT照片及断口电镜扫描照片,解释材料面内剪切强度分散性微观机制,基于分布规律,最终计算得到2D-C/SiC复合材料面内剪切强度威布尔B基准值。结果表明:强度和模量均同时服从威布尔、正态和对数正态分布,且理论模型与实验结果吻合良好,两种经验失效概率不影响力学性能分布规律;面内剪切强度分散性与最窄净截面致密度和界面脱粘长度有关;2D-C/SiC复合材料面内剪切强度威布尔B基准值为80.41MPa。     

扩展有限元方法与内聚力模型耦合下斜接修补复合材料的胶层损伤和缺陷

将扩展有限元方法（XFEM）与内聚力模型（CZM）耦合用于斜接修补复合材料的胶层分析,实现了对复合材料与修补胶层之间的脱粘以及胶层内部裂纹扩展现象的描述,模拟得到的结构强度与试验结果吻合较好。对复合材料与胶层的界面缺陷和胶层内部缺陷展开分析,讨论了缺陷长度和缺陷位置对结构强度的影响。结果表明：在相同条件下,结构具有界面缺陷比具有胶层内部缺陷更加危险;结构强度受缺陷长度和与缺陷尖端相邻复合材料铺层角度的共同影响,随着缺陷长度的增加而降低,降低速率大于缺陷长度增长比例;当缺陷位置不同时,结构强度主要与缺陷对应位置的平均剪应力水平相关。最后,通过参数分析讨论了界面剪切强度的影响。     

玻璃纤维/聚脲复合材料的性能研究

为研究玻璃纤维对聚脲性能的影响，分别以聚脲和玻璃纤维作为基体和增强体，合成了玻璃纤维/聚脲复合材料。通过扫描电子显微镜、傅里叶变换红外光谱仪和动态热机械分析仪，探究玻璃纤维长度在0.2～0.8mm、添加量在0.5%～1.5%(wt,质量分数，下同)范围时对复合材料微观结构、力学性能和动态力学性能的影响规律，分析复合材料的耗能机理。结果表明：玻璃纤维在基体中分布均匀，降低了复合材料的氢键化程度、氢键结合强度以及微相分离程度；复合材料的拉伸强度、撕裂强度随玻璃纤维长度和添加量的增加而提高，当玻璃纤维长度为0.8mm、添加量为1.5%时，复合材料的拉伸强度为30.14MPa,撕裂强度为127.48kN/m,力学性能最好；随着玻璃纤维长度和添加量的增加，复合材料的储能模量和损耗模量逐渐增加，玻璃化转变温度向高温移动；复合材料的主要耗能机理为本征阻尼和界面阻尼，本征阻尼随着玻璃纤维长度的增加而减小，界面阻尼随着玻璃纤维添加量的增加而增大。     

聚合物基复合材料界面剪切强度的测试

用声发射技术确定纤维断裂的位置,从而决定纤维断裂段的长度分布。采用含有单纤维丝的聚合物基复合材枓试件,应用细观力学模型,根据纤维断裂段的长度,确定纤维和基体之间的界面剪切强度。这种方法适用于不透明的复合材料基体,有可能用来测定金属基和陶瓷基复合材料的界面剪切强度。     

混杂短纤维增强聚苯硫醚复合材料的老化研究Ⅰ.破坏行为研究

本文研究了经80℃热水老化4000小时和加速气候老化1200小时的短碳纤维与玻璃纤维混杂增强聚苯硫醚复合材料的力学性能变化,并对复合材料中的纤维长度分布进行了统计。研究表明,纤维长度减小主要发生在挤出造粒阶段,而且大多数纤维的长度小于临界长度。混杂纤维增强的聚苯硫醚复合材料的拉伸强度和弯曲强度与混杂纤维比例基本上是线性关系,而冲击强度与混杂纤维比的曲线呈现下凹的趋势。加速气候老化对PPS损害较热水老化明显。老化后的复合材料力学性能保留率与老化方式和纤维种类有关。弯曲性能受老化影响较小,而拉伸性能受影响较显著。热水老化对玻璃纤维含量高的复合材料影响较显著。     

剑麻/聚丙烯复合材料的冲击性能及其预测

采用注塑工艺制备剑麻纤维增强聚丙烯复合材料,研究纤维含量、长度及其分布、不同基体树脂和相容剂类型等对复合材料冲击性能的影响。分析单纤维强度的分散性,采用修正的Weibull分布模型估算临界纤维强度,并对复合材料的冲击强度进行预测。结果表明：剑麻/聚丙烯的冲击强度随纤维含量增加而升高,树脂基体的性质对冲击强度具有显著的作用;界面层为刚性层的相容剂MAPP对冲击强度具有负作用,而界面层为柔性层的相容剂PP-g-GMA对冲击强度具有提高作用;同等含量下,使用PP-g-GMA后复合材料的冲击强度比使用MAPP提高21.7%。通过KH550硅烷溶液处理后的纤维与PP-g-GMA反应,在界面处引入更加柔性的界面层,使冲击强度比引入MAPP提高50.7%。将纤维取向因子引入冲击强度模型后,预测值与实测值符合较好。     

石英纤维及其 Mini复合材料强度及分布规律

针对国产石英纤维强度，本工作采用液相浸渍法（硅溶胶、石英浆料和氮化硅浆料）制得Mini复合材料，利用两参数Weibull分布，对其强度及分布进行了研究，采用Kolmogrov非参数检验对其分布进行了检验．同时研究了热处理对纤维束强度分布的影响．结果表明，可用两参数Weibull分布表征纤维束及其Mini复合材料强度分布．热处理使纤维强度急剧下降，且强度分散性变大；相同处理温度下，由硅溶胶制得的Mini复合材料强度较高，分散性较小；而石英或氮化硅浆料制备的Mini复合材料强度较低．     

纤维缝合结构对夹芯结构复合材料力学性能的影响

通过RTM工艺成型了点阵增强夹芯结构复合材料,研究了纤维缝合结构对复合材料平压及侧压力学性能的影响,并探索了侧向压缩载荷下夹芯结构复合材料的破坏模式。结果表明,采用纤维缝合的方式可显著提高夹芯结构复合材料的力学性能。双向增强夹芯复合材料在长度和厚度方向上的侧压强度和模量相同,单向增强的侧压强度和模量表现出方向性,且长度方向上的模量明显高于宽度方向的。     

螺杆结构及转速对玻璃纤维增强PA66复合材料力学及流变性能的影响

通过改变挤出机的螺杆结构及螺杆转速,研究了熔融挤出过程中,剪切强度的变化对聚酰胺66/玻璃纤维复合材料力学及流变性能的影响。结果表明,当螺杆后段的捏合块数量由7块减少到4块,且螺杆转速为120r/min时,熔体受到的机械剪切应力最小,在挤出过程中有效地减少了玻纤的断裂,使其平均长度最长,复合材料的力学性能最高。聚酰胺66中加入玻璃纤维能显著影响复合材料的流变行为,玻纤的平均长度越长,与基体间的作用就越强,共混体系的复数黏度及动态储能模量也越高。     

The structure and tensile properties of Al-Si alloy hybrid reinforced with alumina-aluminosilicate short fibre

Alumina-aluminosilicate fibre hybrid reinforced aluminium-silicon alloy was fabricated by pressure infiltration route. Tensile test results at room temperature and at 300°C are reported. It is shown that the alumina-aluminosilicate fibre ratio does have a strong influence on the ultimate tensile strength (UTS) of these hybrid composites. At an alumina-aluminosilicate ratio of 32, the optimum UTS of hybrid metal matrix composites (MMC) was obtained. The UTS of only alumina fibre reinforced MMC was improved with increasing fibre volume fraction at 300°C. No fibre put-out was observed on the fracture surface and longitudinal section.     

Controlled retting of hemp fibres: Effect of hydrothermal pre-treatment and enzymatic retting on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this work was to investigate the use of hydrothermal pre-treatment and enzymatic retting to remove non-cellulosic compounds and thus improve the mechanical properties of hemp fibre/epoxy composites. Hydrothermal pre-treatment at 100 kPa and 121 °C combined with enzymatic retting produced fibres with the highest ultimate tensile strength (UTS) of 780 MPa. Compared to untreated fibres, this combined treatment exhibited a positive effect on the mechanical properties of hemp fibre/epoxy composites, resulting in high quality composites with low porosity factor (α_pf) of 0.08. Traditional field retting produced composites with the poorest mechanical properties and the highest α_pf of 0.16. Hydrothermal pretreatment at 100 kPa and subsequent enzymatic retting resulted in hemp fibre composites with the highest UTS of 325 MPa, and stiffness of 38 GPa with 50% fibre volume content, which was 31% and 41% higher, respectively, compared to field retted fibres.     

Structure and properties of some vegetable fibres

The stress-strain curve for sisal fibres has been experimentally determined. Ultimate tensile strength (UTS), initial modulus (YM), average modulus (AM) and per cent elongation at break of fibres have been measured as function of fibre diameter, test length and test speed. UTS, YM, AM and per cent elongation lie in the range 530 to 630 MN m^–2, 17 to 22 GN m^–2, 9.8 to 16.5 GN m^–2 and 3.64 to 5.12 respectively for fibres of diameters ranging between 100 and 300m. No significant variation of mechanical properties with change in diameter of the fibres was observed. However, with increase in test length of the fibres, the UTS and per cent elongation are found to decrease while YM and AM increased in the test length ranging from 15 to 65 mm. With the increase in speed of testing from 1 to 50 mm min^–1, YM and UTS are found to increase whereas per cent elongation and AM do not show any significant variation. At a test speed of 500 mm min^–1 the UTS value decreases sharply. The above results are explained in terms of the internal structure of the fibre such as the cell structure, microfibrillar angle, defects, etc. Scanning electron microscope (SEM) studies of the fractured tips of the sisal fibres reveal that the failure of the fibre is due to the uncoiling of microfibrils accompanied by decohesion and finally tearing of cell walls. The tendency of uncoiling seems to decrease with increasing speed of testing.     

Structure and properties of some vegetable fibres

The stress-strain curves for pineapple leaf fibre have been analysed. Ultimate tensile strength (UTS), initial modulus (YM), average modulus (AM) and elongation of fibres have been calculated as functions of fibre diameter test length and test speed. UTS, YM, and elongation lie in the range of 362 to 748 MN m^–2, 25 to 36 GN m^–2, and 2.0 to 2.8%, respectively for fibres of diameters ranging from 45 to 205m. UTS Was found to decrease with increasing test lengths in the range 15 to 65 mm. Various mechanical parameters show marginal changes with change in speed of testing in the range of 1 to 50 mm min^–1. The above results are explained on the basis of structural variables of the fibre. Scanning electron microscope studies of the fibres reveal that the failure of the fibres is mainly due to large defect content of the fibre bo1h along the fibre and through the cross-section, The crack is always initiated by the defective cells and further aggravated by the weak bonding material between the cells.     

光纤复合材料界面力学传感器初探

本文将单模光导纤维代替普通玻纤埋设于聚酯之中,将He-Ne激光分光后接入这一信号光纤及另一同样长度的参考光纤中,利用这两根光纤输出的激光的干涉效应来测试埋设于聚酯之中光导纤维的各种应力应变情况(在复材受各种外力时),从而得到玻纤同聚酯的界面微观力学的各种结果,开拓了一种新的复合材料的测试方法。     

Effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this study was to investigate the effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of hemp fibre/epoxy composites. Pectin removal by EDTA and endo-polygalacturonase (EPG) removed epidermal and parenchyma cells from hemp fibres and improved fibre separation. Hemicellulose removal by NaOH further improved fibre surface cleanliness. Removal of epidermal and parenchyma cells combined with improved fibre separation decreased composite porosity factor. As a result, pectin removal increased composite stiffness and ultimate tensile strength (UTS). Hemicellulose removal increased composite stiffness, but decreased composite UTS due to removal of xyloglucans. In comparison of all fibre treatments, composites with 0.5% EDTA + 0.2% EPG treated fibres had the highest tensile strength of 327 MPa at fibre volume content of 50%. Composites with 0.5% EDTA + 0.2% EPG → 10% NaOH treated fibres had the highest stiffness of 43 GPa and the lowest porosity factor of 0.04.     

等效介质理论数值方法应用于随机取向纤维复合材料的杨氏模量

本文运用了等效介质理论数值方法[4],计算单向纤维增强复合材料的弹性常数,进而透过Christensen & Waals[3]的一套平均公式,计算二维及三维随机取向纤维复合材料的杨氏模量,以探讨等效介质理论对此类材料的适用性.计算结果与基于Halpin-Tsai[8]式及Christensen[7]式的结果甚为相近,与实验值也有很好的符合.     

A probabilistic theory of the strength of short-fibre composites with variable fibre length and orientation

This paper adopts a probabilistic approach to examine the effects of fibre length and orientation distribution on the strength of short fibre composites. A general theory has been formulated in terms of fibre length and orientation distribution function as well as the composite geometrical and physical properties. The final result is presented in the form of a modified rule of mixtures. The result has been applied to discuss several special cases of fibre arrangements. They are (a) unidirectional short fibre composites with uniform fibre length, (b) unidirectional short fibre composites with fibre length distribution, (c) random short fibre composites with uniform fibre length and (d) partially-aligned short fibre composites with uniform fibre length. Comparisons of the present results with previous work are also discussed.On leave from the Institute of Space and Aeronautical Science, University of Tokyo, Japan.     

Fibre fragment distribution in a single-fibre composite tension test

Single fibre fragmentation tests are performed for brittle fibres with Weibull strength distribution and different surface treatments. The fragmentation process is modelled and closed-form expressions for break spacing distribution are obtained. The model accounts for the effect of finite fibre length on the initial fragmentation as well as for break interaction on the advanced fragmentation stage. It is assumed that the exclusion zone due to fibre–matrix interface failure and stress recovery in the fibre is linearly dependent on the applied load. This assumption is validated experimentally. The derived theoretical average fragment length dependence on applied load is used to determine the fibre strength distribution parameters and the effective interfacial shear stress for carbon/epoxy single fibre composites with different fibre surface treatment and for glass/vinylester single fibre composite. Fragment length distribution is predicted for several load levels. Predictions are in good agreement with experimental data.     

纤维取向对复合材料磨损性能影响的统计学研究

采用挤压铸造法制备了3Al₂O₃·2SiO_2f/ZL109复合材料.利用统计学方法研究了载荷为600N、滑动速度为1.05m/s的润滑滑动磨损条件下纤维取向对复合材料磨损性能的影响.研究结果表明:纤维平行取向与垂直取向复合材料的磨损体积均符合概率密度f(x)的同一总体的正态分布[式(1)],纤维取向对复合材料的耐磨性影响不大.通过磨面的SEM分析,发现两种纤维取向的复合材料的磨损均为纤维断裂与磨粒磨损.