基于介电性能研究碳纤维/环氧复合材料单向板电热作用机制

采用复合材料电热试验机对碳纤维/环氧复合材料(CF/EP)单向板进行0.05~0.2A·mm~(-2)直流电流通电处理,每次通电1.5h,同时对其电热作用下的表面温度场进行测量;分析电热作用后CF/EP试样的纵向体积电阻和介电性能变化;通过三点弯曲测试表征电热作用前后的弯曲性能。结果表明:试样的温度场随通电时间均呈现先迅速上升后稳态平衡的趋势。低于0.125A·mm~(-2)的电热作用使温度场分布均匀,纵向体积电阻降低以及介电性能提升;高于0.125A·mm~(-2)的电热作用使中间区域温度场高于两边区域,纵向体积电阻上升以及介电性能下降。介电常数和损耗角正切随测试频率增大而降低,交流电导率随频率增大先稳定后上升。受电热作用影响最大的损耗角正切可作为特征参量。弯曲性能测试表明,低于0.125A·mm~(-2)的电热作用使CF/EP试样的弯曲强度和弯曲模量最大提升11.8%和7.32%,而高于0.125A·mm~(-2)的电热作用使试样的弯曲强度和弯曲模量最大降低8.26%和6.52%。     

Microstructure and mechanical properties of hot extruded 6016 aluminum alloy/graphite composites

The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/(0-20 wt%) graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases(free graphite and in-situ formed carbides) on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide(SiC) and aluminum carbide(Al_4 C_3). The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.     

Effect of material and process parameters on the mechanical properties of unidirectional and multidirectional flax/polypropylene composites

Unidirectional (UD) and multidirectional (MD) flax/polypropylene composites were studied. Flax with varying retting degree and boiled flax was used as reinforcement for the UD composites and unmodified and maleic acid anhydride modified polypropylene (MAA-PP) was used as matrix. Multidirectional flax/polypropylene composites were manufactured on laboratory scale and on pilot scale. They were made from needle-punched hybrid flax/PP non-wovens. Normally retted flax as well as boiled flax was used. For the specimens made on pilot scale, a third kind of flax, namely bleached flax was also studied. The influence of different process times and temperatures on the mechanical properties of the composites was analysed. Generally, the composites have adequate good mechanical properties. The unidirectional composites of boiled flax combined with MAA-PP show the best mechanical properties. Contrary to the UD composites, flax treatment did not lead to the expected property improvements for MD composites.     

Effect of holding pressure on densification and mechanical properties of Cf/Mg composites

Carbon fibre reinforced magnesium alloy matrix composites were fabricated by using liquid–solid extrusion directly following vacuum infiltration technique. The experimental results showed that the microstructures of C_f/Mg composites depended on the holding pressure. The porosity was reduced gradually, and the densification was improved obviously, respectively, with the increase of the holding pressure. The densification, hardness and Ultimate tensile strength of C_f/Mg composites were significantly improved as the holding pressure increased in the range of 0.1–15 MPa. The densification was not obvious, but the UTS of the C_f/Mg composites decreased gradually as the holding pressure increased in the range of 25–45 MPa. The C_f/Mg composites presented a good performance when the holding pressure was about 15 MPa.     

石墨表面镀Si对石墨/Al复合材料热物理性能的影响

研究了石墨粒径及表面镀Si处理对石墨/Al复合材料热物理性能的影响。结果表明:在盐浴过程中石墨表面形成了SiC层,这不仅增强了石墨-Si/Al复合材料的界面结合力,而且抑制了Al4C3相的产生。随着石墨鳞片体积分数从50%增加到70%,复合材料X-Y方向的热导率从492 W/(m·K)增加到654 W/(m·K),而且体积分数为50%的镀Si石墨/Al复合材料抗弯强度达到了81 MPa,相比未镀覆的提高了53%,是理想的定向导热电子封装材料。随着石墨粒径从500μm减小到150μm,石墨-Si/Al复合材料X-Y面方向的热导率由654 W/(m·K)降低到445 W/(m·K),但Z方向的热导率和复合材料抗弯强度变化不明显。     

真空热循环对M40J/环氧复合材料力学性能的影响

分别测量了经不同次数单向真空热循环试验(93～413 K,10-5Pa)后M40J/5228A复合材料的拉伸强度、弯曲强度和层剪强度,研究了真空热循环对M40J/环氧复合材料力学性能的影响.结果表明,随着真空热循环次数的增加,90°和0°拉伸强度下降,并分别于48次和40次真空热循环后趋于平缓.弯曲强度随着真空热循环次数的增加表现出先上升后下降再趋于平缓的特征,而层剪强度变化不大.90°和0°拉伸强度的变化与界面脱粘程度密切相关.弯曲强度变化主要反映真空热循环时树脂基体后续固化效应的影响.层剪强度变化是界面脱粘与树脂基体后续固化两种因素综合作用的结果.     

石墨烯/铜复合材料剪切性能的分子动力学模拟

采用分子动力学方法系统地研究了石墨烯/铜复合材料的剪切力学性能,包括剪切弹性模量、剪切屈服强度、剪切破坏强度及剪切变形机制。研究发现,与单晶铜的剪切模拟相比较,石墨烯的加入显著增强了石墨烯/铜复合材料的剪切强度,并且剪切强度随着石墨烯体积分数的增大而提高。复合材料中的石墨烯层与铜层产生了协同作用,即石墨烯层阻碍了铜的位错扩展,铜层限制了石墨烯的结构屈曲。对含球形缺陷的石墨烯/铜复合材料的剪切性能也进行了研究。结果表明,不同位置和数量的球形小缺陷对复合材料的剪切性能影响不大,小缺陷石墨烯/铜复合材料仍具有较好的性能和使用价值。但随着缺陷直径的增大,复合材料的剪切强度明显减小。     

添加铜网对片层石墨/Al复合材料热物理性能的影响

使用盐浴法对片层石墨（GFs）进行表面镀Si处理,采用真空热压法制备片层石墨/Al复合材料（Si-GFs/Al）。向Si-GFs/Al复合材料中添加10vol%的铜网,研究了铜网对Si-GFs/Al复合材料热导率和力学性能的影响。使用SEM、聚焦离子束（FIB）和TEM对Si-GFs/Al复合材料的微观结构和微观界面进行表征,并分析了复合材料的断裂机制。结果表明,添加铜网使Si-GFs/Al复合材料内部出现了高聚集定向GFs带,形成高导热通道。当GFs体积分数为30vol%~40vol%时,Si-GFs/Al复合材料的热导率提升了约20%,弯曲强度提升了40%以上。当GFs体积分数为40vol%时,Si-GFs/Al复合材料热导率和弯曲强度同时达到一个优值,分别为512 W/（mK）和127 MPa。      

Effect of UV and water spraying on the mechanical properties of flax fabric reinforced polymer composites used for civil engineering applications

The lack of data related to durability is one major challenge that needed to be addressed prior to the widespread acceptance of natural fibre reinforced polymer composites for engineering applications. In this work, the combined effect of ultraviolet (UV) radiation and water spraying on the mechanical properties of flax fabric reinforced epoxy composite was investigated to assess the durability performance of this composite used for civil engineering applications. Specimens fabricated by hand lay-up process were exposed in an accelerated weathering chamber for 1500 h. Tensile and three-point bending tests were performed to evaluate the mechanical properties. Scanning electron microscope (SEM) was used to analyse the microstructures of the composites. In addition, the durability performance of flax/epoxy composite was compared with synthetic (glass and carbon) and hybrid fibre reinforced composites. The test results show that the tensile strength/modulus of the weathered composites decreased 29.9% and 34.9%, respectively. The flexural strength/modulus reduced 10.0% and 10.2%, respectively. SEM study confirmed the degradation in fibre/matrix interfacial bonding after exposure. Comparisons with other composites implies that flax fabric/epoxy composite has potential to be used for civil engineering applications when taking its structural and durability performance into account. Proper treatments to enhance its durability performance will make it more comparable to synthetic fibre reinforced composites when considering as construction building materials.     

多壁碳纳米管/聚醚砜环氧树脂复合材料的制备及力学性能

环氧树脂具有优异的热性能及力学性能,但本身脆性较大。为制备低成本、高性能的环氧树脂体系,使用聚醚砜（PES）和多壁碳纳米管（MWCNT）对环氧树脂进行增韧,制备了不同PES含量的PES-环氧树脂共混物,讨论了PES含量对环氧树脂力学性能的影响;采用熔融法,并配合使用机械搅拌、高剪切分散和超声分散制备了MWCNT/PES-环氧树脂复合材料,测试了其拉伸性能及断裂韧性,用SEM观察了MWCNT在树脂中的分散状态以及拉伸试样的断口形貌。结果表明：MWCNT的加入能够提高PES-环氧树脂体系的综合力学性能,且当MWCNT含量为0.7wt%时,树脂体系的综合力学性能最好;低PES含量下,小于1.0wt%的MWCNT的加入使材料力学性能超过用20.0wt%PES改性的环氧树脂;PES与MWCNT对环氧树脂具有协同增韧作用。     

The effect of hydrostatic pressure and loading rate on compressive failure of fiber-reinforced ceramic-matrix composites

The influence of hydrostatic confinement on compressive strength and corresponding failure mechanisms is explored for SiC-reinforced glass-ceramics tested at different strain rates. Two composite architectures (0° and 0°/90°) are studied, and their behavior is compared with that of monolithic glass-ceramic tested under similar conditions. Composite confined pressure results are interpreted in terms of fiber buckling under quasi-static conditions and fiber kinking at high pressures, and compared with monolithic (non-composite) microfracture coalescence at low pressures and shear band formation under more intense confinement. In particular, dilatational fracture within the matrix dominates composite failure at low pressures, while high pressures cause a transition to shear-dominated mechanisms based on fiber kinking.     

Analysis of mechanical properties and SEM for laminated SiC/W composites

In this letter, it is reported that a laminated SiC/W composite has been developed using the hot pressing method. It is found that a chemical reaction between W and SiC occurs during the preparation process. Making use of SEM, the components within the sandwiched-in metal and the fracturing crack for the laminated SiC/W composite are determined. Testing mechanical properties of the laminated SiC/W composite indicates that fracture toughness increases while bending strength reduces, with an increase of the thickness of the sandwiched-in metal ranging from 10–50-μm thickness.     

Effect of strain rate on interlaminar shear properties of carbon/epoxy composites

In this paper, the effect of strain rate on interlaminar shear properties of laminates is studied. The material tested was a T300/5208 carbon/epoxy composite, and the range of strain rates explored was about 10⁻³ − 10³ s⁻¹. The specimens used were designed and optimized by finite element analysis, and the calculations are presented here. One of the specimens permitted the determination of the interlaminar shear modulus, G₁₃, and the other permitted the determination of the interlaminar shear strength, S₁₃. No influence of testing speed on interlaminar properties was observed at low, intermediate and high strain rates. Fracture surfaces were studied by scanning electron microscopy: a slight difference was observed between specimens tested at low and high strain rates.     

Effect of the shear and coupling elements of the Aij and Dij matrices on the impact behavior of glass, aramid and hybrid fabric composites

The impact behavior of glass, aramid and glass–aramid hybrid fabric epoxy matrix composites was evaluated. Delamination was identified as the main macroscopic failure mode of the composites. A simple relationship based on the macromechanical behavior of laminated composites was established, relating coupling—A₂₆, D₂₆—and shear—A₁₆, D₁₆—elements of the extensional and bending stiffness matrices to the total energy absorbed at impact. The results obtained show that the A₆₆/D₆₆ ratio is a relevant parameter of concern, correlated with the behavior of the composites under impact. Additionally, the coupling matrix B_ij was shown to restrain the macroscopic delamination of the composites.     

C/C-Cu复合材料等离子体烧蚀性能

为了研究渗铜对C/C复合材料烧蚀性能的影响,利用化学气相渗透(CVI)和液态压力浸渗工艺制备了C/C-Cu复合材料,并采用等离子体烧蚀装置对C/C-Cu复合材料进行烧蚀,研究其烧蚀性能。结果表明: Cu的加入有效缩短了材料的制备周期;Cu均匀分布在C/C坯体内,呈连续的网状结构;在烧蚀前30 s阶段,Cu通过熔化吸热降低了C/C-Cu试样的升温速度,C/C-Cu复合材料的线烧蚀率低于C/C复合材料,耐烧蚀性能优异;随着烧蚀时间的延长,C/C-Cu复合材料表层的Cu液被火焰带走,表层变为多孔低密度的C/C层,C/C-Cu复合材料的线烧蚀率迅速增加并超过C/C复合材料,耐烧蚀性能降低。     

MWCNTs对环氧树脂及多尺度MWCNTs-碳纤维/环氧树脂复合材料力学性能的影响

通过对胺基化多壁碳纳米管（MWCNTs-NH₂）进行改性,得到改性MWCNTs悬浮液（MWCNTs-NH₂（M））。分别将羧基化MWCNTs （MWCNTs-COOH）和MWCNTs-NH₂（M）分散在环氧树脂（EP）中,采用热熔法制备了多尺度MWCNTs-碳纤维（CF）/EP复合材料。研究了MWCNTs对EP模量、韧性及EP与CF之间界面黏结强度的影响,并分析了MWCNTs与CF上浆剂的作用,评价了多尺度MWCNTs-CF/EP复合材料的力学性能。结果表明：官能团化的MWCNTs可对EP的模量和韧性起到更好的增强作用。MWCNTs接枝的-COOH或-NH₂可与CF上浆剂中的环氧基团发生化学反应,提高EP与CF之间的界面剪切强度。MWCNTs-NH₂（M）对多尺度MWCNTs-CF/EP复合材料力学性能的增强效果优于MWCNTs-COOH,当MWCNTs-NH₂（M）的含量为1wt%时,多尺度复合材料的0°压缩强度、90°压缩强度、弯曲强度、弯曲模量、冲击后压缩强度（CAI）分别提高了16.7%、16.3%、40.9%、30.3%、20.6%。     

基于纤维束/环氧树脂复合材料试验的单向层合板横向拉伸强度预测方法

实验研究表明,纤维束/环氧树脂复合材料试件的横向拉伸强度与工程上常用的单向层合板横向拉伸强度在趋势上具有很好的相关性,但是数值上存在一定差距。本文使用两种碳纤维和两种环氧树脂制备了三种纤维束/环氧树脂复合材料和单向层合板,并分别测量了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度,以及环氧基体的拉伸强度。在实验基础上,应用Griffith断裂强度理论建立了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度的关系模型,通过两种复合材料实验的结果拟合了该模型中的参数。利用第三种复合材料实验进行校验,发现该模型预测的单向层合板横向拉伸强度与实测强度之间达到很好的一致性,相对偏差为9%。采用本文提出的方法,可以用较为简单的纤维束/环氧树脂复合材料和环氧基体拉伸试验预测单向层合板的横向拉伸强度。     

C/ C坯体对 C/ C2Cu复合材料摩擦磨损行为的影响

采用无压熔渗方法制备炭纤维整体织物/炭2铜 (C/ C2Cu) 复合材料 , 在 MM22000型环2块摩擦磨损试验机上考察复合材料的摩擦磨损性能 , 利用扫描电子显微镜观察分析磨损表面形貌 , 研究 C/ C坯体对材料的摩擦磨损行为的影响及机制。结果表明 : 随着 C/ C坯体密度的增加 , 摩擦系数及 C/ C2Cu材料自身和对偶的磨损量均降低 ; 采用浸渍/炭化 ( I/ C) 坯体的 C/ C2Cu材料摩擦系数及自身和对偶件的磨损量均高于采用化学气相渗透(CVI) 坯体的试样; 摩擦面平行于纤维取向的试样摩擦系数低于垂直于纤维取向的试样 , 但磨损率较高。     

Machining and surface integrity of fibre-reinforced plastic composites

The current focus of manufacturing research on fibre-reinforced plastics (FRP) is composed of the search for efficient processing techniques capable of providing high quality machined surfaces. Very limited work has been performed to identify the influence of manufacturing processes like edge-trimming and drilling on material performance. Recent reports suggest that process-induced damage may affect the mechanical behaviour of FRP materials. Therefore an experimental study of orthogonal cutting was conducted on the edge trimming of unidirectional and multi-directional graphite/epoxy composites with polycrystalline diamond tools. The effects of tool geometry and operating conditions were evaluated from an analysis of chip formation, cutting force, and machined surface topography. All aspects of material removal were found to be primarily dependent on fibre orientation. Discontinuous chip formation was noted throughout this study, regardless of machining parameters. Three distinct mechanisms in the edge trimming of fibre-reinforced composite material including a combination of cutting, shearing, and fracture along the fibre/matrix interface were observed. An investigation conducted on the compression, flexural and impact strength of graphite/epoxy composites machined by both traditional and non-traditional techniques, confirms that manufacturing characteristics may not only affect bulk properties but also influence the initiation and propagation of failure.     

包覆混料对镀铜混合尺寸SiCp/Fe力学性能的影响

为探索提高SiCp/Fe力学性能的途径,采用包覆混料工艺,研究了该工艺对镀铜SiCp/Fe力学性能的影响,以及该工艺下增强粒子混合尺寸的影响.结果表明:包覆混料相比于普通混料,可显著改善SiC粒子在基体中分散的均匀性,而镀铜的作用是显著消除界面缺陷;性能的改善是包覆混料改善粒子分散性和镀铜改善界面结合的综合结果.对于体积分数30%SiCp/Fe的抗拉强度,通过包覆改善均匀性的贡献可提高7.2%,通过镀铜消除界面缺陷的贡献可提高12.5%,因此减少界面缺陷对颗粒增强复合材料力学性能的提高更重要.混合尺寸粒子对力学性能的增强效果明显高于其对应单一尺寸,这是由于小尺寸粒子能有效地提高基体的强度,而大尺寸颗粒更有效地承担载荷传递的作用.