碱处理对剑麻连续长纤增强聚丙烯复合材料力学性能的影响

以丙纶长纤为经纱,剑麻连续长纤为纬纱,织成剑麻/PP平纹机织物。采用不同浓度的氢氧化钠对织物进行碱处理,将处理后的织物与聚丙烯薄板模压成型,制备出剑麻连续长纤增强聚丙烯复合材料。采用SEM对碱处理前后的剑麻纤维形貌进行分析,讨论不同碱处理浓度对复合材料力学性能的影响。结果表明：碱处理对剑麻连续长纤的表面具有刻蚀作用,以及对剑麻连续长纤增强聚丙烯复合材料的动态热机械性能、拉伸性能、弯曲性能均有一定的影响。     

Mechanical behavior and failure mechanism of 2.5D (shallow bend-joint,deep straight-joint) and 3D orthogonal UHWMPE fiber/epoxy composites by vacuum-assistant-resin-infused

Ultra-high molecular weight polyethylene(UHMWPE) fiber/epoxy composites were fabricated by a vacuum assisted resin infused(VARI) processing technology. The curing condition of composites was at a cure temperature of 80 ℃ for 3h in a drying oven. The characteristics of 2.5D(shallow bend-joint and deep straight-joint) structure and 3D orthogonal structure were compared. The failure behavior, flexural strength, and microstructures of both composites were investigated. It was found that the flexural property was closely related to undulation angle θ. The flexural strength of 3D orthogonal structure composite was superior to the other two structures composites with the same weave parameters and resin.     

Mechanical Properties of Phenolic-Resin Composites Reinforced with CF/BF Interlayer Hybrid Fibers

Phenolic-resin composites reinforced with carbon fiber (CF) and basalt fiber (BF) interlayer hybrid fibers plain fabric were fabricated. The tensile strength, compressive strength and interlaminar shear strength of the prepared composites were studied. The results indicated that hybrid fibers reinforced composites possessed the advantages of both CF and BF. When resin content was 35% by volume fraction, the comprehensive mechanical performance of BF/CF reinforced phenolic resin composites reached the optimal values with the warp and weft direction tensile strength, compressive strength and interlayer shear strength being 252 MPa and 487 MPa, 105 MPa and 129 MPa, 21 MPa and 20 MPa, respectively. The scanning electron microscope (SEM) observations showed that the BF/CF hybrid fibers reinforced composites had better interfacial adhesion.     

Mechanical behavior and microstructure characterization of 3D stitched quartz fibers-reinforced silica composites

The mechanical properties of silica material in the monolithic form are ;far from acceptable levels. In this paper, 3D stitched quartz preform was used for the fiber reinforcement, and quartz fibers- reinforced silica composites were prepared by the silica sol-infiltration-sintering method. The density of the composite was up to 1.71 g/cm3 after 10 infiltration-sintering cycles. The flexural strength and the in-plane shear strength were 61.7 MPa and 20.3 MPa, respectively. The flexural stress-deflection curve exhibited mostly nonlinear behavior, which was different from that of monolithic ceramics. Because of the existence of the fiber in Z axis direction, shearing property between the different layers of 3D stitched composites were greatly enhanced. Toughness effect of the 3D stitched quartz preform was conspicuous. The as-fabricated composites showed non-catastronhic failure behavior resulting from weak fiber/matrix interface.     

Processing and properties of 2D SiC/SiC composites by precursor infiltration and pyrolysis

Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide (2D-SiC/SiC) composites were molded by stacking method and densified through precursor infiltration and pyrolysis (PIP) process. SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition (CVD) technique. Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces. Additionally, the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test. The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2% (volume fraction) and 11.1%, and 40.7% (volume fraction) and 7.5%, respectively. And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa, and 180.2 MPa and 97.2 GPa, respectively. With a proper thickness, the coating can effectively adjust the fiber/matrix interface, thus causing a dramatic increase in the mechanical properties of the composites. Foundation item: Project(NCET-07-0228) support by the New Century Excellent Talents in University     

冷轧带肋钢筋焊接网混凝土板抗弯性能试验

为研究冷轧带肋钢筋焊接网混凝土板的抗弯性能,通过拉伸试验,获得了CRB600H与CRB550冷轧带肋钢筋的力学性能指标;进行了32块冷轧带肋钢筋焊接网混凝土板的受弯性能试验,测定了试验板的开裂弯矩、裂缝分布情况、变形发展规律和正截面承载力.研究结果表明:焊点未对CRB600H与CRB550冷轧带肋钢筋的力学性能产生影响;横向钢筋对试验板的开裂弯矩、裂缝间距和裂缝宽度无明显影响.建立了这类板的短期刚度计算公式,与普通混凝土板相比,这类板的抗弯刚度高约10%.根据配置CRB600H和CRB550钢筋网试验板的破坏模式,提出了这两种板正截面承载力的计算方法.     

Property of three-dimensional silica composites

Silica fibers-reinforced, fused silica composites were fabricated with repeated vacuum-assisted liquid-phase infiltration. The mechanical properties, thermal properties, and ablative properties of the samples were evaluated. The effect of the silica fiber content and treatment temperature on the flexural strength of the three-dimensional SiO2 （3-D SiO2） composites also was investigated. The SiO2 composites show good mechanical properties and excellent ablative performance. The flexural strength increases with an increase in silica fiber content, and decreases with an increase in treatment temperature. When the volume fraction of the silica fiber is 50vo1% and the treatment temperature is 700℃ the flexural strength of the composites reaches a maximum value of 78 MPa. By adding cyclohexanone surfactant, the infiltration property can be largely improved, resulting in the density of SiO2 composites increasing up to 1.65 g/cm^3. The fracture surfaces of the flexural specimens observed using SEM, show that the pseudoplasticity and the toughening mechanisms of the composites are caused by absorption of a lot of energy by interface debonding and fiber pulling out.     

阻燃粘胶纤维/腈氯纶混纺织物的制备及性能研究

以阻燃粘胶纤维和腈氯纶为原料,按照不同的混纺比制备了阻燃机织物.采用垂直燃烧法、极限氧指数(LOI)法和强力仪对织物的阻燃性能和力学性能进行测试分析.结果表明:随混纺织物中阻燃粘胶纤维含量的增加,织物的续燃时间和阴燃时间均缩短,而损毁长度大大增加,织物的LOI值下降,织物的经纬向断裂强度及断裂伸长率均下降,说明混纺织物中阻燃腈氯纶含量对混纺织物性能的贡献要大于阻燃粘胶纤维.     

圆环形机织布的织造与设计

在现有的织机基础上：通过对送经系统、织物成形和打纬等机构的改造，织制出了圆环形织物．为使圆环织物的纬纱密度均匀，需在圆环大半径处引入只与部分经纱相交织的短纬，且短纬应分布在长纬之间．不同长度的短纬在圆环织物中的分布规律对织物的结构影响很大，分散配置的短纬有助于获得均匀的织物结构,织制的圆环形织物，不需裁剪即可缠绕圆台形复合材料管道，从而简化了成型工艺．     

超高韧性水泥基材料的制备技术

分别采用活性粉末混凝土（RPC）和渗浇钢纤维混凝土（SIFCON）两种制备工艺,根据水泥基材料结构的多尺度特征,研究了由碳酸钙晶须和微钢纤维复合增强的超高韧性水泥基材料（Ultra-High-Toughness Cementitious Composite,简称UHTCC）的制备技术,测试UHTCC不同配比的抗压强度、抗折强度、抗弯强度以及单轴拉伸性能,采用折压比、韧性指数等多个指标对UHTCC的韧性进行了评价。试验表明：UHTCC的抗压强度、抗折强度、抗弯强度以及延性和韧性都远高于普通钢纤维混凝土,其抗弯强度最高达65.1 MPa、韧性指数I₂₀最高达49.21,单轴拉伸试验时呈现明显的假应变硬化行为,极限拉应变可达4%~8%。相对而言,利用SIFCON工艺制得的水泥基材料韧性更高。     

Fabrication of high performance 3D SiO<Subscript>2</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite via perhydropolysilazane infiltration and pyrolysis

The continuous fiber reinforced ceramic matrix composites have received consider-able attention for structural applications because of their excellent thermal stability, light weight, and damage tolerance imparted by the reinforcing fibers. Silica fibers, with ex-cellent ablative resistance, thermal shock damage resistance, dielectric properties, chemical stability and flexibility, are suitable for fabricating high temperature antenna window materials to meet the requirements of communication, …     

Effects of oxidation treatment on properties of SiO2f/SiO2-BN composites

The silica fiber reinforced silica and boron nitride-based composites (SiO_2f/SiO₂-BN) were prepared firstly via the sol-gel method and then the urea route, and the effects of oxidation treatment on the component, structure, mechanical and dielectric properties of the composites were investigated. The results show that the oxidation treatment at 450 °C will not impair the structure of boron nitride, and carbon is the main impurity with the excessive urea. The density of SiO_2f/SiO₂-BN composites is 1.81 g/cm³, and the flexural strength and elastic modulus are 113.9 MPa and 36.5 GPa, respectively. After oxidation treatment, the density varies to 1.80 g/cm³, and the flexural strength and elastic modulus are decreased to 58.9 MPa and 9.4 GPa, respectively. The mechanical properties of the composites are severely damaged, but they still exhibit a good toughness. The composites show excellent dielectric properties with the dielectric constant and loss tangent being 3.22 and 0.003 9, respectively, which indicates that the oxidation treatment is ineffective to improve the dielectric properties of SiO_2f/SiO₂-BN composites.     

Effect of nano-silica modification on the tensile property of SMA/GF/CF/epoxy super hybrid woven fabric composites

Tensile properties of epoxy casts together with shape memory alloy (SMA), glass (GF) and carbon (CF) woven fabric reinforced epoxy matrix super hybrid composites were investigated, respectively. In order to enhance the mechanical strength of this advanced material, two categories of modifications including matrix blending and fiber surface coating by nano-silica were studied. Scanning electron microscopy (SEM) and fiber pull-out tests were adopted to complement the experimental results, respectively. Experimental results reveal that the toughness of epoxy matrix is enhanced significantly by adding 2wt% nano-silica. The failure mechanism of SMA reinforced hybrid composites is different from that of GF/CF/epoxy composites. Compared with the matrix modification, the fibers modified by coating nano-silica on the surface have better tensile performances. Moreover, the fiber pull-out test results also indicate that composites with fiber surface modification have better interfacial performances. The modification method used in this paper can help to enhance the tensile performance of the mentioned composite materials in real engineering fields.     

玻璃纤维增强环氧树脂单向复合材料力学性能分析

采用连续玻璃纤维与环氧树脂相复合,通过金属模压成型工艺,制备出单向玻璃纤维／环氧树脂复合材料。通过三点弯曲实验论证单向纤维对树脂基体的增强作用,从而研究不同纤维含量下复合材料的弹性模量、纵向拉伸强度、纵向压缩强度的变化趋势。结果表明：随着纤维含量的增加,复合材料的力学性能均增强,当纤维体积含量为50％时,其各项性能均较好,弹性模量为40GPa,纵向拉伸强度为1200MPa,纵向压缩模量为700MPa。此外,对复合材料的其他常用力学性能参数进行检测。     

Physical and Mechanical Properties of PP Composites based on Different Types of Lignocellulosic Fillers

The presents preparation and characterization of different types of lignocellulosic fillers (pine wood sawdust/ walnut shell flour/ black rice husk powder) reinforced polypropylene composites were presented. The effect of MAPP as coupling agent (4wt%) on the physical and mechanical properties was also investigated. Polypropylene composites were prepared at different rates of filler/matrix (wt%) by using extrusion (for melt blending) and hot compression molding process. Maximum values of tensile and flexural strength were obtained as 26.1 and 43.4 MPa, respectively, whereas the elongation at break value was 4.11% at 10% pine wood sawdust reinforced PP. Tensile and flexural modulus of composites reached the maximum values as 3855 and 3633 MPa with the composite of 30% walnut shell flour reinforced PP. Characterization of composites was carried out by using tensile test, flexural test, FT-IR, and SEM.     

基于弹簧-滑块模型的平纹织物几何结构模拟研究

基于力学原理研究了平纹织物几何结构的计算方案,并对该平纹结构进行三维模拟显示.根据平纹织物的交织规律和纱线材料及加载张力,提出了串联的滑块-弹簧模型,进而从力学的角度分析纱线的运动趋势、变形情况.不断进行力学公式的迭代计算,得到机上平纹织物稳定状态下的几何结构.利用B样条曲线曲面造型技术,构建截面形态变化的立体纱线模型以探索纱线截面的变化规律,并模拟显示平纹织物的几何结构.     

基于3ds Max软件的机织物结构三维建模研究

开发了基于3ds Max软件建立机织物结构三维模型的方法,并实现了平纹、斜纹、缎纹等典型机织物组织结构的三维建模.根据机织物结构相理论,确定了表达经纬纱轴线状态的空间曲线,结合3ds Max软件的截面放样技术实现了纱线的建模.按照经纬纱交织规律,建立了机织物结构的三维模型.研究表明,3ds Max软件具有操作简单、三维建模功能丰富的特点,是进行机织物结构立体表现及研究机织物纱线空间位置关系的有效工具.     

原位合成Al_2O_3/FeAl复合材料的组织与性能

利用Fe-Al-Fe2O3体系的放热反应,原位热压合成了Al2O3/FeAl复合材料.借助XRD和SEM等研究了复合材料的物相组成和显微结构,以及Al2O3生成量对复合材料显微结构和力学性能的影响.结果表明:经1 250℃保温1.5h热压烧结的块体材料主要由FeAl及少量Al2O3相构成,FeAl基体为片层结构,增强相Al2O3分散在基体和晶界处.随着Al2O3含量的增加,基体晶粒尺寸明显减小,同时对材料起增强增韧作用.在Al2O3含量为1.2wt%时,试样的抗弯强度达到最大值1 329.22MPa;在Al2O3含量为0.8wt%时,试样的断裂韧性达到最大值29.95MPa·m1/2.此值正好处于金属与陶瓷材料性能链的断缺处.因此,本研究结果对于完善材料性能体系具有重要意义.     

Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction

Carbon fibre reinforced carbon and silicon carbide dual matrix composites(C/C-SiC) were fabricated by the warm compacted-in situ reaction.The microstructure,mechanical properties,tribological properties,and wear mechanism of C/C-SiC composites at different brake speeds were investigated.The results indicate that the composites are composed of 58wt%C,37wt%SiC,and 5wt%Si.The density and open porosity are 2.0 g.cm~(-3) and 10%,respectively.The C/C-SiC brake composites exhibit good mechanical properties.The ...     

Effects of fibers on mechanical properties of high-performance concrete subjected to elevated temperatures

The compressive strength and ilexural toughness as well as fracture energy of fiber reinforced highperformance concrete （FRHPC） subjected to different high temperatures were studied. The results showed that after exposure at 300,600 and 900℃, the concrete mixes retained 88.1% , 41.3% and 10.2% of the original compressive strength on average, respectively. Steel fiber and polypropylene （PP） fiber were both effective in minimizing the damage effect of high temperatures on the compressive strength. The HPC reinforced with steel fibers showed higher flexural toughness and fracture energy before and after the high-temperature exposures. In comparison, PP fibers had minor beneficial effects on the flexural toughness and fracture energy. The mechanical properties of HPC reinforced with hybrid fibers （steel fiber ＋ PP fiber） were equivalent to or better than those of HPC reinforced with steel fibers alone. In addition, the failure pattern of FRHPC beams changed from pull-out of steel fibers at lower temperatures （20, 300 and 600℃） to tensile failure of steel fibers at higher temperature （900 ℃）.