基于搜索锥算法的纤维分布特征及对BFRC的增强机制

混凝土基体内部纤维的取向、分布及纤维的接触点是影响纤维混凝土力学性能的重要因素,也是目前研究的薄弱环节.本实验研究纤维掺量对玄武岩纤维增强混凝土(BFRC)三轴力学性能的增强机制,采用CT技术和搜索锥算法实现BF的获取与识别,重点分析纤维掺量在1.5 kg/m3、3 kg/m3、4.5 kg/m3时BF分布角度、效率指数及接触点变化规律,揭示纤维形态学特征对BFRC力学性能的增强机理.结果表明:纤维掺量保持不变,峰值应力随围压的增大而增大;围压保持2 MPa不变,随着纤维掺量的提高,材料的峰值应力先增加后下降,最佳掺量为3 kg/m3,此时峰值应力为44.48 MPa,相比普通混凝土增加了99.64％.纤维追踪后发现:纤维在混凝土基体中乱向分布;在笛卡尔坐标系Z轴的方向角γ下,80～90°范围内纤维分布较多,纤维倾向于水平放置,近似与竖向裂缝垂直;在方向角α下,30～50°范围内纤维分布较多,对于控制斜向裂缝最为有利;不同掺量下的纤维效率指数eiy分别为0.57、0.65、0.55,进一步说明纤维倾向于平行Y轴;随着纤维掺量的增加(1.5 kg/m3、3 kg/m3、4.5 kg/m3),纤维接触率分别为0％、25％、49％,纤维结团现象愈发明显,三轴强度分别为26.63 MPa、44.48 MPa、42.43 MPa,纤维接触在一定程度上影响BFRC的三轴力学性能.     

短切玄武岩纤维混凝土力学性能试验与分析

为了研究短切玄武岩纤维掺量变化对混凝土基本力学性能的影响,对6种不同体积掺量的短切玄武岩纤维混凝土(BFRC)分别进行立方体抗压、轴心抗压、劈裂抗拉、抗折试验;基于试验结果,通过BP(Back Propagation)神经网路强度预测模型的构建,对附加纤维掺量的混凝土进行强度训练及预测。试验实测数据表明:掺入短切玄武岩纤维对混凝土早期抗压强度的发展有着延缓作用;当纤维掺量为0.1%时,抗压强度达到峰值。随着纤维掺量的增加,劈拉强度增幅较大,抗折强度保持上升趋势。通过BP神经网络的训练及发展趋势预测,结果表明:当纤维体积掺量为0.1%时,抗压强度达到最大值;劈拉强度与抗折强度则随着纤维掺量的增加而持续增大。基于试验数据及预测结果,得出短切玄武岩纤维的最佳体积掺量。     

纤维增强水泥基复合材料的动力拉伸性能研究

采用分离式霍普金森杆对聚乙烯醇(PVA)纤维增强水泥基复合材料(PRCC)、基体材料、不同相对掺量的钢纤维和PVA纤维混合增强水泥基复合材料(HFRCC)进行了四种不同应变率下的动态劈拉试验,通过对材料的劈拉强度、能量吸收和破坏形态等方面的对比分析,探讨了三种材料的动力拉伸性能,结果表明材料表现出应变率敏感性,随着应变率的提高,动态劈拉强度和能量吸收能力相应增加。HFRCC对基体材料的劈拉强度提高可达到34%,而PRCC材料提高约20%。PVA纤维对材料的耗能能力的影响比钢纤维具有更强的应变率敏感性。钢纤维掺量占总纤维掺量25%的HFRCC材料耗能能力比PRCC略低5%,而钢纤维掺量达到总纤维掺量的62.5%时,HFRCC材料的耗能能力比PRCC的耗能能力显著提高。HFRCC在动态劈拉强度和能量吸收能力方面更加均衡,具有更好抵抗冲击的能力。     

纤维聚苯乙烯泡沫颗粒轻质土的制备及力学性能

为促进轻质土在岩土工程中的广泛应用,添加改性聚丙烯纤维改善其力学性能,通过无侧限抗压强度试验分析探讨了纤维聚苯乙烯泡沫（EPS）颗粒轻质土强度-变形特性、受压破坏模式和无侧限抗压强度的影响因素,并运用SEM从微观层次上分析了其力学机制。结果表明:不同EPS颗粒、纤维及水泥掺量时,纤维EPS颗粒轻质土的应力-应变曲线不同;EPS和水泥掺量是强度的主要影响因素,其次为纤维掺量;强度随EPS掺量的增大而显著降低,随水泥掺量增大而显著提高;未加纤维的EPS颗粒轻质土松散且易破碎,强度骤然丧失;添加纤维能提高轻质土的峰值强度、残余强度、整体性和韧性,改善其脆性破坏模式;但EPS掺量较高（大于干土质量的3%）时,纤维与水泥土粘结有限,EPS颗粒轻质土力学性能改善效果较弱;EPS颗粒为空心蜂巢结构,纤维表面布满针状的水泥水化物并形成空间网状结构。所得结论表明纤维改善了轻质土力学性能。      

高性能PVA纤维增强水泥基复合材料单轴受拉特性

高韧性PVA纤维增强水泥基复合材料具有很高的能量吸收能力,但强度通常较低,采用我国地方材料资源和工业废料,可制备出高强度同时极限变形量满足实际工程要求的高性能PVA纤维增强水泥基复合材料(HPFRCC),以应用于高层抗震建筑结构的关键部位。通过单轴受拉强度和变形特性试验,研究PVA纤维体积率、粉煤灰掺量、硅灰掺量、水胶比及砂胶比对HPFRCC抗拉性能的影响,研究结果表明:随着PVA纤维体积掺量的增加,HPFRCC的抗拉强度与极限拉应变增大;大掺量粉煤灰替代水泥及增大水胶比可降低HPFRCC的抗拉强度,但明显改善其受拉应变硬化特性;HPFRCC中掺入适量硅灰及细砂可提高其抗拉强度,但极限拉应变降低,尤其当砂胶比较大时,HPFRCC的受拉应变硬化现象不明显;基于细观力学模型,分析了各因素对HPFRCC拉伸应变硬化特性影响的原因,研究结果可为今后HPFRCC的实际工程应用提供基础依据。     

不同方法测试的超高性能混凝土抗拉强度

通过16组不同钢纤维掺量超高性能混凝土(UHPC)轴心抗拉强度、抗折强度和劈裂抗拉强度的试验,并结合各单位试验数据的统计分析,开展不同试验方法下UHPC抗拉强度的研究。结果表明,不同UHPC抗拉强度均随钢纤维掺量的增加而提高,但强度提高幅度各不相同,其中劈拉强度增幅较大;相同钢纤维掺量时,UHPC的抗折强度和劈拉强度相近,且远大于轴拉强度。UHPC轴拉强度和抗折强度的比值与钢纤维混凝土和普通混凝土的抗拉强度之间的比值较接近,而劈拉强度相关的其他2个比值则相差较大。建议以抗折强度试验作为工程实践中UHPC抗拉强度的间接测试方法。     

聚丙烯纤维增强混凝土研究进展

聚丙烯纤维具有耐化学腐蚀、加工性好、质轻、蠕变收缩小、价格低廉和在低掺量时对混凝土的塑性干缩开裂改善效果显著、抗渗性好、防止火灾中混凝土爆裂等优良的技术经济性能。但同时也存在一些缺点,如随着纤维掺量的增加,混凝土工作性降低、弹性模量低、增韧效果差以及低掺量下对混凝土的强度(抗拉、抗压、抗折)无显著影响等等。综合论述了改善聚丙烯纤维增强混凝土目前的研究进展,展望了其发展趋势。     

聚酯纤维对石灰煤渣砂砾抗弯拉性能试验研究

针对石灰煤渣砂砾抗弯拉强度低、性能差的问题,通过添加不同长度和不同掺量的纤维进行试验及比对实验数据,进行理论分析,研究了石灰煤渣砂砾的抗弯拉强度,提出了抗弯拉强度最佳效果的聚酯纤维掺加量和长度。研究显示:当养护龄期较短时,纤维的掺加对石灰煤渣砂砾的抗弯拉强度无明显的影响,当养护龄期较高时,聚酯纤维对石灰煤渣砂砾的抗弯拉性能有一定的提高。     

低压片状模塑料纤维的取向

低压片状模塑料(LPMC)模压流动成型后玻纤在平面内发生取向,导致模压件呈各向异性。文中从成型后制品上取样烧尽树脂,由扫描仪获取纤维数值图像,用Photoshop软件将图像反相、增强,再利用MATLAB软件确定纤维取向分布。并讨论了纤维取向的影响因素、控制方法及对复合材料力学性能的影响。研究表明,LPMC片材的黏度、加料面积及闭模速度是影响制品纤维分布的主要因素,增大片材黏度、增大加料面积及适当提高闭模速度都可以提高制品纤维分布的均匀性。LPMC制品的弯曲强度几乎不随试样的取样位置不同而改变,但在纤维平行取向方向上具有比垂直取向方向上更高的强度和模量。     

C/C-Cu复合材料的压缩性能及其破坏机理

以预浸炭布和铜网为原料用模压压制法制备炭纤维体积分数分别为35%、40%和45%左右的三种C/CCu复合材料,用Instron3369力学试验机测试了压缩性能。结果表明:炭纤维的体积分数是影响材料压缩性能的重要因素。在垂直方向上,材料的压缩性能随着炭纤维体积分数的增加而提高。炭纤维体积分数为40%的试样其压缩性能比35%的试样提高了20%,炭纤维体积分数为45%的试样比40%的试样提高了13%,提高的幅度呈先大后小的趋势。而在平行方向上,炭纤维的体积分数对压缩性能的影响没有垂直方向的显著,与试样的致密度有一定的关系。在三种试样中,炭纤维体积分数为45%的试样无论在垂直方向还是平行方向上的压缩强度都最大,分别为190.13 MPa和83.39 MPa。在平行方向和垂直方向上压缩强度的差异表明,C/C-Cu复合材料的压缩性能具有明显的各向异性。关于材料压缩的破坏方式,在垂直压缩受力方向近似沿45°对角线方向时,破坏方式为纤维层、铜网与基体炭的分离以及基体炭的压溃破坏。在平行方向压缩时炭纤维发生褶皱,并在褶皱区域产生拉压应力,使纤维发生折曲或者断裂,最终使炭纤维和基体炭以及基体炭和铜网的界面分层劈裂。     

Processing and characterization of aligned vapor grown carbon fiber reinforced polypropylene

This investigation describes a method for aligning vapor grown carbon nano-fibers suspended in a polymer flow during extrusion to produce an improved thermoplastic composite. A twin-screw extruder was used to shear mix and extrude fiber/polypropylene mixtures through a converging-annular die that generates fiber alignment along the flow direction. The degree of fiber alignment was quantified by using X-ray diffraction. It was shown that fiber alignment could be improved by increasing the residence time in the die channel. Tensile specimens were fabricated by molding the extruded strands and the strength properties of the aligned samples increased with fiber content. The tensile strength improved with greater fiber orientation, however, more fiber alignment had little affect on the modulus. The addition of vapor grown carbon nano-fiber also increased the thermal conductivity and decreased the electrical resistivity.     

晶须取向对SiCw／Al复合材料力学性能的影响

研究了压铸态及挤压态20％（体积分数SiCw/6061Al复合材料中晶须取向及其拉伸力学性能,结果表明,压铸态复合材料中晶须取向趋于混乱分布状态,因而其力学性能具有较高的各向均匀性,复合材料经过挤压变形后晶须呈定向排列,沿挤压方向的各项力学性能均有所提高,尤其是伸长率得到显著改善。     

碳纤维-玻璃纤维层内混杂单向增强环氧树脂复合材料拉伸性能

采用不同混杂比的碳纤维-玻璃纤维层内经向混编单轴向织物制备了混杂纤维增强环氧树脂复合材料, 研究了不同混杂结构和不同混杂比的碳纤维-玻璃纤维/环氧树脂复合材料拉伸性能的变化及破坏形式。0°拉伸结果表明:同种混杂织物的不同混杂结构中, 碳纤维相对集中的完全对齐结构强度最高, 不同混杂比织物的完全对齐结构强度相当;碳纤维-玻璃纤维/环氧树脂复合材料的模量遵循混合定律。90°拉伸结果表明:纤维与树脂间的界面结合强度为碳纤维/树脂>玻璃纤维/树脂, 碳纤维-玻璃纤维/环氧树脂复合材料的强度、模量与材料厚度方向上界面的不同形式(单一或交替界面、碳纤维或玻璃纤维的分布位置等)有关, 与碳纤维的含量基本无关。      

Effect of microstructure and texture on the mechanical properties of the as-extruded Mg–Zn–Y–Zr alloys

This work mainly studied the influence of the microstructure and crystallographic texture on the mechanical properties of the as-extruded Mg–Zn–Y–Zr alloys with different Y contents. The samples were machined from thick plates obtained by extrusion and the tensile tests were performed parallel to extrusion and transverse directions, respectively. Microstructure observation firmly indicated that the grain-refining effect of icosahedral quasicrystal phase (I-phase) was superior to that of the cubic W-phase. In addition, the tensile results indicated that I-phase could effectively improve the strength (yield strength and ultimate tensile strength) of alloys. However, strengthening effect of W-phase was lower. With the quantity of W-phase increasing, the strength of alloys was degraded. It also showed that the alloys were mechanically anisotropic, i.e. the longitudinal strength was higher than that of the transverse direction. However, the ductility of the transverse direction was superior. With the increase of Mg–Zn–Y phases, the anisotropy of the ultimate tensile strength (UTS) between the longitudinal and transverse directions increased remarkably. SEM fracture observations showed that the fractures of the TD samples were characterized by the typical “woody fracture”, with a large amount of cracked Mg–Zn–Y particles (I-phase and W-phase) distributed at the bottom of dimples. With Y content increasing, the average spacing of the zonal distributed Mg–Zn–Y particles on the fracture surface became narrow, which influenced the transverse mechanical properties greatly.     

对位芳纶/尼龙66的加工工艺对其力学性能的影响研究

由不同的加工工艺来研究对位芳纶/尼龙66(PPTA/PA66)复合材料的力学性能,结果表明:①随着PPTA纤维含量的增多,使用黏度较大的PA66基体进行复合时,PPTA/PA66复合材料的拉伸强度、弯曲强度都随之变大;对于冲击强度来说,PPTA纤维的加入,增加了其脆性,造成PPTA/PA66复合材料冲击强度不如原基体的冲击强度;②PPTA纤维含量在5%的情况下,当挤出机转速达到300r/min时材料的拉伸强度、冲击强度和弯曲强度出现极大值,此时的混合效果最理想;③较高的挤出温度有助于提高复合材料的拉伸强度和弯曲强度,对于冲击强度来说,PPTA/PA66复合材料冲击强度同样不如原基体的冲击强度;④PPTA纤维的长径比集中在65左右,芳纶纤维起到了增强效果。     

Mechanical properties of pultruded glass fiber-reinforced plastic after moistening

The kinetics of moisture sorption under immersion in water at room and elevated temperatures and flexural characteristics of dry (conditionally initial) and wet (moistened up to saturation level) composite material were investigated on flat specimens of polyester based glass fiber-reinforced plastic, cut from I-beam pultruded profile. It was found that the coefficients of diffusion and swelling are different in three principal axis of the composite. The former have the largest value in fiber axis direction, but the latter – in transverse to fiber axis direction out of plane of the layers. The observed difference in kinetics of mass gain and change of volume strain for the specimens of various sizes allowed evaluate the volume of pores, filled with water. The large data spread for the specimens, cut from the flanges, was found. Edge specimens have lower density and showed lower elastic and strength characteristics. The material specimens moistened up to saturation level showed the decrease in flexural modulus and strength for 8% and 16.5%, respectively. No effect of sorbed moisture on tensile modulus and strength of the composite (tension along the fiber axis direction) was found.     

Bearing strength of commingled boron/glass fiber reinforced aluminum laminates

The bearing properties of recently developed hybrid fiber/metal laminates, or COmmingled Boron/glass fiber Reinforced Aluminum laminates (COBRA), are investigated in this study. The bolt-type bearing tests on GLass REinforced aluminum laminates (GLARE), non-commingled hybrid boron/glass/aluminum fiber/metal laminates (HFML) and COBRA were carried out as a function of e/D ratio, metal volume fraction, fiber volume fraction, and fiber orientation. Experimental results show that with the same joint geometry and metal volume fraction, the commingling of boron fibers improves the bearing strength of fiber/metal laminates. Observations show the boron/glass fiber prepreg, transverse to the loading direction, results in a bearing mechanism that effectively increases the bearing strength. The bearing strength of COBRA with longitudinal fibers is lower than that with transverse fibers due to the fact that shearout failure takes place before maximum bearing strength is reached. The experimental results show that, with only either transverse fiber orientation or longitudinal fiber orientation, COBRA with 18% boron fiber volume fraction possesses a higher bearing strength when compared to HFML with 6% boron fiber volume fraction. In addition to the properties in COBRA with parallel-plies commingled prepreg, the bearing properties of various COBRA with [0°/90°] and [0°/90°/90°/0°] cross-ply commingled prepregs are also discussed.     

Microstructure and mechanical properties of Mg -2Gd -3Y -0.6Zr alloy upon conventional and hydrostatic extrusion

The Mg-12Gd-3Y-0.6Zr (wt. %) alloy was subjected to conventional and hydrostatic extrusion in two subsequent steps. The best combination of mechanical properties (strength and ductility) was achieved by RT hydrostatic extrusion following conventional extrusion at 430 °C, with the ultimate tensile strength (UTS), tensile yield strength (TYS) and elongation being 485 MPa, 413 MPa and 5.2% at room temperature. The texture results of extruded rods indicate that the c-axis of most grains was aligned preferentially perpendicular to the extrusion direction, forming a typical extrusion Mg fiber texture.     

炭纤维的环氧树脂浸润特性

良好的界面粘结是制备高性能复合材料的关键之一，而树脂与纤维的优良浸润则是其首要前提。通过考察环氧618树脂与环氧AG80树脂在T300和T700两种炭纤维堆积体中分别沿垂直于纤维方向和平行纤维方向的浸润特性，同时模拟实际复合材料成型工艺条件，分析了浸润速率随树脂温度和纤维体积分数的变化规律。研究结果表明，树脂在垂直于T700炭纤维方向的浸润速率明显慢于相同条件下其在平行纤维方向的浸润。并且纤维含量对两种方向的浸润影响不同，垂直纤维方向的浸润速率随纤维体积分数的增加而减缓，而平行纤维方向的浸润速率则随纤维体积分数的增加而加快。以上研究结果均可用于指导复合材料成型工艺，具有较好的实际参考价值。     

陶瓷纤维增强氧化硅气凝胶复合材料力学性能试验

氧化硅气凝胶具有极低的热导率和密度,可作为很好的隔热材料,而脆弱的力学性能限制了其在隔热领域的应用。在不影响隔热效果的前提下,通过复合陶瓷纤维可增加氧化硅气凝胶的强度及韧性。试验探索了陶瓷纤维增强氧化硅气凝胶在室温下的拉伸、压缩和剪切等基本力学性能,分别研究了300℃、600℃和900℃下复合材料纤维铺层面方向的压缩性能,并采用扫描电子显微镜对高温试样微观结构进行了观察分析。结果表明：陶瓷纤维增强氧化硅气凝胶的性能表现出方向性,弹性模量在铺层面内方向与厚度方向的数值最大相差约28倍,强度极限亦然;在室温条件下,复合材料的拉伸和压缩弹性模量不同,X 、Y 和 Z 方向拉伸模量与对应的压缩模量之比分别为1.60、1.83和0.56;高温下复合材料沿厚度方向收缩,收缩量随温度升高而增大,900℃下的最大收缩量可达10.8%;高温下复合材料铺层面内方向压缩性能随温度升高而增强。