聚丙烯纤维水泥稳定碎石断裂性能试验研究

通过30个尺寸为100mm×100mm×515mm的聚丙烯纤维水泥稳定碎石和普通水泥稳定碎石三点弯曲试件断裂试验,探讨了聚丙烯纤维对水泥稳定碎石断裂韧度(KIC)、断裂能(GF)、临界裂缝嘴张开位移(CMODC)、临界裂缝尖端张开位移(CTODC)、极限裂缝嘴张开位移(CMODmax)和极限裂缝尖端张开位移(CTODmax)的影响。试验结果表明:聚丙烯纤维的掺入可增大水泥稳定碎石的断裂韧度、断裂能、临界裂缝嘴张开位移、极限裂缝嘴张开位移、临界裂缝尖端张开位移和极限裂缝尖端张开位移;随着聚丙烯纤维体积掺量的增加,断裂韧度、临界裂缝嘴张开位移和临界裂缝尖端位移的变化无明显规律,但断裂能、极限裂缝嘴张开位移和极限裂缝尖端位移基本上呈线性增加的。     

纤维对开裂后混凝土渗透性及裂缝恢复的影响

通过劈裂试验和渗透试验,研究了结构型钢纤维、聚丙烯粗纤维和聚丙烯细纤维对开裂后混凝土的裂缝恢复率、劈裂韧性和渗透系数的影响。研究结果表明:钢纤维和聚丙烯粗纤维的掺入可限制裂缝扩展,使混凝土由脆性破坏转为韧性破坏,提高开裂混凝土在卸载后裂缝的恢复作用,显著减小开裂后混凝土的渗透系数。钢纤维掺量越高,裂缝恢复和渗透性降低越明显,钢纤维掺量由25kg/m~3增加至55kg/m3时,渗透系数减小了87%。钢纤维和聚丙烯粗纤维的掺入具有较好的正混杂效应,当裂缝宽度为150μm时卸载,单掺25kg/m~3钢纤维和4kg/m~3聚丙烯粗纤维与单掺35kg/m~3钢纤维相比,渗透系数减小了60%。而聚丙烯细纤维对开裂混凝土的裂缝恢复和渗透性影响较小。     

SMA纤维混杂层合梁的振动分析

提出一类形状记忆合金(SMA)纤维混杂层合梁的数学模型。采用多胞模型、形状记忆合金一维本构关系分析方法,同时考虑铁木辛柯剪切和马氏体相变的影响。目的是为了更进一步了解层合梁的振动控制。SMA纤维用来作为驱动器,它能够改变弹性模量和回复力,以此改变梁的频率。分析了SMA纤维含量、铺设角度和横向剪切变形的影响。结果表明,通过激活形状记忆合金纤维及改变初始变形,对层合梁的自振频率有很强的控制和调节能力。     

Modal analysis of cracked, unidirectional composite beam

In this paper, a model and an algorithm for creation of the characteristic matrices of a composite beam with a single transverse fatigue crack are presented. The element developed has been applied in analysing the influence of the crack parameters (position and relative depth) and the material parameters (relative volume and fibre angle) on changes in the first four transverse natural frequencies of the composite beam made from unidirectional composite material.     

Fracture processes of hybrid fiber-reinforced mortar

Subregion Scanning Computer Vision (SSCV), a digital image based method for measuring surface deformation is used to examine the role of the fibers in the fracture process of mortars reinforced with hybrid blends of microfiber (less than 22 μm in diameter) and macrofiber (500 μm in diameter). Closely-spaced microfibers interact with cracks at the microstructural level and hamper the widening of coalesced microcracks, thus encouraging the growth of multiple cracks. The microfibers improved pre-peak mechanical performance and strength by delaying the formation of a through-specimen macrocrack. Macrofibers were most effective at bridging macrocracks and imparting ductility to the composite due to their geometry and greater length. Compared to mortar reinforced with a single fiber type, an increase in strength and toughness was seen with a blend of steel macrofibers and either steel or PVA microfibers. Finally, based on the crack topography observed, the reduction in water permeability of cracked mortar achieved with hybrid fiber-reinforcement, measured directly in a parallel study, was governed by multiple crack development.     

Influence of redmud particle hybridization in banana/sisal and sisal/glass composites

A novel hybrid composite is developed by adding redmud as the secondary reinforcing filler with banana/sisal and sisal/glass fiber reinforced polyester composites. The composites are prepared by the hand layup technique followed by compression molding. The tensile, flexural, and impact strength of the composites are investigated by varying the parameters such as particle size (4 and 13?µm) and weight percentage (2, 4, 6, and 8?wt%) of redmud particle addition. The experimental result shows that the addition of redmud enhances the mechanical property of the hybrid composite. The maximum increase of 33% in tensile strength and 54% in flexural strength is observed for the sisal/glass composite and 25% increase in impact strength for the banana/sisal composite. The linear regression analysis is also introduced to predict the errors in the scatter plot. Furthermore, the Scanning Electron Microscopy (SEM) is used to study the effect of redmud on the interfacial bonding in the banana/sisal and sisal/glass fiber reinforced polyester composites.     

颗粒粒度分布对树脂基磁致伸缩复合材料性能的影响

已有研究在Terfenol-D颗粒粒径及粒度分布对树脂基磁致伸缩复合材料性能的影响规律上存在分歧。本文中以Terfenol-D为磁致伸缩颗粒,以不饱和聚酯树脂为基体,采用5 种窄分布颗粒(30～53μm、53～150μm、150～300μm、300～450μm、450～500μm)和1种宽分布颗粒(30～500μm)制备颗粒体积分数为20 %的磁致伸缩复合材料,并测试其动静态磁致伸缩系数、磁机械耦合系数、弹性模量及抗压强度等性能参数。在窄分布颗粒制备的试样中,以53～150μm制备的复合材料的磁致伸缩性能最佳;而采用宽分布颗粒制备的试样其性能优于窄分布颗粒制备的试样。该结果表明,增大颗粒粒径同时具有积极作用与消极作用, 其对复合材料磁致伸缩性能的影响取决于哪一个居主导地位。      

6061-T6 铝合金激光焊接接头腐蚀疲劳裂纹扩展

目的研究6061-T6铝合金激光焊接接头的腐蚀疲劳裂纹扩展特性,并分析裂纹扩展的影响因素。方法利用光纤激光器,焊接尺寸为150 mm×100 mm×4 mm(焊接方向、横向、熔深方向)的6061-T6铝合金,采用SE(B)三点弯曲疲劳裂纹扩展试验并利用连续降K法,分别在空气和人工海水中进行疲劳裂纹扩展试验,通过使用金相显微镜(OE)和扫描电子显微镜(SEM),对金相结构进行观测分析。结果同样工艺参数的焊接接头,在海水中疲劳裂纹门槛值(4.063 016 MPa·m~(0.5))大于空气中的门槛值(3.479 166 MPa·m~(0.5));在疲劳裂纹扩展中速区(da/dN10~(-5) mm/cycle)时,海水焊接接头疲劳裂纹扩展速率大于空气中的,低速区(da/d N10~(-5) mm/cycle)则小于在空气中的。结论成形良好的焊缝、晶粒细小的焊缝组织有助于接头疲劳裂纹扩展性能的提高;中速区,海水中疲劳裂纹扩展速率偏大,主要是由腐蚀条件下焊缝裂纹尖端阳极溶解和交变载荷共同作用导致;低速区,海水中疲劳裂纹扩展速率偏小,主要原因是腐蚀产物堆积于疲劳裂纹扩展尖端,产生较强裂纹闭合效应。     

增强颗粒含量和尺寸对SiCp/Fe复合材料性能的影响

利用电流直加热动态热压烧结工艺,分别制备了增强颗粒体积含量从5%到15%,尺寸从3 μm到45 μm的SiCp/Fe复合材料,研究了粒子含量与尺寸对复合材料硬度、强度、延伸率和耐磨性能的影响.研究表明:增强颗粒的体积含量从5%提高到10%,可以明显提高材料的性能;随着增强颗粒含量进一步提高,颗粒团聚将导致材料性能降低;...     

粒径对Ni/硅橡胶复合材料压敏性及介电性质的影响

采用不同粒径的Ni粉与硅橡胶(110型)按质量比2.4∶1.0制成Ni/硅橡胶复合材料, 分别测量了其压敏导电性及介电性质, 并结合扫描电镜照片对其微观导电机制进行了分析。结果表明随着填料Ni粉粒径的减小, Ni/硅橡胶复合材料的直流电阻率对外加压强更加敏感: 在低压强下, 粒径为74、48和18 μm的样品的电阻率随压强的变化率分别为1.73×104、2.59×104和3.71×10 4 Ω·m/kPa。样品直流电阻率陡降的区域随粒径的减小向压强较小的方向移动, 显示出复合材料的渗流阈值与填充粒子的粒径有关: 粒径越小, 渗流阈值也越小。Ni/硅橡胶复合材料的交流电导率、介电常数、介电损耗均随填料Ni粉粒径的减小而变大: Ni粉粒径为18 μm的Ni/硅橡胶复合材料的电导率约为10-2 S·m-1, 比74 μm粒径样品的电导率(约10-7 S·m-1)提高了5个数量级; 对应的介电常数由约102提高到约103。改变填料Ni粉粒径可以有效地调节复合材料的弹性和压敏、电输运特性。      

颗粒尺寸对SiC_P预制体孔洞三维特征的影响

通过模压成型和高温烧结制备了不同SiC_P颗粒尺寸(20、50、100和150μm)的预制体,采用高分辨率(~1.0μm)三维X射线断层扫描和三维孔隙网络结构模型,研究了SiC_P颗粒尺寸对预制体孔洞三维特征的影响。结果表明:随着SiC_P颗粒尺寸的增大,淀粉的间隙膨胀作用逐渐减弱,而颗粒堆积间隙逐渐增大。当SiC_P颗粒尺寸由20μm增大到100μm时,截面孔洞形貌更加平齐,面孔隙率均值减小,孔洞体积的空间分布均匀性和连通性都变差,孔洞和喉道的平均尺寸增大,而小尺寸孔喉数量减少,平均孔洞配位数减小;当颗粒尺寸继续增大至150μm时,间隙被更多较小尺寸颗粒填充,且颗粒表面残留网状粘结剂,都大大降低了孔洞体积的空间分布均匀性和连通性,使小尺寸孔喉数量增多,平均孔洞配位数增大。     

聚乙烯醇乳液改性对汉麻秸秆纤维/水泥基复合材料性能的影响

为解决汉麻秸秆纤维/水泥基复合材料力学性能较差的问题,本文提出采用聚乙烯醇(PVA)乳液对汉麻秸秆纤维/水泥基复合材料进行改性。在优化秸秆纤维的粒径和掺入量后,采用PVA乳液与秸秆纤维和水泥进行共混成型,制备了改性后的汉麻秸秆纤维/水泥基复合材料。研究了不同质量比的PVA乳液对汉麻秸秆纤维/水泥基复合材料的抗折强度、密度、比强度和弯曲韧性的影响,通过含水率、吸水率及红外光谱测试揭示了PVA乳液对汉麻秸秆纤维/水泥基复合材料的改性机制。结果表明:汉麻秸秆纤维粒径为1700 μm及掺入量为12%时,秸秆纤维对汉麻秸秆纤维/水泥基复合材料的增强作用最好。随着PVA乳液质量比的增加,改性后汉麻秸秆纤维/水泥基复合材料的密度逐渐减小,弯曲韧性逐渐提高。当PVA乳液质量比为4.8%时,相较于未改性的汉麻秸秆纤维/水泥基复合材料,改性后的汉麻秸秆纤维/水泥基复合材料抗折强度和比强度分别提高了17.17%和20.50%。通过PVA乳液改性使汉麻秸秆纤维/水泥基复合材料中秸秆纤维与水泥之间的界面得到改善,并缓解了秸秆纤维对水泥水化反应的阻碍作用。      

纤维对混凝土裂缝宽度、曲折度及渗透性的影响

为研究不同纤维（钢纤维（SF）、聚丙烯长纤维（Macro-PP）、聚丙烯短纤维（Micro-PP））对荷载作用下带裂缝混凝土渗透性能的影响,通过劈裂试验引入不同宽度的结构裂缝（50~200 μm）,比较不同纤维对卸载后混凝土裂缝宽度及曲折度的影响。利用自主研发的渗透装置,分析了不同纤维类型、掺量及混杂方式对荷载作用下不同裂缝宽度混凝土渗透性的影响。研究发现:单掺55 kg/m3 SF比25 kg/m3渗透系数降低95.7%。与单掺SF相比,SF和Macro-PP的掺入具有正混杂效应;Micro-PP与SF混杂体系中渗透系数基本无变化,研究表明Micro-PP对结构裂缝间桥接作用甚微,对渗透性的作用不明显。SF和Macro-PP可有效限制裂缝的扩展,增大表面曲折度,降低开裂后混凝土的渗透性。      

Dynamics of anisotropic composite cantilevers weakened by multiple transverse open cracks

In this paper an exact solution methodology, based on Laplace transform technique enabling one to analyze the bending free vibration of cantilevered laminated composite beams weakened by multiple non-propagating part-through surface cracks is presented. Toward determining the local flexibility characteristics induced by the individual cracks, the concept of the massless rotational spring is applied. The governing equations of the composite beam with open cracks as used in this paper have been derived via Hamilton's variational principle in conjunction with Timoshenko's beam model. As a result, transverse shear and rotatory inertia effects are included in the model. The effects of various parameters such as the ply-angle, fiber volume fraction, crack number, position and depth on the beam free vibration are highlighted. The extensive numerical results show that the existence of multiple cracks in anisotropic composite beams affects the free vibration response in a more complex fashion than in the case of beam counterparts weakened by a single crack. It should be mentioned that to the best of the authors' knowledge, with the exception of the present study, the problem of free vibration of composite beams weakened by multiple open cracks was not yet investigated.     

共挤出法制备双层中空纤维陶瓷复合膜

中空纤维陶瓷膜具有装填密度高, 传质阻力低, 使用寿命长等优点, 被广泛用于膜分离领域。高度非对称结构的中空纤维膜有利于同时实现高通量与高截留率, 本研究采用共挤出法制备双层中空纤维陶瓷复合膜, 内外层纺丝液分别掺杂平均粒径为1 μm和300 nm的α-Al₂O₃粉体。系统考察了内层纺丝液TiO₂掺杂量、外层纺丝液Al₂O₃/聚醚砜(PESf)质量比和煅烧温度对膜的结构与性能的影响。结果表明, 在内层纺丝液TiO₂掺杂量为2wt%, 外层纺丝液Al₂O₃/PESf质量比为5.60, 烧结温度为1350 ℃的最优条件下, 中空纤维膜断裂负荷为24 N、平均孔径为0.15 μm、去油率为97.5%。     

Effect of particle size on fatigue behaviour in SiC particulate-reinforced aluminium alloy composites

The effect of particle size on rotary bending fatigue behaviour was studied for powder metallurgy 2024 aluminium alloy composites reinforced with 10 wt% silicon carbide particles (SiC_p ). Average particle sizes of 5, 20 and 60 μm were evaluated. Particle size had a significant influence on fatigue strength, indicating an increased fatigue strength with decreasing particle size. The composite with 5 μm SiC particles showed higher fatigue strength than the unreinforced alloy. The incorporation of 20 μm SiC particles led to an increase in fatigue strength at a high stress level, but the improvement diminished with decreasing stress level, and a slightly decreased fatigue strength was observed at low stress level, as compared with the unreinforced alloy. The composite with 60 μm SiC particles exhibited a considerable decrease in fatigue strength. Fatigue cracks initiated at several different microstructural features, e.g. surface defects, inclusions and particle–matrix interfaces, and crack initiation was considerably affected by particle size. Fatigue strength was found to depend strongly on the resistance to crack initiation, because there was no discernible difference in small crack growth between the unreinforced alloy and the composites, particularly at a low maximum stress intensity factor.     

石墨气溶胶粒度分布及远红外消光因子研究

在烟幕试验箱中测试了不同湿度条件下超细石墨气溶胶的粒子分布及其随时间变化的规律。根据Mie散射理论计算了石墨气溶胶粒子对8～14μm远红外的消光因子。分析表明,石墨气溶胶的粒度随着分散时间延长和空气相对湿度减小而变小。小尺度的石墨气溶胶粒子对8～14μm红外的消光效率因子非常小,但随着气溶胶粒子直径的增加,消光效率因子显著变大并趋于稳定。直径大于2.5μm的石墨气溶胶粒子均能够对8～14μm远红外产生良好的消光效果。     

Microwave-assisted hydrothermal synthesis of fine BaZrO<Subscript>3</Subscript> and BaHfO<Subscript>3</Subscript> powders

Fine BaZrO₃ and BaHfO₃ powders have been prepared by a microwave-assisted hydrothermal (MWHT) process. The powders have been characterized by x-ray diffraction and scanning electron microscopy, and their particle size distribution has been assessed from dynamic light scattering data. The results indicate that microwave processing during hydrothermal synthesis notably reduces the average particle size of the resulting powder and ensures a narrower particle size distribution. BaHfO₃ particles prepared under the optimal MWHT synthesis conditions are predominantly spherical in shape and uniform in size, with an average size (1.2 μm) a factor of 2.5 smaller in comparison with particles prepared by a conventional hydrothermal process (2.9 μm).     

镍包覆氧化铝复合粉末的制备

研究探索了一种新的制备热喷涂用镍包氧化铝复合粉末的方法——配位均匀沉淀-碳热还原法,并成功地制备出了黑色镍包覆氧化铝复合粉末,利用X射线衍射(XRD)和透射电镜(TEM)等测试方法对产品进行分析表征。结果表明:制备的镍包覆氧化铝粉色泽均匀,平均粒径小于0.3μm,且原料利用率高,无其他杂质。     

U形CFRP条带混锚加固混凝土梁抗剪试验

为解决纯粘贴U形纤维增强聚合物基复合材料（FRP）加固钢筋混凝土梁中FRP端部容易发生剥离破坏等问题,自主研发了对纤维布条带端部进行自锁锚固的方法和锚板,提出了端锚与粘贴并用的混锚U形条带抗剪加固方法。通过2根未加固梁、1根纯粘贴和2根混锚U形碳纤维增强聚合物基复合材料（CFRP）带抗剪加固梁的对比试验,证实了混锚抗剪加固的有效性：混锚能够对纤维带端部进行可靠锚固,阻止端部剥离破坏的发生,实现纤维拉断破坏,大幅度提高材料强度利用率。混锚加固在抑制混凝土梁斜裂缝开展、延缓箍筋屈服、提高箍筋和CFRP的极限应变以及提高抗剪承载力等多个方面的表现均明显优于纯粘贴加固。