高强不锈钢绞线网增强工程水泥基复合材料弯曲性能试验

为了研究高强不锈钢绞线网增强工程水泥基复合材料(Engineered cementitious composites,ECC)的受弯性能,考虑纵向高强不锈钢绞线配筋率、ECC抗压和抗拉强度等影响因素,对设计的8个高强不锈钢绞线网增强ECC试件进行四点弯曲试验.结果 表明,随着纵向高强不锈钢绞线配筋率增大,其开裂荷载基本...     

高强不锈钢绞线网增强工程水泥基复合材料受拉应力-应变关系

为了研究高强不锈钢绞线网增强工程水泥基复合材料(Engineered cementitious composites,EEC)的受拉性能,考虑高强不锈钢绞线配筋率、ECC抗拉强度、高强不锈钢绞线网增强ECC试件宽度3个影响因素,对设计的27个高强不锈钢绞线网增强ECC试件进行了单轴拉伸试验。试验结果表明,高强不锈钢绞线网增强ECC受拉试件的开裂应力和极限应力随着钢绞线配筋率、ECC抗拉强度的增大而增大;增大试件宽度对试件的开裂应力和极限应力几乎无影响。基于试验结果,提出并建立了高强不锈钢绞线网增强ECC受拉本构模型,推导了开裂应力和极限应力计算公式。经验证,计算结果与试验结果吻合良好,说明所建立的受拉本构模型可准确描述高强不锈钢绞线网增强ECC的受拉应力-应变关系。      

高强不锈钢绞线网增强ECC加固RC短柱轴心受压试验

在新型复合材料“高强不锈钢绞线网增强工程水泥基复合材料(ECC)(简称HSME)”的力学性能和约束素混凝土受压性能研究基础上,将钢筋混凝土(RC)短柱配筋率和混凝土强度以及加固层的ECC强度和横向钢绞线配筋率作为参数,试验研究高强不锈钢绞线网增强ECC加固RC短柱轴心受压性能。结果表明,和未加固RC短柱相比,HSME加固RC短柱不仅承载力大幅度提升,而且破坏时裂而不碎、具有明显的延性破坏特征,开裂荷载、峰值荷载及峰值位移显著提高;荷载达峰值荷载80%左右和峰值荷载时,试件表面最大裂缝宽度仅为0.09 mm和0.25 mm,表现出优良的多缝开裂和裂缝控制能力。HSME加固RC短柱荷载-位移曲线属于偏态的单峰曲线,包含弹性、裂缝发展、最大荷载和承载力下降四个阶段。随着ECC抗压强度和横向不锈钢绞线配筋率增大,HSME加固柱开裂荷载和峰值荷载均明显增大;增大RC柱配筋率和混凝土强度可提高加固柱峰值荷载和延性。     

玻璃纤维增强聚合物复合材料筋与工程水泥基复合材料黏结性能

为了研究玻璃纤维增强聚合物（GFRP）复合材料筋和工程水泥基复合材料（ECC）黏结性能的影响因素,对42个GFRP/ECC试件进行了拉拔试验,分析了GFRP复合材料筋表面形式、直径、ECC基体强度及保护层厚度等因素对GFRP复合材料筋与ECC基体黏结性能的影响。结果表明:GFRP/ECC试件的破坏形式主要有拔出破坏、筋剥离剪切破坏、劈裂破坏三种形式。表面带肋GFRP复合材料筋黏结强度比光滑GFRP复合材料筋高约66%;当ECC保护层厚度由1.5D（D为GFRP筋直径）增大至4D时,GFRP/ECC黏结强度提高了约58%;当GFRP复合材料筋直径为12~18 mm时,GFRP/ECC黏结强度随着GFRP复合材料筋直径的增大而降低;ECC强度由33.7 MPa增大至73.3 MPa时,GFRP/ECC黏结强度增大约3倍。增加GFRP复合材料筋表面形式复杂程度,或一定程度上提高ECC基体保护层厚度、提高ECC强度等级,有助于提高GFRP复合材料筋与ECC的黏结强度。      

高强不锈钢绞线网/ECC约束高强混凝土受压本构模型

为将新型复合材料“高强不锈钢绞线网/ECC约束素混凝土”用于实际工程结构,基于高强不锈钢绞线网/ECC约束高强混凝土(简称HSME约束高强混凝土)复合材料轴心受压试验结果,分析ECC强度、核心混凝土强度以及横向钢绞线体积配网率等对其受压性能的影响规律。试验结果表明：HSME能够有效约束核心混凝土轴心受压,破坏模式具有明显的延性性能,根据试验数据绘出HSME约束高强混凝土复合材料受压应力-应变曲线,可以分为三个阶段：弹性阶段、弹塑性阶段和下降段。根据各阶段曲线的数学特征,建立HSME约束高强混凝土复合材料受压本构关系的全过程模型表达式。引入ECC特征值和横向钢绞线特征值,对本构模型的各参数进行分析,提出HSME约束高强混凝土复合材料的开裂压应变、峰值应力、峰值压应变和极限压应变等参数的表达式。将各参数代入所建立的受压本构关系绘出其应力-应变曲线,模型结果与试验所得应力-应变曲线吻合良好,开裂压应变与极限压应变的计算值与试验值对比范围分别为0.949～1.068和0.938～1.039。表明所提出的受压本构模型能够较好地反映HSME约束高强混凝土复合材料的应力-应变关系。     

高强钢绞线网增强ECC与混凝土界面黏结-滑移关系研究EI北大核心CSCD

良好的界面黏结是保证高强钢绞线网增强工程用水泥基复合材料(HSSWM-ECC)与混凝土协同工作的前提,其界面黏结的有效程度决定着HSSWM-ECC材料性能的发挥。为研究HSSWM-ECC与混凝土界面黏结性能,以混凝土抗压强度、界面黏结长度、黏结宽度和界面处理方式为参数,对设计制作的9组27个梁铰式试件进行了界面黏结性能试验。试验结果表明:界面黏结-滑移受力过程呈现明显的两阶段特征:非线性上升段和下降段。基于试验结果,探究了HSSWM-ECC与混凝土间界面黏结破坏特征和受力机理,构建了考虑各参数影响的界面黏结-滑移关系模型;采用微段分析法对模型特征参数进行了分析,结果表明:所建模型及特征参数计算与试验结果吻合良好,可较好表征HSSWM-ECC与混凝土界面黏结-滑移关系力学行为。     

粉煤灰细度对超高韧性水泥基复合材料性能的影响

为了探究粉煤灰细度对超高韧性水泥基复合材料(ECC)性能的影响,设计对比三组由不同细度粉煤灰制作的ECC试件的抗拉及抗压试验性能,并进行了灰色关联度分析。结果表明:ECC的拉伸应变与粉煤灰细度之间不呈简单的线性关系;对于ECC的抗压强度,其主导因素并非是粉煤灰的细度,而是粉煤灰的活性。在特定条件下,通过改变粉煤灰的细度,可以在不影响基体强度的情况下改善ECC的延性。     

冻融损伤后钢筋与再生混凝土黏结滑移性能试验研究

对经过0次、25次、50次、75次、100次冻融循环作用后的再生混凝土(粗骨料取代率100%)进行拉拔试验研究,得出不同冻融循环次数、保护层厚度和锚固长度下钢筋与再生混凝土间黏结性能的变化规律。结果表明:随着冻融循环次数的增加,钢筋与再生混凝土间的黏结强度逐渐降低,而滑移值逐渐增加;黏结强度随着相对保护层厚度的增加而增大且呈线性关系,随着相对锚固长度的增加,黏结强度却随之减小,当相对保护层厚度和锚固长度增加到一定值后,黏结强度基本保持不变。基于试验结果给出黏结-滑移曲线,曲线分为微滑移线性阶段、滑移阶段、滑移加速阶段、非线性下降段和残余阶段等5个阶段。通过分析试验数据提出不同影响因素下各阶段黏结锚固特征值的拟合计算公式,为我国冻融环境下再生混凝土结构的耐久性设计提供参考。     

Diffusion bonding of titanium alloy to stainless steel wire mesh

Abstract

The feasibility and appropriate processing parameters of diffusion bonding of titanium alloy to stainless steel wire mesh directly and with a nickel interlayer have been investigated. The microstructures of the diffusion bonded joints were observed by optical microscopy, scanning electron microscopy, X-ray diffraction, and electron probe microanalysis and the main factors affecting diffusion bonding were analysed. The maximum shear strengths of the joints were 72 and 148 MPa for direct bonding and indirect bonding using a nickel interlayer respectively. Atomic diffusion and migration between titanium and iron are effectively prevented by adding pure nickel as the interlayer metal, and a firm joint is obtained.     

超高韧性水泥基复合材料自愈合研究进展

在总结了最近几年国内外相关研究进展的基础上,对超高韧性水泥基复合材料(ECC)及裂缝自愈合进行了综述。着重介绍了裂缝自愈合的最大允许宽度限值以及自愈合机制。提出利用ECC所独具的对裂缝宽度的可控性及紧密细小的微裂纹、较低的水胶比及矿物掺合料的二次水化效应可实现其良好的自愈合特性。最后指出该研究领域所面临的挑战及今后的研究方向,为ECC裂缝自愈合的研究提供有价值的理论参考。     

Analysis of the performance of a sintered stainless steel wire mesh filter for cryogenic liquid purification

As a traditional and mature solid-liquid separating technique, filtration has been adopted in cryogenic liquid purification system owing to its low energy cost, simplified system, long lifetime and high purifying efficiency. Whereas, few data or result of filtration performance at low temperature is put forward in literatures, most of which are related to room and high temperatures applications. Furthermore, as an excellent cryogenic material, stainless steel medium is suitable for cryogenic liquid filtration, which is also seldom reported. In this paper, we propose a filtration system for purifying CO₂ particles from liquid nitrogen using a sintered stainless steel wire mesh filter with a nominal filtration degree of 0.5 μm, and characterize the separation behavior of this kind of filter medium at cryogenic temperature. Experimental results show that the whole filtration process can be divided into three stages with sufficient particle concentration in the feed slurry according to the evolution of pressure drop. Differences between surface filtration and depth filtration are demonstrated, and the influence of growth of filter cake is characterized. Pressure drop increases with increasing feed slurry flow and CO₂ concentration, and evolution tendency of filtration efficiency is affected by its calculation method. By comparison with the filtration at room and high temperatures, the effects of temperature on the fluid and media are emphasized.     

制备参数对不锈钢丝网催化剂结构和性能的影响

采用阳极氧化工艺在不锈钢丝网载体上自生长一层氧化膜,再在其上负载活性组分铈、铂和钯,制备了金属丝网催化剂.研究了阳极氧化的电流密度和电解液种类等因素对阳极氧化膜形成的影响,以及还原时间和焙烧温度对催化剂氧化活性的影响.结果表明,改变制备参数对氧化膜结构有较大影响,进而影响到催化剂的活性.采用10%H2SO4电解液,控制电流密度为1.0 A时得到的氧化膜载体浸渍活性组分后,具有良好的催化活性和稳定性.     

Influence of micro-cracking on the permeability of engineered cementitious composites

Engineered Cementitious Composites (ECC) forms multiple micro-cracks under tension when loaded to beyond the elastic stage. Unlike normal concrete, such tight cracks help to maintain low water permeability even in the cracked stage. Therefore ECC shows great potential for application in hydraulic structures, such as dams and levees for which water seepage control is critical for their performance. In this paper, the permeability of ECC under constant tensile load was experimentally studied using a specially designed displacement-control loading device, providing permeability data for ECC under realistic loading conditions. In addition, an analytical model capable of predicting permeability property of ECC composite based on tensile strain and crack patterns has been proposed and experimentally verified on two different ECC mixtures. The findings of this research are expected to support future design and application of ECC for hydraulic structures.     

Diffusion bonding between commercially pure titanium and micro-duplex stainless steel

Diffusion-bonded joints between commercially pure titanium and micro-duplex stainless steel were prepared in the temperature range of 800–950 °C for 1.5 h under 3 MPa uniaxial load in vacuum. The diffusion bonds were characterized using light and scanning electron microscopy. The composition of the reaction products were determined by energy dispersive spectroscopy. Up to 850 °C, -Fe + λ and λ + FeTi phase mixtures were formed at diffusion interface; however -Fe + λ, λ + FeTi and FeTi + β-Ti phases mixtures were formed at 900 °C and above. The presence of these intermetallics was confirmed by X-ray diffraction technique. The maximum tensile strength of 96% of Ti and shear strength of 81% of Ti along with 6.9% ductility were obtained for the diffusion couple processed at 850 °C due to the finer width of intermetallic phases. With a rise in the joining temperature the bond strength drops owing to an increase in the width of reaction products.     

High pressure squeeze casting of stainless steel wire reinforced aluminium matrix composites

Stainless steel wire-reinforced aluminium matrix composites with a fibre volume fraction up to 40% were fabricated by high pressure squeeze casting. The mechanical properties of these composites were investigated and it was found that their tensile strength was somewhat lower than that predicted by the rule-of-mixtures; failure occurred predominantly by fibre pull-out. Details of the optical microscopic studies and the microhardness data are presented. This reveals that the fibre-to-matrix bonding is relatively weak as a result of the more-than-desirable interfacial reaction. Several inter-metallic compounds have been identified at the interface. Growth kinetics of these interface intermetallic compounds are discussed.