Toughness enhancement and equivalent initial fracture toughness of cementitious composite reinforced with aligned steel fibres

Based on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at the crack tip of the composite. The equivalent initial fracture toughness was used to characterize the crack initiation of SFRC. A simplified method for determining the of SFRC was proposed based on a linear regression method. Fracture tests were conducted on three‐point bending notched beams with different steel fibre volume fractions and specimen sizes to study the crack initiation behaviour of aligned steel fibre reinforced cementitious composite (ASFRC). of ASFRC was calculated, and the size effect of was analysed. The results showed that slightly increased with the steel fibre volume fraction and gradually became stable. For the tested specimens, whose heights varied between 40 and 100 mm, the specimen size had little impact on the .     

镁对非调质钢中组织及硫化物的影响

摘要：为了探究不同镁含量对非调质钢中组织和硫化物形态、尺寸、分布及成分的影响，采用蔡司金相显微镜、扫描电子显微镜、小样电解等方法，分析了经高温电阻炉冶炼不同镁添加量的49MnVS3非调质钢。结果表明，由于镁蒸气压较高，在实验室冶炼中大量挥发，导致钢中镁的实际平均收得率仅为310%；镁的质量分数为0～22×10-6时，随着镁的质量分数的增加，钢中硫化物形态由Ⅱ类逐渐向Ⅰ类、Ⅲ类转变；钢中硫化物尺寸增大，硫化物的分布均匀性得到显著改善；钢中复合夹杂物比例明显增加，但MnS的比例出现下降；形成了细小弥散的氧化物，增加了奥氏体形核质点，具有细化组织的趋势。     

Room temperature R-curve and stable crack growth behaviour of ZrB2–SiC ceramic composites

ABSTRACT

R-curve and controlled stable crack growth behaviour of ZrB₂–17vol.-%SiC and ZrB₂–45vol.-%SiC ceramic composites was studied on V-notched samples using four-point bending at room temperature. The rising K_1R behaviour was determined as a function of the crack extension Δa with a crack bridging mechanism being dominant in such behaviour. Significant differences in crack growth rates were found within the same composition of ceramics simply as the crack length varied during crack growth processes. These differences are indicative of the significant influence of microstructural parameters of the ceramics on crack propagation. The peculiarities of stress intensity factor K₁ and the crack growth-specific behaviour in ZrB₂–SiC particulate ceramic composites are discussed.     

复合管膜的润湿性及过滤污水机理

为了研究多孔复合管膜对钢铁产业污水的过滤性能及其过滤机理，采用静滴法做了水滴和油滴在复合管膜上的润湿性研究。采用扫描电镜、EDS等手段分析了使用前后的多孔复合管膜外壁及内壁的结构及成分，分析了含油污水中固体颗粒及油的过滤机理，并利用视频光学接触角测量仪测量水滴和油滴在复合管膜上接触角随时间的变化速率。结果表明，在污水过滤过程中，水中小于管膜表层微孔孔径的氧化铁等杂质进入复合管膜内部，无法随水流穿过复合管膜膜层，积累在管膜内部；随着管膜使用时间延长，氧化铁等杂质在复合管膜内部积累量增多。水在复合管膜上的润湿性良好，油滴在复合管膜上是不润湿的。     

等离子弧异质异构增材制造构件的组织与力学性能分析

采用等离子弧增材系统实现了不锈钢/高强钢异质异构增材构件制备，等离子弧增材构件具有良好的沉积形貌及优异的力学性能.为揭示叠合方式对等离子弧异质增材构件的宏微观组织和力学性能特征影响，研究采用了体视显微镜、金相显微镜、拉伸及硬度等测试方法.结果表明，不锈钢/高强钢异质异构增材构件中存在两种过渡形式，即以奥氏体枝晶过渡和马氏体组织过渡.增材构件横截面硬度波动较大，主要是混合过渡区域的高合金元素导致的组织变化引起的.叠合方式的改变能够显著影响材料性能，在强度下降不多的情况下，提高材料的冲击韧性.     

微生物质水热碳锰复合材料对铀的吸附行为研究

以工业啤酒酵母为碳源，采用一步法合成了微生物质水热碳锰复合材料（MHTC），并利用XRD、FT-IR和SEM等对材料进行了表征。在此基础上，系统研究了不同C/Mn原子比、初始pH值、接触时间、初始铀浓度对MHTC吸附铀性能的影响。结果表明：C/Mn原子比为1∶10的碳锰复合材料（MHTC-10）对铀的吸附性能最优。在铀初始浓度为50 mg/L、初始pH=4.5条件下，12 h可达吸附平衡，最大吸附量为371 mg/g。吸附过程符合准二级动力学模型以及Freundlich等温模型。热力学数据表明，铀在MHTC-10上的吸附是一自发、放热的过程。该研究结果可为含铀环境中铀的分离富集提供新的思路。     

Rheology evolution of a geopolymer precursor aqueous suspension during aging

Geopolymer-based glass-ceramic matrix composites can be processed at room temperature and a heat treatment below 100°C leads to matrix hardening thanks to the geopolymerization mechanisms. The stabilization of the matrix into glass-ceramics is achieved via a post-curing at high temperature. This paves the way of the utilization of cost-effective liquid composite molding processes, for which all the necessary equipment is already available for processing temperature ranges related to polymer matrix composites, provided that the rheological behavior of the precursor is suitable to conveniently permeate the fibrous preform. The paper describes the thixotropic rheological behavior of a reference suspension at processing temperature (10°C-20°C) and its evolution along aging at −18°C. The changes are interpreted in terms of geopolymerization mechanisms (dissolution and polycondensation) and suspension rheology (predominance of hydrodynamic effects at high shear rate). On this basis, a phenomenological modeling framework, combining two Krieger-Dougherty equations, is proposed to build a relationship between the effective viscosity of the suspension and the phenomena involved during aging (dissolution of aluminosilicate particles) and shearing (microstructure scalar variable).     

基于镧锶锰氧化物基阴极的中温固体氧化物燃料电池的性能优化研究

为了提高基于镧锶锰氧化物(LaxSr1-xMnO3,LSM)阴极的中温固体氧化物燃料电池(Solid Oxide Fuel Cell,SOFC)的电化学性能,文章利用CuO清扫Ce0.85Sm0.15O2-δ(SDC)晶界的SiO2杂质以提高SDC的离子电导率,制备了复合电解质材料SDC-CuO,并将SDC-CuO和LSM结合成复合阴极材料,随后分别制备了以LSM和LSM/SDC-CuO作为阴极的SOFC,并研究了这两种SOFC的电化学性能。研究结果表明:在开路电压和工作温度为800℃的条件下,LSM/SDC-CuO基阴极的SOFC的极化电阻为0.14Ω·cm2,明显低于LSM基阴极SOFC的极化电阻(0.36Ω·cm2);LSM/SDC-CuO基阴极的SOFC的最大输出功率密度为237 mW/cm2,显著高于LSM基阴极的SOFC的最大输出功率密度(132 mW/cm2)。     

碳纤维/乙烯基酯树脂复合材料拉伸性能研究

研究了碳纤维进行氧化处理、铺层形式,以及紫外光照射和不同溶液介质浸泡处理等,对碳纤维/乙烯基酯树脂复合材料拉伸性能的影响。结果表明:碳纤维最佳氧化工艺为浓硝酸氧化1 h,空气氧化温度250℃,空气氧化30 min。碳纤维最佳铺层设计为[0°,0°,45°]2s。随紫外光照射时间增加,复合材料拉伸强度呈先增后降趋势,120 h时达最大值。溶液介质浸泡会降低复合材料的拉伸强度。温度相同溶液介质不同时,复合材料在NaOH溶液中拉伸强度降低程度最大,温度提高会加速复合材料失效老化。     

基于临界钙矾石膨胀破坏的磷石膏基复合胶凝材料的配料计算研究

为制备大掺量磷石膏基复合胶凝材料,在确定主要水化产物类型的基础上,通过计算临界钙矾石膨胀破坏的边界条件,确定各组分最佳掺量范围,研究其对复合胶凝材料力学性能、干缩性能的影响,并通过X射线衍射（XRD）、扫描电镜（SEM）等测试方法研究水化产物的组成及发展规律。研究结果表明：通过理论配料计算,矿粉掺量为50%（质量分数）时,最大磷石膏掺量为26.3%（质量分数）,最小熟料掺量为23.6%（质量分数）。最佳配比组28 d胶砂抗压强度为45.2 MPa,线膨胀率小于0.04%;对比组28 d抗压强度仅有36.4 MPa,线膨胀率远大于0.04%。XRD、SEM表征结果表明,磷石膏基复合胶凝材料的水化产物主要是钙矾石（AFt）和水化硅酸钙（C-S-H）凝胶,氢氧化钙几乎反应完全;对比组钙矾石生成量远大于最佳配料组,微观结构存在大量裂缝。这说明理论配料计算可以有效用于磷石膏基复合胶凝材料的配比优化。