Anti-penetration performance of high entropy alloy–ceramic gradient composites

A high-entropy alloy–ceramic gradient composite of TiC–TiB_2/75vol% Al_(0.3) CoCrFe Ni was successfully prepared by combustion synthesis under an ultra-high gravity field, which is a low-cost method with high efficiency. The ceramic particles were gradient distributed in the Al_(0.3) CoCrFe Ni matrix, and the hardness of the composite material gradually decreased along the thickness direction. The anti-penetration performance of the gradient composites was simulated using the ANSYS/LS-DYNA explicit simulation program. The results demonstrate that the distribution of the ceramic particles strongly affected the mechanical properties and the anti-penetration performance of the composites. With the same total ceramic volume fraction, the gradient composites exhibit better anti-penetration performance than the corresponding ceramic–metal interlayer composites. The more uneven the ceramic distribution, the greater the elastic modulus and yield stress of the surface layer and, thus, the better the anti-penetration performance.

Preparation technology and anti-corrosion performances of black ceramic coatings formed by micro-arc oxidation on aluminum alloys

In order to prepare ornamental and anti-corrosive coating on aluminum alloys, preparation technology of black micro-arc ceramic coatings on Al alloys in silicate based electrolyte was studied. The influence of content of Na2WO4 and combination additive in solution on the performance of black ceramic coatings was studied; the anticorrosion performances of black ceramic coatings were evaluated through whole-immersion test and electrochemical method in 3.5% NaCl solution at different pH value; SEM and XRD were used to analyze the surface morphology and phase constitutes of the black ceramic coatings. Experimental results indicated that, without combination additives, with the increasing of Na2WO4 content in the electrolyte, ceramic coating became darker and thicker, but the color was not black; after adding combination additive, the coating turned to be black; the black ceramic coating was multi-hole form in surface. There was a small quantity of tungsten existing in the black ceramic coating beside α-Al2O3 phase and β-Al2O3 phase. And aluminum alloy with black ceramic coating exhibited excellent anti-corrosion property in acid, basic and neutral 3.5% NaCl solution.

Anti-Noise Performance of the FT Continuous Zoom Analysis Method for Discrete Spectrum

As a discrete spectrum correction method, the Fourier transform （FT） continuous zoom analysis method is widely used in vibration signal analysis, but little effort had been made on this method＇s anti-noise performance. It is widely believed that the analysis accuracy of the method can be substantially improved by increasing the zoom multiple, however, with the zoom multiple increases, the frequency estimation accuracy may decline sometimes in practices. Aiming at the problems above, this paper analyzes the sources of frequency estimation error when a harmonic signal mixed with and without noise is processed using the FT continuous zoom analysis. According to the characteristics that the local maximum of the zoom spectrum may be wrongly selected when the signal is corrupted with noise, the number of wrongly selected spectrum lines is deduced under different signal-to-noise ratio and local zoom multiple, and then the maximum frequency estimation error is given accordingly. The validity of the presented analysis is confirmed by simulations results. The frequency estimation accuracy of this method will not improve any more under the influence of noise, and there is a best zoom multiple, when the zoom multiple is larger than the best zoom multiple; the maximum frequency estimation error will fluctuate back and forth. The best zoom multiple curves under different signal-to-noise ratios given provide a theoretical basis for the choice of the appropriate zoom multiples of the FT continuous zoom analysis method in engineering applications.

Performance Analysis of RFID Framed Slotted Aloha Anti-Collision Protocol

In this paper, we develop a novel mathematical model to estimate the probability distribution function of the number of tags discovered after a certain number of interrogation rounds. In addition, the pdfs of the number of rounds needed to discover all the tags are also calculated. The estimation of such pdfs will be helpful in estimating the number of interrogation rounds and the optimal parameter configuration of the RFID system which in turn will be helpful in estimating the time needed to discover all tags. Our results show that the proposed model accurately predicts the tags detection probability. We then use the proposed model to optimally configure the reader parameters (i.e. the frame size and the number of interrogation rounds).

Influence of graphene on the anti-corrosion performance of epoxy-based coatings

In this work, graphene-modified epoxy-based anti-corrosion coatings were prepared and the influence of graphene on the anti-corrosion performance of the epoxy-based coatings was investigated with water contact angle test ,chemical solution immersion test, and electrochemical test. The water contact angle and chemical solution resistance of the epoxy-based coatings were improved with an increase in graphene content from 0 to 0.4%. These results prove that addition of graphene can significantly improve the hydrophobicity and impermeability of epoxy- based coatings. However, when the graphene content was increased to 0.5%, the performance of the epoxy-based coatings decreased because of graphene aggregation. Tafel polarization results show that graphene addition can significantly reduce the corrosion current density and corrosion potential of epoxy-based coatings, which enhance their anti-corrosion performance.

Design of Small Stone Asphalt Mixture based on Anti-skidding Performance

Small stone asphalt mixture（SSAM） was designed by Bailey method and coarse aggregate voids-filling method.The optimum asphalt content was determined by Marshal test.Surface texture depth for SSAM with different voidage,and the BPN of SSAM and SMA before after wet track abrasion were measured.The experimental results indicate that the surface texture depth increases with the decreasing of asphalt aggregate ratio.The SSAM with the optimal asphalt content has a good skid resistance.BPN of asphalt mixture decreases with the increasing of wearing time,but the extent of reduction is different.The reduction rate of BPN for SSAM is smaller than that of SMA,indicating that SSAM has a good skid resistance attenuation capacity.Finally,the other properties of SSAM are also evaluated,showing that the splitting strength and modulus and SSAM are higher than those of SMA,and the other properties of SSAM,such as high-temperature performance and water stability can also satisfy the technical requirements.

PREDICTION OF RIME ICE ACCRETION AND RESULTING EFFECT ON AIRFOIL PERFORMANCE

The roughness effect based on the wall function method is introduced into the numerical simulation of the rime ice accretion and the resulting effect on the aerodynamic performance of the airfoil. Incorporating the two-phase model of air/super-cooled droplets in the Eulerian coordinate system, this paper presents the simulation of the rime ice accretion on the NACA 0012 airfoil. The predicted rime ice shape is compared with those results of measurements and simulations by other icing codes. Also the resulting effects of rime ice on airfoil aerodynamic performance are discussed. Results indicate that the rime ice accretion leads to the loss of the maximum lift coefficient by 26%, the decrease of the stall angle by about 3° and the considerable increase of the drag coefficient.

Improvement to anti-rust property of hot rolled rebar by compact oxide scale

A method was proposed to improve the anti-rust property of hot rolled rebar, which uses oil–water emulsion cooling instead of water cooling after hot rolling. The experiments were carried out by two cooling methods, one cooled by water, the other cooled by oil–water emulsion. The results of wet/dry cyclic accelerated corrosion test showed that the anti-rust property of rebar cooled by oil–water emulsion was better than that by water obviously. The results of OM, SEM and EPMA analysis indicated that these two scales contained three layers: an outer Fe_3O_4 layer, an intermediate Fe O layer with island-shaped pro-eutectoid Fe_3O_4, an inner eutectoid Fe_3O_4 layer. For the water cooled rebar, all three layers of oxide scale were relatively thin. Moreover, the scale had plenty of defects such as porosity, and crack. However, for the oil–water emulsion cooled rebar, all three layers of oxide scale were relatively thick and compact, which played an important role in protecting the rebar from atmospheric rust.

Preparation of High Performance Non-dispersible Concrete

A new-type underwater non-dispersible concrete admixture NDA was prepared,its function mechanism was analyzed,and C40 high performance non-dispersible underwater concrete was manufactured by applying NDA.The results indicate that NDA has a suitable workability,low strength loss,and excellent anti-dispersion;the fresh non-dispersible underwater concrete with NDA has high anti-dispersion,excellent workability such as self-compacting and not bleeding;hardened non-dispersible underwater concrete with NDA has a high strength,high durability such as high anti-abrasion,impermeability and anticorrosion.

Lubricating Performance of Rapeseed Oil Under Electromagnetic Field

Considering electromagnetic effect when investigating tribological properties of rapeseed oil is benefical not only to the improvement of green lubrication, but also to the development of tribology theories and practices. In the present paper, the tribological properties of rapeseed oil under different intensity of electromagnetic field and normal loads were evaluated on a modified tribo-tester. The results indicated that the electromagnetic field could improve the anti-wear and friction-reducing property of the rapeseed oil. Furthermore, the influencing mechanisms were discussed from the perspective of electromagnetism according to the analytical results of SEM, EDS and XPS techniques.

Reproductive and Growth Performance of Rabbit Fed Different Inclusion Levels of African Yam Bean (<i>Sphenostylis stenocarpa</i>)

A feeding trial was conducted to determine the effect of dietary inclusion of Processed African Yam Bean (AYB) at 0%, 10%, 20% and 30% levels respectively, on the growth and reproductive performance of Rabbits. The AYB inclusion was to ascertain the best (%) level that would give better performance in rabbits. Complete randomized design was used to allot twenty (20) grower rabbits of both sexes into four treatments in three replicate with each group having three does and two bucks. Each of the treatment diets formulated at different growth stages was fed to the rabbits. The rabbits were kept in hutches inside the rabbit house and given feed and water ad libitum. Growth and reproductive parameters were measured. The proximate analysis and anti-nutritional factor of processed AYB showed that it contained values of 26.88%, 92.97%, 5.26%, 61.89%, 7.04%, 3.79% and 2.17% for Crude protein, Dry matter, Crude fibre, Nitrogen-free extract, Moisture content, Ash content and Ether extract respectively while the anti-nutritional factor contained 0.11%, 14.02 mg/g, 0.19 mg/g, 0.21 mg/g, 0.14 mg/g, 0.21 mg/g, 0.13 mg/g and 0.01 mg/g of Tannin, Alkaloid, Oxalate, Phytate, Saponin, Flavonoids, Trypsin inhibitor and Lectin. From this study, the rabbit group on 10% AYB inclusion significantly (p 0.05) affected by the diets. The results of this experiment concluded that AYB can be included in the diet of rabbits with 10% inclusion giving a better reproductive performance and growth rate without any negative effect.

杭州世纪中心西天窗索夹抗滑移试验研究

索夹是预应力索结构中拉索与其他构件连接的重要节点构件,若索夹和拉索之间发生滑移,会产生较大的预应力损失,甚至改变结构的受力性能。杭州世纪中心西天窗采用箱形桁架+钢索结构,其结构特殊性决定了拉索在施工张拉和施工完成后的状态不同,即施工张拉时要求拉索对索夹是可相对滑移的,而施工完成后需要锁定拉索和索夹的相对位置,不允许发生滑移。通过拉索施工张拉、高强螺栓紧固力衰减、索夹顶推三个阶段的全过程模拟试验确定了索夹与拉索之间的摩擦力情况。试验结果表明,在拉索施工张拉阶段,索夹对索体产生的摩擦力较小,通过锌板垫层能够有效降低铸钢索夹节点处的摩擦损失,保证拉索张拉过程中索力的有效传递;高强螺栓终拧后12h内会产生不可忽视的紧固力损失;使用阶段索夹的抗滑移承载能力能够确保索夹节点安全。

基于性能的通航桥梁抗船撞评估方法及应用研究

为合理有效地开展通航桥梁抗船撞性能评估,提出基于性能的桥梁抗船撞标准化评估方法。基于现行《公路桥梁抗撞设计规范》(JTG/T 3360-02-2020),从抗撞性能等级确定、设防代表船型确定、船撞力计算、船撞效应计算以及抗撞性能验算等方面,采用结构性能目标作为评估准则,建立桥梁抗撞性能评估各环节流程的标准化评估方法。以江苏扬中三桥为应用实例,运用该方法进行该桥20号墩抗撞性能评估,结果表明:20号墩桩基顺桥向抗弯性能不满足JX1级要求,其余验算结果满足要求,桥墩抗撞性能综合评估结果为不满足要求。参照评估结果该桥加装了浮动式防撞设施。桥梁抗撞性能评估标准化,可准确高效实现桥梁抗撞性能等级确定、船撞效应计算、抗撞性能验算等预期的评估功能要求。

不同风化程度花岗岩的动态力学特性及抗侵彻性能

风化会使岩石材料孔隙发育,严重影响其工程性能,研究风化作用对花岗岩力学特性及抗侵彻性能的影响,对侵彻战斗部毁伤效能评估及地下工程防护能力分析具有重要意义。选用两种不同风化程度的花岗岩为研究对象,基于试验法系统分析其物理特性、静/动态压缩性能及抗侵彻性能的差异。结果表明:风化作用会造成花岗岩中黑云母和斜长石含量降低,孔隙率增加、内部组织变松散,缺陷加剧;风化作用将导致花岗岩抗压强度劣化、应变率效应降低,破坏模式从脆性破坏向弱剪切破坏转变;三轴围压作用下,两种花岗岩的静、动态抗压强度随围压的增大显著提升,且中风化花岗岩的抗压强度对围压的作用更敏感;高速(873~1040 m/s)侵彻条件下,两种风化花岗岩的抗侵彻性能差异较小,无量纲侵深不超过3倍弹长,岩石靶中不存在明显的侵彻弹道区,但有明显的压碎区,压碎区长度约为弹径的5~8倍。

潮湿基材涂装对海洋平台通用配套涂层体系防腐性能影响研究

海洋石油工程股份有限公司制造场地分别位于天津、青岛和珠海,其中青岛场地夏季经常出现相对湿度超过85%对涂装不利的极端天气。在此环境下,基材表面的潮湿现象,极大影响施工效率并影响交付工期。该文对比环氧富锌+环氧云铁+聚氨酯、环氧铝粉漆体系、环氧玻璃鳞片体系等三个涂层体系在潮湿基材以及经过Sa2.5除锈的基材涂装后防腐性能的影响。通过对防腐体系的附着力、耐盐雾、冷凝试验等测试,得出结论,在涂膜外观无缺陷的情况下,潮湿基材表面涂装对三个涂层体系防腐性能有不利影响,但仍能满足配套涂层体系的防腐要求。

高速冲击加载下碳纤维复合材料层合结构抗侵彻特性及响应机理

碳纤维复合材料层合结构在高冲击服役环境中常遭受外来物体冲击作用,使之出现一些不可预测的各种损伤形式,甚至会出现不可控的损伤模式。为确保这些结构的安全性和可靠性,对碳纤维复合材料层合结构抗冲击响应及防护机理展开了研究。以碳纤维复合材料层合结构作为研究对象,基于一级轻气炮构建高速冲击加载试验装置,探明了碳纤维复合材料层合结构能量吸收特性与冲击能量之间的联系规律,结合弹道极限方程,确定了其弹道极限,并明确了不同冲击速度作用下的损伤模式。同时引入内聚力单元进行数值模拟仿真研究,探明了碳纤维复合材料层合结构层与层之间内聚力单元的损伤模式,揭示了其在高速冲击加载环境下的损伤机制。研究结果为反向设计适用于高速冲击加载环境复合材料层合结构提供理论依据。

改性彩色沥青路面色彩耐久性与抗滑性能研究

为提高彩色沥青路面色彩耐久性并研究其抗滑性能,采用有机硅-聚丙酸酯(silane-modified polyacrylate,SMP)对彩色沥青玛蹄脂碎石混合料(color stone mastic asphalt,CSMA)和彩色开级配抗滑表层(color open graded friction course,COGFC)2种混合料改性,借助小型加速加载设备进行对彩色沥青路面进行色彩耐久性评价,并通过三维扫描仪进行路面纹理信息采集,分析路面三维参数与其抗滑性能之间的关系。结果表明,SMP改性剂可有效提高CSMA、COGFC两种混合料的抗磨耗能力,提升彩色沥青色彩耐久性;CSMA及COGFC路面抗滑性能受到不同三维参数的影响,路面的摩擦系数模型由各自相关因子控制,增加路面暴露的集料数量和使用尖角集料能使彩色沥青路面的抗滑性能得到提升。

改性橡胶颗粒对超高性能混凝土耐久性及抗冲磨性能影响

橡胶颗粒加入到超高性能混凝土(UHPC)中,会使其强度显著下降。通过对橡胶颗粒进行表面改性,研究改性后的橡胶颗粒掺量对UHPC的基本力学性能、耐久性、抗冲磨性能以及抗冲击性能影响。研究结果表明:采用多巴胺盐酸盐溶液对橡胶颗粒进行改性,可以在橡胶颗粒表面引入亲水基-OH和-NH_(2),改善橡胶颗粒与水泥基体之间界面黏结性能,使UHPC的力学性能降低幅度减小,明显提高UHPC抗冲磨性能以及抗冲击性能;在改性橡胶颗粒掺量10%时,UHPC的抗冲磨性能和抗冲击性能分别提高了28.6%和65.2%;与掺未改性橡胶颗粒的UHPC相比,掺入改性橡胶颗粒的UHPC抗氯离子侵蚀能力得到加强。

电气化铁路接触网地震作用与抗震性能分析

研究目的:高地震烈度区域电气化铁路沿线途经多条地震断裂带,接触网系统在地震作用下易出现损坏,影响列车的正常运行。本文结合高地震烈度区电气化铁路,基于接触网系统服役特性,开展了4柱3跨原型足尺振动台试验,建立并验证地震响应下的接触网系统有限元模型,开展地震作用下接触网系统的地震响应仿真计算,对比分析接触网导线、腕臂、定位器、支柱等关键装备的抗震性能,并比较分析不同的接触网导线工作张力、跨距以及锚段长度对接触网系统抗震性能的影响,提出高地震烈度区接触网系统的抗震设计原则及措施,全面分析与研究地震作用下接触网系统响应规律和抗震性能。本文提出的关于接触网系统抗震性能分析数据及研究结论,能有效补充和完善接触网抗震设计规范及标准,有力支撑铁路工程建设,提升电气化铁路防灾抗灾能力。研究结论:(1)地震激励对接触网腕臂装置的影响较小,定位器出现受压,导致钩环结构易脱落;(2)地震激励对接触网支柱、接触线具有十分明显的影响,可造成支柱柱底应力增大和接触线跨中位移增大;(3)锚段长度对抗震性能无明显影响,适当增大接触线工作张力、减小跨距可有效降低接触网系统的地震响应;(4)本研究成果可为轨道交通领域防灾减灾设计提供指导。

钢橡胶组合防撞装置试验与动力性能研究

为减少船桥撞击损伤,提出一种新型的钢-橡胶组合防撞装置.首先设计3组大比例试验构件,通过拟静力试验研究装置整体受力性能、破坏模式以及承载力;然后通过试验验证有限元模型,明确了焊缝对结构受力的影响,进行了装置整体动力性能分析.结果表明:钢-橡胶组合防撞装置由于填充轮胎的支撑作用,承载能力明显高于空筒防撞装置;钢-橡胶组合防撞装置具有很好的缓冲消能效果,在正撞和20°斜撞工况下耗能均达到35%以上,满足阻碍船舶与桥墩撞击的功能;回收轮胎不仅实现了一定的拨转功能,还起到耗能作用,轮胎填充能提升耗能5%以上,对船有回弹作用;同时,轮胎的填充不仅能提升自浮性能,更提升了装置整体性能.