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.

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.

基于无人机果树冠层卷吸效应的窄弧扇形防漂移喷嘴设计

针对植保无人机对果树冠层喷洒易产生的药液漂移问题,结合植保无人机对果树喷洒时产生的卷吸效应和扇形喷嘴雾化原理,设计了一种窄弧扇形喷嘴结构,并通过对不同冠层压力损失系数下的喷洒过程进行仿真分析,得到最佳防漂移的窄弧扇形喷嘴结构参数。研究结果表明:喷嘴内径增大,液膜与液带结构趋于稳定,液滴分布均匀,沉积率呈先降后升趋势;冠层压力损失系数降低,粒径频谱宽度减小,但沉积率总体提高;对较厚冠层果树植保时,选择内径1.3 mm、狭缝宽度0.15 mm的喷嘴,防漂移性能较好;对较薄冠层果树植保时,选择内径1.03 mm、狭缝宽度0.2 mm的喷嘴,防漂移性能较好;采用窄弧扇形喷嘴的液滴频谱宽度>0.7,沉积率>94.1%。

苯并芘DNA加合物anti-BPDE-N^2-dG四种立体异构体的合成及色谱分离

体外合成了苯并芘DNA加合物-邻二醇环氧苯并芘-脱氧鸟苷加合物(anti-BPDE-N2-dG)四种立体异构体(两对手性异构体)。通过优化体外反应条件,anti-BPDE-N2-dG四种异构体的合成产量较现有合成方法提高了2倍多,为定量检测生物体中anti-BPDE-N2-dG提供了标准品。并首次将五氟苯基色谱柱应用于该立体异构体的色谱分离提纯,通过优化色谱条件,采用常规的五氟苯基色谱柱(250 mm×4.6 mm,5μm),以乙腈-0.1%甲酸水(22.5∶77.5)为流动相,流速1.2 mL/min条件下,45 min内即可分离提纯四种立体异构体。该方法与常规C18柱(250 mm×4.6 mm,5μm)需要160 min,苯基柱(250 mm×4.6 mm,5μm)需要85~100 min才能将四种立体异构体实现色谱分离相比,缩短了分离时间,提高了提纯效率。通过紫外吸收光谱、质谱、圆二色谱对四种立体异构体进行表征,确定出峰顺序为trans(-)、trans(+)、cis(+)、cis(-)-anti-BPDE-N2-dG。此外,利用高效液相色谱-串联质谱(HPLC-MS/MS)检测anti-BPDE-N2-dG四种立体异构体标准品时,使用常规的五氟苯基色谱柱可在30 min内完成分离检测,与相同规格的苯基柱需要60 min相比提高了检测效率。

基于转矩电流分层控制的转速伺服系统Anti-Windup调节器设计

当转速调节器处于饱和非线性时,理论上基于积分状态值预测控制方法设计的转速调节器可使控制系统具有优秀的anti-windup性能,以及使系统性能不受负载转矩的影响,但该方法没有考虑负载转矩的估计时间和积分器时间常数对控制性能的影响,也没有考虑转速调节器处于线性区时,控制系统受负载转矩的影响。该文针对转速伺服系统中的anti-windup性能和负载鲁棒性进行研究,提出一种基于转矩电流分层控制的方法,使转速调节器在饱和非线性条件下,具有优秀的anti-windup性能,在线性条件下和饱和非线性条件下,都具有良好的负载鲁棒性,并且通过与积分状态预测值控制方法的仿真和实验对比分析,验证了所提方法的有效性。

Preparation and property of spinel LiMn_2O_4 material by co-doping anti-electricity ions

LiMn2-xMxO4-yFy(x=0.05; y=0.05; M=Al, Co, Cr and Mg, separately), as the cathode material, was synthesized by the method of high temperature solid-state reaction in laboratory. The results of charge-discharge test show that the properties of LiMn1.95M0.05O3.95F0.05(M= Al, Mg) are obviously superior to those of LiMn2O4. Through the condition experiments on sintering temperature, it is found that the materials present the integrate crystal structure and favorable cycle performance at 800 ℃. The research on the effects of different Mg2+ sources on the properties of LiMn2-xMgxO4-yFy shows that, with Mg(OH)2 and LiF as the reagents respectively offering Mg2+ and F?, LiMn1.95Mg0.05O3.95F0.05 synthesized has integrate crystal structure and its capacity hardly fades. The results of cyclic voltammetry indicate that the shape of two couples of redox peaks of the material synthesized by co-doping anti-electricity ions is more integrate and symmetrical than that of pure spinel LiMn2O4, which reveals that the co-doping material possesses preferable electrochemical reversibility.

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。

Relationship of Anti-Mullerian Hormone to Reproductive Traits in Katahdin Ewes Bred in Late Spring or Fall

Anti-Mullerian hormone (AMH) is an endocrine marker for fertility in many species. This study investigated possible correlations between serum AMH concentrations, mean number of lambs born (out-of-season in spring or fall), and estimated breeding values (EBVs) for number of lambs born (NLB), number of lambs weaned (NLW), maternal weaning weight (MWWT), weaning weight (WWT), and maternal index (determined by Sheep Genetics Australia). Blood was collected at breeding from Katahdin ewes between 0.7 and 7 years of age in 2015 (n = 163) for the analysis of serum concentrations of AMH. Anti-Mullerian hormone concentration was either expressed quantitatively or divided into quartiles (AMH Q1 through Q4, with Q1 the lowest and Q4 the highest, pg/ml). Data were analyzed by PROC CORR, GLM or chi-squared using SAS. Mean serum AMH was 182 ± 11 pg/ml and ranged from 0 to 1112 pg/ml. There was no correlation between serum AMH and EBVs for NLB, NLW, MWWT, WWT and the maternal index. Serum AMH concentration was similar in ewes in different age categories (P = 0.157). There was a correlation between EBV for NLB (0.29;P = 0.0002) and NLW (0.19;P = 0.013) with average number of lambs born. Ewes in the lowest AMH quartile (Q1) had a lower mean number of offspring born from spring breeding compared with ewes in other AMH quartiles (Q2, Q3, and Q4;P < 0.05). Further study is needed to determine the effectiveness of using serum AMH for selecting ewes for out-of-season (spring) breeding.

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。