TEMPERATURE EFFECT ON LOW-CYCLE FATIGUE BEHAVIOR OF NICKEL-BASED SINGLE CRYSTALLINE SUPERALLOY

The low-cycle fatigue （LCF） behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T0℃ and a higher temperature of To ＋ 250℃ under a constant low strain rate of 10^-3 s^-1 in ambient atmosphere. The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temperature and applied strain amplitude. Analysis on the fracture surfaces showed that the surface and subsurface casting micropores were the major crack initiation sites. Interior Ta-rich carbides were frequently observed in all specimens. Two distinct types of fracture were suggested by fractogaphy. One type was characterized by Mode-I cracking with a microscopically rough surface at To ＋ 250℃. Whereas the other type at lower temperature T0℃ favored either one or several of the octahedral {111} planes, in contrast to the normal Mode-I growth mode typically observed at low loading frequencies （several Hz）. The failure mechanisms for two cracking modes are shearing of γ＇ precipitates together with the matrix at T0℃ and cracking confined in the matrix and the γ/γ＇interface at To - 250℃.

Effects of Annealing Process on Crystallization and Low Temperature Resistance Properties of PP-R Composites

The effects of the annealing process on the mechanical properties and crystallization behaviors of polypropylene random copolymer（PP-R） composites were investigated using differential scanning calorimetry（DSC）, wide-angle X-ray diffraction（WAXD）, and dynamic mechanical analysis（DMA）, and scanning electron microscopy（SEM）. The experimental results indicated that the annealing process significantly influenced the comprehensive properties of PP-R composites. At temperatures below 23 ℃, the impact strength of the PP-R composites annealed at 120 ℃ for 6 h was relatively high at 74.73 k J/m^2, which was 16.8% higher than that of the samples annealed at 80 ℃ for 6 h. At low temperatures（-30-0 ℃）, the impact strength ranged from approximately 13.31 k J/m^2 to 54.4 k J/m^2. In addition, the annealing process conducted at 120 ℃ for 6 h improved the crystalline structure and low-temperature toughness of the PP-R composites and induced α-form to β-form crystal transformation. The work provides a possible method to reinforce and toughen the semicrystalline polymer at low temperatures（-30-0 ℃） by annealing.

LOW MACH NUMBER LIMIT OF A COMPRESSIBLE NON-ISOTHERMAL NEMATIC LIQUID CRYSTALS MODEL

In this paper, we study the low Mach number limit of a compressible nonisothermal model for nematic liquid crystals in a bounded domain. We establish the uniform estimates with respect to the Mach number, and thus prove the convergence to the solution of the incompressible model for nematic liquid crystals.

Optimizing Vitamin E Purification from Unsaponiable Matter of Palm Fatty Acids Distillate by Low Temperature Solvent Crystallization

Palm fatty acid distillate （PFAD）, a by-product of deodorization in palm oil refining, contains about 0.7%-1% vitamin E. The advantage of PFAD over other vitamin E sources is higher amount of tocotrienols than that of tocopherols. Vitamin E purification of unsaponiable matter of PFAD was aimed to remove other impurities to obtain high vitamin E concentration, mainly tocotrienols. This research used low temperature solvent crystallization to purify vitamin E. To optimize response of vitamin concentration, a response surface method was applied with three factors, i.e., the ratio between solvent and unsaponifiable matter （A）, crystallization temperature （B）, and crystallization time （C）. The relation of three factors was quadratic with equation Y = -128.54361 ＋ 41.33904A - 0.87995B ＋ 1.58941C ＋ 0.00290AB - 0.044324AC ＋ 0.00120BC - 3.33113A2 - 0.039535B2 - 0.02710C2. The optimum crystallization condition was obtained at ratio of solventto unsaponifiable matter of 6.04：1, crystallization temperature of-10.54 ℃, and crystallization time of 24.16 hours. Vitamin E enriched fraction from optimum crystallization conditions contained vitamin E of 20.13% （w/w）.

Extracting structural information from low symmetry crystal field parameters-case study:Er^(3+) and Nd^(3+) ions in YAlO_3

The experimental monoclinic CF parameter （CFP） sets obtained by Duan et al. （Phys. Rev. B 75 （2007） 195130） for Er3＋ and Nd3＋ ions in YAIO3 were reanalyzed. These CFPs fitted using R-approach, i.e. with the monoclinic second-rank CFP set to zero, and additionally with one six-rank CFP fixed to zero, turned out to be non-standard. In order to understand better the low symmetry aspects involved in the fitted CFPs and extract useful structtral information inherent in monoclinic CFPs, an approach comprising four methods was utilized. First, superposition model （SPM） was applied to calculate CFPs in the crystallographic axis system. Second, the principal values for the SPM determined CFPs and the orientation of the principal axis system w.r.t, the crystallographic axis system were obtained using the procedure 3DD for diagonalization of the 2rid-rank CFPs. Third, analysis of higher symmetry approximations, i.e. orthorhombic and tea＇agonal, was carried out using the pseudosymmetry axes method. Fourth, the closeness factors and norm ratios were employed for quantitative comparisons of various CFP sets. Partial results for Er3＋ ions in YAlO3 were presented here, whereas detailed results would be given in a follow-up paper.

A CRYSTALLOGRAPHIC MODEL FOR THE ORIENTATION DEPENDENCE OF LOW CYCLIC FATIGUE PROPERTY OF A NICKEL-BASE SINGLE CRYSTAL SUPERALLOY

Fully reversed low cyclic fatigue (LCF) tests were conducted on [0 0 1], [0 1 2], [(1) over bar 1 2], [0 1 1] and [(1) over bar 1 4] oriented single crystals of nickel-bared superalloy DD3 with different cyclic strain rates at 950 degrees C. The cyclic strain rates were chosen as 1.0 x 10(-2), 1.33 x 10(-3) and 0.33 x 10(-3) s(-1). The octahedral slip systems were confirmed to be activated on all the specimens. The experimental result shows that the fatigue behavior depends an the crystallographic orientation and cyclic strain rate. Except [0 0 1] orientation specimens, it is found from the scanning electron microscopy(SEM) examination that there are typical fatigue striations on the fracture surfaces. These fatigue striations are made up of cracks. The width of the fatigue striations depends on the crystallographic orientation and varies with the total strain range. A simple linear relationship exists between the width and total shear strain range modified by an orientation and strain rate parameter. The nonconformity to the Schmid law of tensile/compressive flaw stress and plastic behavior existed at 95 degrees C, and an orientation and strain rate modified Lall-Chin-Pope ( LCP) model was derived for the nonconformity. The influence of crysrallographic orientation and cyclic strain rate on the LCF behavior can be predicted satisfactorily by the model. In terms of an orientation and strain rate modified total strain range, a model for fatigue life was proposed and used successfully to correlate the fatigue lives studied.

A low-dimensional crystal growth model on an isotropic and quasi-free sustained substrate

A new crystal growth theoretical model is established for the low-dimensional nanocrystals on an isotropic and quasifree sustained substrate. The driven mechanism of the model is based on the competitive growth among the preferential growth directions of the crystals possessing anisotropic crystal structures, such as the hexagonal close-packed and wurtzite structures. The calculation results are in good agreement with the experimental findings in the growth process of the lowdimensional Zn nanocrystals on silicone oil surfaces. Our model shows a growth mechanism of various low-dimensional crystals on/in the isotropic substrates.

Low Frequency Dispersion Law for Two-Dimensional Metallic Photonic Crystals

Using the rigorous multiple-scattering theory, we study the dispersion relation of electromagnetic （EM） waves in two dimensional dielectric photonic crystals （PCs） and metallic photonic crystals （MPCs） in the low-frequency limit. Analytic formula for the effective velocity of EM waves in PCs and MPCs is obtained. Accuracy of our formula is checked by comparing the results with rigorous calculations. For PCs, our result is exactly the same as the coherent potential approximation （CPA）, which is accurate even when the filling fraction is high. But for MPCs, our approach demonstrates special advantages, while the CPA theory fails, in predicting the effective velocity of EM waves in MPCs at low frequency.

A Study on the Raman Spectrum of the LiNbO_3－doped Mg Crystal at Low Temperature

The Raman Spectra of LiNbO3:MgO(6.7mol%) at both lowtemperature and room temperature were studied. The results showed that the crystal structure had changed little after doping Mg++. At room temperature the lattice distorted a litlte, which caused the appearance of couping phenomenon of some individual scattering peaks. As the temperature decreased, the coupling reduced gradually.

沙漏型声子晶体的中低频隔声减振性能研究

针对机械工业装备上难以解决的低频振动与噪声问题,提出一种小尺寸、轻量化的新型声子晶体结构,研究其隔声减振特性,通过有限元仿真计算该声子晶体无限周期排列时的隔声量、能带结构以及有限周期排列时的振动响应,分析该结构的隔声机理及减振特性,并研究了关键几何参数、散射体材料和声波入射角度对该结构的隔声特性的影响规律,以及板结构减振频带的拓宽方法.结果表明:该声子晶体结构在1 000 Hz以下频率范围内具有优越的隔声减振性能,通过将不同参数的结构进行组合的方法可以拓宽声子晶体板的减振频带,为工程结构的中低频隔声减振及声子晶体的应用提供了新的思路与可行性参考.

小晶粒高硅铝比NaY分子筛低温合成研究

采用自制的偏铝酸钠为合成导向剂,在低温下水热晶化合成出了小晶粒高硅铝比的NaY分子筛。考察了合成导向剂的陈化温度、陈化时间、晶化碱度、晶化温度和晶化时间对产品的影响,得到了制备NaY分子筛最佳的工艺条件,并进行了放大制备。在此条件下,NaY分子筛结晶度(峰面积)≥90%,结晶度(峰高)≥85%,硅铝比≥5.5,晶粒尺寸均在(100~200)nm,不仅优于工业标样的指标要求,且易于放大。

废液晶玻璃再生制备低膨胀硼硅玻璃及其理化性能研究

基于废液晶玻璃的高值化再生利用,以废液晶玻璃作为主要原料,石英砂、硼酸、纯碱为辅助原料,制备了低膨胀硼硅玻璃。通过浮力法、压痕法、石英膨胀法和重量试验法,探究了废液晶玻璃和辅助原料(Na_(2)O和B_(2)O_(3))掺量对玻璃理化性能的影响。结果表明:随着废液晶玻璃掺量增加,玻璃密度、线热膨胀系数和耐酸质量损失增大,维氏硬度和耐碱质量损失减小;随着辅助原料中Na_(2)O含量增大,玻璃密度、线热膨胀系数、耐酸质量损失和耐碱质量损失增大,维氏硬度减小;随着辅助原料中B_(2)O_(3)含量增大,玻璃密度和维氏硬度减小,线热膨胀系数和耐酸耐碱质量损失增大;当废液晶玻璃、辅助原料中Na_(2)O和B_(2)O_(3)质量分数分别为60.00%、1.00%和14.72%时,玻璃维氏硬度最大、密度和线热膨胀系数最小,分别为7.1430 GPa、2.3097 g·cm^(-3)和3.5317×10^(-6)℃^(-1);当废液晶玻璃、辅助原料中Na2O和B2O3质量分数为60.00%、3.00%、9.72%时,玻璃耐酸质量损失最小,为0.6140 mg·cm^(-2);当废液晶玻璃、辅助原料中Na2O和B2O3质量分数为70.00%、2.00%、11.67%时,玻璃耐碱质量损失最小,为1.2140 mg·cm^(-2)。

超声波技术在铼酸铵结晶过程中的应用研究

铼是钼矿中的一种稀散伴生金属,本文介绍了一种在铼酸铵结晶过程中使用超过20 kHz超声波辅助结晶的新技术。经小试及工业验证:利用超声波技术,在超声空化作用下,含铼液结晶过程的结晶率提升约3%,产品75μm粒度通过率达到了100%,晶型有了显著改善;新技术具备能耗低、易操作的特点。该研究在提升铼酸铵生产的产品质量方面具有积极意义。

基于声子晶体的高速列车地板支撑层隔声研究

随着高速列车运营速度不断提高,轨道交通产生的振动噪声会严重影响列车的车内声环境,进而降低乘坐舒适性,因此针对列车噪声源部位的车体隔声设计至关重要。目前的隔声措施能够有效控制车内中高频噪声,而对于低频噪声的抑制效果还有待进一步提升。声子晶体是一种具有弹性波带隙的周期性结构材料,该结构不需要大尺寸即可在局域共振作用下形成低频带隙,进而抑制弹性波的传播从而起到低频降噪作用。基于声子晶体周期性理论,以车辆转向架部位地板的木骨支撑层为对象,研究声子晶体在木骨支撑层隔声中的应用,系统分析声子晶体结构的带隙特性和隔声特性以及基于声子晶体结构的支撑层隔声性能。研究结果表明:通过改变结构形式及其参数可实现对于声子晶体结构的带隙形成频带及其隔声特性的人为设计和控制;以高速列车地板中的木骨结构为对象,结合声子晶体理论将其设计为木骨和声子晶体组合结构形式,不仅能够保持声子晶体在0~220 Hz低频段和620~710 Hz频段优越的隔声性能,同时可极大提升220~620 Hz频段的隔声性能;既维持该层结构的支撑作用,又能很好提升隔声性能,在高速列车地板设计中具有很强的有效性和适用性。

超低温结晶器磁流体密封设计及仿真优化分析

针对传统密封应用在结晶器时存在泄漏及磨损等难题,以连续冷冻结晶器为研究对象,设计一种带有升温功能的新型磁流体密封装置。通过有限元软件对磁场及温度场进行分析,得到关键参数对密封耐压值的影响;采用正交实验法对参数进行优化,并采用控制变量法分析不同热水质量流率及密封间隙对磁流体温度的影响。结果表明:结构参数对密封性能的影响程度依次为:密封间隙>永磁体高度>永磁体宽度>槽宽>齿宽>齿高;优化后各结构参数为密封间隙0.3mm、极齿宽度1.2mm、槽宽3.6mm、极齿高度3.2mm时,密封耐压值为0.503MPa,高于优化前的0.384MPa;由于工况温度较低,为保障磁流体密封正常工作,需通入质量流率大于0.1kg/s的常温水。

周期桁架结构设计及振动特性分析

为解决船舶动力系统低频振动噪声问题,本文基于声子晶体局域共振理论,设计了一种带周期振子桁架式浮筏结构。利用有限元法和Bloch理论,分析了周期振子桁架产生带隙的原因,讨论了振子质量、安装形式和桁架结构参数对带隙特性的影响规律,设计了周期振子桁架振动特性试验,探究了桁架结构振动传递特性。结果表明:振子质量越大,带隙宽度增加,胞元尺寸越大,带隙带宽减小;振子排列方式对带隙特性影响较小,增加振子数量,宽带特性显著;采用振子间隔安装方式,相较全安装方式,带隙特性变化较小,可有效减少振子数量。

火电厂锅炉水冷壁焊缝泄漏失效分析

某12Cr1MoV水冷壁对接焊缝中部出现周向裂纹导致泄漏失效,为调查泄漏失效原因,对焊缝进行了宏观检查、磁粉检测、硬度检验、金相分析、全元素分析和能谱分析,并建立模型分四个阶段讨论了水冷壁焊缝泄漏失效的原因。研究表明:焊缝中夹杂的S元素是焊缝泄漏失效的主要因素,收缩拉应力为偏析在晶界的低熔点共晶物提供了形成沿晶热裂纹的条件,氧气的介入造成热裂纹的局部氧化,实际运行的综合应力使氧化的沿晶热裂纹多点扩展、融合,形成宏观裂纹,最终导致焊缝泄漏失效。

中性硝基分子几何形状与晶体特性的关联性

含能晶体堆积结构是影响其感度的重要因素之一,通过晶体中分子层间滑移来缓冲外界刺激是降低含能材料感度的重要机制。为了更好地设计低感高能分子,理解分子的几何形状与其晶体特性的内在关系十分重要。研究以剑桥晶体数据库中的CHNO类中性硝基分子为样本,采用假设检验方法(包括Z检验、t检验和χ2检验)研究了分子的几何形状与其晶体密度、堆积系数及可滑移性之间的关联性。结果表明,在球形、平面和线形分子中,球形分子有最高的晶体密度和堆积系数,但晶体可滑移性较弱;平面度高的平面形分子通过高堆积系数可获得与球形分子相当的晶体密度,同时平面形分子的晶体可滑移性较强,其χ2检验的置信度接近1;线形分子则不如前两者。虽然存在某些高晶体密度和堆积系数的含能晶体不具有可滑移的层状堆积结构,但整体而言,可滑移晶体的晶体密度和堆积系数均比不可滑移晶体大,其Z检验与t检验的置信度均大于0.95,表明通过设计易于发生分子层间滑移的晶体结构来降低其感度与提升晶体密度并不矛盾。平面形分子晶体密度一般较高,与晶体可滑移性强相关,是设计低感高能分子的首选。

复合溶剂低温结晶法富集鱼油中的棕榈油酸

为探究鱼油来源单不饱和脂肪酸的富集工艺,本研究以鳀鱼油为原料,采用复合溶剂-低温结晶法提纯POA。与单一溶剂相比,复合溶剂效果更佳。以POA含量及得率为指标,采用单因素实验对单一/复合溶剂种类、复合溶剂体积比、油溶比、结晶温度、结晶时间进行优化。确定最佳工艺条件为丙酮-乙腈体积比为1∶10,鱼油与溶剂质量比为1∶6,结晶温度为-60℃,结晶时间为6 h,得到的混合脂肪酸中POA含量为(29.75±0.53)%。进一步进行放大试验,将得率提升至50%左右,总不饱和脂肪酸含量达79%以上。本研究为ω-7单不饱和脂肪酸的富集工艺提供了参考。