破片撞击下YAG透明陶瓷复合靶的破坏特性

YAG透明陶瓷兼具有优秀的透光性能和抗冲击破坏性能,是武器装备透明部分的优秀防护材料,在军事装备、航天等国防领域具有良好的应用前景。冲击载荷下材料的加载响应特性对掌握材料破坏机制至关重要,能为透明复合靶设计提供依据。为获得YAG透明陶瓷多层复合靶的冲击破坏特性,利用内径9 mm的气体驱动发射平台进行了碳化钨球形破片在20～310 m/s速度下撞击YAG透明陶瓷复合靶的实验,通过高速摄影捕捉的陶瓷表面损伤演化过程,计算了典型径向、环向裂纹扩展速度。通过观测回收的靶体和YAG碎片的宏细观破坏特征,分析了撞击速度与靶体破坏特征之间的联系。结果表明,YAG陶瓷层径向裂纹和环向裂纹扩展速度均随着时间的延长线性降低,且裂纹扩展速度几乎不受撞击速度影响。陶瓷层中心粉碎区面积随撞击速度的提高而增大,且中间玻璃层破坏区域面积与陶瓷锥底面积相关联,陶瓷锥角与撞击速度关联性不强。同时,观察到陶瓷层在冲击破坏过程中出现了裂纹簇,获得了裂纹簇数量与破片撞击速度之间的关系,分析了裂纹簇的特征及其成因。裂纹变向、应力波作用会显著影响细观断面破坏特征。径向、环向和锥裂纹中沿晶断裂的比例均随着裂纹扩展距离的增大而增加,且穿晶比例随着撞击速度的提高而增加。     

TiO2-loaded activated carbon fiber： Hydrothermal synthesis,adsorption properties and photo catalytic activity under visible light irradiation

TiO2-loaded activated carbon fibers （ACF） were prepared by a hydrothermal method. The samples were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Fourier transform infrared （FTIR） spectrometry and UV-vis diffuse reflectance spectra （DRS）. SEM images showed that the TiO2 nanoparticles were deposited on the surface of ACF, and the particle size and loading amount of TiO2 were varied by changing the initial concentration of tetrabutyl titanate （TBOT）. The results of an ash experiment showed that the loading amounts of TiO2 were 18.4%, 43.3%, 52.5%, 75.1%, and 91.1% for initial concentrations of TBOT of 0.07,014, 0.21,0.28, and 0.35 tool/L, respectively, Physical interactions played an important role in the formation of TiO2/ACF composite fibers that absorb UV and visible light. Compared with those of ACF, improved adsorption and photocatalytic activity toward Rhodamine B （RhB） were observed for TiO2/ACF composite fiber. The Rhodamine B could be removed efficiently by TiO2/ACF composite fibers, and the TiO2 loading amount had a significant effect on the photocatalytic activity of TiO2/ACF composite fibers.     

Adsorption removal of sulfamethoxazole from water using UiO-66 and UiO-66-BC composites

The adsorption removal of anti-inflammatory drugs from water by diverse materials has drawn great attention. This study investigated the adsorption of sulfamethoxazole (SMX) by two types of materials, UiO-66 and UiO-66-BC composites. Highly porous MOF composites with functional groups were synthesized by combining UiO-66 with corncob-based biochar at different molar ratios. SEM results showed that macroporosity of UiO-66-BC composites was increased by increasing the ratio of biochar. It was found that UiO-66-BC composites displayed highly improved adsorption performance of SMX relative to pristine UiO-66. UiO-66-BC (5%) had the highest SMX adsorption capacity, about 2.4 times those of pristine UiO-66. It was the high surface area of UiO-66 and redundant functional groups of biochar that increased the adsorption performance of composites. Moreover, UiO-66-BC can be reused and displayed the competitive adsorption efficiency after successive adsorption, which made it a potential adsorbent for the removal of SMX from water.     

A 6-DOF passive vibration isolator based on Stewart structure with X-shaped legs

By employing the nonlinear stiffness and damping characteristics of a bio-inspired X-shaped structure (XSS) with passive springs and the Stewart platform with six degrees of freedom, a passive 6-DOF vibration isolation platform is designed and experimentally studied for its vibration isolation performance. A three-layer asymmetrical XSS is adopted as legs to construct a passive Stewart platform. Because of the specially designed XSS, the stiffness and damping properties of the system can be adjusted by changing structural parameters and thus it is designable to achieve an excellent performance including excellent stability and high-static-low-dynamic-stiffness isolation effect in all six directions with satisfactory loading capacity in the vertical direction, without any active control. Analytical and extensive experimental analysis of static stiffness and vibration response of the system revealed that (a) the aXSS Stewart platform has very beneficial high static nonlinear stiffness which can provide sufficient loading capacity; (b) the platform can achieve very low dynamic stiffness in each direction without losing loading capacity; (c) both static and dynamic stiffness is adjustable and designable with structure parameters and very easy to implement in a pure passive manner.     

TiO2-loaded activated carbon fiber: Hydrothermal synthesis,adsorption properties and photo catalytic activity under visible light irradiation

TiO₂-loaded activated carbon fibers (ACF) were prepared by a hydrothermal method. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry and UV–vis diffuse reflectance spectra (DRS). SEM images showed that the TiO₂ nanoparticles were deposited on the surface of ACF, and the particle size and loading amount of TiO₂ were varied by changing the initial concentration of tetrabutyl titanate (TBOT). The results of an ash experiment showed that the loading amounts of TiO₂ were 18.4%, 43.3%, 52.5%, 75.1%, and 91.1% for initial concentrations of TBOT of 0.07, 014, 0.21, 0.28, and 0.35 mol/L, respectively. Physical interactions played an important role in the formation of TiO₂/ACF composite fibers that absorb UV and visible light. Compared with those of ACF, improved adsorption and photocatalytic activity toward Rhodamine B (RhB) were observed for TiO₂/ACF composite fiber. The Rhodamine B could be removed efficiently by TiO₂/ACF composite fibers, and the TiO₂ loading amount had a significant effect on the photocatalytic activity of TiO₂/ACF composite fibers.     

质子型离子液体水基润滑液摩擦学性能研究

配置了不同质量分数的质子型离子液体二乙醇胺月桂酸(Bis[(2-hydroxyethyl)ammonium] lauric，B_OEAL)水溶液，使用MRS-10A摩擦试验仪、NGY-6型纳米膜厚测量仪、接触角测量仪，对B_OEAL水溶液的减摩抗磨性能、极压性能、成膜性能和润湿性等进行试验研究，并用3D共聚焦表面形貌仪和XPS对摩擦磨损机制进行了分析. 结果表明: 质量分数为5%的B_OEAL水溶液最大无卡咬负荷在834~883 N之间，相比纯水(98 N)有较大的提高，即B_OEAL可作为水基润滑液的极压添加剂. B_OEAL的加入显著提高了纯水的成膜能力以及在钢-钢摩擦副表面的润湿性能. 分析原因是B_OEAL中的极性基团可以在金属表面形成致密的化学吸附膜或物理吸附膜，从而使得金属摩擦副的摩擦系数降低，抗磨效果提高，同时由于B_OEAL分子极性较强，低质量分数的B_OEAL水溶液在不锈钢表面就表现出良好的摩擦学性能.      

室温离子液体介质中CdS纳米微粒的制备及其摩擦磨损行为研究

合成了1-甲基-3-己基咪唑四氟硼酸盐离子液体，并以此为反应介质通过有机金属化合物热分解法制备出CdS纳米微粒，采用X射线粉末衍射仪和透射电子显微镜对CdS纳米微粒的结构和形貌进行表征，在四球摩擦磨损试验机上考察了含CdS纳米微粒离子液体的摩擦磨损行为．结果表明：所制备的CdS纳米微粒具有六方相结构，粒径均一，约为15nm；含CdS纳米微粒离子液体的减摩抗磨性能明显优于纯离子液体；CdS纳米微粒以滚动／滑动方式起到了减摩抗磨作用，同时可以加速离子液体中阴离子的分解，促进FeF2和FeF3的形成，使复合体系的减摩抗磨性能有所提高．     

Strip model plasticity analysis of mixed mode crack opening displacement in aluminum alloy LY12

Under mixed mode loading, the crack tip blunts and undergoes displacements in two directions, the normal and shear component corresponding to Mode I and Mode II loading, respectively. These local displacements are determined by the duplicated film method and used to analyze the behavior of mixed mode fracture in aluminum alloy LY12. The mixed mode resultant crack opening displacement (COD) at fracture initiation tends to increase more rapidly with increase of the Mode II shear component. The fracture initiation value of COD for pure Mode II loading is six (6) times greater than that for Mode 1 loading. The same applies to the maximum effective plastic strain crack growth near the crack front. Observed are two typical morphologies, the equal-axes dimples and the parabolic dimples with evidence of slippage as dominated, respectively, by Mode I and Mode II loading.     

Photoelectrochemical glucose biosensor incorporating CdS nanoparticles

A novel photoelectrochemical biosensor incorporating nanosized CdS semiconductor crystals with enzyme to enhance photochemical reaction has been investigated. CdS nanoparticles were synthesized by using dendrimer PAMAM as inner templates. The CdS nanoparticles and glucose oxidase （GOD） were immobilized on Pt electrode via layer-by-layer （LbL） technique to fabricate a biological-inorganic hybrid system. Under ultraviolet light, the photo-effect of the CdS nanoparticles showed enhancement of the biosensor to detect glucose. Pt nanoparticles were mixed into the Nation film to immobilize the CdS/enzyme composites and to improve the charge transfer of the hybrid. Experimental results demonstrate the desirable characteristics of this biosensing system, e,g. a sensitivity of 1.83 μA/（mM cm^2）, lower detection limit （1 μM）, and acceptable reproducibility and stability,     

CoCrFeNiAlx系高熵合金的动态力学性能和本构关系

高熵合金,以其独特的合金设计和优异的综合性能,成为当下材料研究的热点。本文利用高真空电弧熔炼法成功制备出了CoCrFeNiAl_x（x=0, 0.6, 1）系高熵合金,并通过分离式霍普金森压杆对其进行一系列不同应变速率下的动态压缩试验。通过X射线、扫描电镜和透射电镜分析,深入探索了该合金系的晶体结构、微观组织和变形特征。最后,利用修正后的Johnson-Cook (J-C)本构模型,获得了该体系高熵合金的动态本构关系。     

Tensile and mixed-mode strength of a thin film-substrate interface under laser induced pulse loading

Laser induced stress waves are used to characterize intrinsic interfacial strength of thin films under both tensile and mixed-mode conditions. A short-duration compressive pulse induced by pulsed-laser ablation of a sacrificial layer on one side of a substrate is allowed to impinge upon a thin test film on the opposite surface. Laser-interferometric measurements of test film displacement enable calculation of the stresses generated at the interface. The tensile stress at the onset of failure is taken to be the intrinsic tensile strength of the interface. Fused-silica substrates, with their negative nonlinear elasticity, cause the compressive stress wave generated by the pulse laser to evolve a decompression shock, critical for generation of the fast fall times needed for significant loading of surface film interfaces. By allowing the stress pulse to mode convert as it reflects from an oblique surface, a high amplitude shear wave with rapid fall time is generated and used to realize mixed-mode loading of thin film interfaces. We report intrinsic strengths of an aluminum/fused silica interface under both tensile and mixed-mode conditions. The failure mechanism under mixed-mode loading differs significantly from that observed under pure tensile loading, resulting in a higher interfacial strength for the mixed-mode case. Inferred strengths are found to be independent, as they should be, of experimental parameters.     

低速冲击下混凝土少筋梁断裂性能

动态加载下,混凝土中钢筋的阻裂性能一直是冲击动力学研究领域的难点之一。利用落锤试验机对含缺口的混凝土少筋梁进行三点弯曲试验,分析了不同加载速率下梁的冲击力、跨中挠度、混凝土起裂应变率和钢筋应变。实验结果表明:在一定加载速率范围内（0.885～1.252 m/s）,混凝土预制裂缝尖端的裂纹起裂应变率、冲击力最大值、跨中挠度峰值与加载速率呈线性增长关系,当加载速率增至1.771 m/s时,增长趋势减弱;冲击力卸载时,钢筋部分弹性变形恢复导致裂纹产生闭合,裂纹嘴张开位移逐渐减小至恒定值,对裂纹嘴张开位移峰值前的部分曲线进行拟合后得到裂纹嘴张开位移率,结果表明裂纹嘴张开位移率随加载速率的提高而线性增大。     

The area contraction and expansion for a nano-void under four different kinds of loading

This paper provides an explanation for the authors’ recent conclusions as why the M-integral could be negative for a nano-void (hole) in elastic materials under tensile, bi-axes tensile, and bi-axes tensile-compress loadings (Hui T, Chen YH, in ASME J Appl Mech 77:021019-1-9, 2009; 024505-1-5, 2009). Attention is focused on whether the area of the nano-void under each of four different kinds of loading is contractive when compared to the original geometrical area without loading. The four kinds of loading are as follows: (1) simple tensile loading; (2) bi-axes tensile loading; (3) bi-axes tensile-compression loading; and (4) purely shear loading. It is concluded that, unlike those for a macro/micro hole, the area of the nano-void under relatively lower amplitude of the loadings (1) and (2) is always smaller than the original area of the same void before loading. This reduction in the nano-void area is induced from the surface effect including the surface tension and the surface Lamé constants along the nano-void rim. Thus, these two kinds of loading can either decrease or increase the nano-void area depending on the amplitude of the loading. Under a relatively lower tensile loading, the area contraction occurs but not always corresponding to the negative value of the M-integral, whereas under a relatively higher tensile loading, the area expansion occurs but not always corresponding to the positive value of the M-integral. This again verifies that the positive value of the M-integral does not always correspond to the energy release due to the nano-hole expansion, rather, the area contraction might yield the energy release either. Under bi-axes tensile compression or purely shear loading, this feature disappears.     

Multi‐material incompressible flow simulation using the moment‐of‐fluid method

This paper compares the numerical performance of the moment‐of‐fluid (MOF) interface reconstruction technique with Youngs, LVIRA, power diagram (PD), and Swartz interface reconstruction techniques in the context of a volume‐of‐fluid (VOF) based finite element projection method for the numerical simulation of variable‐density incompressible viscous flows. In pure advection tests with multiple materials MOF shows dramatic improvements in accuracy compared with the other methods. In incompressible flows where density differences determine the flow evolution, all the methods perform similarly for two material flows on structured grids. On unstructured grids, the second‐order MOF, LVIRA, and Swartz methods perform similarly and show improvement over the first‐order Youngs' and PD methods. For flow simulations with more than two materials, MOF shows increased accuracy in interface positions on coarse meshes. In most cases, the convergence and accuracy of the computed flow solution was not strongly affected by interface reconstruction method. Published in 2009 by John Wiley & Sons, Ltd.     

On the stress concentration around a hole in a half-plane subject to moving contact loads

We study the stress concentration due to a pore in an elastic half-plane, subject to moving contact loading, in the entire range of possible geometrical parameters (contact area/hole diameter, hole depth/hole diameter). Since the number of cases is very large to study with FEM even with modern machines, the use of a recent simple approximate formula due to Greenwood based on the stress field in the absence of the hole is first attempted, and compared with a full FEM analysis in sample cases. To further distillate the effects of the hole distance from the free surface and of the contact area size, the limiting cases are studied of: (i) concentrated load perpendicular to the surface and aligned with the hole centre; (ii) constant unit pressure on the top surface of the half-plane and (iii) hydrostatic load. A full investigation is then conduced for the case of Hertzian load on the surface, and it is seen that the tensile stress concentration is significantly reduced with respect to that of the concentrated load, when the contact area size is of the same order of the hole radius. Results obtained with the approximate Greenwood formula are generally accurate however only if the hole distance from the surface is greater than two times the hole radius.     

Effective thermal conductivity of CdS/ZnS nanoparticles embedded polystyrene nanocomposites

CdS/PS and ZnS/PS nanocomposites have been prepared by solution casting method with different wt% of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles and characterized through X-ray diffraction and transmission electron microscope measurements. The effective thermal conductivity of polymer nanocomposites has been measured by transient plane source method over the temperature range from room to 150 °C. The experimental results showed that the thermal conductivity has been found to increase up to 4 wt% of CdS/ZnS nanoparticles and then decrease for 6 and 8 wt% of nanoparticles.     

钛合金TC4材料热处理工艺对圆筒在内爆炸载荷下膨胀半径的影响

对采用两种不同热处理工艺的钛合金TC4材料进行了Hopkinson拉伸实验、圆筒爆炸实验和数值仿真,从而确定了两种不同热处理工艺的优劣并通过微观分析揭示了钛合金TC4材料微观组织结构对内爆炸载荷下圆筒膨胀半径的影响。实验和数值分析表明:采用双重退火热处理工艺的钛合金TC4材料具有良好的动态力学性能。在相同的加载条件下,经此工艺处理的TC4圆筒在爆轰产物未泄漏之前有着充分的膨胀半径,而且也不容易形成绝热剪切破坏。同时,给出的依据高速摄影照片确定筒壳断裂点的方法是切实可行的,获得的断裂时间与数值分析结果吻合。     

利用液体炸药爆轰制备石墨烯薄片

强氧化性酸的环境下,石墨易形成石墨层间化合物(GICs),利用石墨这一特性,将天然石墨置于发烟硝酸中,并加入硝基甲烷,配制成液体炸药,使用塑料容器盛装后放入爆轰反应釜中引爆。收集爆轰产物,并利用XRD、EDX、SEM、TEM、Raman光谱、比表面积与孔隙度分析仪进行分析,结果显示:制备出的石墨烯具有良好的晶体特性并呈现极薄的片状结构,其比表面积达到天然石墨的9.16倍,平均厚度约为14.73 nm。     

SYNTHESIS AND COATING OF ORDERED MESOPOROUS SILICA

1,3,5-trimethyl benzene (TMB) was used as organic swelling agent in O/W emulsions to template ultra-large mesoporous materials using the hydrothermal method. The silicas with well-defined mesopores and hydrothermally robust framework were characterized by X-ray diffraction, transmission electron microscopy and BET surface area analysis. The influence of the quantity of TMB during preparation was studied. It has been found that the TMB/CTAB ratio must be controlled for producing high pore volume materials. Polysulfone (PSU), as the usual extraction agent, was coated on the silicas with the solvent evaporation method to produce a solid separation medium. The adsorptivity and the surface area of the coated MCM were determined: 10% PSU coated MCM adsorbed twice as much phenol as the uncoated material, reaching 0.5 mg/g silica. It was found that the surface area of the coated material decreased rapidly with an increase of the PSU Ioadina.     

Simultaneous initiation over large areas of a spray-deposited explosive

In this paper, the authors report the development of a technique for obtaining controlled impulsive loading over relatively large surface areas. The method involves the initiation of thin layers of spray-deposited explosive by focusing on the surface of the explosive intense light flashes from gas-filled tubes. Total durations of pressure loading as short as 6 μsec have been achieved for 10-in. squares, with detonation being initiated nearly simultaneously at over 100 points in each square inch of surface area.