弹簧指数对镍钛合金弹簧缓冲吸能能力的影响

形状记忆合金(SMAs)弹簧具有大应变可逆变形能力,在吸能缓冲和振动控制等领域具有重要应用潜力。本工作研究了弹簧结构设计对镍钛SMAs性能的影响规律。采用冷拉拔和退火相结合的方法制备直径1.2mm的Ti-52.5at%Ni合金丝,并通过室温下芯轴绕制成型和高温退火相结合的方式制备弹簧指数C分别为6.0、7.7和9.3的弹簧,通过测试合金丝和弹簧的超弹性曲线研究弹簧结构的吸能性能。研究表明,基于弹簧的超弹性变形过程,室温(298K)下3类弹簧在120 mm的最大位移幅值下单位体积吸能分别为4618、2225和1143 kJ/m³,弹簧指数C为6.0的弹簧吸能能力最优。318K下,弹簧处于完全奥氏体态,弹簧指数C为6.0的弹簧单位体积吸能(6662kJ/m³)是同等载荷(47 N)条件下合金丝(34.7 kJ/m³)的192倍。同等条件下,弹簧结构具有比合金丝优异的吸能能力。因此,超弹性SMAs弹簧在缓冲减振结构上具有良好的应用前景。     

Fabrication of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method

In this study, we investigate the effect of oxide dispersion strengthening on mechanical properties by dispersion of nano-sized Ta₂O₅ particles in Mo-Si-B alloy. A Mo-Si-B core-shell powder consisting of two intermetallic compounds of Mo₅SiB₂ and Mo₃Si as the core and nano-sized Mo solid solution surrounding intermetallic compounds was fabricated by chemical vapor transport. And Mo-Si-B core-shell powder with uniformly dispersed nano-sized Ta₂O₅ particles on the surface of a Mo solid solution shell was produced by a wet blending process with TaCl₅ solution and heat treatment. Then, pressureless sintering was performed at 1400°C for 3 h under a H₂ atmosphere. The hardness and fracture toughness of the Ta₂O₅-dispersed Mo-Si-B alloy were measured using Vickers hardness and 3-point bending tests, respectively. The Vickers hardness and fracture toughness of the fabricated Mo-Si-B-Ta₂O₅ alloy were more improved than that of the Mo-Si-B alloy fabricated using core-shell powder with no addition of Ta₂O₅ particles (Mo-Si-B alloy: 353 Hv, 13.5 MPa·√m, Mo-Si-B-Ta₂O₅ alloy: 509 Hv, 15.1 MPa·√m).     

Oxidative coupling of methane over promoted strontium chlorapatite

Strontium zirconium phosphate, unpromoted strontium chlorapatite and strontium hydroxyapatite showed low C₂ selectivity for the oxidative coupling of methane, but promoted strontium chlorapatite catalysts showed markedly increased activity and selectivity and also exhibited stable behavior. SrCl₂ was the primary promoter and strontium zirconium oxides were considered to be acting as other promoters, but strontium zirconium phosphate and strontium carbonate seemed to be acting adversely. A promoted strontium chlorapatite catalyst which contained a slightly larger amount of SrCl₂ than needed to form the chlorapatite showed the best performance and was stable up to 50 h at 1,023 K, and the highest C₂₊ selectivity and yield were 52% and 13.8%, respectively. Although SrCl₂ was more stable than NaCl it decomposed slowly during the reaction, leaving strontium oxide or strontium carbonate behind, which is considered to result in slow deactivation of the catalyst.     

A computational study on optimal design for organic tandem solar cells

A new model is developed by combining the optical model and the drift-diffusion model to optimize the thicknesses of active layers of individual sub-cells for high performance of organic tandem solar cell. When the photovoltaic properties of tandem organic solar cells based on poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta (2,1-b;3,4-b′) dithiophene)-alt-4,7-(2,1,3-benzo-thiadiazole))/(6,6)-phenyl C71-butyric acid methyl ester and poly(3-hexylthiophene)/(6,6)-phenyl C61-butyric acid methyl ester are calculated as functions of thicknesses of individual sub-cells using the new model, it is found that the optimum thickness pair of active layers is 150 and 120 nm for the front and back sub-cell, respectively. Comparison of simulation with experiment reveals that the simulated results are very consistent with experimental ones.     

Numerical study for laminar wavy motions of liquid film flow on vertical wall

Film flows are classified into non-wavy laminar, wavy laminar and turbulence along the Reynolds number or the flow stability. Since the wavy motions of the film flows are so intricate and nonlinear, the studies have largely been dependent upon the experimental way. The numerical approaches have been limited on the non-wavy flow regime. To track the free surface position, various numerical techniques such as the VOF (Volume of Fluids), the MAC (Marker and Cell) and the moving grid have been adopted. However those were for a more accurate estimation of the average film thickness and not for capturing the wavy motion. Because the wavy motion highly affects the heat transfer in the film flow, the profound concern for the wavy motion is significant. In this study, the wavy motions of the laminar wavy film flow with the Reynolds number 200–1000 are successfully found by the VOF and PLIC (Piecewise Linear Interface Calculation) method. The numerical results, including the average film thickness, and the wave’s amplitude, frequency and velocity, are compared with the experimental results.     

米氏旋回基本原理及其在陆相湖盆分析中的应用前景

米氏旋回是指峰值时间跨度为20－500ka,日地天轨道参数的周期性变化,以及由此产生的气候和沉积地层的旋回性变化。米氏旋回主要通过改变地球表面的太阳辐射能对气候变化进行控制,并对沉积作用产生重要的影响,通过沉积地层观测数据的时序分析可以重建米氏旋回,对地层的成因和过程进行研究。米氏旋回代表地层学和古气候学研究的前沿课题,不仅在深海沉积物的研究中得到了广泛应用,对陆相含油气盆地地层分析和油气储集层的预测也都具有重要意义。     

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.