Aerodynamic Coefficients and Deformation Measurements on Flexible Micro Air Vehicle Wings

This paper documents the elastic deformations and corresponding aerodynamic coefficients of flexible wings used for micro air vehicles (MAVs). These low-aspect ratio wings, developed and fabricated at the University of Florida, incorporate an elastic latex membrane skin covering a thin carbon fiber skeleton. The wings were tested in a unique low-speed wind tunnel facility integrating a visual image correlation (VIC) system with a six-component strain gauge sting balance. Model characteristics are presented, along with the appropriate specimen preparation techniques and wind tunnel instrumentation. The static response characteristics, including full-field displacements and plane strain measurements, for three distinct MAV wing designs are presented. The full-field deformation results show how passive wing flexibility preferably affects aerodynamic performance when compared to a rigid model of similar geometry.     

Fracture of bicrystal metal/ceramic interfaces: A study via the mechanism-based strain gradient crystal plasticity theory

Two continuum mechanical models of crystal plasticity theory namely, conventional crystal plasticity theory and mechanism-based crystal plasticity theory, are used to perform a comparative study of stresses that are reached at and ahead of the crack tip of a bicrystal niobium/alumina specimen. Finite element analyses are done for a stationary crack tip and growing cracks using a cohesive modelling approach. Using mechanism-based strain gradient crystal plasticity theory the stresses reached ahead of the crack tip are found to be two times larger than the stresses obtained from conventional crystal plasticity theory. Results also show that strain gradient effects strongly depend on the intrinsic material length to the size of plastic zone ratio (l/R₀). It is found that the larger the (l/R₀) ratio, the higher the stresses reached using mechanism-based strain gradient crystal plasticity theory. An insight into the role of cohesive strength and work of adhesion in macroscopic fracture is also presented which can be used by experimentalists to design better bimaterials by varying cohesive strength and work of adhesion.     

材料力学性能显微测试系统

介绍了适用于毫、微米量级材料的力学性能测试系统,该系统包括微型加力装置、显微镜及数字图像处理系统。通过计算机控制,加力机构可以对微小试件按力或位移控制方式加载,载荷大小通过传感器直接由计算机数字化。试件的变形测量采用数字图像相关技术,通过序列图像分析方式,获得试件在不同外力作用下对应的变形,从而获得该材料的应力应变关系。在利用显微镜对微细观图像进行放大时,图像的畸变会影响相关计算的精度,本文采用了精度极高的正交栅板,对成像系统进行标定,有效地消除了高放大倍数下的图像畸变。图像相关技术对被测物体的表面处理非常敏感,本文也对这一问题进行了讨论,并给出两个不同的应用实例。第一个为材料性能试验,对厚度为0.1mm的铝材进行单向拉伸,给出了材料的应力应变关系;第二个为稳态裂纹扩展试验,对用人牙制作的紧凑拉伸试件进行测试,获得裂尖后的COD曲线。实验表明,该测试系统在微细观力学实验中具有广阔的应用前景。     

DYNAMIC MECHANICAL BEHAVIOR AND PENETRATION PERFORMANCE OF WFeNiMo HIGH-ENTROPY ALLOY 1)

为了探究不同应变速率下WFeNiMo高熵合金的变形行为和侵彻性能, 采用万能材料试验机、分离式霍普金森压杆开展了高熵合金的静动态力学性能试验, 讨论了其在不同应变速率下变形特征微观机制. 基于弹道枪试验平台开展了高熵合金与典型钨合金(93W-4.9Ni-2.1Fe,wt%)破片对有限厚钢靶侵彻作用性能试验研究, 分析了两种合金破片侵彻作用过程与靶板破坏特征、侵彻穿孔能量消耗与撞击速度间的关系. 结果表明: 高熵合金、钨合金材料屈服强度与应变率呈正相关, 且在相同的应变率下高熵合金具有更高的屈服强度; 随着应变率的提高, 高熵合金由脆性断裂、韧脆混合的准解理断裂发展至具有黏着特性的破碎变形模式; 高熵合金具有较强的局部绝热变形能力, 在侵彻薄钢靶时体现出较高的剪切敏感性; 相同撞击速度下, 高熵合金破片穿靶消耗的能量低于钨合金破片, 对于薄钢靶具有更强的侵彻穿透能力. 高熵合金具有优异的力学性能和侵彻能力, 在高速撞击薄靶板时除了传统的剪切冲塞作用还具有一定的能量释放特性, 在预制破片上有较好的应用前景.     

Functionalized nanoparticles based solid‐phase membrane micro‐tip extraction and high‐performance liquid chromatography analyses of vitamin B complex in human plasma

Iron nanoparticles were prepared by a green method following functionalization using 1‐butyl‐3‐methylimidazolium bromide. 1‐Butyl‐3‐methylimidazole iron nanoparticles were characterized using FTIR spectroscopy, energy dispersive X‐ray fluorescence, X‐ray diffraction, scanning electron microscopy and transmission electron microscopy. The nanoparticles were used in solid‐phase membrane micro‐tip extraction to separate vitamin B complex from plasma before high‐performance liquid chromatography. The optimum conditions obtained were sorbent (15 mg), agitation time (30 min), pH (9.0), desorbing solvent [water (5 mL) + methanol (5 mL) + sodium hydroxide (0.1 N) + acetic acid (d = 1.05 kg/L, pH 5.5), desorbing volume (10 mL) and desorption time (30 min). The percentage recoveries of all the eight vitamin B complex were from 60 to 83%. A high‐performance liquid chromatography method was developed using a PhE column (250 × 4.6 mm, 5.0 μm) and water/acetonitrile (95:5, v/v; pH 4.0 with 0.1% formic acid) mobile phase. The flow rate was 1.0 mL/min with detection at 270 and 210 nm. The values of the capacity, separation and resolution factor were 0.57–39.47, 1.12–6.00 and 1.84–26.26, respectively. The developed sample preparation and chromatographic methods were fast, selective, inexpensive, economic and reproducible. The developed method can be applied for analyzing these drugs in biological and environmental matrices.     

超声作用下圆板表面液滴铺展雾化特性

对超声激励下圆板表面液滴铺展及雾化行为进行了可视化观测并基于ANSYS Workbench对超声激励下平板表面等效应力分布进行数值模拟,结合等效应力分布特性分析了不同位置液滴雾化行为差异并归纳总结了液滴铺展雾化的三种典型行为,研究结果表明:超声作用可使圆板表面液滴瞬间雾化且表面会形成与应力分布相一致的间隔交替的"雾化环带"和"微滴环带";液滴总是向着等效应力增加的方向铺展雾化;液滴在圆板上的铺展雾化行为包括单侧铺展雾化、两侧同时铺展雾化以及整体均匀雾化三种类型且雾化类型与所处位置等效应力梯度有关。     

双光子光聚合与功能微纳结构制备

随着纳米光电子学及生物医学组织工程领域的发展,器件的小型化、结构多样化及高度集成化,给微纳结构与器件制造领域带来了新的挑战。本文围绕飞秒激光双光子聚合技术,简要综述了双光子光聚合基本原理与双光子引发剂分子的研究进展,并对飞秒激光双光子聚合技术在功能微纳结构与器件制备中的应用及发展前景进行了展望。     

聚多巴胺涂敷的聚酰胺-胺功能化二氧化硅复合材料用于水样中苯甲酰脲类杀虫剂的分散微固相萃取北大核心CSCD

近年来,由农药残留导致的环境污染问题已引起社会的广泛关注,开发便捷高效的分析方法对农药残留进行检测和监测十分必要。研究设计并成功制备了聚多巴胺涂敷的聚酰胺-胺树状分子功能化的二氧化硅复合材料(SiO-PAMAM-PDA),并采用透射电镜对其进行表征。开发了以此复合材料为吸附剂的分散微固相萃取方法(D-μ-SPE),并结合高效液相色谱对水基质中的4种苯甲酰脲类杀虫剂(BUs)残留进行了富集检测。多巴胺结构中含有丰富的苯环、氨基及羟基,可与目标物形成氢键、π-π相互作用,从而增强了材料对苯甲酰脲的萃取能力。对吸附剂用量、萃取时间等可能影响萃取效率的条件进行了单因素优化。在最优条件下,该方法的线性范围在10~500μg/L之间,根据3倍信噪比(S/N)计算所得的检出限(LOD)为1.1~2.1μg/L,回收率为82.8%~94.1%,相对标准偏差(RSD)为2.1%~8.0%。将建立的方法与已报道的以苯甲酰脲作为目标物的方法进行了对比,发现方法样品用量及萃取剂用量均较少,且所需前处理时间较短,有机溶剂消耗也较少,为苯甲酰脲类农药的检测提供了更快速、绿色的选择。为评估所开发方法的实际样品适用性,将其应用于3种河水样品中4种苯甲酰脲类杀虫剂的分析检测,所得回收率及RSD分别为69.5%~99.4%和0.2%~9.5%,表明此方法在实际样品中同样具有较高的准确性和精密度。     

激光陀螺抖动偏频解调与微小角速度检测

—本文讨论了激光陀螺抖动偏频解调与微小角速度检测的主要技术难点。针对难点，在整周期采样解调基础上提出了脉冲边沿触发鉴相解调方案，同时对该方案的合理性进行了详细分析和理论证明。文章最后指出，该方案对大角速度的高精度检测同样适用。