Experimental study of crystal anisotropy based on ultra-precision cylindrical turning of single-crystal calcium fluoride

To realize ultimately efficient signal processing, it is necessary to replace electrical signal processing circuits with optical ones. The optical micro-resonator, which localizes light at a certain spot, is an essential component in optical signal processing. Single-crystal calcium fluoride (CaF₂) is the most suitable material for a highly efficient optical micro-resonator. The CaF₂ resonator can only be manufactured by ultra-precision machining processes, because its crystal anisotropy does not allow the application of chemical etching. However, the optical micro-resonator's performance depends definitely on the surface integrity.This study investigated the relationship between surface quality after ultra-precision machining and crystal anisotropy. Firstly, crack initiation was investigated on the (1 0 0), (1 1 0), and (1 1 1) planes using the micro-Vickers hardness test. Secondly, brittle-ductile transition was investigated by orthogonal cutting tests. Finally, cutting performance of cylindrical turning was evaluated, which could be a suitable method for manufacturing the CaF₂ resonator. The most difficult point in cylindrical turning of CaF₂ is that the crystalline plane and cutting direction vary continuously. In order to manufacture the CaF₂ optical micro-resonator more efficiently, analysis was conducted on crack initiation and surface quality of all crystallographic orientations from the perspective of slip system and cleavage.     

基于十字形阵列和2D-MUSIC算法的Lamb波检测

采用由压电传感器组成的十字形阵列进行Lamb波信号的激励和接收，提出一种二维多重信号分类（2D-MUSIC）方法对铝板中的缺陷进行定位检测。选用合适的频率激励产生单一模态信号，可避免多模态的影响，降低Lamb波的频散；利用2D-MUSIC算法对接收信号进行分段处理，并结合反射信号和二维导向矢量对铝板中的缺陷进行定位。结果表明，提出的2D-MUSIC算法对铝板中的缺陷定位比传统MUSIC算法更精准。     

Acoustic emission source location considering refraction in layered media with cylindrical surface

To solve the problem that the existing acoustic emission (AE) source location algorithms cannot always obtain accurate results for multilayer cylindrical media, a new acoustic emission source location method considering refraction was proposed. AE source coordinates were solved by the complex method. Pencil-lead-break experiments were used to verify this method. The absolute distance errors of location results are less than 3 mm, much less than those by the traditional method. The numerical experiments were used to further analyze factors that affect location accuracy. The results of numerical experiments show that the location accuracy of the proposed method is not affected by the ratio of wave velocities but affected by the measurement accuracy of wave velocity. These results show that new method can obtain accurate AE source location in the two-layered cylindrical surface media such as the triaxial compression test.     

宽频带梯形叉指式换能器优化设计及应用

由声表面波（Surface Acoustic Wave）器件发展而来的叉指换能器（Interdigital Transducer，IDT）由于其工作频率可以设计、频带宽可调、损耗低等特点逐步应用于结构健康监测（Structural Health Monitoring，SHM）系统中，因此在智能材料与结构中有着广泛的应用前景。本文针对现有矩形IDT带宽窄的不足，研究宽频带梯形叉指换能器（Trapezoidal Interdigital Transducer，TIDT）。采用有限元分析方法对TIDT的尺寸进行结构优化设计，并对设计的TIDT进行性能测试，通过实验研究了TIDT用于结构损伤检测的初步应用。实验结果表明，TIDT在实际应用中进一步提高了损伤识别精度，具有广泛的应用前景。     

“方变圆”变径筒状结构滑模施工技术

为解决塔式光热的核心构筑物吸热塔"方变圆"变径超高筒体结构施工难题,选用一套可变形的滑模平台系统,通过操作系统上可调千斤顶支座、门架横向液压千斤顶装置、多处可调节模板角度和收缩模板的丝杆等,使得滑模根据施工需求可在一定的范围内调节模板倾角、间距,并逐步完成收缩变形,其理论滑模允许偏角20°,最终高效完成异形结构施工。该滑模系统刚度大、承载及堆料能力强、空间大、机械化程度高,施工操作简单,安全性高,适应沙漠极端环境。全过程仅需使用一套滑模体系,就能完成方形段、方变圆的变形段及圆形段施工,大大提高了施工效率,为类似环境下相似结构的施工提供了一定的参考。     

Drag Power Loss Investigation in Cylindrical Roller Bearings Using CFD Approach

In high-speed rolling element bearings, the drag forces can be prominent and it is demonstrated in this investigation that the classical models may not be appropriate for correctly estimating this power loss contribution. A modification of the models is thus proposed, including the usual drag forces formulation relying upon the drag coefficient to be evaluated from a numerical computational fluid dynamics (CFD) approach. A three-dimensional approach that considers both the rings and the cylinder ends seems the only adequate approach to be used because a two-dimensional approach predicts a drag coefficient value that is too low. When using the former computed drag coefficient for the evaluation of the total power losses, high values of oil volume fraction must be employed to recover the measured power losses.     

基于模板热压法制备超疏水柱状结构表面

超疏水表面材料在生产生活中具有重要的应用价值,其制备的关键在于构建合适的表面微结构。以多孔阳极氧化铝表面为模板,高密度聚乙烯为压印热塑材料,进行常压工况下的热压印,制备出三维柱状结构表面,表面形貌规整有序,通过调节模板结构参数实现对柱状结构尺寸的精确调控。测试结果显示,制备的不同微结构尺寸的柱状结构表面接触角均在150°以上,具有优异的超疏水性能。     

ZK61M高强镁合金板热变形过程中的韧性断裂预测（英文）

为了预测ZK61M高强镁合金板热变形过程的韧性断裂行为,在一定条件下进行实验和数值模拟。基于获得的各试件断口处的应力状态参数和断裂应变数据,采用粒子群优化算法求解4种断裂模型中的待定系数。依据误差评估结果,确定改进的Wilkins模型精度最高。将改进的Wilkins模型引入有限元中,并与实验进行对比。结果表明,预测的拉伸件断裂位移和断裂载荷的平均误差均小于15%,预测的圆筒形件成形深度的平均误差为13.88%,建立的有限元模型可以较为准确地模拟实验过程并预测断裂位置。     

基于电磁超声的钢板自动检测方法探讨

分析了钢板制造方法及可能存在的缺陷,应用电磁超声技术对钢板进行自动检测,主要从电磁超声检测基本原理与声波产生、换能器波型选择与排列、对比试板及其人工缺陷设计、检测闸门设置及检测结果显示与记录等方面进行研究。结果表明：电磁超声自动检测可以对钢板进行全覆盖非接触扫查,实现高速、高温检测,满足大管径、壁厚和高压油气输送用钢板检测要求,对于研究钢板电磁超声自动检测方法具有参考价值,且对制定相关钢板电磁超声自动检测标准具有借鉴作用。     

早龄期高强混凝土自收缩的测量

文章介绍了用电容传感器测量高强混凝土早期收缩变形的基本原理和测量方法。其测量精度和测量范围能够完全满足对高强度混凝土收缩进行研究的需要 ,同时变形的测量可以从混凝土初凝开始 ,解决了高强混凝土收缩相关课题研究的核心问题