LD31板料激光斜冲击成形后表面残余应力的实验研究

在曲面板料激光冲击成形时,很难满足每次都能法向垂直冲击,因此非常有必要进行激光斜冲击板料研究。文章采用钕玻璃激光器、脉冲能量约42J、脉冲宽度约23ns、脉冲功率≥1.2×109W、激光以30°斜冲击LD 31(6063)方形板料,冲击后板料最大变形点偏离试样中心3mm。采用X-350A型X射线应力测定仪、侧倾固定Ψ法和交相关法定峰,分别测量了板料沿激光冲击方向、板料空间分布的残余压应力,得出试样正反两面均是压应力,均小于100MPa,由于变形最大点与方形板料顶点连线长度大于垂直于边长方向,且经过变形最大点直线长度,其在厚度方向产生压应力2σ比较大,产生相同变形所需的力较大,所以产生的残余压应力也较大。在变形最大点与板料顶点最短连线之间的板料受到挤压,板料变厚,硬化严重,产生残余应力最大。     

Simulation of 3D chip shaping of aluminum alloy 7075 in milling processes

By adopting an equivalent geometry model of machining process and considering thermo-plastic properties of the work material, a finite element method（FEM） to study oblique milling process of aluminum alloy with a double-edge tool was presented. In the FEM, shear flow stress was determined by material test. Re-meshing technology was used to represent chip separation process. Comparing the predicted cutting forces with the measured forces shows the 3D FEM is reasonable. Using this FEM, chip forming process and temperature distribution were predicted. Chips obtained by the 3D FEM are in spiral shape and are similar to the experimental ones. Distribution and change trend of temperature in the tool and chip indicate that contact length between tool rake face and chip is extending as tool moving forward. These results confirm the capability of FEM simulation in predicting chip flow and selecting optimal tool.     

无人测量系统在消力池水下地形测量中的应用

GPS-RTK与测深仪的组合测量手段是现代水下地形测量的重要技术手段,本文采用该测量技术与无人船技术融合,构建了适用于消力池的水下地形测绘无人测量系统,并应用于亭子口水利工程的表孔消力池水下地形测量实践。文中系统地阐述了消力池水下地形无人测量系统的工作原理、标准化作业流程以及水下地形三维构建方法,结合测绘数据和三维模型,对消力池测区的溢流坝段、护坦、尾坎、防冲段、河道衔接段的高程变化趋势进行分析。结果表明：汛后亭子口表孔消力池结构完整,边界清晰,水质良好,从溢流坝段至尾坎处的护坦表面淤积程度均较小,池区尚未发现明显的堆积体或结构异常,受基岩和围堰卵砾石堆积体影响,防冲段与下游衔接段高程增加显著。无人测量技术的使用,提高了消力池水下地形与淤积分布的获取精度与时效性,具备显著的应用研究价值和推广意义。     

斜角切削过程的数值模拟

借助于通用有限元软件ANSYS模拟出斜角切削的动态过程,并在此基础上对切削变形进行了研究,提出了一种获得剪切角的新方法。通过仿真计算和快速落刀试验,验证了该方法的可行性。     

载机飞行参数对倾斜成像重叠率影响及补偿

针对飞机姿态角、速度、高度对重叠率影响进行分析并给出了补偿方法。以图像目标直接地理定位方法为基础,给出了大倾斜成像重叠率的基于坐标变换分析方法;对飞行参数单变量影响给出了几何分析方法及计算公式,两种方法结果是一致的。对于载机姿态角综合作用影响,利用基于坐标变换的方法给出了载机姿态角波动在1°范围内,分析了图像目标区域与预期区域偏离的结果,同时提出了使用相机位角和俯角对飞机姿态角影响进行补偿的方法,并给出了基于坐标变换方法的相机位角和俯角补偿量计算公式;基于几何分析结果,提出了通过调整拍照周期对载机速度和载机高度波动影响进行补偿方法,并给出拍照周期的计算公式。仿真结果和实际飞行数据表明,使用相机位角和俯角进行载机姿态补偿,同时调整拍照周期,可以很好抑制航拍过程中飞机参数波动对重叠率影响,在小视场角0.88°时,在平坦地区重叠率均值与预期值偏差为1%。     

A computational experiment on deducing phase diagrams from spatial thermodynamic data using machine learning techniques

Derivation and discovery of physical dynamics inherent in big data is one of the most major purposes of machine learning (ML) in the field of modern natural science. In the materials science, phase diagrams are often called as “road maps” to perfectly understand the conditions for phase formation and/or transformation in any material system caused by the associated thermodynamics. In this paper, we report a numerical experiment investigating whether the underlying thermodynamics can be derived from the big data constructed of local spatial composition and phase distribution data along with the help of ML. The artificial data analysed have been created assuming a steel composition based on the calculation phase diagram (CALPHAD) thermodynamics combined with the order-statistics-based sampling model. The hypothetical procedures of data acquisition assumed in this numerical experiment are as follows; (i) obtaining local analysis data on the composition and phase distribution in the same observation area using instruments such as electron probe micro analyser (EPMA) and electron backscattering diffraction (EBSD), and (ii) training the classification model based on a ML algorithm with compositional data as input and the phase data as output. The accuracies of the reconstructed phase diagrams have been estimated for three ML algorithms, i.e. support vector machine (SVM), random forest, and multilayer perceptron (MLP). The phase diagrams predicted using SVM and MLP are found to be adequately consistent with those of the CALPHAD method. We have also investigated the regression performance of the continuous data involved in the CALPHAD thermodynamics, such as the phase fractions of body-centred cubic, face-centred cubic, and cementite phases. Compared with the ML algorithms, the CALPHAD method is found to show superior predictive performance since it is based on the sophisticated physical model.     

Analysis of MBE grown AI(x)Ga(1-x)As-GaAs heteroepitaxial layers by rutherford backscattering

The Rutherford Backscattering (RBS) technique has been optimized for the measurement of thin (>85Å) alternating layers of A1(x)Ga(l-x)As and GaAs, which are at the limit of resolution of standard RBS measurements. RBS analysis of these structures provides both layer thicknesses and Al content. This information is useful for device processing since the layer thicknesses impact the FET threshold voltage and the Al content is important for proper selective chemical etching. Experimental conditions for the beam energy, detection angle, and sample rotation have been determined which allow measurement of the layer thicknesses to a precision of ±20-30Å (for layers >85A) and of the Al content,x, to a precision of ±.02. Comparison of the RBS data with Transmission Electron Microscopy (TEM), Cathodoluminescence (CL), and Reflection High Energy Electron Diffraction (RHEED) measurements on the same material showed very good agreement between the different techniques. The advantage of RBS is that it can measure much thinner layers than CL and it provides thickness and composition information at the same time whereas TEM only provides thickness for this particular material. RBS is currently used tocharacterize a monitor wafer from each day’s run to provide a processing baseline for the MBE growth.     

基于时域激电的层状大地视谱参数测深曲线反演

基于时间域Cole-Cole模型及视充电率的观测方式,推导出层状大地时域激电测深正演计算方法,运用最小二乘法对电测深曲线进行反演,得出视相关系数cs、视充电率ms、视时间常数τs等视谱参数测深曲线。对几种层状介质模型视谱测深曲线反演计算表明,基于时域激电数据计算得到的视谱参数测深曲线能够反映出各地层频谱参数特征,可以为时域激电测深提供更为丰富的信息,为激电异常及极化体性质评价和分类提供有利的参考。     

利用Klobuchar模型和载波平滑伪距观测值模型分析电离层变化

在GPS测量中,电离层延迟是一个比较重要的误差来源.对于单频接收机,由广播星历中提供Klobuchar模型参数进行电离层延迟改正;对于双频接收机,采用载波平滑伪距观测值计算电离层延迟改正.利用深圳市连续运行卫星定位参考站系统的双频观测数据,分别用Klobuchar模型和载波平滑伪距观测值两种方法计算深圳市5个CORS站上的电离层延迟值,对两种模型计算的电离层延迟值进行比较,分析深圳市电离层延迟的周日变化规律.     

数学形态滤波在音频大地电磁去噪中的应用

大地电磁去噪方法种类多,且各有其优缺点。本文引入汤井田教授的一种新方法——数学形态滤波法,它是依据形态学原理而创建的一种新型的非线性滤波方法,在信号和图像处理领域中得到广泛的运用。本文通过仿真实验设计一个加噪的正弦曲线,通过经腐蚀运算、膨胀运算、开闭运算、闭开运算和经形态滤波后分析曲线特征,之后对比经组合广义形态滤波在同一结构元素不同长度、同一长度不同结构元素滤波效果,最后将组合广义形态滤波引进到实测的音频大地电磁数据中,对比其滤波前和滤波后的视电阻率曲线,结果表明形态滤波能有效抑制音频大地电磁法中大尺度干扰,取得了良好的应用效果。