Microstructure and Property of HD Die Steel With Unsmoothed Surface With Various Laser Parameters

The reticulate unsmoothed surfaces on HD die steel, which imitate the surface of soil-burrowing animals （such as the dung beetle, earthworm, pangolin, and ant） are produced with various laser parameters. The characteristics （including width, depth, area ratio, and volume）, microstructure, and hardness of the unsmoothed units are studied. At the same time, the wear resistance of the material with an unsmoothed surface is measured. The results show that the width and volume of the unit increase, the microstructure becomes coarser, the hardness decreases, and the wear resistance improves with the increase of the current intensity and pulse duration within a certain range. However, there is little difference between the extent to which the wear resistance of the material increases and the unsmoothed surface, when the current intensity and pulse duration increase to some extent. The wear resistance of the unsmoothed material under 300 A or 20 ms is better in the experiments. The improving extent of the wear resistance lies in a combination of the characteristics, microstructure, and hardness of the unsmoothed unit. An unsmoothed material with better properties can be processed if the laser parameters are well matched.

Study on Laser Transformation Hardening of HT250 by High Speed Axis Flow CO_2 Laser

In this article, laser transformation hardening of HT250 material by high speed axis flow CO2 laser was investigated for first time in China. Appropriate laser hardening parameters, such as laser energy power P(W), laser scanning rate V(m/min), were optimized through a number of experiments. The effect of the mentioned parameters on the hardened zone, including its case depth, microhardness distributions etc., were analyzed. Through the factual experiments, it is proved that axial flow CO2laser, which commonly outputs low mode laser beam, can also treat materials as long as the treating parameters used are rational. During the experiments, the surface qualities of some specimens treated by some parameters were found to be enhanced, which does not coincide with the former results. Furthermore in the article, the abnormal phenomenon observed in the experiments is discussed. According to the experimental results, the relationship between laser power density q and scanning rate V is shown in a curve and the corresponding formulation, which have been proved to be valuable for choosing the parameters of laser transformation hardening by axial flow CO2 lasers, was also given.

基于BIM技术的空间异形赛道成型控制方法研究与应用

国家雪车雪橇中心是空间扭曲的异形赛道,对赛道内曲面平滑度的施工质量要求极高。利用BIM技术对地形逆向建模、空间异形赛道参数化建模、赛道模型深化应用及赛道内曲面成型检测等关键内容进行研究,可为同类型工程的施工和检测提供参考。首先,整合原始地貌模型和设计地形模型进行分析,计算出土方挖填工程量,有利于减少土方开挖和环境破坏;其次,采用Rhino软件拾取关键数据并进行纠偏处理,对异形赛道的夹具、钢筋、表面进行参数化建模及优化,解决赛道夹具安装定位与内曲面平整度控制的难题;最后,采用三维激光扫描技术对赛道内曲面平滑度进行动态控制,保证工程建造品质。

Earth rotation parameter and variation during 2005—2010 solved with LAGEOS SLR data

Time series of Earth rotation parameters were estimated from range data measured by the satellite laser ranging technique to the Laser Geodynamics Satellites（LAGEOS）-1/2 through 2005 to 2010 using the dynamic method. Compared with Earth orientation parameter（EOP）C04, released by the International Earth Rotation and Reference Systems Service, the root mean square errors for the measured X and Y of polar motion（PM） and length of day（LOD）were 0.24 and 0.25 milliarcseconds（mas）, and 0.068 milliseconds（ms）, respectively.Compared with ILRSA EOP, the X and Y of PM and LOD were 0.27 and 0.30 mas, and 0.054 ms, respectively. The time series were analyzed using the wavelet transformation and least squares methods. Wavelet analysis showed obvious seasonal and interannual variations of LOD, and both annual and Chandler variations of PM; however, the annual variation could not be distinguished from the Chandler variation because the two frequencies were very close. The trends and periodic variations of LOD and PM were obtained in the least squares sense, and PM showed semi-annual, annual, and Chandler periods.Semi-annual, annual, and quasi-biennial cycles for LOD were also detected. The trend rates of PM in the X and Y directions were 3.17 and 1.60 mas per year, respectively, and the North Pole moved to 26.8E relative to the crust during 2005—2010. The trend rate of the LOD change was 0.028 ms per year.

基于BIM的超大跨度空间网壳结构场馆三维激光扫描生成方法

受网壳结构场馆跨度大小的影响,导致激光扫描图像空间轴与真实场景图像坐标轴之间的偏离程度较大,为保证扫描图像能准确、真实地反映网壳结构场馆的空间布局形式,提出基于BIM的超大跨度空间网壳结构场馆三维激光扫描生成方法。根据BIM建模原则实施Revit族参数化处理,再联合相关参数指标完成基于BIM的超大跨度空间网壳结构场馆建模。按照点云匹配条件连接提取得到的特征线段,通过解算激光点坐标的方式,确定扫描图像中的激光点布局形式,完成超大跨度空间网壳结构场馆三维激光扫描图像生成。实验结果表明:BIM建模方法可将扫描图像空间轴与真实场景图像坐标轴之间的偏离程度控制在5%以内,能够较好地反映超大跨度网壳结构场馆的空间布局形式。

Effects of laser processing parameters on properties of laserinduced graphene by irradiating CO_(2) laser on polyimide

The emerging technique of carbonization of polyimide(PI)by direct laser writing receives great attention for its flexibility,versatility,and ease-of-patterning capability in creating a variety of functional laser-induced graphene(LIG)sensors and devices.LIG prepared by CO_(2) laser irradiating of the PI film is characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),transmission electron microscope(TEM),specific surface area analyzer,synchronous thermal analysis,and Raman spectroscopy with the focus on investigating the effects of laser parameters(e.g.,power,scanning speed)on the microstructure,thickness,and sheet resistance of LIG.Both TEM and XRD indicate that LIG is composed of many graphene layers with a layer spacing of 0.34 nm.The specific surface area of LIG decreases with the increase of laser power.The ratio of the thickness of LIG over the depth of the carbonized PI film as the expansion ratio characterizes the expansibility of LIG.The influence of image resolution and off-focus value on the sheet resistance of LIG is explained by the superposition mechanism of laser scanning spots.

高超声速低温喷管副喷管参数化设计

通过对DF化学激光器高超声速低温(HYLTE)喷管副喷管流动与几何参数进行制约关系和敏感性分析,确定了能够对副喷管进行参数化设计的4个基本几何控制参数和2个调节参数,初步建立了HYLTE喷管副喷管的参数化设计方法。引入了相对未混合度作为衡量喷管混合效果的性能参数,建立了较完备的3维反应流数值模拟计算程序。结果表明:该方法选择的基本参数能够敏感地反映HYLTE喷管副喷管的尺寸特征和关键性能。

基于地面激光扫描技术的建筑物建模研究

三维激光扫描技术在建筑物建模领域发展迅速。以现代建筑为例,从三维数据获取、数据处理、模型建立等方法进行论述,采用七参数模型进行点云拼接,并对拼接后的点云进行去噪和抽稀处理,分析研究2种不同建模方法的特点,一种是三角网格法,另一种是参数化建模方法。最终采用参数化建模方法完成了大型建筑物的建模。实验表明,在建筑物建模中,参数化建模方法更为适用。

面向五轴数控激光加工的纹理映射参数化求解数值方法

针对激光加工设备制造商对纹理映射技术的强劲需求,介绍了基于三维激光振镜系统的五轴数控激光加工系统的工作原理,研究了面向激光加工的三维曲面的纹理映射的参数化求解数值方法,具体涉及到基于LSCM中的自由边界方法,进行纹理映射的位置、大小,朝向的约束和控制、二维矢量图的三维映射,以及三维纹理网格的交互显示等方面的研究,并针对某鼠标零件模具型腔进行了激光蚀刻加工实验,验证了所开发的纹理映射参数化求解数值方法技术的可靠性和准确性。

3维曲面振镜激光加工FPLSCM算法实践

为了高质量地将目标图像标刻在任意曲面上,需要将计算机中排版的2维数据转换为3维数据从而形成具体振镜加工轨迹数据.在大量激光标刻实验测量与计算的基础上,采用一种对任意自由曲面进行最小化失真展开的区域重点最小二乘共形展开(FPLSCM)算法,完成了实用的3维振镜激光加工系统软件设计,并进行了理论分析和实验验证,取得了大量标刻测量数据.结果表明,在z轴上下300mm范围内,本算法能有效将由于高度与待加工表面形状差异带来的标刻畸变控制在1%左右,并且在各类3维曲面上都得到了很好的加工效果.此研究成功实现了在自由3维曲面上利用动态聚焦技术完成各种表面加工的工作,并通过优化算法有效减少了畸变.

Multi-use laser impulse pendulum and laser propulsion parameters measurement

In order to investigate the mechanisms of both the air-breathing and the ablation modes of laser propulsion under laboratory conditions, a multi-use laser impulse pendulum (MULIP) is developed. The measurable impulse range is from 1.0×10-4 to 3.8×10-3 N·s. The experimental calibration data agree well with the theoretical calculated data. With MULIP, the ablation mode has been performed, in which a high power pulsed Nd:glass laser (λ= 1.06μm, τ=20 ns) and a gray PVC film sample are used. The experimental results show that the maximum momentum coupling coefficient Cm is 7.73×10-5 N/W, and the maximum specific impulse Isp is 208.6 s.

保利国际金融城BIM技术应用总结

超高层总承包施工对深化设计和协同工作具有很高的要求,随着BIM、实景建模、激光扫描等新技术的应用,深化设计、协同管理变得越来越高效和落地。本项目对本文针对保利金融城项目基于BIM的协同工作、深化设计、计划管理等应用进行了简要介绍和总结。

利用仿真数据考察SLR微米级时延模型对PPN参数解算精度的影响

介绍了在广义相对论框架下建立的微米级卫星激光测距时延模型。为考察新模型对于参数化后牛顿系数β和γ解算精度的影响，将该模型用于定轨软件Utopia对Ajisai，Lageos1，Lageos2，Etalon1四颗卫星的模拟观测资料进行批处理，并假设大气、固体潮等观测模型的效应以及动力学模型的误差已精确扣除。结果表明，在当前的仿真条件下采用微米级时延模型解算的参数化后牛顿系数解算精度比采用现有的标准时延模型的解算精度高2个量级。

Numerical simulation for pulsed laser-gas tungsten arc hybrid welding of magnesium alloy

Based on the extended application of COMSOL multiphysics, a novel dual heat source model for pulsed laser-gas tungsten arc （GTA） hybrid welding was established. This model successfully solved the problem of simulation inaccuracy caused by energy superposition effect between laser and arc due to their different physical characteristics. Numerical simulation for pulsed laser-GTA hybrid welding of magnesium alloy process was conducted, and the simulation indicated good agree- ments with the measured thermal cycle curve and the shape of weld beads. Effects of pulse laser parameters （laser-excited current, pulse duration, and pulse frequency） on the temperature field and weld pool morphology were investigated. The experimental and simulation results suggest that when the laser pulse energy keeps constant, welding efficiency of the hybrid heat source is increased by increasing laser current or decreasing pulse duration due to the increased ratio of the weld bead depth to width. With large laser currents, severe spatters tend to occur. For optimized welding process, the laser current should be controlled in the range of 150-175 A, the pulse duration should be longer than 1 ms, and the pulse frequency should be equal to or slightly greater than 20 Hz.

A data-driven framework to predict the morphology of interfacial Cu6Sn5 IMC in SAC/Cu system during laser soldering

A data-driven approach combining together the experimental laser soldering,finite element analysis and machine learning,has been utilized to predict the morphology of interracial intermetallic compound(IMC) in Sn-xAg-yCu/Cu(SAC/Cu) system.Six types of SAC solders with varying weight proportion of Ag and Cu,have been processed with fiber laser at different magnitudes of power(30-50 W) and scan speed(10-240 mm/min),and the resultant IMC morphologies characterized through scanning electron microscope are categorized as prismatic and scalloped ones.For the different alloy composition and laser parameters,finite element method(FEM) is employed to compute the transient distribution of temperature at the interface of solder and substrates.The FEM-generated datasets are supplied to a neural network that predicts the IMC morphology through the quantified values of temperature dependent Jackson parameter(αJ).The numerical value of αJ predicted from neural network is validated with experimental IMC morphologies.The critical scan speed for the morphology transition between prismatic and scalloped IMC is estimated for each solder composition at a given power.Sn-0.7 Cu having the largest critical scan speed at 30 W and Sn-3.5 Ag alloy having the largest critical scan speed at input power values of 40 W and 50 W,thus possessing the greatest likelihood of forming prismatic interfacial IMC during laser soldering,can be inferred as most suitable SAC solders in applications exposed to shear loads.

Microstructure and mechanical properties of in situ(Ti,Nb)C_p/Fe-based laser composite coating prepared with different heat inputs

In this paper, in situ （Ti, Nb）C particle （（Ti, Nb）Cp） reinforced Fe-based composite coatings were produced by laser cladding on the surface of the high carbon steel. The effects of heat input on the microstructure, distribution characteristics of particle, and mechanical properties of the coating were investigated. The results show that （Ti, Nb）C multiple carbide particle is synthesized during solidification of molten pool. The size of particle coarsens gradually, the area ratio of particle increases, and the amount of particles presents a non-monotonous variation with the increase in energy density. The mechanical properties of the coating are improved dramatically compared with those of the substrate, benefiting from its higher hardness and dispersed in situ （Ti, Nb）Cp in it. With the change in heat input, the mechanical performances of the coating vary except the hardness. When energy density is 1 × 10^5 J.mm-2, tensile strength and wear resistance of the coating achieve optimal value due to moderate content and size of the particle in the coating.

基于移动二维激光扫描的单木三维绿量测定

【目的】单木三维绿量的有效测定为森林资源调查、森林生态环境效益评价、林业精准管理提供有用信息,对现代林业发展具有重要意义。为提高单木三维绿量测量效率与测量精度,提出一种基于移动二维激光扫描的低成本单木三维绿量测定方法。【方法】采用二维激光扫描仪对单木进行多角度直线扫描,获取树冠三维形貌信息;融合不同角度的采集数据,建立激光扫描线的向量参数方程;建立树冠体素模型,将待测空间离散化为体素,体素尺寸与扫描系统分辨率一致,以未被扫描线穿透的体素集合表达树冠体积,求取单木三维绿量。【结果】实验选取6株单木,体素分辨率为0.022 m,6株单木三维绿量平均测算时间为105.94 s,平均帧处理时间为0.039s。【结论】基于移动二维激光扫描的单木三维绿量测定,无需人工筛选点云,可自动处理数据,测量效率高,改进后的体素模型充分利用测量数据,能真实反映树冠内部体积及空隙。

单原子光镊的激光强度起伏对原子俘获寿命的影响及改善

使用单束强聚焦的基模高斯光束可以构建光镊装载原子。虽然光镊一般选择远离原子共振跃迁线的激光,但是光镊的强度起伏仍然会导致原子逃逸,这样原子在光镊中的俘获寿命问题就变得至关重要。本实验以声光频移器(AOM)为主要元件,并施加外部反馈控制电路抑制937.7 nm波长光镊频域上的强度噪声以及时域上的功率起伏,降低光镊对原子的参量加热,从而有效延长原子在光镊中的俘获寿命。典型的频域噪声抑制带宽17 kHz,噪声强度抑制10 dB,时域内激光强度起伏可以从峰峰值起伏±1.350%抑制到±0.036%,有效地降低了光镊的强度起伏。实验结果表明我们可以将937.7 nm波长光镊中单个铯原子俘获寿命从200 ms延长至1 180 ms.为后续原子内态的制备、激发等操作提供充足的时间,保证原子处于俘获状态,提高了实验成功率,缩短了实验时长。

Optical properties and Judd-Ofelt analysis of Nd2O3 nanocrystals embedded in polymethyl methacrylate

PMMA matrices were doped with nano-crystalline neodymium oxides synthesized by thermal decomposition process. X-ray diffraction and high-resolution transmission electron microscopy measurements were carried out to investigate the structure, phase, and the morphology of the Nd_2O_3 nanocrystals and those embedded in the PMMA matrix. The average grain sizes were estimated 35 ± 6 nm and 46 ± 4 nm for non-annealed and annealed Nd_2O_3 particles, respectively. The grain size distributions（GSD） were calculated from the diffraction peaks of the annealed and non-annealed Nd_2O_3 powders and doped PMMA samples. The mass density, refractive index. UV-Visible absorption spectra were measured and the data were analyzed using the Judd-Ofelt approach to determine the oscillator strengths, the spontaneous emission probabilities and the branching ratios as a function of the nano-crystalline Nd_2O_3 content in the range of 0.1 wt.%-20 wt.% of MMA. Luminescence spectra upon 808 nm diode laser excitation were carried out in the wavelength range of 850-1550 nm at room temperature. The photoluminescence study has shown that the reasonably sharp emission peaks were observed upon heat treatment at 800 ℃ for 24 h for all concentrations of Nd_2O_3 nanopowders in PMMA. The infrared laser transition of Nd^（3＋） ions at about 1.06 μm due to the ~4F_（3/2）→~4I_（11/2） transition was analyzed and discussed in Nd_2O_3 system for their possible applications in the photonic technology.