Experimental study of free abrasive wire sawing by using multi-strands wire

Grains in the slurry can be brought into cutting zone by steel wire with a certain speed to achieve the purpose of removing the workpiece material in the free abrasive wire sawing machining. Because its own of multi- strands characteristics, we use it to replace the steel wire to do slicing experiment. In this paper, multi-strands wire is made by seven metal wires and has many grooves on its surface. Compared with steel wire, it can carry more grains into cutting zone which is conducive to improving the slicing efficiency. We do some comparative slic- ing experimcnts by applying multi-strands wire （~b0.25 mm） and steel wire （~b0.25 mm） to cut optical glass （K9）. The results show that slicing efficiency and the surface roughness of the workpiece sliced by using multi-strands wire are better than that by using steel wire. but the kerf width of the former is wider than that of the latter in the same experimental conditions.     

Optimization of Cutting Parameters for Face Milling Titanium Alloy Using MQL

When using MQL as a cooling technique, many parameters have to be adjusted. The Taguchi method was used in this study to investigate the cutting characteristics of face milling of titanium alloys using PVD-coated inserts. To find the optimal volume removed and surface roughness, an orthogonal array, the signal-to-noise （S/N） ratio and the analysis of variance （ANOVA） were employed. The optimum cutting parameters was obtained. Throughout this study, it was found that the feed rate is the most influencing cutting parameter in the face milling of titanium alloys.     

Influence Factors of Fractal Characterization of Reciprocating Sliding Wear Surfaces

The principal purpose of this paper is to investigate influence factors of fractal characterization of reciprocating sliding wear surfaces. The wear testing was completed to simulate the real running condition of the diesel engine 8NVD48A-2U. The test results of wear surface morphology dimension characterization show that wear surface profiles have statistical self-affine fractal characteristics. In general, there are no effects of the profilometer sampling spacing and sampling length and evaluation length on the fractal dimensions of the surfaces. However, if the evaluation length is too short, the structure function logarithm of the surface profile is scattered. The sampling length acting as a filter is an important part of the fractal dimension measurement. If the sampling length is too short, the evaluation of the fractal dimension will have a larger standard deviation. The continuous wavelet transform can be used to improve surface profile dimension characterization.     

Application of ANSYS 3D FEM in Studies of Surface Deformation Caused by Pipe Jacking

By using site observation data and establishing 3D model using ANSYS software,this paper has discussed the strain change of stratum stress during process of jacking-in and the im-pact of machine head on ground surface under different frontal resistances. Analysis of the two cases shows that soil pressure reaches its maximum point when the soil is right above machine head,and soil stress will gradually decline when machine head passes over it. It also shows that impact brought by pipe-jacking construction on stress change of the surrounding soil is limited. The thesis suggest that road surface should be consolidated and soil condition be improved before construction to prevent loss and disaster caused by road surface deformation,jacking force can be increased so that jacking efficiency can be enhanced when ground stratum is well filled with soil,but the frontal resistance facing machine head should be equal to surrounding soil pressure in order to avoid rise of ground surface.     

The modeling analysis of microwave emission from stratified media of non-uniform lunar cratered terrain surface for Chinese Chang-E 1 observation

In China’s first lunar exploration project,Chang-E 1,the multi-channel (3.0,7.8,19.35,37 GHz) microwave radiometers were aboard the satellite,with the purpose of measuring microwave brightness temperature from lunar surface and surveying the global distribution of lunar regolith layer thickness,and global evaluation of 3He content.To analyze the modeling of microwave radiative transfer from three-layered media of lunar surface,some factors,such as the cratered lunar surface roughness,scattering of regolith particulate medium with temperature profile,are discussed.Based on the statistics of the lunar cratered terrain and using Monte Carlo (MC) method,the cratered lunar surfaces are numerically generated.The triangulated network is utilized to divide the undulated lunar surface into discrete triangle meshes with the size 10 m as a digital surface topography.The reflectivities of each plane mesh are calculated,and the average reflectivity for all MC-realized lunar surfaces is obtained.It is found that under the spatial resolution of 30 km×30 km of Chang-E 1 radiometer observation,the lunar surface can be well modeled as a flat surface.It makes the predominance of the parameters,such as the regolith layer thickness and stratified structures,to be studied.Using the radiative transfer equation of stratified media with dense scatterers,the scattering coefficient of the regolith particulate medium is found negligible,and the emission is mainly governed by the absorptive property of the medium.Brightness temperature of multi-layered media,i.e.lunar soil,regolith layer with temperature profile and underlying rock media,are derived and calculated,and relevant main factors to affect the modeling and emission simulation are analyzed.     

Morphology observation for surface orange peel and fracture in tension sample of aluminum alloy sheet and characterization of nano hardness

The tension property of aluminum-alloy sheet with different microstructures is measured,and the surface and tension fracture morphology of tension sample with and without orange peel are observed by using scanning electron microscope(SEM).Surface roughness and nano hardness of tension sample are measured.The results show that the average elongation of the samples with orange peel is lower than that without orange peel;especially the r value of perpendicular to the rolling direction is much lower than that without orange peel.The tension surface of the orange peel samples is very rough;various parameters of surface roughness are higher.Under the observation of SEM,a wider sliding band with a micro crack on the surface of orange peel sample can be found.The various parameters of surface roughness without orange peel sample are near to zero,the sliding band is narrow and without micro cracks.The dimple width in tensile fracture of orange peel sample is larger than that without orange peel sample,but shear lip is narrower.The nano hardness testing results show that samples with orange peel behave high elastic modulus,high hardness,and high maximum load,but low plastic deformation depth.These mentioned features can completely describe surface and fracture morphology of tension samples with orange peel.     

Approach to Weighted Geometric Evaluation Based on Projection Pursuit

Weighted geometric evaluation approach based on Projection pursuit （PP） model is presented in this paper to optimize the choice of schemes. By using PP model, the multi-dimension evaluation index values of schemes can be synthesized into projection value with one dimension. The scheme with a bigger projection value is much better, so the schemes sample can be an optimized choice according to the projection value of each scheme. The modeling of PP based on accelerating genetic algorithm can predigest the realized process of projection pursuit technique, can overcome the shortcomings of large computation amount and the difficulty of computer programming in traditional projection pursuit methods, and can give a new method for application of projection pursuit technique to optimize choice of schemes by using weighted geometric evaluation. The analysis of an applied sample shows that applying PP model driven directly by samples data to optimize choice of schemes is both simple and feasible, that its projection values are relatively decentralized and profit decision-making, that its applicability and maneuverability are high. It can avoid the shortcoming of subjective weighing method, and its results are scientific and objective.     

Real Time Simulation of Large Scale Ocean Surface near the Seashore

A new wave modeling method and a level of detail (LOD) scheme are proposed for ocean surface simulation in this paper.The modeling method describes ocean wave by modifying the sine wave,and gets wave direction at any position of ocean surface under any ocean floor conditions using wave num decomposition.LOD scheme is proposed based on quad-tree block,which simplifies the ocean surface regular mesh and realizes the real-time rendering of large-scale ocean surface.Experimental results show that these methods can get realistic effect and fast rendering speed,which are appropriated to the applications of 3D games and battlefield simulation.     

Parameterization for fitting triangular mesh

In recent years, with the development of 3D data acquisition equipments, the study on reverse engineering has become more and more important. However, the existing methods for parameterization can hardly ensure that the parametric domain is rectangular, and the parametric curve grid is regular. In order to overcome these limitations, we present a novel method for parameterization of triangular meshes in this paper. The basic idea is twofold: first, because the isotherms in the steady temperature do not intersect with each other, and are distributed uniformly, no singularity (fold-over) exists in the parameterization; second, a 3D harmonic equation is solved by the finite element method to obtain the steady temperature field on a 2D triangular mesh surface with four boundaries. Therefore, our proposed method avoids the embarrassment that it is impossible to solve the 2D quasi-harmonic equation on the 2D triangular mesh without the parametric values at mesh vertices. Furthermore, the isotherms on the temperature field are taken as a set of iso-parametric curves on the triangular mesh surface. The other set of iso-parametric curves can be obtained by connecting the points with the same chord-length on the isotherms sequentially. The obtained parametric curve grid is regular, and distributed uniformly, and can map the triangular mesh surface to the unit square domain with boundaries of mesh surface to boundaries of parametric domain, which ensures that the triangular mesh surface or point cloud can be fitted with the NURBS surface.     

Preparation and oxidation characteristics of ZrC-ZrB2 composite powders with different proportions

ZrC and ZrB2 are both typical ultra-high temperature ceramics,which can be used in the hyperthermal environment.In this study,a method for preparing ultrafine ZrC-ZrB2 composite powder was provided,by using the raw materials of nano ZrO2,carbon black,B4C,and metallic Ca.It is worth pointing out that ZrC-ZrB2 composite powder with any proportion of ZrC to ZrB2 could be synthesized by this method.Firstly,a mixture of ZrC and C was prepared by carbothermal reduction of ZrO2.By adjusting the addition amount of B4C,ZrC was boronized by B4C to generate ZrC-ZrB2 composite powder with different compositions.Using this method,five composite powders with different molar ratios of ZrC and ZrB2(100ZrC,75ZrC-25ZrB2,50ZrC-50ZrB2,25ZrC-75ZrB2,and 100ZrB2)were prepared.When the temperature of boronization and decarburization process was 1473 K,the particle size of product was only tens of nanometres.Finally,the oxidation charac-teristics of different composite powders were investigated through oxidation experiments.The oxidation resistance of ZrC-ZrB2 composite powder continued to increase as the content of ZrB2 increased.     

碳/碳复合材料表面烧蚀多尺度粗糙度模拟简

通过建立碳/碳（C/C）复合材料在宏观、微观不同尺度上的烧蚀模型,利用有限元方法分析了C/C复合材料在烧蚀过程中的体积损失、表面粗糙度以及烧蚀性能的变化规律。微观上,模拟了材料烧蚀呈现的尖笋状粗糙度形貌。宏观上,采用ALE方法,并基于实验结果通过Fortran编程控制材料表面烧蚀后退运动,建立了C/C复合材料表面烧蚀的多尺度热力耦合分析模型,并进行瞬态有限元分析。结果表明：材料烧蚀表面粗糙度程度与烧蚀速率、材料性能密切相关;并且随着材料烧蚀程度的不同,材料的表面应力也相应变化。     

C/SiC复合材料摩擦性能及储油性能分析

复合材料因性能独特而备受关注,但其自身结构复杂且受到诸多因素的影响,因而对其摩擦学性能的研究仍有待进一步加强。为了对比不同摩擦配副对C/SiC复合材料摩擦性能及储油性能的影响,以C/SiC复合材料为研究对象,运用销盘摩擦学试验方法,研究了C/SiC复合材料与45#钢以及C/SiC复合材料与ZrO₂材料摩擦配副的摩擦学性能,采用三维形貌仪等仪器对C/SiC复合材料摩擦后的表面进行表征分析,研究其摩擦后的表面质量及其储油性能。结果表明,C/SiC复合材料与45#钢磨损剧烈,摩擦后表面储油性能严重下降;其与ZrO₂对磨则摩擦系数较低,磨损量较小,摩擦后的表面仍保持了较好的承载性能及储油性能,是一种良好的摩擦配副。研究结果为拓展C/SiC复合材料的应用及揭示其摩擦学特性提供了有力支撑。     

高导热碳/碳复合材料的制备

以中间相沥青和中间相沥青基碳纤维为原料, 采用碳布热压法、液相浸渍法制备了二维和三维高导热碳/碳复合材料, 且所制得复合材料的热导率分别高达443和340 W/(m·K). 依据碳/碳复合材料的热导率模型, 分析了不同结构特征参数对材料热导率的影响. 结果表明, 基体碳热导率、孔隙率以及界面相厚度均会在一定程度上影响材料的导热性能.     

激光切割表面三维形貌的分形特征

利用白光干涉仪测量激光切割碳素钢表面轮廓数据,应用分形几何学分析激光切割表面的三维形貌特征.采用盒计数法计算激光切割表面的三维分形维数.结果表明：不存在一个超越尺度范围普适的分形维数,只有当尺度r小于轮廓最大高度Ry,才表现出分形特征.对同一激光切割表面进行表征时,同尺度的Ra沿厚度方向变化波动较大,分形维数Db能够对整体表面形貌的复杂程度有着较稳定的表征.分析激光切割表面的三维形貌特征,分形维数表征激光切割表面微观结构的复杂程度,表面粗糙度可对激光切割表面轮廓高度特性进行辅助评价.     

微细铣削加工表面形貌的分形特征

微细铣削加工表面形貌特征的评价与表征对微细切削加工表面的形成机理、加工表面的形成与工艺参数之间的关系等的研究有重要意义。应用分形几何理论,采用盒计数法对微细铣削加工表面形貌进行研究。结果表明:微细铣削表面具有明显的分形特征,其盒计数维数在1.32～1.42之间,说明其加工表面形貌比较复杂,同时证明加工表面轮廓的分形维数D与表面粗糙度Ra没有相关性,进而可以从分形维数D与表面粗糙度Ra两方面对微细铣削加工表面形貌特征进行综合评价。     

碳/氧化锌纳米线阵列/泡沫石墨烯电化学检测叶酸

通过化学气相沉积法制备三维(3D)泡沫石墨烯(GF),然后利用水热合成法在泡沫石墨烯表面生长氧化锌纳米线阵列(ZnO NWAs),再利用化学气相沉积法在其表面沉积碳(C),得到碳/氧化锌纳米线阵列/泡沫石墨烯(C/ZnO NWAs/GF)复合材料.用该复合材料做电极,采用电化学方法检测叶酸(FA).结果表明,三维泡沫石墨烯具有和模板泡沫镍一样的三维孔状结构,ZnO NWAs均匀且垂直地生长在泡沫石墨烯表面,碳沉积在ZnO NWAs表面.在线性范围为0~60 μmol·L-1内,C/ZnO NWAs/GF电极检测FA时,灵敏度为0.13 μA·μmol-1·L,且在尿酸(UA)干扰下检测 FA具有良好的选择性.C/ZnO NWAs/GF电极有良好的稳定性和重复性.     

混联压电式三维椭圆振动切削过程中颤振现象的研究

三维椭圆振动辅助切削是近年来发展起来的一种很有潜力的精密超精密加工方法;其特有的摩擦力逆转和间歇切削特性不仅能有效地减少切削力,提高加工性能,理论上可以达到抑制切削颤振的目的。但是,实验中三维椭圆振动辅助切削对于颤振抑制的问题缺少相关研究;另外在不同切削条件下其本身是否具有稳定切削、防止颤振发生的能力也不得而知。为了研究三维椭圆振动切削过程中颤振现象,通过实验分析了普通切削与三维椭圆振动辅助切削过程中的时域振动信号,证明了后者对于颤振抑制的有效性;并对混联压电式三维椭圆振动切削过程中不同切削参数下的加工状态进行了划分。通过快速傅里叶变换以及计算相应切削状态下的表面粗糙度值,验证了三维椭圆振动辅助切削过程中的颤振现象。为进一步完善三维椭圆振动辅助切削技术,通过抑制颤振发生提高其加工精度以及表面质量提供了基础。     

表面纹理的参数评定研究

针对表面纹理的参数评定问题,提出了表面纹理可以从纹理图案和纹理粗糙度两方面入手加以评定的观点．重点探讨了运用三维粗糙度的几项特征参数定量地评定表面纹理问题．介绍了特征参数的计算原理、测量方法,并且对所测的数据进行了统计分析,拟定了部分纹理的参数标准,验证了采用特征参数评定表面纹理的可行性     

钠钙玻璃微磨削表面粗糙度与表面形貌

针对钠钙玻璃材料进行了一系列的微磨削实验研究,主要探讨了不同磨削因素对工件加工表面粗糙度和三维表面形貌的影响.根据微磨削加工的特点,在不同的加工条件下,分别用200#和500#两种磨粒微磨棒对钠钙玻璃材料进行三因素五水平正交试验.通过分析加工后表面粗糙度和表面形貌的变化规律,找出影响加工质量的主要因素.研究结果表明:主轴转速与进给速度是影响表面粗糙度和三维表面形貌的主要因素,磨削深度对其影响不大,为今后提高微磨削加工的表面质量以及微磨削领域的深入研究提供了参考.     

线切割加工SiCp/LY12复合材料的试验研究

研究了电参数对电火花线切割加工SiCp/LY1 2复合材料的切割速度和表面粗糙度的影响 ;用扫描电镜分析了复合材料线切割加工表面的SEM形貌。试验结果表明 :峰值电流和脉冲宽度对切割速度和表面粗糙度有较大的影响 ,其次是加工电压 ;脉冲间隔对表面粗糙度影响不大 ,当其达到一定程度时 ,表面粗糙度基本不受其影响 ;选用较大的峰值电流和较短的脉冲宽度 ,可对复合材料进行较理想的电火花线切割加工。