碳纤维增强树脂基复合材料切削机理研究

碳纤维增强树脂基复合材料（Carbon fiber reinforced plastic,CFRP）在细观尺度上由纤维、树脂及界面不同相组成,在宏观尺度上呈层叠特征,具有非均质性和各向异性。CFRP切削过程的实质是在切削力、热共同作用下同时去除高强度纤维和低强度树脂的复杂过程,极易出现加工损伤。抑制加工损伤的前提是准确揭示CFRP切削机理,而揭示其切削机理的关键是分析材料去除过程。由于纤维是复合材料内部承受主要载荷的组成相,材料的去除过程主要由纤维的断裂过程决定。因此,通过分析切削过程中纤维的受力状态,以双参数弹性地基梁理论为基础,建立了虑及纤维所受法向及切向约束,且兼虑树脂及界面温变特性的单纤维切削模型,可准确表征纤维实际受力状态,实现纤维断裂过程的准确求解。研究发现：切削深度和纤维角度影响纤维变形深度,即切深越大,纤维变形深度越大,更易产生加工损伤;随着纤维角度增加,纤维变形深度减小。同时,为解决单纤维切削模型难以直接验证的难题,利用其求解得到宏观切削力理论值,通过与试验值对比,间接验证了单纤维切削模型的正确性。同时与未考虑被切削纤维所受切向约束和树脂及界面温变特性时相比,同时考虑这两个因素可使CFRP宏观切削力计算精度平均提升20%。所建立的单纤维切削模型不仅能够从细观尺度准确揭示CFRP去除机理,而且可为后续有关损伤抑制的研究提供理论依据。     

基于CFRP切削过程仿真的面下损伤形成分析

由于碳纤维增强树脂基复合材料(Carbon fiber reinforced plastic,CFRP)宏观上呈现非均质、各向异性,细观上表现为纤维和树脂的特殊混合形态,导致其制件加工过程中极易产生分层、开裂等损伤,严重影响其制件的加工精度及承载性能。研究CFPR加工损伤产生机理并以此降低加工损伤是提高其加工质量的关键。基于宏观各向异性本构、Hashin失效起始准则及损伤演化,建立了可实现任意纤维角度单向板连续动态切削过程仿真分析的直角切削有限元模型,分析了任意纤维角度CFRP单向板连续切削过程面下损伤,得到了纤维角度、切削参数、刀具结构对面下损伤深度的影响规律。具体结果:纤维角度为影响面下损伤的主要因素,随纤维角度增大,切削力增大同时面下损伤深度也明显增加;面下损伤的主要原因为切削力过大导致的基体破坏及扩展;对于135°单向板面下损伤深度随刀具前角增大呈先增大后减小的趋势。     

涂层刀具高速铣削碳纤维复合材料的铣削力研究

由于碳纤维复合材料(CFRP)的各向异性,纤维的铺层方向对其整体性能有重要的影响。本文采用斜角自由切削方法对具有12种不同纤维方向的T800、T700和T300碳纤维复合材料的切削力进行了试验研究,得出了CFRP单向层合板在不同基体类型和不同纤维方向下切削力的变化规律,并分析了纤维结构对切削力的影响机理。结果表明:基体类型对切削力的影响均匀稳定,无方向性;纤维方向对切削力的影响具有显著的方向性,对切削力影响的强弱关系为F_XF_ZF_Y。     

Thermal influence on surface layer of carbon fiber reinforced plastic (CFRP) in grinding

In this study, we investigated thermal influence on surface layer of CFRP in grinding with heat conduction analysis using grinding temperature at wheel contact area on dry and wet condition. Moreover, the thermal affected layer was analyzed through an experiment to examine the temperature of glass transition and thermal decomposition of the matrix resin that composes the CFRP used in this study. The influence of thermal effect on grinding of CFRP was verified based on observation of ground surface finish after grinding using SEM and the measurement of surface roughness. From the measurement result of DSC (Differential Scanning Calorimetry),TG-DTA (Thermogravimetry-Differential Thermal Analysis), It was found that the thermal affected layer of CFRP includes a layer in which the matrix resin is changed in quality by exceeding the glass transition temperature and a layer in which the matrix resin is thermally decomposed by exceeding the thermal decomposition temperature. In addition, it was found that the surface roughness was significantly reduced if the thermal affected layer with thermal decomposition was generated. In each grinding atmosphere, it tended to increase of grinding temperature at wheel contact area with increasing in the setting depth of cut. In the case of dry grinding, grinding temperature at wheel contact area increased up to t thermal decomposition temperature of the matrix resin. However, in the case of the wet grinding, grinding temperature at wheel contact area did not increase until thermally decomposition temperature. From the result of simulation about thermal affected layer, influence of grinding heat increased with increasing in the setting depth of cut. Ultimately, the thermal affected layer with thermal decomposition was generated in dry grinding. Moreover, from the results of SEM observation, it was confirmed that the surface finish properties deteriorated significantly due to thermal decomposition of the matrix resin in the case of Δ = 400 μm in the setting depth of cut at fiber angle θ = 0°. On the other hand, it was confirmed that the micro damage of carbon fiber was occurred in wet grinding at each setting depth of cut.     

Suppression of thermal deformation of machine tool spindle using TiC-Fe composite

The minimization of error generation in machine tool spindle is important because high-speed and ultra-precision machining are extensively utilized in industrial fields. The thermal deformation of the machine tool spindle generated by the frictional heat between the outer and inner bearings can deteriorate the machining accuracy. In this study, a TiC−SUS431 composite was fabricated using the liquid pressing infiltration method to suppress thermal deformation, and its thermal properties were obtained by thermal characteristic tests. For the transient thermal analysis with finite element analysis, the parameters of the machine tool spindle-bearing model were selected, and the boundary conditions were calculated. The temperature and thermal deformation of the analysis model were compared by applying SCM415 and TiC−SUS431 to the material of the machine tool spindle and changing the rotation speed. From the analysis results, it was demonstrated that the TiC−SUS431 machine tool spindle can improve the machining accuracy by minimizing the spindle thermal deformation.

     

Surface error decomposition for fixture development

As an integrated element of the manufacturing system of components, the machining fixture is a major contributing factor of the profile and orientation errors of component features. An effective way to control the accuracy of components is to decompose error sources and evaluate individual influential factors. This paper proposed a systematic method of error identification and calculation, in which locating error and machining error were studied. The locating error, which is the surface error generated before machining, is obtained from the calculation of the surface error based on tolerances of the locating positions and the decomposition of clamping deformation using finite element analysis (FEA). The machining error, the surface error generated from machining operations, is gained mainly from the coordinate measurement machine’s (CMMs) measurements. The surface error of multi-machining operations is investigated and the resultant surface error is evaluated against tolerance. The analysis of a sample feature of a turbine blade is provided as an example.     

某星载反射面天线结构设计

反射面天线结构是天线电气性能实现的载体和保障。文中详细阐述了某星载反射面天线的结构设计要点,重点论述了碳纤维复合材料反射面的具体结构形式和反射面及背筋的详细结构设计。建立了天线的有限元模型,进行了模态分析、正弦振动仿真分析、热变形分析。仿真分析和振动试验结果表明：该天线有足够的刚强度,满足设计要求。研究结果可以为星载反射面天线结构设计提供工程参考。     

An analytical approach to cutting force prediction in milling of carbon fiber reinforced polymer laminates

ABSTRACT

A prediction model of cutting force for milling multidirectional laminate of carbon fiber reinforced polymer (CFRP) composites was developed in this article by using an analytical approach. In the predictive model, an equivalent uniform chip thickness was used in the case of orthogonal plane cutting, and the average specific cutting energy was taken as an empirical function of equivalent chip thickness and fiber orientation angle. The parameters in the model were determined by the experimental data. Then, the analytical model of cutting force prediction was validated by the experimental data of multidirectional CFRP laminates, which shows the good reliability of the model established. Furthermore, the cutting force component of flank contact force was correlated with the surface roughness of workpiece and the flank wear of tool in milling UD-CFRP composites. It was found that surface quality as well as flank wear has a co-incident varying trend with the flank contact force, as confirmed by the observations of the machined surfaces and tool wear at different fiber orientations. So, it can be known that low flank contact force be required to reduce surface damage and flank wear.     

Shape Error Analysis of Functional Surface Based on Isogeometrical Approach

The construction of traditional finite element geometry(i.e., the meshing procedure) is time consuming and creates geometric errors. The drawbacks can be overcame by the Isogeometric Analysis(IGA), which integrates the computer aided design and structural analysis in a unified way. A new IGA beam element is developed by integrating the displacement field of the element, which is approximated by the NURBS basis, with the internal work formula of Euler-Bernoulli beam theory with the small deformation and elastic assumptions. Two cases of the strong coupling of IGA elements, ‘‘beam to beam' and‘‘beam to shell', are also discussed. The maximum relative errors of the deformation in the three directions of cantilever beam benchmark problem between analytical solutions and IGA solutions are less than 0.1%, which illustrate the good performance of the developed IGA beam element.In addition, the application of the developed IGA beam element in the Root Mean Square(RMS) error analysis of reflector antenna surface, which is a kind of typical functional surface whose precision is closely related to the product's performance, indicates that no matter how coarse the discretization is, the IGA method is able to achieve the accurate solution with less degrees of freedom than standard Finite Element Analysis(FEA). The proposed research provides an effective alternative to standard FEA for shape error analysis of functional surface.     

考虑太阳照射的地基面天线机电耦合分析

下一代深空探测的地基面天线的面精度要求达到亚毫米级,必须考虑太阳照射导致的温度的影响。针对这一问题,以"嫦娥工程"的40 m通信面天线为研究对象,根据天线的地理位置和时间日期,计算天线受到的热流密度;考虑对流、传导和辐射三种传热方式计算天线的温度分布,并用某7.3 m卡式天线设计温度试验,结果表明温度分析是有效的;将温度作为载荷计算天线的结构变形;根据天线远区的电场公式计算电性能,并提取增益损失、副瓣电平和指向误差等主要电性能指标。仿真结果表明,温度对电性能的影响不但体现在结构变形的均方根值上,更与变形的分布形式密切相关。分析的方法和结论可用于指导下一代面天线结构设计,也可供同类型面天线设计时参考。     

Thermal deformation analysis of tabbed solar cells using solder alloy and conductive film

Finite element analysis (FEA) has been carried out with the aim of understanding the thermal deformation characteristics of two solar cell configurations. One of the solar cell models is tabbed by lead-free solder, the other model by Conductive film (CF). A high temperature soldering process could weaken the bond and reduce the reliability of the cells because of the residual stress caused by the different thermal expansion coefficients of the materials. Moreover, solar irradiation generates temperature distribution across the surface of the solar cell, and the development of solar cells made of thinner crystalline silicon wafers will lead to the reduction in manufacturing costs. In this study, Finite element analysis (FEA) of the manufacturing process has been carried out using both solder and CF bonding. Three temperature cycles were applied to analyze different environmental operating conditions and understand how thermal cycles affect the residual stress during actual service conditions. This investigation provides a comparison of thermal deformations between solder and CF bonded solar cells in order to understand which offers substantial reliability in the long term. Also this study explores the effects of various thicknesses of the silicon wafer on the residual stress and deformation of the solar cells.     

基于MARC平台的连续铸轧热力耦合分析

综合考虑辊套与铸轧板的弹塑性变形对温度场和应力场的影响，建立了铝带坯双辊连续铸轧过程的二维动态热力耦合计算模型；通过热模拟试验得出了纯铝高温流变本构关系和接触热阻计算模型；在MARC有限元分析软件平台上开发了粘塑性材料本构用户子程序URPFLO．F和接触表面传热系数用户子程序UHTCON．F；采用更新的拉格朗日方法（UL法）进行分析，得出铝带坯连续铸轧过程温度场和应力场的分布。实例计算表明，所得结果与实测结果相吻合，模型和子程序能够很好地应用于连续铸轧过程的计算与研究。     

球铰刚度计算模型及靠冗余支链实现并联机床刚度的改善

以Stewart机构为例提出一种基于解析法和有限元法的刚度分析新方法。应用有限元软件模拟球铰内的非线性接触变形,将计算结果抽象成一个特征参数带入机构的刚度解析模型中,然后得到机构的刚度矩阵,以解决在解析模型中无法处理铰链刚性的问题,并采用有限元软件证实该方法的可靠性。如果在解析模型中忽略球铰变形,则整个机构的刚度解析结果将产生较大误差。在此基础上,应用该方法定量研究采用主动冗余支链对提高并联机床刚性的效果。结果表明,在一定工作空间范围内,主动冗余支链可以显著提高并联机床的刚性。     

高精度碳纤维反射器制造技术

碳纤维复合材料制件在雷达产品中的应用越来越广,文中介绍了一种获得毫米波高精度反射器的先进工艺方案。首先设计研制高精度母模和碳纤维复合材料模具,然后以该高精度复合材料模具为基础,筛选高性能、成型工艺性好的碳纤维预浸料,通过铺层设计、工艺参数优化等手段,采用热压罐法成型出高精度的碳纤维反射器,之后利用先进的真空镀膜金属化方法对反射器进行金属化。最后获得的Φ400 mm反射器的型面精度为0.039 mm,达到了毫米波的精度要求,其重量仅0.9 kg,较原铝反射器减重80%以上。     

基于三维多相有限元的CFRP细观切削机理研究

为深入揭示碳纤维增强树脂基复合材料(Carbon fiber reinforced plastic/polymer,CFRP)切削机理,针对目前宏观单相有限元方法无法直观体现纤维和基体的失效形式、切屑类型等问题,借助数值仿真方法建立了CFRP直角切削的三维多相有限元模型。测量刀具刀尖形貌,根据刀具和CFRP设计数据提取CFRP纤维、基体细观几何信息,建立直角切削细观几何模型;基于定义材料本构用户子程序(User subroutine to define material behavior,VUMAT)分别定义纤维和基体的材料本构(弹塑性、失效准则、损伤演化方式),对不同纤维方向角的三维多相CFRP直角切削模型进行仿真分析;设计直角切削试验对仿真结果进行对比验证。仿真结果直观地展示了基体和纤维的失效形式、切屑形成过程、不同情况下切削亚表面损伤深度,通过各种情况下切削力数据的分析,揭示了切削力随纤维方向角的变化规律,并通过试验验证了该有限元建模仿真方法的有效性。     

面向快速探测的坐标测量机动态误差分析

坐标测量机在快速探测时，由于惯性力和驱动力的作用，引起机体变形，从而导致了动态误差的产生。分析了引起坐标测量机动态误差的原因，建立了坐标测量机的动态误差模型。采用有限元方法分析计算了快速探测过程中惯性力和驱动力产生的动态误差，验证了动态误差模型的应用，分析结果是合理的，方法是可行性的。     

基于能量偏差的机床热变形仿真预报研究

数控机床热变形是影响其加工精度的重要因素,当前使用的热弹塑性理论、有限元分析方法以及神经网络热变形预报方法等都存在缺陷。本研究通过对一维主轴热传导差分模型的推导发现,主轴能量输入、耗散与热变形之间存在着密切的相互关系,进而将该结论进行了拓展,建立了基于反馈原理的机床能量输入、输出的热变形预报模型。实验结果表明,该模型具有相当高的预报精度。     

用缓冲层结构抑制碳纤维表面复制中的纤维印透

针对碳纤维光学元件复制过程中的纤维印透现象,提出了镍-环氧树脂-镍的缓冲层方法.以单向碳纤维材料为基底,采用传统方法制备了碳纤维-环氧树脂-银膜结构的光学反射镜;采用缓冲层方法,制备了碳纤维-镍-环氧树脂-镍-银膜的光学反射镜.用台阶仪测试了这两种光学元件在垂直纤维方向和沿纤维方向的表面形貌.结果表明,纤维印透现象主要...     

High-speed milling of CFRP composites: a progressive damage model of cutting force

Three-dimensional Hashin failure criterion and material stiffness degradation model were compiled by VUMAT subroutine. The Abaqus/Explicit solver was performed to establish progressive damage model of cutting force for CFRP high-speed milling, and high-speed milling experiments with different cutting parameters were carried out. Further, the impact mechanism of fiber cutting angle and cutting parameters on cutting force, stress, and material failure during milling was explored, and the material removal mechanism in high-speed milling of CFRP was revealed. The results show that the error between the experimental and simulated of cutting forces is less than 5%, which indicates that the progressive damage model is feasible. The fiber cutting angle has significant influence on cutting force and stress in cutting process, and the cutting direction has a significant influence on cutting force. In addition, cutting parameters play a critical role in cutting force, and the feed per tooth is the most significant factor affecting the cutting force. Simultaneously, the progressive damage model predicts that the shear failure of materials mainly concentrates in the cutting area and extends along the feed direction. Finally, the material removal mechanism of CFRP in high-speed milling was revealed combining cutting force experiment.     

主动主反射面天线促动器调整量计算与误差分析

主动主反射面天线通过调整安装在面板下方的促动器来提高表面精度,现有的促动器调整量计算方法多数忽略了面板弹性变形对调整精度的影响。文中通过力学仿真模拟来表征促动器调整过程对面板自身弹性变形的影响。首先,构建单块反射面面板变形拟合模型,并对拟合模型的权重进行优化,进而推导出整个反射面的变形拟合模型;其次,考虑到实际工程中相邻面板共用促动器,因此对促动器编号进行归并,进而推导出相邻面板共用促动器时促动器最佳调整量的计算模型。为了验证面板变形拟合模型的计算精度,分别从拟合模型的变形表征能力和促动器调整量的计算精度两个方面开展仿真验证工作,并从促动器调整误差和促动器故障两个方面分析促动器调整误差对反射面调整精度的影响,为工程中评估促动器调整精度提供参考。