Compression after low-velocity impact (CAI) properties of multistitched composites

The objective of this work was to investigate compression after low-velocity impact (CAI) properties of a multistitched composite. It was found that the CAI strength of the multistitched composite was high compared to the unstitched composites. In addition, stitching density, stitching type, stitching direction, and stitching fibers were found to be important structural parameters. The CAI load on the multistitched composites resulted in lateral damages near the impacted indentation region. The structures showed large damaged areas, but the out-of-plane layer delamination was confined to relatively small areas. Thus, the multistitching enhanced the CAI properties of the composite.     

Testing of large optical surfaces with subaperture stitching

Based on our previously proposed subaperture stitching and localization (SASL) algorithm, we present strategies and a prototype for testing of large optical surfaces with subaperture stitching. First, several strategies are introduced to deal with new problems when applying the SASL algorithm to large surfaces. The uncertainty of the lateral scale of the interferometer is compensated in the same manner as that of the radii of best-fit spheres in the algorithm. Then the coarse-fine stitching strategy is proposed to stitch tens of subapertures efficiently. Second, a prototype for testing of large surfaces with subaperture stitching is developed with a welded structural base. The model of kinematics is built to determine the initial configuration of each subaperture, according to the records of nulling motion. The uncertainty of linear motion is required to be no more than 1 mm, taking advantage of the large range of convergence of the SASL algorithm. Finally we present an experiment to verify the validity of the method and the prototype. A spherical surface is tested and successfully stitched with 37 subapertures.     

基于尺度不变特征变换特征的显微图像在线拼接方法

为解决显微镜观测视野狭小的问题,提出了一种基于尺度不变特征变换(SIFT)特征的显微图像自动拼接方法.该方法充分考虑了显微图像采集过程以及显微图像自身的特点,通过一系列适用于显微图像拼接的算法,控制单幅图像拼接时间在1秒内,进而可以保证显微图像拼接随图像采集在线完成,同时,利用SIFT特征匹配准确度高的优点,可达到亚像素级的拼接精度.该方法拓展了显微镜的应用,尤其适用于生物和医学显微图像观测.     

复合材料开口缝合补强结构力学性能实验研究

对复合材料开口缝合补强结构进行了实验研究,测试了不同缝合参数(针距、行距、边距、单重和双重缝合)补强的含孔复合材料层板的拉伸强度,研究了孔边应力集中、应变集中对强度、刚度等力学性能参数的影响,分析讨论了孔边及邻近区域应变集中及应变分布的规律,比较全面地揭示出不同缝合参数补强的试样孔边应变随载荷的变化规律。结合实验结果和分析讨论,给出较为合理的孔口缝合补强设计参数。     

纤维缝合结构对夹芯结构复合材料力学性能的影响

通过RTM工艺成型了点阵增强夹芯结构复合材料,研究了纤维缝合结构对复合材料平压及侧压力学性能的影响,并探索了侧向压缩载荷下夹芯结构复合材料的破坏模式。结果表明,采用纤维缝合的方式可显著提高夹芯结构复合材料的力学性能。双向增强夹芯复合材料在长度和厚度方向上的侧压强度和模量相同,单向增强的侧压强度和模量表现出方向性,且长度方向上的模量明显高于宽度方向的。     

利用鱼眼镜头生成全景图像的方法

介绍了一种利用鱼眼镜头在特殊角度下所拍摄成的图像,以优化的快速展开模型为基础,经过像点坐标变换、双三次插值及内部拼接,生成全景图像的方法。该方法无须运用多幅标准照片拼接,且无须运用柱面模型及成像仪器的参数。最后从MATLAB仿真的实例中验证了此方法的有效性。     

Nanopattern fabrication by tip plowing technology on 55 nm grating with stitching image method

An appropriate calibration positioning method is imperative to examine localized tip on nanoscale patterns for scanning probe microscopy (SPM). This paper is to develop a new nanofabrication processes for AFM tip positioning with image stitching method in tip plowing technology. Moreover, this paper adjusts the set-point amplitude (A(sp)) to develop the tip plowing technology for fabricating nanopattern on 55 nm grating gage of a silicon substrate. The developed image stitching program is based on an iterative closet point (ICP) algorithm which has six degrees of freedom alignment. A closed-loop piezo motor is used to tip approach and plow in Z-axis. Experimental result of fabricating nanobagua on 55 nm grating of silicon substrate show that the developed positioning processes with image stitching method verify the feasibility of repeatability for the tip plowing technology successfully. This developed method can be further performed by a commercial atomic force microscope (AFM) with CAD/CAM. This technology can also be applied in dip pen nanolithography (DPN), SPM oxidation lithography and related fabrication technology with AFM tips.     

开口层板孔口缝合补强的有限元研究

为了研究复合材料开口缝合补强结构的不同缝合参数(针距、行距、边距、缝合线模量等)对孔边应力、应变分布的影响, 提出了一种缝合线计算模型。通过有限元模拟计算, 并结合实验结果, 分析讨论了孔边及邻近区域应力、应变的分布规律, 给出了孔口缝合参数合理的设计方法及相关结论。研究表明, 不同缝合参数对于孔边附近应力及应变集中有明显的影响。     

Design of Tailored Non-Crimp Fabrics Based on Stitching Geometry

Automation of the preforming process brings up two opposing requirements for the used engineering fabric. On the one hand, the fabric requires a sufficient drapeability, or low shear stiffness, for forming into double-curved geometries; but on the other hand, the fabric requires a high form stability, or high shear stiffness, for automated handling. To meet both requirements tailored non-crimp fabrics (TNCFs) are proposed. While the stitching has little structural influence on the final part, it virtually dictates the TNCFs local capability to shear and drape over a mold during preforming. The shear stiffness of TNCFs is designed by defining the local stitching geometry. NCFs with chain stitch have a comparatively high shear stiffness and NCFs with a stitch angle close to the symmetry stitch angle have a very low shear stiffness. A method to design the component specific local stitching parameters of TNCFs is discussed. For validation of the method, NCFs with designed tailored stitching parameters were manufactured and compared to benchmark NCFs with uniform stitching parameters. The designed TNCFs showed both, generally a high form stability and in locally required zones a good drapeability, in drape experiments over an elongated hemisphere.     

环形子孔径检测技术中测量数据的准确提取方法

环形子孔径拼接测试技术是一种无需辅助元件就能检测旋转对称大口径非球面镜的有效手段。根据该技术的检测原理及基于Zemike多项式的“拼接”算法,提出了一种相应的环形子孔径数据提取方法。该方法基于商用相移干涉仪的CCD成像系统和其数据处理软件提供的Mask编辑功能,利用被测镜面上方的三个可移动的基准标记进行绝对定位,给出了具体的实施方案。对一口径700mm、F2的抛物面主镜进行实验,研究结果表明,该数据提取方法操作简单可行,适合于加工车间的实施,取得了符合“拼接”算法需求的子孔径测试数据和对应环带的内外半径值。     

Shear and drape behavior of non-crimp fabrics based on stitching geometry

Non-crimp fabrics (NCFs) enable relatively high mechanical properties by keeping the reinforcement tows straight. Handling of those fabrics is improved by stitching the reinforcement tows together. While the stitching has little structural influence on the final part, it highly affects the NCFs capability to shear and drape over a mold during preforming. High tensile strain in the stitching yarn has been correlated to the NCF resistance to shearing and even adverse drape defects such as tow undulations. Furthermore, stitching causes the shear behavior of the fabric to be anisotropic, with different behavior in positive and negative shear. In the current study, a model based on the stitching geometry and reinforcement tow directions has been created to find the tensile strain in the stitching yarn as the NCF is being sheared. It was found that the stitch angle was the main driving stitching parameter, and that this angle could be selected so that shearing in both positive and negative directions produces no tensile strain in the stitching yarn. The model showed good correlation with uniaxial bias-extension and drape tests for NCFs with different stitching parameters. Finally, design charts are displayed which can be used to select the stitching parameters of standard industrial NCF-machines which results in NCFs with near-symmetric shear behavior and thus good shear and draping performance.     

2D Permeability changes due to stitching seams

Textile preforming is the stitching, cutting, and assembling of reinforcement textiles to enhance mechanical properties or optimize the RTM-tool loading. The stitching of the reinforcing textile has direct influence on the permeability of the preform. In this paper the influence on permeability of two different stitching patterns with five different seam distances is described. The two-dimensional permeability has been determined continuously in a matched metal tool incorporating capacitive sensors. Beforehand, the glass twill weave textile has been thoroughly evaluated to determine the permeability behavior of the textile without stitching in dependence on the fiber volume fraction and the cavity height. The paper reveals the significant influence of the stitching seam distance and the stitching pattern on the permeability values K1 and K2, the orientation angle of the flow front ellipse, and the anisotropy of the preform for two different fiber volume contents.     

长导轨直线度分段测量拼接方法研究

激光干涉仪测量超长导轨直线度时,因导轨长度超出干涉仪直线度测量范围,需分段测量后拼接,测量数据易受噪声和激光漂移等因素影响,导致拼接可能引入较大误差。通过分析拼接过程中的影响因素,结合长导轨结构特性,提出了一种将拼接公共点分布在相邻两节子导轨上,利用相邻两节子导轨夹角的稳定特性来实现长导轨直线度拼接的方法。通过仿真与实验,对比了30 m范围内的直接测量法与坐标变换拼接法的测量结果,2种方法的直线度结果相差<10μm,表明所提出的方法能有效减小拼接误差。将此方法应用于72 m导轨的直线度测量,并与电子水平仪测量方法比较,2种方法结果相差10μm,表明所提出的方法可实现高精度的直线度拼接。     

缝合复合材料的细观力学分析

采用三维细观有限元模型,研究了缝合复合材料的力学性能.模型中引入了保证单胞边界面的应力和位移周期连续的边界条件,分析了缝合对层合板面内力学性能的影响,着重考察了缝合区域内细观应力和应变的分布,以及缝合对材料弹性常数的影响,并分析了缝线附近和富树脂区应力集中的规律.算例结果表明本文方法可以有效地预测缝合复合材料的弹性性能.研究还发现,受面内剪切作用时原来单胞的平面边界不再保持平面,各层间铺设角度相差越大,单向拉伸时应力集中现象越显著.     

曲面复合材料缝合机器人自动路径规划技术

为提高复合材料预制件缝合机器人的灵活性与加工柔性,针对缝合机器人自动路径规划问题,研究了基于三维光栅扫描技术的曲面复合材料缝合机器人视觉接缝提取技术.针对三维扫描摄像机视场固定的特点,对摄像机进行标定实验,改进传统的手眼标定方法,提出一种用于求解手眼关系矩阵的四点标定新方法,建立了机器人坐标系与摄像机坐标系的位姿映射关系.经过手眼关系标定,三维光栅扫描仪采样得到的缝合预制件点云数据可转化为机器人坐标系下的点云数据坐标.进一步对采集的预制件点云数据进行接缝中心线提取,提出了一种缝合轨迹及姿态规划算法,采用三次多项式对接缝中心线进行空间曲线拟合,采用最小二乘法对缝合微切平面进行平面拟合,完成机器人操作空间前进矢量及接近矢量的计算.最后,将规划结果应用于缝合机器人的离线编程仿真与实验中.实验结果表明,该系统精度高,线迹成型良好,可以满足机器人缝合系统的要求.     

基于经验模态分解的图像拼接

对待拼接图像分别进行经验模态分解,对分解得到的第一个固有模态函数与第二个固有模态函数的叠加进行特征点提取、特征点匹配与变换矩阵的估计以实现图像的拼接,文中提出的方法有效提高了特征点匹配的正确率,具有很强的鲁棒性。在图像融合方面文中提出一种新的基于余弦关系变换的加权融合技术,在实现图像无缝拼接的同时,可有效去除拼接图像重叠区域的重影与鬼影现象。     

对亮度和平移鲁棒的彩色全景图拼接算法

目的为了实现存在纵向错位和亮度差异的彩色全景图的拼接,提出一种基于HSV颜色空间的全景图拼接技术。方法提出了一种可变特征向量匹配算法,并且结合重叠区域对应特征匹配向量相关系数最大准则遍历搜寻对应的特征匹配向量,从而找到相邻子图的重叠区域,通过加权模板对重叠区域进行加权融合实现拼接。结果新算法对全景图的拼接效果优于常规算法,拼接质量Do EM值为0.999 d B,拼接平均耗时为499 ms,融合区域有渐进渐出的效果,有效解决了拼接错位和亮度突变问题。结论该算法对彩色全景图的拼接具有很好的适应性和可重复性,对子图的大小和颜色无严格要求。不仅拼接速度快,而且拼接精度高,是一套完整地针对存在纵向错位和亮度差异的彩色全景图的全自动拼接方案。     

含分层损伤缝合复合材料层板的剩余压缩强度

基于渐进损伤方法,研究了含单脱层缝合复合材料层板在压缩载荷下的剩余强度。通过商用软件ABAQUS建立了含单脱层缝合复合材料层板剩余压缩强度计算模型,考虑了子层屈曲和分层扩展对剩余强度的影响。通过UMAT子程序实现了层板失效、层间失效和缝线失效的模拟。通过嵌入式杆单元结构模拟了缝线桥联作用及失效。采用Hashin准则及刚度折减法对纤维拉压、基体拉压失效进行了模拟。通过渐进损伤分析,揭示了缝合情况下含单脱层复合材料层板的失效机理,讨论了缝合参数对剩余压缩强度的影响。所预测的破坏模式和剩余强度结果与实验能较好地吻合。分析表明缝合可以明显提高含分层损伤复合材料层板的子层屈曲载荷,抑制分层扩展,并提高层板的剩余压缩强度。     

Self-calibrated subaperture stitching test of hyper-hemispheres using latitude and longitude coordinates

Limited by the f-number of the transmission sphere, it is impossible to test the whole surface of a hyper-hemisphere using a standard interferometer directly. This paper presents an extension of the subaperture stitching test method to hyper hemispheres. The stitching algorithm is based on the coordinate mapping from local measurement frame to a global frame, and overlapping correspondence is calculated by virtue of coordinates of latitude and longitude. The reference surface error is represented by Zernike polynomials and self-calibrated during the stitching to achieve higher accuracy. Then the stitched surface error distribution is presented by map projection. To realize accessibility to the whole surface of a hyper-hemisphere, we also propose a design for the subaperture test platform, according to the subaperture lattice design. Finally, a hemisphere and a full sphere are tested and figured, respectively, to validate the method and the experimental setup.     

Cf/Al复合材料异形件预制体制备及其力学性能研究

目的解决铝基复合材料异形件形状特征复杂,对良好的抗拉和抗剪切等使用性能有较高要求,制备难度较大等问题。方法提出了"铺层-缠绕-缝合"碳纤维异形件预制体制备方法,设计了直接式缝合、插销式缝合、整体式缝合3种成形方案,通过理论计算分析不同方案预制体的力学性能;在此基础上,采用液固高压成形Cf/Al复合材料异形件,并通过断口形貌、微观组织以及致密度的分析,解释了其力学性能提升的原因。结果根据较佳的预制体成形方法,成功制备了预制体和复合材料异形件;异形件内部未发现气孔、微裂纹等缺陷,Cf/Al复合材料拉伸强度达278MPa,较基体提高了114%。结论整体缝合法为较佳的预制体成形方案,可使构件具有较高的连接强度和定位精度;复合材料内部浸渗良好,致密度达98.59%,故该复合材料的力学性能较铝合金基体提升较多。