三维编织复合材料预制表面图象计算机分析系统

介绍了三维编织复合材料预制件表面图像检测与纹理分析的基本原理。该系统以ＣＣＤ为传感器,与微型计算机连接,进行三维编织复合预制件表面编织角的检测。本系统对改善三维编织复合预制件的加工工艺具有指导作用,同时也为纺织复合材料新的性能指标建立提供了有利条件,为纺织复合材料在各个领域的广泛应用提供理论基础。     

三维编织复合材料预制件表面图象滤波与纹理分析研究

首先介绍了三维编织复合材料预制件表面图象的采集方式、滤波技术以及平均编织角的测试过程;然后介绍了采用基于边缘方向判决的自适应滤波器对采集的三维编织复合材料预制件表面图象进行滤波和边缘提取以及对处理后的预制件图象进行纹理分析,而得到功率谱图的方法。通过纹理分析方法对预制件的滤波图象进行平均编织角测量的结果,及通过标准图象验证了系统的可行性试验结果说明,系统具有较高的精度,是一种行之有效的测量三维编织复合材料预制件平均编织角的新方法。     

编织复合材料预制件花节长度的自动化测量系统实现

花节长度是复合材料编织体的一种重要的参数,为了进一步研究三维编织复合材料的性质,提出了一种可行的、能够自动测量三维编织复合材料预制件花节长度的技术,实现了一套自动化的测量系统;系统的实现基于一种小波变换的多分辨率分析,整个过程完全自动化并且与图像象素点的灰度值信息、象素点的小波变换的模极大值密切相关,并通过在碳纤维和玻璃纤维预制件上进行实验,得出了编织花节长度的不均衡能够影响预制件及其复合材料的机械性能的结论.     

三维编织复合材料几何成型算法及仿真研究

本文总结广泛应用的四步编织法工艺中携纱器的运动规律,建立了纺织工艺参数与几何结构参数之间的数学模型,针对四步法编织工艺的特点提出了固定网格法来分步模拟。首先解决了方形四步编织工艺算法的设计,然后分析了方形四步编织工艺和圆形四步编织工艺的异同点;最后实现了三维编织预制件的几何成型仿真。     

三维编织结构的计算机图形显示

通过计算机图形建模解决了三维编织复合材料内部编织结构分析困难的问题,从而便于进行下一步编织复合材料力学性能的分析,同时针对三维编织复合材料中目前较为流行的一种编织工艺－四步法,提出了一种定量描述三维编织物内部复杂杂造的方法,即首先利用计算机绘制三维实体模型来模拟织物内部各纱线的空间位置,并用动画显示纱线的运动过程,从而能够方便直观地观察到各纱线具体走向,进而通过对已生成的三维实体模型完成简单的操作     

基于小波变换的复合材料预制件花节长度测试研究

讨论了小波变换在复合材料预制件花节长度测量中的应用技术,建立了花节长度自动测量系统。该系统基于小波变换的多尺度分析,通过合理选择小波基,对预制件表面图象进行处理,可以得到理想图象的边缘信息。选用纹理模板,对处理后图象利用相关算法计算图象匹配点输出,再通过匹配点的距离可以测量预制件的花节长度。该方法与其他滤波方法的比较,证实了小波变换可以保持预制件图象的边缘特征。实验结果说明,该系统的测试结果与手工测量结果相吻合,从而还证实了小波变换用于复合材料预制件花节长度测量是可行的。     

C/SIC复合材料结构动态特性研究

针对C/SiC轻质复合材料结构,将三维编织C/SiC复合材料看作是组分材料的空间结构物,由有序的细观结构单胞叠合而成.采用细观结构单胞作为离散单元对三维编织复合材料结构进行宏观网格剖分,利用有限元方法研究复合材料悬臂板动态特性.计算结果与理论值符合较好.     

试析三维四步法编织复合材料结构的计算机仿真

本文主要对四步法编织技术的特点进行了分析,并根据其编制的特点在计算机相关软件模拟了编制纱线的运 动轨迹,采用计算机图形技术显示出三维编织的结构,利用计算机将三维四步法编制复合材料的设计和实现过程模拟出来。 以编织工艺参数的关系为依据,在计算机软件中设置仿真参数,以便于各种尺寸和编制角的三维编织模型的生成,这种计算机 模拟方法能够让模型无限接近编织物的真实结构。     

两种复合材料几何建模算法

复合材料几何模型可用于计算其物理性能和力学性能.对于随机分布的椭球颗粒复合材料和三维编织复合材料提出几何建模方法.首先针对随机分布颗粒为椭球的情况进行了阐述,对现有生成椭球颗粒分布样本的方法进行改进,消除了随机颗粒重叠的情况;为了应用多尺度有限元方法,对单胞边界之外的椭球进行处理,得到基体和增强体的边界.另外,针对三维四向编织方法,在纤维束不重叠并尽可能排列紧密的情况下给出了构建每根纤维束的运动规律.最后通过实例验证了该方法的有效性.     

基于MSC Patran参数化建模的飞艇蒙皮织物面内刚度预测

为研究飞艇蒙皮PBO织物的编织单胞并优化编织方案,假设单胞为宏观均匀的复合材料,基于MSC Patran,借助PCL建立参数化2D平纹织物模型,并分析编织纤维间隙、编织纤维截面夹角和树脂层厚度等参数与面内刚度的关系.结果表明,降低编织纤维间隙、减小编织纤维截面夹角、减薄树脂层厚度,可以提高织物面内刚度. 该模型及其模块可以拓展MSC Patran的功能,所开发的程序可为该类材料的编织设计提供便捷的开发工具.     

Computational analysis of fatigue behavior of 3D 4-directional braided composites based on unit cell approach

The fatigue behavior of 3D 4-directional braided composites was investigated based on the unit cell approach. First, the unit cell models of 3D 4-directional braided composites with different braiding angles and fiber volume fraction were built up using ABAQUS. Then, the fatigue behavior of the 3D 4-directional braided composites was analyzed, and the effect of fatigue loading direction on the fatigue damage evolution and fatigue life was studied. Finally, the effect of braiding angles and fiber volume fraction of the unit cell on the fatigue behavior of 3D 4-directional braided composites was analyzed. These results will play an important role for evaluating the fatigue behavior of 3D 4-directional braided composites in engineering.     

Processing of fiber architecture data for finite element modeling of 3D woven composites

An efficient procedure to process the textile simulation data and generate realistic finite element meshes of woven composites is proposed. The textile topology data in point cloud format is used to identify individual yarns, interpolate their cross-sectional contours, and generate smooth yarn surfaces. A robust algorithm to repair possible interpenetrations between yarn surfaces is developed and implemented in MATLAB. A 3D finite element mesh of the unit cell of composite material is generated based on the obtained yarn surfaces. The anisotropic material properties of the constituents are assigned with proper orientations.The procedure is successfully applied to generate four finite element models with 1–10 million degrees of freedom. The models are used to predict effective elastic properties of an orthogonal 3D woven composite. The sensitivity of results to the level of finite element discretization is investigated.     

Exploiting the structural reserve of textile composite structures by progressive failure analysis using a new orthotropic failure criterion

In this paper, a novel orthotropic layer based failure criterion for modelling progressive failure of non-crimp fabrics is presented. The strength parameters and stiffnesses needed for this failure criterion are obtained from virtual material tests. Therefore, a finite element multiscale algorithm is used to model the effect of lower scale inhomogeneities on macroscale material behavior. With this multiscale approach it is possible to make predictions for one single layer within a textile preform solely from the knowledge of the mechanical behavior of the constituents fiber and matrix and from the textile fiber architecture. The obtained stiffnesses and strengthes for one textile layer are used as input data for the novel orthotropic failure criterion presented in this paper. In order to show the workability of this failure criterion, finite element simulations of coupon tests and of a three-point bending test of a textile composite are shown and compared to experimental data.     

基于II三维重建的facet-braiding现象分析

三维全景图像技术(Integral Imaging,简称II)是一种能够记录和显示全真三维场景的图像技术。该技术采用微透镜阵列记录空间场景,空间任意一点的深度信息只需通过一次成像即可直接获得。Facet braiding是三维全景图像中一种很重要的视觉现象,该现象造成图像失真,影响了图像的观看效果。Ref. 6中Martine} Cuenca从单个元素图像的角度对该现象进行了分析,现从三维重建的角度对该现象的出现与否进行对比验证。先用光学软件模拟深度优先、参考平面在无穷远处的传统II成像系统,然后在该模拟系统中进行对比实验,结果并未出现Ref. 6中提到的facet braiding现象。该结果对II的视角分析、物体的精确三维重建及空间分辫率分析具有重要意义。     

Micromechanics of braided composites via multivariable FEM

A new method for micromechanical properties of three-dimensionally braided composite materials via homogenization theory and incompatible multivariable FEM is proposed in this paper. An incompatible displacement element and a hybrid stress element are developed to model the effective mechanical properties of three-dimensional textile composites. Some illustrative applications are presented for a typical class of four-step braided composites. Results of the hybrid stress element approach compare more favorably with the experimental data than other numerical methods widely used.     

3D woven composite design using a flattening simulation

Fiber composite materials have unique, advantageous mechanical properties that have made them highly desirable in a range of industries. In particular, 3D woven-fiber composites are highly resistant to delamination compared with laminated 2D woven-fiber composites and have been adopted in various advanced products. This paper focuses on the design of 3D woven-fiber composite products and proposes a flattening simulation method for designed 3D models with constant thickness. The proposed method estimates the shape of a flat material and the fiber directions in the 3D model design; deformation phenomena of 3D woven-fiber materials are also considered in order to improve the accuracy of the proposed method. CT images are used to compare the simulation results with the actual deformation of 3D woven-fiber materials and confirm the ability of our method to effectively design the fiber direction base on the 3D model and to estimate the shape of flat materials.