Reorientation of short steel fibres during the flow of self-compacting concrete mix and determination of the fibre orientation factor

A simple method has been developed to assess the orientation and distribution of short steel fibres in self-compacting concrete mixes during flow. The flow of self-compacting fibre reinforced concrete has been simulated using three-dimensional Lagrangian smooth particle hydrodynamics (SPH) which is simpler and more appropriate to use to simulate the flow and to monitor the distribution of fibres and their orientation during the flow. A probability density function (PDF) has been introduced to represent the fibre orientation variables in three dimensions. Moreover, the orientation variables of each individual fibre in an arbitrary two dimensional cross-section have been calculated using the geometrical data obtained from the three dimensional simulations. From these a new definition of the fibre orientation factor has been introduced and a method proposed for its determination from the fibre orientations monitored during the simulations. It is shown that this new definition gives results that are consistent with the expected reorientation of fibres towards the principal direction of flow. A method has also been proposed for its determination from image analysis on cut sections.     

Recolouring digital textile printing design with high fidelity

An algorithm of recolouring of polychromatic digital textile printing images is proposed based on the investigation of texture and colour distribution in different channels and image segmentation. A polychromatic image is first separated into monochromatic regions based on watershed transformation in CIELAB colour space. The initial markers are selected by hierarchical histogram analysis to eliminate the inherent drawbacks of over-segmentation in the watershed algorithm. Then the individual monochromatic regions can be mapped with different colours to obtain desirable designs. The artefacts in the boundaries of different regions are reduced by a technique of colour mixing through Gaussian blurring. The experimental simulation results indicated that the performance of the algorithm was quite good in both texture and colour fidelity.     

Geometrical range of microscopic stress distribution change due to fibre array irregularities for thermally and transversely loaded CF/epoxy composites

Abstract

A detailed numerical investigation has been carried out to investigate the effect of local fibre array irregularities on microscopic interfacial normal stress for transversely loaded unidirectional carbon fibre/epoxy composites with random fibre arrangement. Linear elastic finite element analyses were carried out for a two-dimensional image based model composed of 70 fibres. One fibre in this image based model is replaced with resin as the resin equivalent fibre, and the resulting change in microscopic interfacial normal stress distribution is investigated. Three fibres are selected for the resin equivalent fibres to clarify the individual local geometrical irregularity. Calculations were carried out for three loading conditions: case A, cooling of –155 K from the curing temperature; case B, transverse loading of 75 MPa chosen as an example of macroscopic transverse fracture strength and case C, both cooling from the curing temperature and transverse loading of 75 MPa. The effect of fibre array irregularities on the interfacial stress state is limited to the region between the resin equivalent fibre and its first neighbouring fibres. The contribution of the second neighbouring fibre is small and that of further fibres is negligible.     

An unsupervised method for dominant colour region segmentation in yarn‐dyed fabrics

This paper presents a novel unsupervised approach to detect dominant colour regions standing out conspicuously in yarn‐dyed fabric images. For a dominant colour region of a yarn‐dyed fabric, measured by an imaging system, its individual yarn has an irregular three‐dimensional shape resulting in significant colour difference among pixels of the yarn. This difference leads to difficulty in segmenting yarns into dominant colour regions. A probabilistic model is proposed in this study to associate the colour of a dominant colour region with the colours of its yarns. Based on this model, the colour histograms of a dominant colour region are first estimated from those of yarns in a yarn‐dyed fabric image. Then, a hierarchical segmentation structure is devised to detect dominant colour regions in the image. Experimental results show that the proposed approach achieves satisfactory performance for dominant colour region segmentation in yarn‐dyed fabric images, with high computational efficiency.     

A smoke segmentation algorithm based on improved intelligent seeded region growing

Image segmentation method based on region growing has the advantages of simple segmentation method and complete segmentation target. Because the color discrimination and gray gradient of smoke are not obvious, the traditional region growing segmentation method is difficult to separate it from the image, resulting in an unsatisfactory segmentation effect. To solve this problem, this paper partially improved the region growing method and proposed a new smoke segmentation algorithm based on the improved intelligent seeded region growing (IISRG) method. First, smoke images obtained from experimental videos were converted from the RGB color space to the HSV color space, and image binarization was achieved using background subtraction with an adaptive threshold in the V channel. Then, a pixel in the binary image was selected intelligently as the seed point, which was used for the regional growth. The final smoke segmentation images were obtained by the morphological processing of region growing images. Experimental smoke segmentation results show that the proposed algorithm has a higher overlap rate and a lower overflow rate, and performs a better smoke segmentation effect compared with the other two approaches. In addition, this algorithm can also effectively solve the problems of under‐segmentation and over‐segmentation of smoke images.     

用图象分析技术测PAN纤维的直径及分布

采用图象分析技术来测定PAN原丝的直径及直径分布,通过计算机软件来进行图象的处理和计算,可提高测量精度,减少人为因素;因测量及数据处理速度快,可大大增加统计的样本量,使测量值更接近于真值,统计的结果可靠。本实验测定了国内(J_3k)、国外(E_3k)两种PAN纤维的直径及直径分布。结果表明,虽然两种纤维的直径相近,但直径分布不同,作为制取碳纤维的原丝,直径分布集中对提高碳纤维性能,降低不匀率更为有利。     

Change in the supermolecular structure of highly oriented fibres under the action of epoxy binders or their components

Conclusions The effect of the epoxy binders ÉDT-10 and ÉKhD, and of their components, on the structure of highly oriented amorphous poly-p-amidobenzimidazole (PABI) and of amorphous-crystalline poly-p-phenylene terephthalamide (PPTA) fibres has been examined; it was investigated by the large-angle x-ray diffraction method.It has been found that for PPTA fibres, a surface interaction with ÉDT-10 binder and its components is characteristic; but for PABI fibres, diffusion of the components into the bulk of the fibre and a change in its structure is characteristic.On interacting with both types of fibre, ÉKhD resin and the binder based on it impair the fibre structure.Translated from Khimicheskie Volokna, No. 1, pp. 36–37, January–February, 1984.     

基于快速曲波变换的陶瓷显微图像处理

陶瓷内部结构信息对于陶瓷质量分析、生产工艺控制是非常重要的。由于陶瓷显微图像在采集和传输过程中不可避免地要受到光照分布不均匀、电子噪声等干扰因素的影响而使得图像的质量变差。需要首先对其进行去噪、增强处理,然后才能进行图像分析。曲波变换是在小波变换的基础上发展起来的一种新的多尺度分析方法,比小波更加适合分析二维图像中的曲线或直线状边缘特征,而且具有更高的逼近精度和更好的稀疏表达能力。快速曲波变换理论的提出也使得其理论更易理解和实现。因此,提出了一种基于快速曲渡变换的图像去噪、增强方法,并将其引入陶瓷显微图像的处理中,然后按照分水岭算法进行粒度分割,得到陶瓷粒度分布的统计结果。实验结果表明,该方法是可行的,并且效果良好。     

机器视觉在小型管道探伤中的应用研究

设计了针对小型管道内部缺陷检测的螺旋管道机器人系统,基于该机器人系统提出了图像处理的改进算法。首先采用结合中值滤波思想的双边滤波器,解决了双边滤波无法去除孤立噪声点的问题;其次采用了二维最大熵的阈值分割方法进行图像分割;最后根据管道缺陷的特点提取适合分类器分类的代表特征点进行分类。仿真研究表明:所提算法能够更加完整地提取缺陷信息。     

三维图像特征点匹配与拼接

随着三维图像在生活中的广泛应用,三维图像处理技术逐渐成为研究的热点。不同的三维图像匹配技术在不同的应用领域具有各自的优点及不足。本文基于对几种主要的三维图像拼接算法如迭代最近点算法（ICP）、穷举搜索算法、标准化匹配算法、Spin Images描述算子及积分卷机描述算子的分析,提出了一些相应的优化方法,可为相关学者提供参考。     

Structure of Coreless, Long Silicon Carbide Fibres and Aluminum—SiC Composites

Using electron microscopic, x-ray, and sorption methods, the internal structure, surface, and porosity of coreless silicon carbide fibres and composites were investigated. A model of the interaction at the aluminum melt —SiC fibre interface was proposed. The effect of low-temperature annealing on the structure and properties of domestic and Japanese coreless silicon carbide fibres was observed. The reaction rate in composites reinforced with domestic annealed fibres decreased.     

Effect of short fibers on residual permeability and mechanical properties of hybrid fibre reinforced high strength concrete after heat exposition

Mechanical and permeability performance of fibre reinforced high strength concrete after heat exposition were evaluated in the experimental study. Cylindrical concrete specimens were exposed to heat with the rate of 10 °C/min of up to 400 °C. In order to study the effect of short fibres on residual performance of heated high strength concrete, polypropylene and steel fibres had been added into the concrete mix. The melting and vaporization of its fibre constituents were found to be responsible for the significant reduction in residual properties of polypropylene fibre reinforced high strength concrete. In terms of non-destructive measurement, UPV test was proposed as a promising initial inspection method for fire damaged concrete structure. Furthermore, the effect of hybrid fibre on the residual properties of heated fibre reinforced high strength concrete was also presented.     

炭素材料X射线图像的缺陷区域提取

针对炭素材料X射线检测图像的特点，对其缺陷提取技术进行了研究，设计了目标边界提取算法和基于小波变换的图像增强算法。鉴于图像边缘特征易受噪声影响，而区域特征受噪声影响要小得多，提出利用数学形态学和最佳阈值分割相结合的方法来实现缺陷区域提取。实验结果表明，该法受噪声影响较小，能较好地实现缺陷的自动提取与分割，为进一步的缺陷特征参数的提取与选择奠定了良好的基础。     

中值改进的分割算法在钢缺陷检测中的应用

针对压力钢管内壁表面缺陷图像在直方图呈偏态或重尾时图像分割效果差的问题,在传统的图像分割思想的基础上,提出了一种基于灰度中值和灰度平均离差分生成图像最佳分割阈值主变量的改进算法。实验结果表明,改进后的算法对于能够稳定有效地分割压力钢管内壁正常部位与缺陷部位,并将缺陷部位的细节特征增强显示,为后续分析缺陷原因提供了很好的形态学依据;显示了其在化工设备的完整性检测技术中的应用意义。     

An integrated approach for modelling the tensile behaviour of steel fibre reinforced self-compacting concrete

The present work resumes the experimental and numerical research carried out for the development of a numerical tool able of simulating the tensile behaviour of steel fibre reinforced self-compacting concrete (SFRSCC). SFRSCC is assumed as a two phase material, where the nonlinear material behaviour of SCC matrix is modelled by a 3D smeared crack model, and steel fibres are assumed as embedded short cables distributed within the SCC matrix according to a Monte Carlo method. The internal forces in the steel fibres are obtained from the stress–slip laws derived from the executed fibre pullout tests. The performance of this numerical strategy was appraised by simulating the tensile tests carried out. The numerical simulations showed a good agreement with the experimental results.     

An adaptive color similarity function suitable for image segmentation and its numerical evaluation

In this article, we present an adaptive color similarity function defined in a modified hue‐saturation‐intensity color space, which can be used directly as a metric to obtain pixel‐wise segmentation of color images among other applications. The color information of every pixel is integrated as a unit by an adaptive similarity function thus avoiding color information scattering. As a direct application we present an efficient interactive, supervised color segmentation method with linear complexity respect to the number of pixels of the input image. The process has three steps: (1) Manual selection of few pixels in a sample of the color to be segmented. (2) Automatic generation of the so called color similarity image (CSI), which is a gray level image with all the gray level tonalities associated with the selected color. (3) Automatic threshold of the CSI to obtain the final segmentation. The proposed technique is direct, simple and computationally inexpensive. The evaluation of the efficiency of the color segmentation method is presented showing good performance in all cases of study. A comparative study is made between the behavior of the proposed method and two comparable segmentation techniques in color images using (1) the Euclidean metric of the a* and b* color channels rejecting L* and (2) a probabilistic approach on a* and b* in the CIE L*a*b* color space. Our testing system can be used either to explore the behavior of a similarity function (or metric) in different color spaces or to explore different metrics (or similarity functions) in the same color space. It was obtained from the results that the color parameters a* and b* are not independent of the luminance parameter L* as one might initially assume in the CIE L*a*b* color space. We show that our solution improves the quality of the proposed color segmentation technique and its quick result is significant with respect to other solutions found in the literature. The method also gives a good performance in low chromaticity, gray level and low contrast images. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 156–172, 2017     

Tensile deformation of regenerated and native cellulose fibres

The tensile deformation of well-oriented cellulose fibres has been reexamined. It is demonstrated that not only the fibre structure but also the deformation mechanism is similar to that found in high performance aramid fibres. An explanation is proposed for the difference between the elastic moduli of cellulose I and II. In view of these results it is possible to assess the prospect for improving the mechanical properties of cellulose fibres.     

Structural and thermal characteristics of polyacrylonitrile fibres as raw material for production of carbon fibres

Three samples of polyacrylonitrile fibres used for production of carbon fibres were investigated by x-ray diffraction, differential scanning calorimetry, and thermogravimetry. It was found that spinning of polyacrylonitrile fibre with the thiocyanate method ensures a smaller crystallite size, while the composition of the copolymer affects the thermogravimetric parameters.     

Compressive behaviour of rigid rod polymer fibres and their adhesion to composite matrixes

Abstract

The deformation behaviour of the new high performance polymer fibres, poly(p-phenylene benzobisoxazole) (PBO) and polypyridobisimidazole (PIPD) and their adhesion to an epoxy composite matrix have been investigated. Both fibres give well defined Raman spectra, and the deformation micromechanics of PBO and PIPD single fibres and composites were studied from stress induced Raman band shifts. Single fibre stress-strain curves were determined in both tension and compression, thus providing an estimate of the compressive strength of these fibres. It was found that the PIPD fibre has a higher compressive strength (~1 GPa) than PBO (~0·3 GPa) and other high performance polymer fibres, because hydrogen bond formation is possible between PIPD molecules. It has been shown that when PBO and PIPD fibres are incorporated into an epoxy resin matrix, the resulting composites show very different interfacial failure mechanisms. The fibre strain distribution in the PBO-epoxy composites follows that predicted by the full bonding, shear lag model at low matrix strains, but deviations occur at higher matrix strains due to debonding at the fibre/matrix interface. For PIPD-epoxy composites, however, no debonding was observed before fibre fragmentation, indicating better adhesion than for PBO as a result of reactive groups on the PIPD fibre surface.     

Effect of stretching temperature on structure and properties of polyethylene terephthalate (lavsan) fibre

Conclusions 1. With an increase in the stretching temperature up to a definite limit (170°C) the tensile strength of PETP and other fibres from crystalline polymers increases. However, at higher temperatures (230°C) the strength diminishes. This is evidently due to a reduction in the density of the intercrystallite regions of the fibrils, in which there is greater probability of polymer failure originating. Such behaviour of fibre made from PETP at elevated stretching temperatures is evidently associated both with the polymer structure and with its low molecular weight.2. For the preparation of a PETP fibre with high mechanical strength high orientation is a necessary but not sufficient condition; the fibre must be strengthened at these temperatures in order to form dense intercrystallite regions in the fibre fibrils together with a high degree of orientation.May we express our gratitude to Yu. A. Zubov and V. I. Selkhova (L. Ya. Karpov Physico-Chemical Scientific Research Institute) for the x-ray determination of the structure of the fibres investigated and also for the interest shown in discussions on the present.All-Union Synthetic Fibre Research Institute. Translated from Khimicheskie Volokna, No. 3, pp. 43–45, May–June, 1969.