三维编织复合材料拉伸损伤声发射监测与显微CT表征

为了准确评估碳纤维三维编织复合材料力学行为及损伤特性,利用声发射技术对复合材料的拉伸损伤过程展开实时监测,并基于概率熵统计分析方法研究材料损伤演化所产生声发射信号的动态响应行为。此外,采用显微CT扫描技术对复合材料的内部损伤状态进行可视化表征。结果表明,声发射信号的特征能够很好地反映复合材料的破坏过程,声发射信号概率熵的演变描述了复合材料内部不可逆的损伤与失效机制。声发射结合显微CT技术能够有效地获取三维编织复合材料内部不同截面上的微观结构及其损伤特征,为该类复合材料的无损检测与寿命评估提供技术支撑。     

碳纤维复合材料孔隙分布及形貌分析研究

通过改变固化工艺制备了含孔隙的碳纤维复合材料试样,采用超声检测对试样进行了初步的孔隙检测与筛选,采用金相显微法对典型区域的孔隙率、孔隙分布和形貌特征进行统计。实验结果表明,固化压力不足和袋内真空不合适会引起复合材料内部孔隙的产生,且孔隙的分布存在必然性和随机性,孔隙形貌与孔隙率存在一定的联系。     

快速固化环氧树脂/碳纤维复合材料的性能

利用差示扫描量热分析仪研究了一种快速固化环氧树脂体系的固化工艺参数,确定了以真空辅助树脂灌注工艺制备快速固化环氧树脂/碳纤维复合材料的成型方法,并与常规固化环氧树脂体系制备的碳纤维复合材料进行对比,采用傅里叶变换红外光谱仪对两种材料的树脂基体进行了分析,考察了两种复合材料的纤维含量、孔隙率及力学性能,最后通过扫描电子显微镜观察了快速固化树脂基体与碳纤维的界面结合性。结果表明,快速固化树脂在99℃下固化6 min后固化度可达96%,能够大幅缩减碳纤维复合材料的成型时间,以其制备的碳纤维复合材料拉伸强度比常规固化环氧树脂复合材料高11.20%,弯曲强度高16.92%,纵横剪切强度高7.44%,快速固化树脂与碳纤维界面结合性良好。     

Cu＋Ni复合镀碳纤维增强堇青石基复合材料的研究

通过化学镀方法，在碳纤维表面分别镀上Ni和Cu Ni镀层，以这种表面改性碳纤维与堇青石陶瓷复合，制备表面改性碳纤维增强堇青石基复合材料；研究碳纤维，镀镍碳纤维，铜镍复合镀碳纤维的含量对复合材料的抗弯强度，尺寸变化率，密度和孔隙率等的影响规律。结果表明，碳纤维可以显著地提高材料的性能，表面改性碳纤维可以进一步提高材料性能，尤其是铜镍复合镀碳纤维的增强效果更好，其抗弯强度比基体的抗弯强度提高3．5倍，纤维与基体的复合质量较好。     

碳纳米管-水泥基复合材料的力学性能和微观结构

研究了掺碳纳米管水泥砂浆的力学性能和微观结构,并与掺碳纤维水泥砂浆的性能进行了对比。低含量的碳纳米管-水泥复合材料具有良好的抗压强度和抗折强度。用扫描电镜对碳纳米管-水泥复合材料以及碳纤维-改性水泥复合材料的微观结构进行了分析。结果表明：复合材料中碳纳米管表面被水泥水化产物包裹,同时碳纳米管水泥砂浆的结构密实。碳纤维表面光滑,在碳纤维与水泥石之间存在明显裂缝。孔隙率测试结果表明碳纳米管的掺入改善了材料的孔结构。     

碳纤维复合材料孔隙率及其检测方法

本文分析了碳纤维复合材料孔隙形成的原因,指出孔隙的定量指标孔隙率及其两种定义方法即面积孔隙率和体积孔隙率,分别阐述了孔隙对碳纤维复合材料剪切性能和弯曲性能的影响程度,同时介绍了密度测量法、吸水测量法、显微照相法三种破坏性检测法和射线检测法、超声衰减法、导波法、超声声阻抗法、极角背反射法五种无损检测法,简述两类孔隙率的检测方法的基本原理,并对两类方法进行了比较分析.     

热固性碳纤维编织复合材料C形结构隔膜成型工艺

详细介绍了热固性碳纤维编织复合材料C形结构的热隔膜成型工艺。测量了CYCOM970/PWC-T300预浸料在60~120℃不同温度下的滑动摩擦系数。采用烘箱固化和热压罐固化两种方式,进行了热隔膜预成型体的固化试验。通过对试件进行三维激光扫描,得到了C形结构隔膜成型体的厚度、回弹大小分布规律以及滑移角的大小。通过对截面进行扫描,得到了成型试件的孔隙率。     

基于CT纤维增强复合材料三维变形场的测量与分析

利用工业计算机层析技术(Computed Tomography,简称"CT")和自制的加载装置,实现了玻璃纤维增强复合材料试件三点弯曲加载过程的原位扫描,获取了不同加载阶段的CT图像。采用数字体图像相关法(Digital Volume Correlation,简称"DVC")测量分析了试件内部三维位移场和应变场,揭示了试件内部的应变演化特征及破坏机理。纤维增强复合材料内部细观结构特征可以作为变形信息的载体,实验中测量精度为0.063体素(2.8μm)。DVC获取的位移场及应变场分布能直观反映试件内部的结构特征,由横向切应变的分布显示出在试件破坏前已产生了剪切带,最终导致试件在该区域产生层间开裂。此外,由横截面位移分布验证了因横向切应力而导致截面产生翘曲的现象。结果表明,DVC法与工业CT结合所得测量结果能够直观地反映出复合材料内部结构的变形特征,为研究材料内部变形破坏及验证理论模型提供了新方法。     

复合材料孔隙率检测方法的比较研究

针对纤维增强复合材料制件中孔隙率测量的问题,采用了基于显微镜照相法的四种图像处理方法即Pho-toshop、Image Tool、Matlab和Visual C对同一图片中孔隙率的确定进行了比较研究。结果表明,使用Photoshop计算孔隙率是一种适合于纤维增强复合材料孔隙率测量的方法。     

碳纤维编织复合材料技术在羽毛球拍制造中的应用

传统材料在应用羽毛球拍制造中,耐磨性差,使用寿命短.为了解决这一问题,阐述了碳纤维复合材料在羽毛球拍制造中的应用,分析了碳纤维编织复合材料的性能优势,通过与传统材料进行对比,阐述了碳纤维编织复合材料的性能特点.探讨了碳纤维编织复合材料在羽毛球拍制造中的应用,紧接通过实验分析,与使用传统材料制作的羽毛球拍进行性能上的对比...     

Porosity,Bulk Density,and Volume Reduction During Drying: Review of Measurement Methods and Coefficient Determinations

Several experimental methods for measuring porosity, bulk density, and volume reduction during drying of foodstuffs are available. These methods include, among others, geometric dimension, volume displacement, mercury porosimeter, micro-CT, and NMR. However, data on their accuracy, sensitivity, and appropriateness are scarce. This article reviews these experimental methods, areas of applications, and limits. In addition, the concept of porosity, bulk density, and volume reduction and their evolution as a function of moisture content during drying are presented. In this study, values of initial porosity (?₀) and density ratio (β) of some food products are summarized. It has been found that ?₀ is highly dependent on the type of food products, while β ranges from 1.1 to 1.6. The possibility of calculating solid density based on food compositions has also been validated. The inter-predictions between porosity, bulk density, and volume density have been made mathematically evident.     

Breakdown phenomenon of ZnO varistors caused by non-uniform distribution of internal pores

Here, we analyzed the internal structure of ZnO varistors with X-ray micro-CT technology and showed that the porosity and pore volume at the radial edge is considerably higher than at other regions. Experimental results showed that the breakdown phenomenon usually occurs near the outer edge of circular varistors. The distribution of impulse currents applied to concentric ring electrodes indicated that the current ratio at the edge region increased as the total current increased. The pores are insulating under low electric fields and the current through the pores is almost zero. Hence, the voltage gradient at the edge region is higher than that elsewhere. Additionally, the simulation results were consistent with this assumption. The amounts of open pore defects, which showed a conductive state after break down, increased, and the proportion of the current flow through the pores increased accordingly, which lead to a local temperature rise and breakdown.     

Structure of Crack in Thermally Dried Sludge Cake

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50-60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

Structure of Crack in Thermally Dried Sludge Cake

Abstract

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50–60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

Porosity Characterization of Carbon Fiber/Epoxy Composite Using Hg Porosimetry and Other Techniques

In polymer composites, the porosity acts mainly as a stress concentrator, which has detrimental effects depending on the shape and position of the voids. Also, the presence of voids is detrimental to the mechanical properties, which results in the need for an accurate method for their characterization in terms of morphology, position, and volume fraction. The aim of this study was to establish an appropriate procedure for the measurement of voids in a polymer composite using the mercury porosimetry technique. Data were also collected using the Taguchi approach. Subsequently, the feasibility of applying the Hg porosimetry methodology was confirmed through a comparison with standard techniques. Statistical analysis was used to determine the best Hg porosimetry parameters and pressures between 203 and 231 MPa was found to generate reliable results for the maximum porosity measurement, with no dependence on other parameters. Since the Hg porosimetry, acid digestion, and optical microscopy methods provided porosity results with a statistically significant similarity, it can be concluded that all these methods are feasible for the analysis of voids. Finally, potential benefits of the proposed porosity analysis methodology were highlighted through the characterization of the void volume, position, and morphology. POLYM. ENG. SCI., 60:841–849, 2020. © 2020 Society of Plastics Engineers     

The measurement of porosity for an individual taconite pellet

The knowledge of the variability in the properties of individual taconite pellets as a function of processing conditions may lead to the improvement of the production of iron. An important property is porosity. Pellets with high porosity are desirable for the reduction to iron in the blast furnace. There is a published work describing the measurement of porosity on collections of pellets. Here I describe a method for the determination of the porosity of an individual pellet.Recent determinations of porosity have used the measurements of the skeletal volume and the envelope volume. Helium pycnometry is the method of choice for the measurement of the skeletal volume, whereas volumetric displacement of dry material is now the preferred method for the envelope volume, requiring collections of pellets. I have adapted a method of silhouettes, developed for single items of fruit, to measure the envelope volume of a single pellet. The porosities of six individual sintered pellets from a facility in North-Eastern Minnesota, USA, range from 33 to 38% with a relative uncertainty of about 1%. Certain pellets have significantly different porosities from each other. The magnitudes are comparable to published porosities on green pellets, ranging from 30 to 36%, and to fired pellets, ranging from 28-38%.     

Characterization of the pore labyrinth geometry of sea sponges imaged by micro-CT

The internal pore labyrinths of sea sponges were characterized via the analysis of 3D micro-CT images. Methods were developed to isolate and segment the pores and to extract the pore ‘skeleton’, which facilitated the measurement of local pore dimensions and connectivity. These methods were also used to characterize the bulk pore properties such as porosity and structural surface-to-volume ratios, as well as individual pathway analysis in terms of lengths, diameters, and tortuosity. Also, the role that ciliated cells (lining the pores) might play in the transport of fluids throughout the pore labyrinth was explored. It was deduced that cilia may play a larger role in the transport of fluids through smaller diameter pathways and the highly interconnected pathways of the sponge results in a robust network that can maintain nutrient delivery/waste removal in the case of obstruction of some of the pore pathways. Finally, it is discussed how the information gained from this study might be applied to design synthetic porous tissue scaffolds.     

Effects of aluminum on micro-sized pore structure of porous MoAlB ceramics fabricated via reactive synthesis

By using mixtures of Mo, Al and B powders with a molar ratio of 1/n/1 (n, 1.4–1.9 in 0.1 increments), porous MoAlB ceramic was successfully synthesized thorough activation reaction technology. The effects of aluminum content on phase transformation, volume expansion, microstructure and pore structure parameters (including pore size, porosity and permeability) were investigated systematically. With an increasement of Al content from 1.4 to 1.9, the open porosity reveals a trend of slowly increasing first and then the increment of growth rate. Meanwhile, the volume expansion, pore size and permeability show a similar trend with the open porosity. The reasons for these pore structure parameters alteration evolution are thoroughly explored. The pore forming mechanism is also investigated.     

矿井乏风低浓度瓦斯氧化数值模拟研究

针对矿井回风流中的低浓度瓦斯进行回收技术的研究,利用FLUENT软件,建立物理模型和数学模型,针对陶瓷蜂窝蓄热氧化装置的情况,对乏风中的甲烷浓度,蜂窝陶瓷的孔隙率,乏风的风量对低浓度瓦斯氧化效果的影响进行研究,研究结果表明：乏风中甲烷浓度要适中才能更好的氧化效果,浓度过大影响CH4的转化率;蜂窝陶瓷的孔隙率越大越有利于乏风中甲烷的转化;乏风量对CH4的转化有着重要的影响,风量应当适中,不宜太大或者太小。