Wood_1995_Composites-Science-and-Technology
A pattern recognition approach to the detection of complex edges
* Corresponding author. Email: dori@ie.technion.ac.il 0167-8655/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 01 67-8655(95)00118-9
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1. Introduction
Physical edges of the objects are fundamental descriptions of physical objects as they relate to transitions in surface orientation or texture. Edge detection is the identification of the intensity changes corresponding to the underlying physical changes. Detecting edges in a radiograph is a first step in taking measurements. Edges in radiographs differ from " c o n v e n t i o n a l " edges, because X-rays, unlike visible light, are only partially absorbed by the object they hit. The physical properties of the object and the width the X-rays must traverse before hitting the photographic film determine the brightness level of each point in the radiograph. Edges in radiographs have therefore a pattern of edge function that is more complex than the step function that models edges in ordinary images. To achieve radiograph understanding, computer systems must relate the raw input data to the physical structure that cause it, i.e., the object being radiated. Davis (1975) provides a survey of edge detection techniques prior to 1975. One of these methodes is the " g r a d i e n t " operator I g(i, j ) - g ( i + 1, j + 1) 1 + ] g(i, j + 1) - g(i + 1, j) 1, proposed by Roberts (Davis,
工具书与文献检索试题(整理)
一、单项选择1、纸质信息源的载体是（纸张）2、逻辑“与”算符是用来组配( 不同检索概念，用于缩小检索范围 )。
3、关于搜索引擎的查询规则，正确的是：（ D ）A.引号（“”）的作用是括在其中的多个词被当作一个固定短语来检索。
B.标题检索是在网页标题中查找输入的检索词，其命令一般用“title”，其格式为title：检索式。
C.站点检索是在网站地址域名中检索输入的词，其命令一般用“host”，其格式为host：检索式。
D.以上都正确。
4、以作者本人取得的成果为依据而创作的论文、报告等，并经公开发表或出版的各种文献，称为( 一次文献. )5、中国国家标准的代码是（ GB ）6、根据国家相关标准，文献的定义是指“记录有关（知识）的一切载体。
”7、利用文献后面所附的参考文献进行检索的方法称为（追溯法）。
8、如果检索结果过少，查全率很低，需要调整检索范围，此时调整检索策略的方法有（用逻辑“或”或截词增加同族概念）等9、数据检索以特定的数值为检索对象,它包括（数据、图表、公式）10、《中国学术期刊全文数据库》的词频控制应在（文摘、全文等字段检索所得的文献量过大）场合下使用11、如果打算了解最新即时的专业学术动态，一般可参考（专业学会网站）12、（雅虎 )属于目录引擎。
13、搜索含有“data bank”的PDF文件，正确的检索式为：（ "data bank" filetype:pdf )14、就课题“查找‘钱伟长论教育’一文他人引用情况而言”，选择（中国知网中的中国引文数据库），可以得到相关的结果。
15、要从事物名称角度全面地查找互联网上的信息，可使用（主题）搜索引擎。
16、（主题检索途径）是指通过文献信息资料的主题内容进行检索的途径。
17、《中国期刊网CNKI》是（全文数据库）数据库。
18、要查找李平老师所发表的文章，首选途径为（著者途径）19、关于搜索引擎的一般查询规则，不恰当的是：（截词符通常用星号（*）表示，一般只用在词的前面。
信息检索练习题(1)
1.小王在某个数据库中检索到了50篇文献，查准率和查全率分别为40％、80％，则全部相关文档有25篇。
2.INTERNET是基于TCP/IP 协议的。
3.文件ABC.001.TXT的后缀名是TXT 。
文件类型是文本文件。
4.多数网页采用HTML编写，这里的HTML指的是：超文本标识语言。
5.目录型搜索引擎主要提供族性检索模式，索引型搜索引擎主要提供特性检索模式。
6.在使用搜索引擎检索时，URL:ustc可以查到网址中带有ustc的网页。
7.根据索引编制方式的不同，可以将搜索引擎分为索引型搜索引擎和网络目录型搜索引擎。
8.按文献的相对利用率来划分，可以把文献分为核心文献、相关文献、边缘文献。
9.定期（多于一天）或不定期出版的有固定名称的连续出版物是期刊。
10.检索工具具有两个方面的职能：存储职能、检索职能。
11.以单位出版物为著录对象的检索工具为：目录。
12.将文献作者的姓名按字顺排列编制而成的索引称为：作者索引。
13.利用原始文献所附的参考文献，追踪查找参考文献的原文的检索方法称为追溯法，又称为引文法。
14.已知一篇参考文献的著录为：”Levitan, K. B. Information resource management. New Brunswick: RutgersUP,1986”，该作者的姓是：Levitan 。
15.检索语言可分为两大类：分类语言、主题词语言。
16.LCC指的是美国国会图书馆分类法。
17.当检索关键词具有多个同义词和近义词时，容易造成漏检，使得查全率较低。
18.主题词的规范化指的是词和概念一一对应，一个词表达一个概念。
19.国际上通常根据内容将数据库划分为：参考数据库、源数据库、混合数据库。
20.查询关键词为短语"DA TA OUTPUT"，可以用位置算符(W)改写为：DA TA(W) OUTPUT 。
21.著录参考文献时，对于三个以上的著者，可以在第一著者后面加上et al. ，代表"等人"的意思。
认知心理学注意课件
自动化与注意（控制）加工
• 练习似乎可以改变完成任务时所需要注 意的程度。几乎不需要心理能量就可以 完成的任务被称为自动化任务。
• Posner & Snyder (1975)将一个任务或加 工判定为自动化的标准是：
– 没有意图； – 无意识中产生； – 不干扰其他心理活动。
Schneider & Shiffrin (1977) 实验
对AB干扰的理论解释
（1）工作记忆中维持记忆痕迹所需的容量 有限。 Chun & Potter (1995), Jolicoeur (1999) （2）维持用来指导外部行为的内部表象所 需的资源是有限的。Duncan, Ward, Shapiro(1994) （3）有限资源池理论。Shapiro, Caldwell, Sorensen (1997)
Wood and Cowen实验
衰减器理论
• Treisman(1960) 的attenuation model认为， 接收的信息要经历三种分析或检验：
– 分析刺激的物理属性； – 确定刺激是否语言，如果是，就将它们分为 音节和单词； – 识别单词并赋予意义。
• 三个阶段并非全部需要。
后期选择理论
Object-based attention: Egly et al. (1994)
图式理论
• Neisser(1976) 提出的一个完全不同的注意 理论——图式模型（schema model） • 注意如同采摘苹果，注意到的事物就是采 下来的苹果，没有注意到的事物就是还在 树上的苹果。 • 注意不是过滤器，也不是衰减器，而是熟 练的知觉。 • 拍手与传球
• Deutsch and Deutsch(1963)的后期选择模 型（late-selection model） • 所有的信息都被传送到工作记忆中，这 种传送是以平行的形式进行的。 • 在工作记忆中，依据材料的重要性做出 判断决定是被精细加工还是被遗忘。
大学生信息检索习题以及答案
《大学生信息检索概论》模拟试题一、填空题1、文献的级次分为零次文献、一次文献、二次文献、三次文献2、《中图法》有五个基本部类，分别是马克思主义、列宁主义、毛泽东思想_、哲学；社会科学；自然科学和综合性图书，在此基础上又划分为_22_个大类。
3、按内容可将计算机检索系统的数据库类型分为：文献书目型数据库、事实型数据库、数值型数据库和全文型数据库。
4、我国标准可分为国家标准、部标准和企业标准三大类。
5、在实际检索中，文献的检索方法主要有：直查法、追溯法、工具法和综合法。
6、国际标准化组织简称：ISO 、本标准每5 年修订一次二、选择题1、如果需要检索某位作者的文献被引用的情况，应该使用（ C ）检索。
A．分类索引B．作者索引C．引文索引 D．主题索引2、利用图书馆的据库检索期刊论文时，可供选择的中文数据库是（ D ）。
A．超星数字图书馆 B．万方学位论文 C．国研网 D．维普科技期刊 E.高校财经库3、如果检索有关多媒体网络传播方面的文献，检索式为（A D）。
A．多媒体and 网络传播 B．多媒体＋网络传播 C．多媒体or 网络传播D．多媒体*网络传播4、如果对某个课题进行主题检索时，可选择的检索字段有（ A D E ）。
A．关键词 B．作者 C．刊名 D．题名 E．文摘5、二次文献又称检索工具，包括：（ A C D ）。
A．书目B．百科C．索引D．文摘E．统计数据三、名词解释题1、文献用文字、图形、符号、声频、视频等技术手段记录人类知识的一种载体，或理解为固化在一定物质载体上的知识。
也可以理解为古今一切社会史料的总称。
2、体系分类语言体系语言是以科学分类为基础，运用概念的划分与概括的逻辑方法，形成一个概念等级体系，按知识门类的逻辑次序，按照从总到分，从一般到具体，从低级到高级，从简单到复杂的原则进行概念的综分，层层划分，累累隶属，逐步展开而形成的一个等级体系。
3、引文语言引文语言是根据文献所附参考或引用文献的特征进行检索的语言。
简版SpectRx近红外光谱系统课件
Incoming Inspection and Verifications 输入检验和确认
In-process Inspection
在线检测
Maintains Consistent Quality
保持品质一致性
Accuracy ( Concentration ): 0.01% 含量精确度:万分之一
Active Ingredients 活性成分 Impurities 杂质 Concentration 浓度 Homogeneity 同质性
简版SpectRx近红外光谱系统课件
6
SpectRx™ NIR
Tablets/Capsules
Diffused Reflectance 漫反射系数 Tablet Hardness 硬度 Tablet Disintegration 崩解 Tablet/Capsule Moisture Contents 湿度含量 Tablet Friability 脆性 Tablet Capsule Active Ingredients 活性组分 Tablet/Capsule Impurities 杂质 Tablet Cracks 裂纹 Capsule Deterioration 变质 Tablet/Capsule Homogeneity 药片-胶囊同质性
库）， 95％的机会可以发现一个未知的成分，除非组成的信号信噪比太小。
简版SpectRx近红外光谱系统课件
10
On Line Production 在线生产 （Including raw materials release 包括原材料放行)
简版SpectRx近红外光谱系统课件
11
Rotary Inspection in Lab (实验室旋转式检测)
杉木木材形成过程扩展蛋白基因的克隆与表达分析
纤维素纳米纤维增强聚乳酸
Cellulose nanofiber-reinforced polylactic acidAtsuhiro Iwatake,Masaya Nogi,Hiroyuki Yano *Research Institute for Sustainable Humanosphere,Kyoto University,Uji,Kyoto 611-0011,Japana r t i c l e i n f o Article history:Received 18September 2007Received in revised form 4March 2008Accepted 18March 2008Available online 26March 2008Keywords:A.FibersA.Nano compositesB.Stress–strain curvesB.Thermo-mechanical propertiesa b s t r a c tThe reinforcement of polylactic acid (PLA)using microfibrillated cellulose (MFC,mechanically fibrillated pulp,mostly consisting of nanofibers)is reported,with the goal of making sustainable ‘green-compos-ites’.The production procedure to attain uniform dispersion of MFC in a PLA compound was assessed,and then mechanical and thermo-mechanical properties of the sheets after hot-pressing of the com-pounds were studied.Needle-leaf Bleached Kraft Pulp (NBKP)and refiner-treated NBKP were also used to study the effects of filler morphology.When MFC was premixed with PLA using organic solvent and the mixture was kneaded after the removal of the solvent,the MFC was uniformly dispersed in the PLA.The MFC increased Young’s modulus and tensile strength of PLA by 40%and 25%,respectively,with-out a reduction of yield strain at a fiber content of 10wt%.On the other hand,NBKP reduced the yield strain by 30%and reduced the strength by 15%at a fiber content of 5wt%.Ó2008Published by Elsevier Ltd.1.IntroductionThe plant cell wall consists of nanofibers called cellulose micro-fibrils.Since the nanofibers are composed of extended cellulose chains forming a semi-crystalline structure,their thermal expan-sion is as low as that of quartz [1],and their tensile strength is esti-mated to be about five times that of mild steel,based on the tensile test of kraft pulp single fibers [2].Recently,we demonstrated that microfibrillated cellulose (MFC),which consists of mechanically fibrillated pulp into nano to submicron wide fibers forming a web-like network,shows much promise as reinforcement of composites [3–6].MFC sheet-molded phenolic resin composites with 80–90wt%fiber content exhibited strength equivalent to that of mild steel or magnesium alloy.Because of the high performance of these composites and the fact that cellulose nanofibers are the most abundant and renewable biomass resource on earth,MFC has attracted attention as poten-tial reinforcement of materials for use in automobiles,buildings,mobile computers,and many other products.In this study,the potential of MFC reinforcement of thermoplas-tic polymer subjected to compression and injection moldings was studied.To develop fully bioresource-based nanocomposites,we used polylactic acid (PLA)as the resin.The reinforcement of PLA using plant and pulp fibers has been studied with the aim of developing sustainable ‘green-composites’[7,8].Although the Young’s modulus of the PLA could be increased significantly with an increase of plant fiber content,the yield strain decreased,and as a result,the strength decreased.To overcomethese drawbacks,reinforcement with cellulose nanowhiskers or microcrystalline cellulose has been studied by melt extrusion com-pounding using twin screw extruders [9,10].However,since the kneading process resulted in the flocculation of the microcrystal-line cellulose and whiskers as well as deterioration of the PLA,composites exhibiting higher strength than neat PLA could not be obtained.Considering that phenol-formaldehyde (PF)resin-impregnated MFC sheet moldings demonstrated a large yield strain [4,5]and the casting film prepared from MFC and polyvinyl alcohol (PVA)solution resulted in a two-fold increase in strength over that of neat PVA along with high yield strain [11],it appears that uniformly dispersed cellulose nanofibers in PLA can increase the strength of PLA composites.Thus,we first studied the pro-duction procedure to attain uniform dispersion of cellulose nanofibers in a PLA compound,and we then found out that the prepared sheet at a fiber content of 10wt%,after kneading and hot-pressing of the compounds,exhibited 25%higher tensile strength than that of a neat PLA resin sheet without a reduction of yield strain.2.Experimental 2.1.MaterialsPolylactic acid (LACEA H-280,Mitsui Chemicals,Inc.,Japan)was used as matrix.Microfibrillated cellulose (MFC,Celish KY110G,water slurry containing 10wt%fiber,Daicel Chemical Industries,Ltd.,Japan)was used as filler.NBKP (Needle-leaf Bleached Kraft Pulp)and refiner-treated NBKP (eight passes)were also used to investigate the effects of filler morphology.0266-3538/$-see front matter Ó2008Published by Elsevier Ltd.doi:10.1016/pscitech.2008.03.006*Corresponding author.Tel.:+81774383669;fax:+81774383658.E-mail address:yano@rish.kyoto-u.ac.jp (H.Yano).Composites Science and Technology 68(2008)2103–2106Contents lists available at ScienceDirectComposites Science and Technologyj o ur na l h o me pa ge :w w w.e ls e v ie r.c o m/lo c a t e/c om p s c it e ch2.2.Preparation of PLA and MFC mixtureMFC slurry containing3gfiber was mixed with270g of acetone to make1wt%MFC suspension.When the MFC was thoroughly dispersed in the solvent by stirring,adequate amount of PLA was added gradually and stirring was kept for5h at ambient tempera-ture.The acetone and water of the mixture was evaporated under vacuum at70°C.The mixture from which water and acetone had been removed was kneaded by a twin rotary roller mixer(Labo Plastomill,Toyo Seiki Seisaku-sho,Ltd.,Japan).The compounding was carried out for12min at a rotary speed of40rpm at140°C. We hereafter call it the solvent method.As a comparison,MFC water slurry containing10wt%fiber was added directly to the melted PLA,and the mixture was kneaded at 140°C,which we hereafter refer as the direct mixing method.The compound was crushed into small pieces and compressed in a die at160°C and0.5MPa for5min followed by1MPa for another5min.The resulting sheet was0.3mm thick.Specimens 40mm long and5mm wide were prepared from the sheet.2.3.Mechanical testingTensile properties of the neat PLA and composite materials were measured using a universal mechanical testing machine(Instron 3365).The specimen gage length was20mm and the testing speed was set to1mm/min.Six composite specimens were tested for each set of samples.2.4.Dynamic mechanical thermal analysisTemperature dependency of dynamic viscoelastic properties of the composites were measured by the forced vibration method in tensile mode(RHEOVIBRON DDV-25FD,Orientec A&D Co.Ltd., Japan),with a chuck distance of20mm,preload of5g,frequency of1Hz,and heating rate of1.5°C/min.3.Results and discussion3.1.Premixing of MFC and PLA using acetoneThe tensile stress–strain curves of the sheets prepared from the compounds by the solvent method and direct mixing method are compared in Fig.1.MFC content in the sheets was5wt%.As can be seen from Fig.1,the Young’s modulus of the MFC/PLA compos-ite prepared by the solvent method is higher than that of a neat PLA sheet.In addition,contrary to the previous results of research on the microcrystalline cellulose-reinforced PLA composite[7],the MFC/PLA composites maintained the yield strain of neat PLA.As a result,the MFC/PLA composites exhibited higher tensile strength than that of neat PLA.Specifically,the average values of Young’s modulus and tensile strength of the PLA increased from3.4GPa and56.2MPa to4.3GPa and66.0MPa,respectively.Meanwhile, the MFC/PLA composites made by the direct mixing method did not show any improvement in Young’s modulus.In addition,the yield strain of the composites was smaller than that of neat PLA, resulting in the reduction of tensile strength by about10%.Fig.2shows the microscopic images of composites prepared by the solvent method and the direct mixing method.The image of the composite made by the solvent method shows that cellulose nanofibers were dispersed uniformly in the PLA,while many agglomerations were observed in the composite made by the direct mixing method.The reduction in yield strain of PLA in the latter case can be attributed to these agglomerates.The sheet prepared by the solvent method but without the kneading process exhibited a Young’s modulus of4.2GPa and a tensile strength of60.7MPa,indicating that the cellulose nano-fibers were more uniformly dispersed bykneading.Fig.1.Typical stress–strain curves comparing the solvent method,direct mixingmethod compounding,and neatPLA.Fig.2.Microscopy images of composites prepared by the solvent method(upper)and the direct mixing method(lower).2104 A.Iwatake et al./Composites Science and Technology68(2008)2103–21063.2.Effects offiller morphology on the mechanical properties of PLA compositesTo investigate the effects of microfibrillation of pulp on the mechanical properties of PLA composites,three types offiller,that is,NBKP,refiner-treated(eight passes)NBKP,and MFC were mixed with PLA by the solvent method.Thefiller content was5wt%.Fig.3shows typical morphology of thefillers.Pulp has a smooth surface with30–50l m in diameter,refiner-treated pulp has a fibrillated surface with a diameter similar to pulp and MFC is com-pletely disintegrated into nano to submicron widefibers forming a network.As shown in Fig.4,the addition of pulp slightly increased the Young’s modulus,but reduced the yield strain by30%and reduced the strength by15%.Thefibrillation of the pulp’s surface(refiner-treated)improved the Young’s modulus as well as the yield strain, resulting in strength increase by10%.Significant improvement was observed in the MFC-reinforced PLA.Since MFC attained the in-crease of Young’s modulus,as much as25%,without a reduction of the yield strain,the strength improved by20%compared to neat PLA.It should be emphasized that the reinforcement of refiner-treated pulp slightly increases the Young’s modulus of PLA, whereas MFC increases Young’s modulus of PLA by25%,as shown in Fig.4.Favier et al.[12]studied the effect of cellulose nanowhis-ker reinforcement of latex of poly(styrene-co-butyl acrylate)and found that the presence of percolated nanowhiskers,that is,the formation of a rigid network resulting from strong interactions between adjacent whiskers by hydrogen bonding,enabled effective reinforcement of the matrix and achieved a drastic increase of shear modulus at a whisker content of6wt%.Furthermore,Samir et al.[13]proved that the percolation effect is more pronounced when cellulose nanofiber is used as reinforcement due to the addi-tional entanglement effect of the elements.Thus,as can be specu-lated based on the comparison of SEM images(Fig.3),the fibrillation of pulp’s surface is not enough to create a strong network at a lowfiller content.On the other hand,microfibrillated cellulose creates afine network even at a lowfiller content such as 5wt%,restraining polymer deformation.3.3.Effects of MFC content on the mechanical and thermo-mechanical properties of PLA compositesThe effect offiller morphology indicated the importance of net-work formation in improving mechanical properties.Hence,the reinforcement effect of MFC on the mechanical and thermo-mechanical properties of PLA composites was studied as a function of MFC content.Fig.5shows the stress–strain curves of tensile test of MFC/PLA composites with differentfiber contents.As can be seen,the3wt% MFC/PLA composite showed a stress–strain curve similar to that of neat PLA.In other words,the effect of the addition of MFC could not be observed.However,5wt%MFC/PLA composites evidenced a reinforcing effect.Young’s modulus increased by25%compared to neat PLA while retaining the same yield strain of2.5%.Hence, the tensile strength of PLA increased from about50MPa to 70MPa.Similar results were observed in temperature dependency of storage modulus at1Hz(Fig.6).The storage modulus of3wt% MFC/PLA composites did not show a significant difference com-pared to PLA above100°C.On the other hand,5wt%MFC/PLA Fig.3.Filler morphology of Needle-leaf Bleached Kraft Pulp(NBKP),refiner-treated(eight passes)NBKP,and MFC.Scale bar:10lm.Fig.4.Effects of morphological changes offiller on stress–straincurves.Fig.5.Effects of MFC content(wt%)on stress–strain curves.A.Iwatake et al./Composites Science and Technology68(2008)2103–21062105composites showed a higher Young’s modulus than that of neat PLA.Additional improvements in Young’s modulus and strength were observed when the MFC content increased from 5wt%to 10wt%as shown in Fig.5.The average Young’s modulus and tensile strength of 10wt%MFC/PLA composites attained 4.7GPa and 75.0MPa,respectively,without a reduction of yield strain.It is worthy to note that the addition of 10wt%MFC could improve the Young’s modulus of PLA by 40%and the strength by 25%.However,a 15wt%or 20wt%addition of MFC made the compos-ites brittle and decreased their strength.Fracture initiating points such as flocculated nanofibers increased and dominated the mechanical properties of MFC/PLA composites.The improvement of the procedure for making high fiber content compounds is necessary to obtain further increments in strength as well as Young’s modulus of PLA.The constant storage modulus of 10wt%MFC/PLA composites above glass transition temperature (T g )of PLA,that is,from 70°C to 120°C should be emphasized (Fig.6).Similar phenomena were observed in cellulose nanowhisker reinforcement of latex of poly(styrene-co -butyl acrylate)[12]and MFC reinforcement of amylopectin-glycerol blend [14].The constant storage modulus suggests that the cellulose fiber network interconnected by hydro-gen bonds resists the applied stress independently of the softening of PLA.The result shows clearly the advantage of MFC over plant and pulp fibers in the reinforcement of thermoplastic polymer.4.ConclusionsThe reinforcement of PLA using microfibrillated cellulose (MFC)was studied to know the potential of reinforcement by a nanofibernetwork,with the goal of making sustainable ‘green-composites’.MFC was premixed with PLA using organic solvent and the mixture was kneaded to attain uniform dispersion of MFC in PLA.The uni-formly dispersed MFC reinforcement increased the Young’s modu-lus and tensile strength of PLA by 40%and 25%,respectively,without a reduction of yield strain at a fiber content of 10wt%.Fur-thermore,the storage modulus of the composites was kept con-stant above glass transition temperature of matrix polymer.MFC is a promising reinforcement of PLA composites.AcknowledgementsThe authors would like to thank Dr.A.N.Nakagaito,Research Institute for Sustainable Humanosphere,Kyoto University for valu-able suggestions.This research was supported by a Grant-in-Aid for Scientific Re-search (B)(No.1538012,2003.4–2007.3)from the Ministry of Edu-cation,Culture,Sports,Science,and Technology,Japan,and a Grant-in-Aid for Research and Development for regional innova-tion consortium (No.17S5018,2006.9–2007.3)from the Ministry of Economy,Trade and Industry,Japan.References[1]Nishino T,Matsuda I,Hirao K.All-cellulose composites.Macromolecules2004;37:7683–7.[2]Page DH,EL-Hosseiny F.The mechanical properties of single wood pulp fibres.JPulp Paper Sci 1983(September):99–100.[3]Yano H,Nakahara S.Bio-composites produced from plant microfiber bundleswith a nanometer unit web-like network.J Mater Sci 2004;39(5):1635–8.[4]Nakagaito AN,Yano H.Novel high-strength biocomposites based onmicrofibrillated cellulose having nano-order-unit web-like network structure.Appl Phys A 2005;80(1):155–9.[5]Nakagaito AN,Yano H.The effect of morphological changes from pulp fibertowards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites.Appl Phys A 2004;78(4):547–52.[6]Nakagaito AN,Iwamoto S,Yano H.Bacterial cellulose:the ultimate nano-scalarcellulose morphology for the production of high-strength composites.Appl Phys A 2005;80(1):93–7.[7]Oksman K,Skrifvars M,Selin JF.Natural fibers as reinforcement in polylacticacid (PLA)p Sci Technol 2003;63(9):1317–24.[8]Huda MS,Drzal LT,Misra M,Mohanty AK,Williams K,Mielewski DF.A studyon biocomposites from recycled newspaper fiber and poly(lactic acid).Ind Eng Chem Res 2005;44(15):5593–601.[9]Mathew AP,Oksman K,Sain M.Mechanical properties of biodegradablecomposites from poly lactic acid (PLA)and microcrystalline cellulose (MCC).J Appl Polym Sci 2005;97(5):2014–25.[10]Oksman K,Mathew AP,Bondeson D,Kvien I.Manufacturing process ofcellulose whiskers/polylactic acid p Sci Technol 2006;66(15):2776–84.[11]Zimmermann T,Pohler E,Geiger T.Cellulose fibrils for polymer reinforcement.Adv Eng Mater 2004;6(9):754–61.[12]Favier V,Chanzy H,CavailléJY.Polymer nanocomposites reinforced bycellulose whiskers.Macromolecules 1995;28(18):6365–7.[13]Samir MASA,Alloin F,Paillet M,Dufresne A.Tangling effect in fibrillatedcellulose reinforced nanocomposites.Macromolecules 2004;37(11):4313–6.[14]Svagan AJ,Samir MASA,Berglund LA.Biomimetic polysaccharidenanocomposites of high cellulose content and high toughness.Biomacro-molecules2007;8(8):2556–63.Fig.6.Effects of MFC contents (wt%)on the temperature dependency of storage modulus.2106 A.Iwatake et al./Composites Science and Technology 68(2008)2103–2106。
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spectroscopห้องสมุดไป่ตู้,
thermal strain, fragmentation, compression, microcomposite
Raman
1 INTRODUCTION When fibre-reinforced thermoplastic composites are cooled from the melt, stresses build up in the fibre as a result of the mismatch between the thermal expansion coefficients of the fibre and matrix. These microstresses are additional to the stresses produced by external loads and are often sufficient to cause microcracks in the matrix or fragmentation of the fibres.’ Such spontaneous fragmentation will be therefore a direct measure of the thermal compressive stress in the system. Although the testing of macrocomposite systems or the engineering component itself ultimately determines the utility of a composite to a particular application much information can be gained from investigating microcomposites. Recently, a novel microcomposite test was developed that utilised thermal strains to induce compressive fibre fracture.’
(Received
13 March
1995; revised
version
received
31 May 1995; accepted
1 June 1995)
Abstract
Raman spectroscopy has been used to evaluate thermal strains before, during and after the manufacture of single-jibre composites. The fragmentation of highmodulus carbon fibres embedded in polycarbonate is found to relieve strains in the jibres although the strain profile along the length is unaffected by the breaks, in agreement with a recently proposed compressive fragmentation model. Deviations from linearity on a weakest link theorem/Weibull statistics plot are considered to reflect both this strain-relieving mechanism and the eficiency of stress transfer across the interface. The lower residual strain in PTFE coated fibres with respect to the unmodified fibres is explained by this competitive mechanism. Keywords:
“Casali Institute of Applied Chemistry, The Hebrew University, 91904 Jerusalem, Israel “Manchester Materials Science Centre, UMIST/lJniversity of Manchester, Manchester Ml 7HS, UK
224
J. R. Wood et al.
2 THERMAL
FRAGMENTATION
calculated as long as the strength at one length (cri, L,) and the Weibull shape parameter, p, are known. 3 EXPERIMENTAL 3.1 Specimen preparation and fragmentation Single-fibre composites were produced by carefully placing one or two carbon fibres between thin sheets of polycarbonate (Axxis, DSM).‘O High-modulus pitch-based fibres were tested (PRD-172 from E. I. du Pont de Nemours, Inc.) which had a tensile Young’s modulus of 769 GPa.” The coefficient of thermal dependent with a expansion, a,,,, was temperature room temperature value of 65 x lop6 K-’ but could be adequately represented by a linear relationship for the temperature range under investigation. A release agent (Molykote, Dow Corning Corp.) containing l,l,land polytetrafluoroethylene (PTFF) trichloroethane was applied in some tests to the high-modulus fibres. The fibres were pulled through the solution and the solvent was evaporated in an oven at 353 K. The specimens were sandwiched between Kapton polyimide films (Du Pont). The equipment consisted of a Nikon stereoscope equipped with a Mettler FP82 hot stage in which the specimen was inserted. The temperature of the hot stage was increased to 500K for 20min which ensured that the polycarbonate completely melted around the fibres (this also allowed any entrapped bubbles to dissolve or escape). The hot stage was then cooled at a rate of 2 K/min during which time the fibres were monitored using Xl00 and ~400 magnification and polarised light. An optical scale provided accurate measurement of the fibre gauge length and the number of fragments was recorded at incremental temperatures as the system was cooled. Temperatures below room temperature were achieved by passing nitrogen gas from a liquid nitrogen dewar flask through the hot stage. Although the aperture of the hot stage was only 2mm, the specimen was placed on a movable stage which enabled a 6 mm fibre length to be monitored. All fibres were in this length range and the number of fragments (breaks + 1) was counted over the sample gauge length and the corresponding temperature to attain this length was recorded. 3.2 Raman spectroscopy At room temperature the samples were examined using laser Raman spectroscopy. Raman spectra of the carbon fibres were obtained using a Renishaw Ramascope and a 632*8nm line of a helium-neon laser. The incident laser beam was focused on the fibre through a X50 objective lens with the polarisation direction parallel to the fibre axis. The laser spot on the sample was about 2 pm in diameter