Nonray‐tracing determination of the 3D refractive index profile of polymeric fibres using single‐frame computed tomography and digital holographic interferometric technique

In this paper, we present a nonray‐tracing technique for evaluating the three dimensional distribution of the refractive index values inside polymeric fibres. This technique, named ‘single‐frame computed‐tomography (SFCT)’, is applied to digital holography. A comparative study between the calculated optical phase values using ordinary tomography and SFCT is carried out, and a negligible deviation is detected. The proposed technique is used to determine the three‐dimensional refractive index profile of isotactic Polypropylene fibres, IPP. The variation of the optical properties is measured before, during and after the formation of the necking phenomenon. In addition, SFCT technique is applied to the online determination of the change of the optical properties of IPP fibres. Holograms are given for illustration.     

A proposed method to reconstruct the three‐dimensional dispersion profile of polymeric fibres based on variable wavelength interferometry

In this paper, we suggest a modification to the conventional variable wavelength interferometry. This modification allowed us to calculate the dispersion curve of each point inside polymeric fibres instead of calculating the mean dispersion of these fibres. This modified mathematical treatment was used to calculate the three‐dimensional dispersion profile of isotactic polypropylene fibres suffering from necking deformation. The different steps of calculating the three‐dimensional dispersion profile of the fibre were demonstrated. The application of this modified method revealed the variation of the fibre material dispersion before, inside and after the necking region. In addition, the birefringence profile of the necked isotactic polypropylene was determined using the proposed mathematical treatment. This allowed us to diagnose the interaction of the incident waves with necked polypropylene fibres, which gives extensive information on the orientation of the molecular chains during the formation of the necking phenomenon.     

X-ray tomographic imaging of Ti/SiC composites

In this paper, high‐resolution tomographic synchrotron X‐ray imaging is applied to study the occurrence and evolution of damage in Ti‐6Al‐4V/SCS6 SiC fibre composite materials. Three composite morphologies of increasing complexity have been studied, namely single fibre, single‐ply and multi‐ply composites. The single fibre composite was strained to full fibre fragmentation and the progressive introduction of damage monitored. For the single‐ply composite, damage was introduced deliberately by laser drilling to establish the effect of damaged fibres on their neighbours, whereas for the multi‐ply composite the morphology of a fibre bridging fatigue crack was studied. In addition to traditional mode I fibre fractures, subsequent fibre wedge cracks were observed presumably nucleating from damage introduced into the fibre surface by the first fracture event. In addition to these crack morphologies, spiral defects were observed for the single ply during failure. Finally, for the multi‐ply composite, the matrix crack front showed a number of characteristic features, including advancement in fibre‐free regions, crack bifurcation near fibres and different crack plane heights either side of a fibre.     

Automated segmentation of wood fibres in micro‐CT images of paper

A novel algorithm has been developed and validated to isolate individual papermaking fibres in micro‐computed tomographic images of paper handsheets as a first step to characterize the structure of the paper. The three‐step fibre segmentation algorithm segments the papermaking fibres by (i) tracking the hollow inside the fibres via a modified connected component methodology, (ii) extracting the fibre walls using a distance transform and (iii) labelling the fibres through collapsed sections by a final refinement step. Furthermore, postprocessing algorithms have been developed to calculate the length and coarseness of the segmented fibres. The fibre segmentation algorithm is the first ever reported method for the automated segmentation of the tortuous three‐dimensional morphology of papermaking fibres within microstructural images of paper handsheets. The method is not limited to papermaking fibres, but can be applied to any material consisting of tortuous and hollow fibres.     

Experimental investigation on the essential work of mixed-mode fracture of PC/ABS alloy

The mixed-mode fracture of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) alloy is experimentally investigated in this work. The essential work of fracture method is employed to measure the mixed-mode fracture toughness of PC/ABS alloy. Results show that the essential fracture work w _e increases significantly with the decrease in loading angles. Crack initiation angles are measured on the fractured specimens. The deviation of crack growth direction from the initial crack plane also increases with the decrease in loading angles, which corresponds to the increase of shear components. Microfracture processes of PC/ABS alloy with different loading angles are examined in situ by a scanning electron microscope. Crazing structures are clearly seen around the crack tip. The appearance, growth, and coalescence of crazes can be observed in the microfracture processes, and the macrocrack propagation direction is finally determined by the coalesced direction of crazes.     

Imaging cells on polymer spherulites

Polymers are commonly used to construct tissue‐engineered medical products and the conditions used to process these polymeric materials can affect their biological performance. For semi‐crystalline polymers, thermal processing conditions can induce crystallization of the polymer chains into spherulites, which cause the polymer surface to become roughened. This change in surface topology can influence cell behaviours such as adhesion, morphology and proliferation. Herein, a simple microscope technique is presented, which combines fluorescence microscopy with transmitted white light microscopy using crossed polarizers. This technique allows simultaneous imaging of cells and polymer spherulites, which enables the biomaterials researcher to observe the effects of spherulites on cell alignment and morphology.     

高撕裂阻力金属延性断裂韧度测试方法探讨

讨论现行J积分测试方法在测定高撕裂阻力(dJ/da)金属延性断裂韧度JIC时所遇到的困难,结合工业金属冶金组织特性分析裂纹试样受力后的钝化、启裂及裂纹稳态扩展过程,并给出此类材料的JIC测试方法.研究指出,裂纹启裂过程是一个由塑性变形为主导的裂纹顶端伸张变形和裂尖钝化向微孔型断裂过渡的过程;开裂点实际上是在漫长的裂纹前沿上大部分地方完成这一过渡,裂尖伸张区(stretched zone, SZ)达到饱和,微孔开裂机制开始占据主导地位的标志.采用直线和幂函数形式拟合启裂后的J-Δa关系,以及采用幂函数形式拟合启裂前与启裂后全过程的J-Δa关系均可得到很相近的相关性,且在一定程度上,后者显得更合理.     

Al2O3(sf)／Al-5．3Cu复合材料断裂过程与界面

利用ＳＥＭ拉抻装置对Ａｌ２Ｏ３（ｓｆ）Ａｌ－５．３Ｃｕ复合材料微观断裂过程进行了原位观察,并用ＴＥＭ分析了该复合材料的界面状况。研究表明：复合材料的断裂是一种复合断裂机制,界面存在ＣｕＡｌ２化合物。提出了判断合金元素对界面影响的分析方法。     

Rapid cryofixation of rabbit muscle fibres after a temperature jump

We describe a procedure whereby structural changes that occur in muscle fibres after a rapid temperature jump can be captured by cryofixation. In the thick filament from rabbit and other mammalian skeletal muscles there is a rapid transition from a non‐helical to a helical structure as the temperature is raised from 273 K towards physiological levels. This transition is accompanied by characteristic intensity changes in the X‐ray diffraction pattern of the muscle. In our experiments to capture these changes, single fibres of glycerinated psoas muscle were subjected to a Joule temperature jump of 15–30 K from ~278 K in air. We have developed a freezing method using a modified Gatan cryosnapper in which a pair of liquid nitrogen‐cooled copper jaws were projected under pressure and closed on the fibre between 50 and 100 ms after the temperature jump. The frozen fibres were freeze‐substituted and embedded for electron microscopy. Transverse and longitudinal sections of relaxed ‘cold’ (~278 K) and temperature‐jumped fibres as well as rigor fibres were obtained. Fourier transforms of the images from the three preparations showed differences in the relative intensities of the reflections from the hexagonal filament lattice and in those of the helix‐based layer lines, similar to the differences seen by X‐ray diffraction. We conclude that we have preserved the ‘hot’ structure and that cryofixation is sufficiently fast to prevent the transition back to the ‘cold’ state.     

化工机械设备地脚螺栓断裂失效分析

某化工设备地脚螺栓在运行过程中发生断裂,通过对断裂螺栓采用化学成分分析、断口形貌分析、金相组织分析、扫描电镜、显微硬度分析等方法分析了其断裂原因。一系列分析表明,正常断裂与异常断裂螺栓在化学成分、显微硬度、金相组织等方面没有明显差异,说明这些均不是造成螺栓异常断裂的主要原因;正常断裂与异常断裂微观断口形貌分析结果表明,螺栓芯部出现偏聚现象,螺栓在调质高温回火的过程中,发生偏聚继而导致了疲劳裂纹的萌生及扩展,最终引发螺栓断裂。     

Systematic variation of polymer jacketed fibres and the effects on tip etching dynamics

Using a chemically etched fibre probe through a plastic jacket provides a simple way to smooth a tip's surface. Convection flow in the plastic tube and lateral diffusion with fixed meniscus height has been proposed to explain such improvement. Fibres with additive thin polymer layers and bare fibres with thick untapered/tapered plastic layers have been prepared to verify the dominant mechanism. The additive layers greatly change the tip's geometry and bare‐fibres with untapered plastics cannot form tips. This confirmed that lateral diffusion dominates the etching process. Based on our investigation, we propose a new non‐meniscus end‐etching method by using tapered plastics. Unlike etching methods with meniscus, the end‐etching method can regularly form very smooth tips. It is insensitive to vibrations and temperature drifts and also suitable for most fibres.     

Online interferometric study of viscoelastic rupture and necking deformation of as‐spun (iPP) fibres due to creep process

Creep deformation under constant load leads to rupture when the polymer chains can no longer separate and accommodate the load. This fracture phenomenon is investigated interferometrically. The creep behaviour of as‐spun isotactic Polypropylene (iPP) fibres is studied at different stresses, different initial lengths and different radii. The creep rate, which defines the velocity of the creep deformation and the dimensional stability of the material, is studied. The failure time and stress of iPP due to creep process is determined. The necking deformation was in situ detected during creep process. The mean refractive indices (n^P and) profiles of iPP fibres were determined at different positions along the fibre axis before and after necking. The relation between the creep behaviour and different optical and structural parameters is investigated. Microinterferograms are given for illustration.     

往复式甲烷压缩机曲轴断裂原因

某往复式甲烷压缩机曲轴在运行过程中发生断裂,通过断口宏观和微观形貌观察、化学成分分析、显微组织观察和力学性能测试等方法,研究了曲轴断裂的原因。结果表明:曲轴发生了扭转疲劳断裂;在交变扭转应力的作用下,曲轴主轴颈不规则且粗糙的过渡圆角和油孔附近粗糙的机械加工痕迹处产生应力集中,导致微裂纹萌生;组织中严重的带状回火屈氏体、大小不均匀的晶粒以及非金属夹杂物导致曲轴的力学性能变差,加速了疲劳裂纹的扩展;建议严格控制曲轴的热处理和制造工艺,优化曲轴结构设计,防止类似事故的再次发生。     

轮胎钢丝生产断丝原因分析

扭转裂纹一直是引起轮胎钢丝生产中断丝的一个重要因素。为找出裂纹来源 ,采用 70 #钢盘条进行生产性实验 ,结果表明裂纹主要来源于原材料、酸洗、热处理及拔丝过程四个方面。     

Structure and morphology of the in situ composites of a liquid crystalline polymer and polycarbonate

In situ composites were prepared via melt blending of a liquid crystalline polymer (LCP) and polycarbonate using a twin screw extruder. The structure and morphology of these composites were analysed using both transmission electron microscopy (TEM) and scanning electron microscopy. The LCP phases were able to orientate and form in situ submicrometre fibres during the extrusion and post-extrusion drawing. TEM images as well as selected-area diffraction patterns were obtained from the materials. The effects of both composition, i.e. LCP content, and post-extrusion draw-down ratio on the development of the in situ formed LCP fibres were studied in detail. A skin–core morphological differentiation is observed in these materials where well-defined LCP fibres of higher aspect ratios were formed in the skin region. However, a significant amount of unelongated LCP particles were found coexisting with the less well-defined fibres in the core region of the extrudates. This skin–core differentiation was found to be dependent on the composition and the processing conditions, e.g. draw ratio. In this instance, electron microscopy is proven to be a powerful technique not only for direct observation of the formation, dimensions and morphology of the in situ LCP fibres, but also for the qualitative and quantitative characterization of the molecular orientation and crystalline structures in these fibres using selected-area electron diffraction. It is observed that the skin–core differentiation becomes more distinct in the in situ composites containing a higher percentage of LCP but diminishes when the material is processed at higher post-extrusion draw ratio.     

Automated image segmentation of haematoxylin and eosin stained skeletal muscle cross‐sections

The ability to accurately and efficiently quantify muscle morphology is essential to determine the physiological relevance of a variety of muscle conditions including growth, atrophy and repair. There is agreement across the muscle biology community that important morphological characteristics of muscle fibres, such as cross‐sectional area, are critical factors that determine the health and function (e.g. quality) of the muscle. However, at this time, quantification of muscle characteristics, especially from haematoxylin and eosin stained slides, is still a manual or semi‐automatic process. This procedure is labour‐intensive and time‐consuming. In this paper, we have developed and validated an automatic image segmentation algorithm that is not only efficient but also accurate. Our proposed automatic segmentation algorithm for haematoxylin and eosin stained skeletal muscle cross‐sections consists of two major steps: (1) A learning‐based seed detection method to find the geometric centres of the muscle fibres, and (2) a colour gradient repulsive balloon snake deformable model that adopts colour gradient in colour space. Automatic quantification of muscle fibre cross‐sectional areas using the proposed method is accurate and efficient, providing a powerful automatic quantification tool that can increase sensitivity, objectivity and efficiency in measuring the morphometric features of the haematoxylin and eosin stained muscle cross‐sections.     

Morphology study of progesterone polymorphs prepared by polymer‐induced heteronucleation (PIHn)

In this article, morphology of progesterone polymorphs prepared by polymer‐induced heteronucleation (PIHn) technique was studied. Hydroxypropyl methylcellulose(HPMC), such as dextran T‐500 and gelatin G‐9382, polyisoprene (PI), and acrylonitrile/butadiene copolymer (NBR) were used as substrates. The crystallizations were performed by solvent evaporation at room temperature from 0.5, 10, and 40 mg/ml solutions in chloroform and acetone. Progesterone polymorphs were identified by X‐ray diffraction. Differential scanning calorimetry and total attenuated reflectance infrared spectroscopy were used as complementary techniques in the identification. Depending on the polymeric matrix and the concentration used, form 1, form 2, or mixture of both polymorphs were obtained. Scanning electron microscopy pictures evidenced difference in morphology and in homogeneity of the two progesterone polymorphs. These polymorphs prepared by PIHn, did not present a distinctive morphology that allows identifying polymorph by its crystal habit. Hence, polymeric matrix induced the crystallization, affecting polymorphism and morphology. SCANNING 35:213‐221, 2013. © 2012 Wiley Periodicals, Inc.     

Electron spectroscopic imaging and X-ray microanalysis of acrylic fibres

Acrylic fibres are synthetic fibres produced by extruding viscous solutions of acrylonitrile co-polymers. A spin finish is applied during the fibre-forming process. In this work the structure of acrylic fibres has been correlated with spin finish distribution by a combined application of transmission electron microscopy (TEM), electron spectroscopic imaging (ESI) and X-ray microanalysis (XRMA). Many irregularly shaped microcavities at the periphery of the fibres were detected by TEM. XRMA revealed that potassium and phosphorus are the elements most often found inside the spin finish material. ESI revealed that phosphorus is constantly present in all the microcavities. Therefore it seems likely that a preferential distribution of the spin finish is found inside the microcavities, just at the periphery of the fibre. This work is also an example of how both ESI and XRMA are powerful tools in morphological studies.     

In-process estimation of fracture surface morphology during wheel scribing of a glass sheet by high-speed photoelastic observation

Defect-free glass separation techniques are in strong demand in glass processing industries. In this study, we intended to observe the internal stress field during/after wheel scribing of a glass sheet using the photoelastic method. First, we visualized the crack propagation behavior in a 0.7-mm-thick non-alkali glass sheet during mechanical scribing with a 2.0-mm-diameter serrated diamond wheel using high-speed imaging techniques. The observation results under various applied load conditions showed that the crack propagation behavior changed dramatically at a load of approximately 9–10 N; the generated crack hardly propagated in the thickness direction under lower load conditions, in contrast to the rapid propagation under higher load conditions. The fracture surface morphology that was observed after cleavage also changed, from damaged to defect-free surfaces with increments in the applied load around the transition point (9–10 N). This result indicated that the fracture surface morphology was determined by the crack propagation behavior. Second, the birefringence phase difference was measured from the upper side of the glass sheet to enable understanding of the stress fields induced by scribing wheel indentations. As a result, the phase differences that were distributed along the scribe line were shown to differ depending on the applied loads; the phase difference changed little under lower load conditions, but vanished immediately under higher load conditions. Therefore, these differences were dependent on whether or not rapid crack propagation occurred. The measured phase difference distribution thus included information about the crack propagation behavior, and this information could be used as a criterion for estimation of the fracture surface morphology. An in-process estimation method for the fracture surface morphology during mechanical wheel scribing was therefore developed based on high-speed polarization imaging techniques.