Strength of thermally exposed alumina fibers Part II bundle behavior

Non-ideal bundle models that predict the effect of filament slack, misalignment and bonding were compared to the predicted ideal bundle stress-strain response and the measured response of an Alumina tow (Nextel 610) as a function of exposure temperature. The ideal bundle model assumes that the filaments are perfectly aligned, independent, and filament strength is characterized by single filament tests; the non-ideal bundle models relax these assumptions. The Nextel 610 tow was found to behave ideally until the sintering bonds between filaments were strong enough to resist fracture during testing. When bonded filament clusters existed throughout testing, the weakest filament in the cluster likely caused failure of the entire cluster. Therefore, the assumption of independence was not valid, and the measured bundle strength was lower than the ideal bundle prediction. The assumption that the strength distribution of the bonded filaments was the same as the filaments removed from bonded filament clusters also appears to be invalid. It is hypothesized that the effective decrease in strength of bonded filaments is a result of induced shear stresses that form along the bond line when bonded filaments are either bent or twisted. However, within a composite this motion is limited. The modeling indicated that 10% clustering can be tolerated with little degradation in composite properties as long as the clusters remain independent from their neighbors.     

Kevlar49单丝和单束的随机破坏及有限元模拟

为研究不同尺度下Kevlar49单丝(微观)和单束(细观)的拉伸力学性能,首先,分别采用MTI微型拉伸试验机和MTS微机控制电子万能试验机对纤维丝和纤维束进行了单向拉伸试验,发现纤维丝和纤维束的力学性能与试样的标距及结构尺度存在很大相关性,试样的拉伸强度会随着其标距的增加和结构尺度从纤维丝增大到纤维束而降低;随后,按照Weibull分布对试验数据进行统计分析,量化了不同标距下纤维丝和纤维束拉伸强度的随机变化程度;接着,考虑到纤维丝的拉伸强度符合Weibull分布随机破坏,利用ANSYS中的用户自定义子程序(USERMAT)建立了纤维丝本构模型;最后,采用纤维丝本构模型模拟纤维束的拉伸破坏行为,并讨论了关键参数对纤维束拉伸破坏行为的影响。结果表明:纤维束的模拟结果与试验结果吻合程度较好,所建模型可以较准确地预测纤维束的拉伸性能。      

Mechanical behaviors of multi-filament twist superconducting strand under tensile and cyclic loading

The superconducting strand, serving as the basic unit cell of the cable-in-conduit-conductors (CICCs), is a typical multi-filament twist composite which is always subjected to a cyclic loading under the operating condition. Meanwhile, the superconducting material Nb₃Sn in the strand is sensitive to strain frequently relating to the performance degradation of the superconductivity. Therefore, a comprehensive study on the mechanical behavior of the strand helps understanding the superconducting performance of the strained Nb₃Sn strands. To address this issue, taking the LMI (internal tin) strand as an example, a three-dimensional structural finite element model, named as the Multi-filament twist model, of the strand with the real configuration of the LMI strand is built to study the influences of the plasticity of the component materials, the twist of the filament bundle, the initial thermal residual stress and the breakage and its evolution of the filaments on the mechanical behaviors of the strand. The effective properties of superconducting filament bundle with random filament breakage and its evolution versus strain are obtained based on the damage theory of fiber-reinforced composite materials proposed by Curtin and Zhou. From the calculation results of this model, we find that the occurrence of the hysteresis loop in the cyclic loading curve is determined by the reverse yielding of the elastic–plastic materials in the strand. Both the initial thermal residual stress in the strand and the pitch length of the filaments have significant impacts on the axial and hysteretic behaviors of the strand. The damage of the filaments also affects the axial mechanical behavior of the strand remarkably at large axial strain. The critical current of the strand is calculated by the scaling law with the results of the Multi-filament twist model. The predicted results of the Multi-filament twist model show an acceptable agreement with the experiment.     

Quantitative measurement of filament ruptures of a multi-filament AR-glass yarn embedded in concrete

This paper presents a new digital image analysis method for quantitative and online measurement of filament ruptures of a multi-filament AR-glass yarn embedded in concrete during pullout loading. The proposed method was developed based on an existing test method for determination of filament ruptures occurring during the loading called failure investigation using light transmitting (FILT) property test, which uses light transmitting property of AR-glass fibers. Artificial light is exposed on the glass filaments from one side of the specimen. On the opposite side, a charge-coupled device (CCD) camera with an optical microscope records the lighted filament cross-sections in the yarn. To detect filament ruptures during pullout loading, the light intensity time history of every individual filament of the yarn was investigated by a digital image analysis method. The number of broken filaments was also investigated by acoustic emission (AE) analysis simultaneously and the results were compared. Test results showed that the light transmitting property of AR-glass can be used to identify filament ruptures and it is possible to determine the failure of the filaments during pullout in the cross-section quantitatively by the improved FILT test.     

Commingled yarns of surface nanostructured glass and polypropylene filaments for effective composite properties

Developing commingled yarn technologies and understanding the fundamental interface nanostructures of reinforcement and thermoplastic filaments are of significant current interest. Previous research on commingled yarns was mainly focused on the air-jet texturing process, while the mechanical properties of the composites are strongly influenced by the impregnation homogeneity, the polymer sizing properties and consolidation process. Here, we report a unique melt spinning equipment for E-glass fiber which is compatibly combined with a melt spinning extruder to manufacture commingled yarns. The in-situ commingling enables to combine homogeneously both glass and polypropylene filament arrays in one processing step and without fiber damage compared to commingling by air texturing. Variation of processing conditions are investigated, i.e. sizings, diameter ratios, and arrangements of sizing/finish application related to intermingling of filament arrays. A rapid processing is achieved because of good intermingling and the low flow paths. We found that the sizing enables a good strand integrity with the polypropylene yarn. The interfacial adhesion can be improved with a sizing for glass fibers consisting of aminosilane and maleic anhydride grafted polypropylene film former, which results in both improved transverse tensile strength and compression shear strength. We also found that a very small amount of single-wall carbon nanotubes (SWNTs) in the sizing provides significantly improved interfacial adhesion strength. This is attributed to the change in fracture behavior of the nano-structured interface and morphology of the model single-fiber composites.     

Prediction of statistical strengths of twisted fibre structures

A new approach, based on Daniels' statistical model for a parallel fibre bundle and the recent results on yarn mechanics by the present author, is introduced to predict the strengths of twisted yarns including the effects of interfibre friction and the fibre fragmentation mechanism during yarn extension. By calculating the lateral pressure in a twisted yarn, the critical fibre length of the fibre fragmentation process has been determined, and was found to decrease together with the increasing yarn strain. This, according to the Weakest link theorem, will lead to a substantial increase of fibre strength. Incorporating this conclusion into Daniels' result yielded a more realistic prediction of the strength and its boundary for a twisted fibre structure. The key differences between a filament yarn and a short-fibre yarn and their effects on strengths are also discussed. The major results from the study are illustrated schematically.     

Statistical fracture of E-glass fibres using a bundle tensile test and acoustic emission monitoring

Mechanical strength studies have been carried out on fibre bundles used in composite manufacturing. The variability in mechanical properties of glass fibres has been studied using bundles of about 2000 filaments. The fibre strength distributions were analysed using the survival probability-applied strain (S–ε) curve, in relation with various experimental conditions. We also examine the effect of lubricant’s viscosity on the fracture behaviour of E-glass fibre bundles. Acoustic emission (AE) was monitored during the bundle tensile tests in order to verify that individual filament failures are statistically independent. On tensile tests with lubricated bundles of E-glass fibres, it is shown that each individual fibre break can be detected using AE. Hence, AE monitoring of a lubricated bundle of E-glass fibres provides a convenient and relatively quick method to obtain the Weibull parameters of strength distribution.     

柔性纺织电阻传感器的研究进展

纺织电阻传感器具有质量轻、柔性好和可拉伸等优良特性,在可穿戴电子产品领域具有很大的应用价值。文中根据近年来不同纺织材料基电阻传感器的研究进展,介绍了无捻纤维(束)基电阻传感器、纱线(长丝纱、短纤维纱、复合纱)基电阻传感器和织物(针织物、机织物、非织造织物)基电阻传感器的制备、性能及应用研究。在纱线基电阻传感器中,主要基于导电涂覆纱线受力过程中纤维的内在弹性或长丝之间接触程度的变化所引起电阻改变的原理,制备电阻传感器;对于织物电阻传感器,主要利用织物结构体的变形特征并结合对织物进行导电涂覆或碳化等方法,制备电阻传感器。     

SMA丝表面纳米SiO_2改性对SMA/环氧树脂复合材料界面粘结强度的影响

为了研究形状记忆合金(SMA)丝增强环氧树脂复合材料的界面粘结行为,首先通过单纤维拔出试验测定了SMA/环氧树脂界面的粘结强度,重点考察了埋入深度对界面极限粘结强度及其拔出行为的影响。然后,结合ABAQUS有限元分析方法,利用基于表面内聚力行为的单元对SMA丝拔出过程中应力分布随拔出时间的变化关系进行了模拟。最后,针对SMA/环氧树脂复合材料界面粘结强度较弱的缺陷,提出了利用纳米SiO2改性SMA丝表面提升材料界面粘结强度的方法,并通过拔出试验进行了验证。结果表明:随着埋入深度从1.0cm增加到1.5cm和2.0cm,最大拔出载荷显著增加,平均界面粘结强度却逐渐下降。当纤维埋入深度为2.0cm时,在0.300s时临界脱粘出现。利用在SMA表面涂覆纳米SiO2颗粒的方法可以增加纤维的表面粗糙度,进而有效提高SMA丝增强环氧树脂复合材料的临界拔出强度。研究结论为SMA丝在实际工程领域中的应用提供了理论指导。     

Chewability testing in the development of a chewable tablet for hyperphosphatemia

The official Pharmacopeia does not include a test procedure for the in vitro estimation of the chewability of tablets and publications in the scientific literature on this subject are rare. The purpose of this study was to evaluate a number of different test procedures for assessing chewability, starting from standard breaking force and strength testing and progressing to develop new procedures that simulate the actual chewing action on tablets. A further goal was to apply these test procedures to characterize the chewability of the novel phosphate binder PA21 in comparison with a commercially available phosphate binder chewable tablet product based on lanthanum (Fosrenol®) and a chewable tablet product containing calcium (Calcimagon®) – the latter being used as a standard for its very good chewability. For this purpose, a number of development formulations (different batches of PA21) were tested. The radial or diametrical tablet breaking force offers a poor means of assessing chewability while the axial breaking force was concluded to better reflect the effect of chewing on the tablet. Measurement of tablet behavior upon repeated loading afforded the best simulation of the actual chewing action and was found to have a good discriminating power with respect to chewability of the tested tablets, especially when the tablet was moistened with artificial saliva. The developed tests are shown to be more suitable for evaluating chewing properties of tablets than currently used Pharmacopeial tests. Following ICHQ6, which calls for specification of hardness for chewable tablets, these test procedures enabled the optimal chewability features of PA21 tablets in development to be confirmed whilst still maintaining capabilities for robust production and transportation processes.     

Comparative post fatigue residual property predictions of reinforced and unreinforced poly(ethylene terephthalate) fibers using artificial neural networks

A set of experiments has been performed on poly(ethylene terephthalate) (PET control) and PET fibers with vapor grown carbon nanofibers (PET–VGCNF) to assess the mechanical integrity of the materials due to a repeated cyclic loading. Artificial neural networks (ANNs) have been used to examine the residual strength and elastic modulus degradation behavior of the filaments as a function of the input mechanical testing variables (maximum fatigue stress – σ_max, stress ratio – R, # cycles – N, undeformed modulus – E) and a damage variable that has been identified as the residual strain from fatigue, ε_R. The relationship of how these input variables relate to the degradation of the elastic modulus, E, and the fracture strength, σ_f, has been determined. The results indicate that ANNs can be used to predict the residual strength and modulus degradation behavior of PET and PET/VGCNF single filaments under various loading conditions. Backpropagation (BP) with momentum and conjugate gradient algorithms have been utilized to successfully train a multilayer perceptron (MLP) network for modeling the mechanical behavior of single polymeric filaments subsequent to fatigue loading. Also, the mechanical behavior of the PET control and PET–VGCNF differs as a function of the input fatigue conditions prescribed. The main difference was that the PET control samples exhibited a distinct hardening effect in the low residual strain limit and this was not observed for the PET–VGCNF samples. The neural networks used in this work were successful at replicating the hardening behavior for the PET control samples and the mechanical behavior changes for the PET–VGCNF samples as a function of σ_max, R, and ε_R.     

Fracture of filaments and its influence on critical current and residual strength of fatigued Nb-Ti/Cu superconducting composite

Fatigue behavior at room temperature and its influence on critical current at 4.2 K and residual strength at room temperature of multifilamentary Nb-Ti/Cu superconducting composite wire with a filament volume fraction of 0.49 (copper ratio of 1.04) were studied. The fatigue crack nucleated in the copper in the circumferential region and propagated stably into the inner region, causing fracture of the Nb-Ti filaments in the late stage of the fatigue life. Once the fracture of the filaments started, the number of the fractured filaments increased steeply with increasing number of stress cycles, and correspondingly, the current-transportable and stress-carrying capacity of the composite decreased steeply. In this process, both the critical current and residual strength of the fatigued composite decreased nearly linearly with decreasing fraction of surviving filaments. Thus, the critical current of the fatigued composite was proportional to residual strength as a first approximation.     

TiO<Subscript>2</Subscript> crystalline structure and electrochemical performance in two-ply yarn CNT/TiO<Subscript>2</Subscript> asymmetric supercapacitors

Solid-state flexible energy storage devices play a crucial role in the development of wearable electronic textiles. In this study, we fabricated flexible asymmetric two-ply yarn supercapacitors from carbon nanotube yarns and surface-oxidized titanium filament. The crystalline structure of the TiO₂ surface layer can be adjusted to amorphous, anatase and rutile states by altering the annealing temperature. The titanium filament with a rutile TiO₂ surface layer produced at high annealing temperature showed far superior electrochemical performance over the filaments with amorphous and anatase TiO₂ surface layers. The as-prepared asymmetric two-ply yarn supercapacitors in aqueous gel electrolyte can achieve a durable operating voltage up to 1.4 V, with a maximum energy density of 11.7 Wh kg^?1 and a maximum power density of 2060 W kg^?1. The asymmetric two-ply yarn supercapacitors exhibited excellent flexibility and cycling stability over 1200 cycles at straight, twisted and bent states.     

Strength variability and size effect of Nicalon fibre bundles

Statistical strength and size effect of Nicalon fibre bundles are studied. The Weibull type of statistical theory underlying predictions of bounding Nicalon fibre bundle strength is presented and discussed. The relationship of bundle strength to single Nicalon filament strength and a model explaining the correlation are also discussed. The predicted values for Nicalon fibre bundles were in close agreement with the experimental data. Characterization of Nicalon fibres or bundles provides an insight into the ultimate mechanical performance of ceramic-matrix composites.     

Behavior of 3D orthogonal woven CFRP composites. Part I. Experimental investigation

This paper presents an experimental investigation of the mechanical behavior and failure mechanism of three-dimensional (3D) orthogonal woven CFRP composite panels. The 3D composite panels are preformed using Torayca T-300 (3K) carbon fiber, and then infused with the Epicote 828 epoxy resin. The nominal proportions of the stuffer yarn, the filler yarn and the warp weaver (or z yarn) are 1:1.2:0.2, respectively, and the overall fiber volume fraction is 43%. The 3D fiber architectures are measured and visualized in a micrograph form. Quasi-static tensile coupon tests are carried out to measure the in-plane Young's modulus, Poisson's ratio, tensile failure strengths and failure strains in both stuffer and filler yarn directions. Test results reveal that the average Young's modulus in the filler yarn direction is higher than that in the stuffer yarn direction, and the average failure strain in the filler yarn direction is lower than that in the stuffer yarn direction. The average failure strength in the filler yarn direction is slightly higher than that in the stuffer yarn direction. The fracture surfaces are studied using the scanning electron microscope (SEM) and the failure mechanism are then discussed. It is noted by studying the fracture surface that the fracture surface is always perpendicular to the loading direction. The crack causes the z yarn/matrix interface to debond. Also, the fracture of specimen cut along the x- (or stuffer yarn) direction causes filler yarn/matrix interface to debond and stuffer yarn to break, and the fracture of specimen cut along the y- (or filler yarn) direction causes stuffer yarn/matrix interface to debond and filler yarn to break. The testing results are then used to validate the developed models in Parts II and III of these series papers. In Part II, simplified analytical and finite element models are proposed to predict the mechanical property and failure strengths for the 3D orthogonal woven CFRP composites. In Part III, a curved beam model resting on an elastic foundation is presented to predict the tensile strength in the filler direction, and then to investigate the effect of some geometrical parameters on the tensile failure strength in the filler yarn direction.     

Load-sharing and Monte Carlo models of defects in a bundle of fibres

Two methods for modelling and random simulation of progressive deformation and breaks in a bundle of parallel fibres are proposed. First, a stochastic load-sharing reliability model of a parallel system and of its resistance against a stress is utilized. The method of its statistical analysis is presented, too. In order to improve certain limitations of such model, a complementary method based on the Monte Carlo simulation is introduced. The bundle of fibres is modelled as a grid consisting of a set of nodes and connecting arcs. The deformation and breaks are caused by an external load stretching the grid. The first objective is to find an optimal, stabilized, states of the grid corresponding to each load level. Optimal configuration is found with the help of Markov Chain Monte Carlo (MCMC) procedures. In order to model the breaking process, the load is increased sequentially. It is shown that the model is applicable also to other structures, namely to the plain weave fabric and its defects simulation. The results with bundle of fibres are compared with real stress–strain curves. The parameters for simulation were selected in such a way that obtained stress–strain curve corresponds to a real experiment with carbon fibres.     

中空涤纶/不锈钢/竹炭保温透湿材料的开发及性能研究

通过花式捻线方法将中空涤纶、不锈钢长丝和竹炭纤维三种功能性纤维并捻获得复合纱线,利用纱线强度、毛羽和实际捻度测试,得到最佳的纱线纺制参数。并采用最佳工艺参数纺制的包绕纱线进行平纹织物织造,对其织物透湿性、远红外发射率以及保温性能进行测试表征,最终制备一种可用于防寒服的新型保温透湿织物。结果表明,缠绕捻度为上捻度200,下捻度0时,纺制的包芯纱具有最佳捻度。中空涤纶/不锈钢/竹炭织物透湿率为5 184g/(m2·24h),达到透湿织物透湿要求的2倍以上。一至四层织物的远红外发射率均在70%及以上,符合远红外发射率具有功能性结果的范围。织物克罗值达到7.355clo,高于极低温作业穿着克罗值51.6%,可满足极低温环境下的织物保温要求。织物保温率为62.43%,相比于棉、毛等传统纺织原料,织物保温率可以提升2倍以上。     

Kevlar纤维织物的性能研究

通过电子织物强力仪、万能试验机、圆盘式平磨仪、广角X-射线衍射(WAXD)、示差扫描量热(DSC)、红外光谱(IR)、热失重分析(TG)对对位芳纶纤维(Kevlar Twaron)织物进行表征,分析了热处理前后KevLar纤维织物的取向结晶行为和热性能.结果表明,KevLar单纱的断裂强力为693.82 cN/tex,...     

Tensile properties and fracture behaviour of carbon fibre filament materials

Monotonic tensile properties and fracture behaviour of carbon fibre filament materials, namely single/mono- and multi-filaments (two and four filaments) as well as virgin carbon tows have been evaluated and discussed. Micro composite or single fibre approach is used in this study, which facilitated the evaluation of tensile properties and nature of fracture of carbon filament materials in a relatively short time with a large number of inexpensive trials. Tensile tests have been conducted on these filament materials at ambient temperature and laboratory air atmosphere. Load–elongation and the corresponding stress–strain plots thus obtained have been analysed to understand the tensile behaviour. The peak tensile strength of single carbon filament is found to be 3.8 GPa, and the value of the resilience obtained is 19 MJ/m³. The peak tensile strength was found to increase moderately with further increase in number of filaments. However, the value of resilience was found to increase with increase in the number of fibres, which is attributed to the controlled failure of multi-filaments. On the other hand, the tensile strength of virgin carbon tow without matrix was found to be 1.13 GPa, and the value of the fracture energy was determined to be 9.9 MJ/m³, which is nearly one fourth or even less than the corresponding values of the mono- and multi-filaments. The data obtained in the case of the virgin carbon tows were further analysed to evaluate the Weibull statistical parameters.