The recoil compressive strength of pitch-based carbon fibres

The recoil compressive strengths of pitch-based carbon fibres with folded-radial and flat-layer textures were compared. Using the recoil test method, it was shown that the compressive strengths of pitch-based carbon fibres with folded-radial textures are superior to pitch-based carbon fibres with flat-layer textures at all modulus levels. Analysis of the failed fibre ends revealed that the folded-radial texture appeared to inhibit shearing of the basal planes. This may account for the superior compressive strengths of pitch-based carbon fibres with folded-radial textures. Procedural differences in the recoil test were shown to influence the calculated recoil compressive strength of pitch-based carbon fibres. Microscopic analysis of the recoil test specimens revealed that some energy is absorbed in the area where the fibre is secured to the support tab.     

Investigation of flow properties of powders by means of a uniaxial tester, in relation to direct tablet compression

Unexpected poor flowability during commercial production of a direct compression tablet formulation initiated an investigation of the flow properties of the powder mixture and its components by means of a uniaxial tester. The failure function—a curve describing the strength of the powder bed as a function of the maximum main stress that has consolidated the bed—of the powder mixture and its components was determined. The drug was more cohesive than the filler, which was somewhat more cohesive than the powder mixture. Three excipients—a binder, a glidant and a lubricant—constituting 3.5 w/w% of the formulation improved the flowability of the mixture of active ingredient and filler. The failure function discriminated powder mixtures with poor flow from mixtures with medium or good flow. However, it was not possible to discriminate medium from good flow by means of the failure function. Attempts to correlate univariately the flow property parameters of the powder mixtures with particle size data or flow property data of included active ingredient and filler batches failed. Therefore a multivariate approach was tested. Principal component analysis (PCA) and projection to latent structures by means of partial least squares (PLS) were employed. An excellent PCA model was obtained with the flow properties of the powder mixture. A good PCA model of tableting performance—based on tablet weight variation and tablet machine speed—was obtained.     

Manufacturing polymer/carbon nanotube composite using a novel direct process

A direct process for manufacturing polymer carbon nanotube (CNT)-based composite yarns is reported. The new approach is based on a modified dry spinning method of CNT yarn and gives a high alignment of the CNT bundle structure in yarns. The aligned CNT structure was combined with a polymer resin and, after being stressed through the spinning process, the resin was cured and polymerized, with the CNT structure acting as reinforcement in the composite. Thus the present method obviates the need for special and complex treatments to align and disperse CNTs in a polymer matrix. The new process allows us to produce a polymer/CNT composite with properties that may satisfy various engineering specifications. The structure of the yarn was investigated using scanning electron microscopy coupled with a focused-ion-beam system. The tensile behavior was characterized using a dynamic mechanical analyzer. Fourier transform infrared spectrometry was also used to chemically analyze the presence of polymer on the composites. The process allows development of polymer/CNT-based composites with different mechanical properties suitable for a range of applications by using various resins.     

Microdefocusing method for measuring acoustic properties using acoustic microscope

Many papers have been reporting on measuring acoustic properties of materials by acoustic microscopy. In a conventional method of V (z) curve analysis, the phase velocity and the propagation attenuation of a leaky surface acoustic wave (LSAW) are determined from the interference period Deltaz and the slope of the V(z) curve, respectively. For this method it is necessary to measure the V(z) curve for a period several times as long as the interference period Deltaz. Therefore, it is difficult to measure the acoustic properties of a sample with high resolution by the method. In order to overcome these problems, a method called the microdefocusing method is proposed. The method determines the acoustic properties of a sample by analyzing V (z) values measured in the microdefocusing region within an interference period Deltaz near a focal plane. An ultrasonic transducer called the butterfly transducer is proposed to be applied to this microdefocusing method and a digital signal processing procedure is developed to analyze the output of the ultrasonic transducer. Basic experiments are performed to confirm the principles of the new method.     

Tensile and compressive moduli of fibres using a two-component beam system

Serious difficulties are associated with the measurement of the compressive modulus of fibres owing to their tendency to buckle during loading. A novel technique is described, based on the theory of two-component materials for determining both the tensile and compressive moduli of reinforcing fibres in composites. It was found, particularly with Kevlar 49, that the two moduli are significantly different.     

机动车前照灯检测仪校准器的光轴角测量方法

研制的检测装置实现了对机动车前照灯检测仪校准器光轴角的检测。该检测装置采用光电检测和计算机数据处理技术相结合的方法,完成数据自动采集,并进行光轴角的示值误差计算。该方法替代使用坐标板的机械测量方法,其测量不确定度满足JJG 967-2001的要求,极大地提高了检测仪的检测效率。     

A method for measuring cyclic microstrains in both tension and compression

Journal of Materials Science -     

一种制备碳纳米管的新方法

以化学改性的膨润土为催化剂，利用化学气相沉积法催化裂解CH4，在高温条件下成功地制备了碳纳米管，并用透射电镜对其形貌与结构特征进行了表征。结果表明，所得产物形状弯曲，管径为15-20nm，长度达微米级的均匀碳纳米管；膨润土释放的金属铁起到了催化CH4的作用，在800℃条件下生长的碳纳米管质量最好、产率最高，若催化反应温度过高则会降低产品的质量，催化温度低于700℃时不能用来制备碳纳米管，与传统的过渡金属催化剂相比，这种矿物催化剂原料成本低廉，制备工艺简单，有利于碳纳米管的工业化生产。     

A novel method for the measurement of elastic moduli of fibres

The elastic modulus of fibres used in composite materials is a parameter of prime importance in the determination of overall mechanical behaviour. However, evaluation of Young’s modulus, E, of a fibre is a delicate operation given the small dimensions (diameter typically a few tens of microns), and therefore low forces involved in tensile testing. This article treats a novel method of modulus assessment involving the bending of fibres, clamped at one extremity, by forced vibrations. The fibre behaves as a beam, and when the forced oscillations approach (one of) the resonant frequency(ies) of the fibre, the bending amplitude increases. Classical beam theory allows evaluation of Young’s modulus from knowledge of resonant frequency, and fibre dimensions and density. Preliminary application of the technique using fibres of E-glass, having well known elastic characteristics, has given good results and shown its inherent potential. Subsequently, the technique developed was used on recycled fibres in order to obtain their Young’s modulus and to assess their loss of mechanical properties when compared to virgin fibres.     

Tensile and compressive properties of flax fibres for natural fibre reinforced composites

Mechanical properties of standard decorticated and hand isolated flax bast fibres were determined in tension as well as in compression. The tensile strength of technical fibre bundles was found to depend strongly on the clamping length. The tensile strength of elementary flax fibres was found to range between 1500 MPa and 1800 MPa, depending on the isolation procedure. The compressive strength of elementary flax fibres as measured with a loop test lies around 1200 MPa. However, the compressive strength can be lowered severely by the decortication process. The standard decortication process induces kink bands in the fibres. These kink bands are found to contain cracks bridged by microfibrils. The failure behaviour of elementary flax fibres under compression can be described as similar to the failure behaviour of a stranded wire.     

The effect of nanostructure upon the compressive strength of carbon fibres

The relationship between the structure and the compressive strength of carbon fibres has been studied in detail. In order to determine the compressive strength, a combination of single-fibre composite tests and Raman spectroscopy was employed. It was found that the compressive stress–strain curves showed nonlinear behaviour, with modulus softening in compression. The compressive strengths for the fibres with a modulus ≥400 GPa were measured as ≤2 GPa and those with a modulus <400 GPa were >2 GPa. We have introduced a model to explain this behaviour that assumes that the fibres behave as composites consisting of both crystallites and amorphous carbon. It is suggested that the compressive strength is controlled by the critical stress for kinking the crystallites in the fibres. Hence, the compressive strength of carbon fibres is found to depend upon the shear modulus of the fibres and the orientation of the crystallites within them.     

A method and a device for measuring the thermophysical properties of liquids

Physical and mathematical models of a method of determining the thermophysical properties of liquids, the design of a measurement device, an automated system of scientific tests of thermophysical properties, and the results of an experimental determination of the thermophysical characteristics of liquid SKU PFL-74 rubber are examined.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 37–41, April, 1994.     

Matrices of water-soluble drug using natural polymer and direct compression method

The objective of this research was to find an optimum Carrageenan matrix formulation with the desired drug release and physical properties prepared by direct compression. In order to achieve this, matrices containing 10% theophylline, different Carrageenan level, and different excipient were prepared and evaluated. A selected matrix containing 40% Carrageenan and lactose fast flo was tested for dissolution in three different dissolution media (distilled water, 0.1 N HCl, and phosphate buffer pH 7.4). The same formulation was also tested for dissolution at 50 rpm, 100 rpm, and 150 rpm, and using different dissolution apparatus (Apparatus 1 and 2).

All matrices showed a decrease in drug release as the polymer level was increased. Only Avicel PH-101 did not show any significant difference between matrices prepared with 30% and 40% polymer. At 10% polymer level, it appears that the type of diluent used controls the drug release. However, at high polymer level, 30% and 40%, it appears that the polymer level controls the drug release. Phosphate buffer pH 7.4 and 0.1 N HCl increase drug release and appear to increase Carrageenan solubility and decrease gel formation. Also, as the rotational speed of the apparatus was increased, the integrity of the gel layer was decreased, and the release of drug was increased. The drug release from Carrageenan matrices appears to follow the diffusion model for inert matrix up to 90 min. After 90 min, the drug release follows a zero-order model.

This study demonstrated that matrices using Carrageenan can be successfully prepared by direct compression.     

Compressive properties of single-filament carbon fibres

Compressive properties of mesophase pitch-based carbon fibres (NT-20, NT-40 and NT-60) were measured using the tensile recoil test and the elastica loop test. The NT-40 fibre with a 400 GPa tensile modulus showed a smaller loop compressive yield strain and a larger recoil compressive strength compared to these values obtained from the longitudinal compression test on its unidirectional composites. Further, the recoil compressive strength of this fibre was higher than that of PAN-based carbon fibre with a corresponding modulus. Under the ideal conditions in the tensile recoil test, the strain energy was conserved before and after recoil, and the initial tensile stress and the recoil compressive stress do not coincide when fibre stress-strain behaviour is non-linear, and the non-linearity in compression and in tension is different. The difference between the composite compressive strength and the recoil compressive strength of NT-40 was quantitatively explained by taking account of the fibre compressive stress-strain non-linear relation. The difference between the loop compressive yield strain and the composite compressive strain to failure was also explained by this non-linearity.     

A new method for evaluating powder flowability using constant-volume shear tester,

This is an article translated from the original version published in the Journal of the Society of Powder Technology, Japan. A new method for evaluating powder flowability is developed using a constant-volume shear tester; this tester measures the upper and lower normal stresses and the shear stress acting on a powder bed. A single shear test provides a series of characteristics, such as the powder yield locus (PYL), consolidation yield locus (CYL), critical state line (CSL), shear cohesion, stress relaxation ratio, stress transmission ratio, and void fraction. The values of shear stress as a function of the normal stress and void fraction are visualized in three-dimensional diagrams. Furthermore, powder flowability is evaluated using a flow function obtained from the PYL.     

Microstructure and compressive properties of carbon microballoons

Carbon microballoons (CMBs) with tap densities of 0.143, 0.161, and 0.177 g/cm³, as measured per ASTM B 527-93, were characterized in terms of individual balloon diameter, wall thickness, and mechanical behavior in compression through a novel uniaxial compression test technique. This compression test, performed on an MTS Nanoindenter XP II, utilized a flat-ended cylindrical tip rather than the common Berkovich indenter. Quantitative microscopy techniques were used to obtain diameter and wall thickness measurements on the polished cross-sections of individual CMBs that had been cold mounted in epoxy resin. Though there was significant overlap in the three populations, a trend toward increasing average wall thickness—from 1.32 to 2.16 μm—with increasing tap density was observed. Compressive property data including failure load, failure strain, fracture energy, and stiffness were obtained for individual microballoons. Comparison of these data, both inter- and intra-tap density, has yielded some viable trends. CMB failure strain exhibited a dependence upon the inverse square root of the CMB diameter, and CMB failure load depended linearly upon CMB stiffness. Averages for each tap density’s failure load, pseudo-stiffness, and fracture energy were also calculated and observed to increase with tap density.     

Evaluation of mechanical properties of nanoparticles using a constant-volume shear tester

Nanoparticles have advantageous small-size and surface effects that impart them with unique mechanical properties. To evaluate these properties, a constant-volume shear tester that can precisely measure stresses on the shear plane was used. Six samples, namely, hydrophilic and hydrophobic silica, alumina, and titania nanoparticles, were prepared for the shear tests. For each sample, a single shear test provided the void fraction, stress relaxation ratio, stress transmission ratio, powder yield locus, consolidation yield locus, critical state line, shear cohesion, and flow function. All the tests were conducted under ambient conditions using powder beds, in which the void fractions were in the range of 0.89–0.96. A series of analyses demonstrated that the hydrophilic nanoparticles have lower flowability than the hydrophobic nanoparticles, indicating that moisture on the surface increases the cohesion and inhibits the flow.     

The tensile properties of nickel-coated carbon fibres

The tensile properties of nickel-coated Grafil HT carbon fibres were studied as a function of the coating thickness, taking into account the diameter-dependence of the properties of the fibres themselves. The stress-strain curve exhibited three stages, following from an initially elastic coating which yields and then extends plastically before failure of the fibre. The behaviour could be described by a simple law of mixtures and the grain size of the coatings.     

Numerical modeling of composite laminated cylinders in compression using a novel imperfections modeling method

The present study presents the finite element modeling procedure of two composite laminated cylinders exhibiting initial geometric imperfections. Using as input a set of experimental measurements of the cylinder geometry, the application of the skinning method leads to the analytical representation of the cylinder imperfect internal, external and middle surfaces. A finite element mesh is then easily constructed over these surfaces. The results of the analysis are in very good agreement with the experimental strains and buckling load measurements and are used to estimate the knockdown effect of the imperfections on the cylinder buckling behaviour. They are also compared to results obtained by other simpler finite element models, in an effort to evaluate the accuracy of various modeling simplifications.