Using Plasma-Activated High Performance Fibers with Nanocrystalline Structure in Producing New Reinforced Composite Materials

A multifilament wet-pull-out method for estimation of physicochemical interaction between the fiber and the matrix in composite materials reinforced with high-strength high-modulus polyethylene fiber has been proposed. Controlled parameters are fiber capillary rise h and pull-out force F. The method allows one to estimate the wettability and multifilament fiber impregnation with the liquid matrix and measure fiber capillary rise and the joint strength after curing process finished. The multifilament wet-pull-out method considers a total interaction between the matrix and filaments in a complex fiber or yarn. It is the advantage of this method in comparison with the tests of individual monofilament. The method makes it possible to model the real operating conditions of CM.     

Cylinder test: Development of a new microbond method

The microbond test has been investigated with respect to test accuracy and repeatability. It has been concluded that the interfacial shear strength deduced from this method is uncertain due to the droplet shape, which can, however, be reduced by modifying the geometry. In the new method it was proposed that the droplet is replaced by a cylinder. Comparative tests proved that the accuracy improved due to the modifications. The effects of test speed and geometrical parameters (height/diameter of the cylinder) on the interfacial shear strength were investigated. It was found that the test results are sensitive to these parameters and the related changes are discussed. It is recommended to perform the cylinder test in the pull-out range of 10-100 mm/min where the interfacial shear strength does not change with testing speed.     

Neural-network modeling of hot-compression test curves for calendering gasket materials

In this paper, we report on the use of neural networks (NNs) to estimate hot-compression test (HCT) curves for calendering gasket materials on the basis of their formulas. The NNs were used to demonstrate their potential during optimizing formulas for new calendering gasket materials. In the past, and to a large extent even now, the optimization of a new calendering gasket material was based on a process of trial and error, which takes a long time and is expensive because of the need for repeated experimental tests. And even after the completion of all this testing the final formula of the gasket material need not necessarily be the optimum one. We have shown that it is possible, with the assistance of a NN that was trained with appropriate data from just a small number of HCT curves, to satisfactorily investigate the valid ranges of the input data. On the basis of this investigation some valuable information was obtained that will make it easier to develop new calendering gasket materials. Using NNs, the speed of convergence to the final formula of the calendering gasket material can be much faster, because there is no need carry out many experimental HCT tests.     

Modified slotted shear test for a thin sheet of solid polymer under large deformations

A modified slotted shear test based on ASTM B831 is proposed and used for determining the mechanical behavior of a solid polymer at large deformations. The shear stress-strain response of a thin sheet of polytetrafluoroethylene was experimentally investigated and a V-notched rail shear test was carried out to validate the experimental results obtained with the proposed approach. Displacement and strain fields of the test specimens were estimated by the Digital Image Correlation method. The results indicate agreement between both tests for small deformations, while for large deformations significant discrepancies in shear stress-strain responses are observed. These discrepancies can be attributed to unwanted distortions of the gage section observed in the V-notched specimens. The modified slotted shear test provided a uniform shear strain distribution across the gauge section of specimens. In addition, the principal advantages of the proposed approach over V-notched rail shear test are a wide range of shear strains and absence of unwanted distortions.     

Design of a modified three-rail shear test for shear fatigue of composites

There are various ways of determining the static in-plane shear properties of a fibre-reinforced composite. One of them is the standard three-rail shear test, as described in “ASTM D 4255/D 4255M The standard test method for in-plane shear properties of polymer matrix composite materials by the rail shear method”. This setup, however, requires drilling holes through the specimen. In this study, a new design based on friction and geometrical gripping, without the need of drilling holes through the composite specimen is presented. Quasi-static tests have been performed to assess the symmetry of the setup and the occurrence of buckling. Then, fatigue tests were done to assess the behaviour of the grips under fatigue loading conditions, yielding excellent results; the specimen fails under shear loading conditions in the loaded area. The material used to validate this setup was a carbon fabric-reinforced polyphenylene sulphide.

During fatigue, this material shows an increase in permanent deformation and a decrease in shear stiffness until a certain point in time, after which a drastic increase in deformation and temperature, higher than the softening temperature of the matrix occurs. Furthermore, the maximum value of the shear stress for fatigue with R=0 has a large influence on the fatigue lifetime.     

5-HT1A Serotonergic, α-Adrenergic and Opioidergic Receptors Mediate the Analgesic Efficacy of Vortioxetine in Mice

Vortioxetine is a multimodal antidepressant drug that affects several brain neurochemicals and has the potential to induce various pharmacological effects on the central nervous system. Therefore, we investigated the centrally mediated analgesic efficacy of this drug and the mechanisms underlying this effect. Analgesic activity of vortioxetine (5, 10 and 20 mg/kg, p.o.) was examined by tail-clip, tail-immersion and hot-plate tests. Motor performance of animals was evaluated using Rota-rod device. Time course measurements (30–180 min) showed that vortioxetine (10 and 20 mg/kg) administrations significantly increased the response latency, percent maximum possible effect and area under the curve values in all of the nociceptive tests. These data pointed out the analgesic effect of vortioxetine on central pathways carrying acute thermal and mechanical nociceptive stimuli. Vortioxetine did not alter the motor coordination of mice indicating that the analgesic activity of this drug was specific. In mechanistic studies, pre-treatments with p-chlorophenylalanine (serotonin-synthesis inhibitor), NAN-190 (serotonin 5-HT_1A receptor antagonist), α-methyl-para-tyrosine (catecholamine-synthesis inhibitor), phentolamine (non-selective α-adrenoceptor blocker), and naloxone (non-selective opioid receptor blocker) antagonised the vortioxetine-induced analgesia. Obtained findings indicated that vortioxetine-induced analgesia is mediated by 5-HT_1A serotonergic, α-adrenergic and opioidergic receptors, and contributions of central serotonergic and catecholaminergic neurotransmissions are critical for this effect.     

Application de la diphényl-acroléine à l'analyse fonctionnelle

In highly acid alcoholic medium, diphenyl-acrolein develops a red colour with m-diphenols, in the cold. This reaction, which makes it possible to carry out determinations, has a sensitivity of one μg. Under the same conditions, yellow colouring is obtained with methylenes in the α position of a carboxyl or with primary aromatic amino groups. Various condensation products have been isolated.     

Determination of slow crack growth behaviour of polyethylene pressure pipes with cracked round bar test

In this work, a short time test method to determine the slow crack growth behaviour of samples made out of pipes was evaluated. The cracked round bar (CRB) method used provides results below 48 h with brittle fracture surfaces, which indicates the type of slow crack growth failure. To evaluate the usability of the method, the results were compared with well-known tests such as notch pipe test, 2 notch creep test and instrumented Charpy impact tests. The results indicate that the CRB test can be used to predict long term slow crack growth behaviour of PE pipes.     

Investigation of minerals and of lunar samples (14163, 14258) by simultaneous thermal and X-ray analysis

Two methods for density determination are compared for test solutions of different apparent relative density (0.9778–1.0648). In case of the conventional method a comparative variation range of ±0.0003 has been found for three test solutions by cooperative experiment. In case of one test solution (liqueur wine) ±0.00042 has been obtained. The automatized digital method described permits the calculation of the density ? or the apparant relative density D′ ₂₀ ²⁰ from the resonance frequency of a flexural oscillator filled with the solution and excited to undamped oscillation by high frequency. The comparative variation range 3σ of this method was <5×10^?5 for three test solutions and standard solutions. For liqueur wine it was 7.8×10^?5. The mean values of the test solutions by the automatized method are within the single standard deviation of the pyknometric mean values. Both values are comparable. The digital method is recommended as reference method. It avoids subjective personal errors and makes possible the measurement of about 20 test solutions per hour.     

Amorçage de la décohésion dans l'essai d'arrachement

By revisiting the classical formulation of fracture mechanics, the study of debonding in composite materials can be modelised by a principle of least energy. We are interested in the study of the fibre pull-out problem. Considering a cylindric reinforced beam characterised by the ε ratio of its radius to its length, an energy study shows, by taking into account free-edge effects near the interface, that debonding happens suddenly when the length is of order √ε.     

Synergistic modification by mercapto hyperbranched polysiloxane and functionalized graphene oxide on the surface of aramid fiber

With the purpose of improving the interfacial properties of aramid fibers reinforced rubber composites and enhancing the tensile strength of aramid fibers simultaneously, mercapto hyperbranched polysiloxane (HPSi) and functionalized graphene oxide (GO) were used to modify the surface of aramid fibers. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and other characterization methods were performed to confirm the process of synergistic modification. Judging from the results of mechanical property tests, it could be acquired that the tensile strength of modified aramid fiber was increased by 16.8%, which could be ascribed to the wrapping effect of GO sheets. The interfacial properties were assessed by the pull-out tests of composites, and the results showed that the maximum pull-out force after synergistic surface modification was increased by 99.3%, which could be mainly related to additive reaction between double bonds and mercapto groups and the promotion of surface energy. More critically, during pull-out test, aramid fiber bundles might bring a part of shear stress into the grafted GO sheets, namely, GO sheets could convert fracture energy into interfacial energy, which would improve interfacial properties dramatically.     

Demethylation of trimethylantimony species in aqueous solution during analysis by hydride generation/gas chromatography with AAS and ICP MS detection

The method of hydride generation for the speciation of antimony compounds was examined with respect to the problem of molecular "rearrangement'. Specifically, demethylation of trimethylstilbine during the analysis of trimethylantimony dichloride (Me₃SbCl₂) was studied. Previously published observations that enhanced demethylation takes place as a result of inadequate preconditioning of the analytical apparatus were found to be not reproducible. However, demethylation was enhanced as the pH decreased when using two different analytical methods: semi-continuous flow hydride generation–gas chromatography–atomic absorption spectrometry (HG– GC–AAS), and batch-type hydride generation– gas chromatography–inductively coupled plasma mass spectrometry (HG–GC–ICP MS). Applications of the hydride generation method to environmental samples revealed differences in analytical results at high and low pH, and enhanced demethylation taking place because of the matrix in a fungal extract sample. The authors recommend that researchers using the method of hydride generation for antimony compounds carefully test the reaction conditions with standard compounds and use the method of standard addition only. © 1998 John Wiley & Sons, Ltd.     

Experimental investigation on the yield loci of PA66

Compression, tensile and mixed compression/shear tests were performed on PA66 by using a universal material testing machine in order to identify the experimental yield loci of PA66. For the mixed compression/shear tests, instead of using a complex loading device, SCS (shear-compression specimens) were used to generate the additional shear stresses. Then, the mechanical behavior of materials under complex stress states can be obtained for further analysis. Results show that the experimental yield loci of PA66 obtained by the test method proposed in the present paper agree well with the theoretical model based on three stresses invariant, which indicates the reliability of the test method.     

Transcrystallization of PTFE fiber/PP composites. II. Effect of transcrystallinity on the interfacial strength

It has been found that transcrystallinity of polypropylene (PP) develops easily on the polytetrafluoroethylene (PTFE) fiber surface in spite of the low surface energy of the fiber. Effect of the transcrystallinity on the interfacial strength has been extensively investigated using a single-fiber pull-out test. By controlling the crystallization temperature, range 25–130°C, the thickness of the transcrystalline layer varied from 0 to 175 μm for thick specimens, ca. 1 mm thick. Measurements of the adhesive fracture energy, the interfacial shear strength and the frictional stress were carried out for specimens with different embedded fiber lengths. Results show that interfacial strength and fracture energy are independent of the transcrystalline thickness. The calculated value of interfacial shear strength is 3.6 MPa, and the fracture energy for debonding is 2.1 J/m². The presence of transcrystallinity does not promote the level of adhesion in PTFE/PP composites. However, the frictional stresses at the debonded fiber/matrix interface increase with transcrystalline thickness. It is attributed to the residual stresses which arise from shrinkage when specimens are cooled from crystallization temperature to room temperature. © 1996 John Wiley & Sons, Inc.     

Rare variants analysis by risk-based variable-threshold method

Genome-wide association studies, as a powerful approach for detecting common variants associated with diseases, have revealed many disease-associated loci. However, the traditional association analysis methods do not have enough power for detecting the effects of rare variants with limited sample size. As a solution to this problem, pooling rare variants by their functions into a composite variant provides an alternative way for identifying susceptible genes. In this paper, we propose a new pooling method to test the variant–disease association and to identify the functional rare variants related with the disease. Variants with smaller and larger risk measures defined as the ratio of allele frequencies between cases and controls are pooled and a chi-square test of the resultant pooled table is calculated. We vary the threshold of pooling over all possible values and use the maximal chi-square as test statistic. The maximal chi-square is in fact the global maximum over all possible poolings. Our approach is similar to the existing variable-threshold method, but we threshold on the risk measure instead of allele frequencies of controls. Simulation results show that our method performs better in both association testing and variant selection.     

Influencing factors for static immersion tests of compatibility between elastomeric materials and lubricants

Material compatibility is an important factor to consider during the development of new lubricants and sealing materials. Static immersion tests provide a first idea about the compatibility between elastomeric materials and lubricants. For the same material combination, significant deviations among the test results of different laboratories have been reported. In order to identify the relevant factors affecting the results, a systematic investigation was carried out. Reproducibility tests show that the estimation of the compatibility is compromised due to the deviations that appear for the change of the mechanical properties of the considered reference elastomers. The influences of the closure of the test apparatus and the volume ratio, as well as the development of the aging process, were investigated. The results showed that, in order to differentiate between elastomer-lubricant material combinations, standard test durations of approximately 1008 h are preferred. Volume ratios of 64 and 80 and small variations of the vessel closure did not lead to significant deviations of the results. In contrast, tests with open and closed vessels showed significant deviations for the hardness and mechanical properties of the elastomeric materials.     

Effect of glue-line thickness on pull-out behavior of glued-in GFRP rods in LVL: Finite element analysis

This paper uses finite element analysis (FEA) to verify the results of previous experimental works conducted on the effect of glue-line thickness and rate of loading on pull-out behavior of glued-in GFRP rods in LVL. For this purpose, the materials were considered as orthotropic for the timber and the GFRP rod, and isotropic for epoxy resin. To determine the effects of thickness on pull-out, four glue-lines namely 0.5, 1, 2 and 4 mm were modelled. To examine the effects of rate of loading, three glue-lines 0.5, 2 and 4 mm were modelled with different values of modulus of elasticity selected for the resin to simulate higher and lower rates of loading. Results showed that with an increasing thickness of glue-line, the concentration of Z-direction stresses declines across the glue-line thickness from the rod-adhesive interface towards the adhesive-timber interface and the magnitude of shear stresses, τ_XZ, increases to a maximum within the glue-line in a zone about 20–30% into the resin layer and this is seen for all glue-line thicknesses. Also, by changing values of elastic modulus for the resin in the FE model to simulate rate of loading, it was shown that thicker glue-lines are more sensitive to loading rate.     

Reaction gas chromatography: Study of the photodecomposition of selected substances

Summary A simple apparatus that permits to carry out photolytic reactions in direct connection with a gas chromatograph has been designed. The photodecomposition of C₅–C₇ aliphatic alkanes, C₁–C₅ primary, secondary and tertiary aliphatic alcohols and of some other substances was studied using this apparatus. The degradation products are characteristic of the individual types of alcohols. The identification of the individual types of alcohols. The identification of the degradation products confirms the proposed schemes for the photodegradation reactions. The apparatus described can also be used for the study of photolysis kinetics, as it permits the easy and rapid variation of the reaction conditions.     

Experimental determination of rheological properties of polydimethylsiloxane

A series of linear polydimethylsiloxane of different molecular weight and with reduced polydispersity were prepared by partial fractionation of commercial products. The rheological functions, i.e. zero shear viscosity (η₀), first and second normal stress coefficients (Ψ₁₀ and Ψ₂₀), of the materials were experimentally measured by conventional rotational rheometers and by a rotation rod apparatus. The relationships between molecular structure (molecular weight and polydispersity index) and rheological functions are presented and discussed on the basis of equations proposed in the literature. Zero shear viscosity data conform to the well-known dependence on a power 3.5 of molecular weight. However, a consistently stronger influence of molecular weight over Ψ₁₀ and Ψ₂₀ is found. The influence of polydispersity over Ψ₁₀ is also analyzed.     

Minimal spanning tree analysis of regular,random and cluster structures

It is shown that a graph called the minimal spanning tree (MST) is capable of detecting several kinds of cluster structure in arbitrary points set. From a MST it is possible to deduce the average edge lengthm and the standard deviationσ, which are characteristics for the corresponding distribution. The use of a diagram involving bothm andσ makes it possible to determine the degree of order by taking a simple reading in the (m,σ) plane. It is also possible, through angular diagrams retrieved from the MST, to bring out directional properties. The method is applied to the study of the growth of granular thin films.