High strain rate in-plane shear behavior of composites

Studies are presented on in-plane shear properties of a typical plain weave E-glass/epoxy composite under high strain rate loading. In-plane shear properties were determined with ±45 degree off-axis compression and tension tests using a split Hopkinson pressure bar apparatus. In-plane shear properties are presented as a function of axial and shear strain rates. The range of axial strain rates for off-axis compression tests was 819–2003 per sec, and for off-axis tension tests was 91–180 per sec, whereas the range of shear strain rates for off-axis compression tests was 1388–3442 per sec and for off-axis tension tests was 153–303 per sec. In general, it was observed that in-plane shear strength was enhanced at high strain rate loading compared to that at quasi-static loading. Also, it was observed that in-plane shear strength increased with increasing strain rate within the range of strain rates considered.     

High strain rate compression testing of intra-ply and inter-ply hybrid thermoplastic composites reinforced with Kevlar/basalt fibers

In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage.     

Development of the split-Hopkinson pressure bar technique for viscous fluid characterization

The split Hopkinson pressure bar (SHPB) technique has been employed to evaluate the dynamic squeeze flow behavior of viscous Newtonian fluids. In this paper, the conditions under which classic Hopkinson bar data analysis is applicable for fluid specimens are discussed in detail. Requirements include the development of a parabolic flow profile and associated pressure distribution across the specimen. The times required for these processes to occur are calculated and compared with the experimental timescale in order to establish a specimen design criterion for valid SHPB testing. To evaluate this design criterion, an isothermal squeeze flow model describing the behavior of a cylindrical fluid specimen which includes inertial forces is used to predict the experimental results for a model Newtonian fluid. Good agreement between the theory and the experiment is obtained for thin specimens (1.0 mm) across a wide range of shear strain rates (over 10⁵ s⁻¹). As a result of this study, the conditions under which valid SHPB experimental results may be obtained for a Newtonian fluid specimen are identified.     

High strain rate behavior of graphene-epoxy nanocomposites

This work consists of the synthesis of high purity graphene nanoflakes (GNF), the manufacturing of GNF-epoxy nanocomposites and the mechanical characterization of the nanocomposite at high and quasi static strain rates, (2750/s - 1.E−5/s). GNF were synthesized by using the electric arc discharge technique. Thermogravimetry/Differential Thermal Analysis (TG/DTA) of synthesized graphene reveals high purity and high crystallinity. Raman spectra and the broad Brunauer-Emmet-Teller (BET) specific surface area indicate that the synthesized graphene has several layers. Following the solution mixing manufacturing process of GNF-epoxy nanocomposites, the influences of strain rate on the mechanical behaviors are investigated under quasi static and dynamic loadings. High strain rate uniaxial compression tests (1270–2750/s) using Split Hopkinson Pressure Bar (SHPB) and quasi static compression tests (1.E−3 and 1.E−5/s) of GNF-epoxy with two graphene contents (0.1 and 0.5 wt %) are performed at room temperature. The maximum elasticity modulus achieved by the GNF-epoxy with 0.5 wt% at the strain rate of 2350/s corresponds to a 68% increase compared to the neat epoxy. The yield strength of the material is doubled under dynamic loading conditions compared to the quasi static loading.     

Towards the development of laser shock test for mechanical characterisation of fibre/matrix interface in eco-composites

This paper deals with the possibility of using the laser shock test for studying the adhesion between fibre and matrix in composite materials. Single hemp yarn in epoxy matrices - a fully synthetic one, Epolam 2020, and a partially bio-based one, Greenpoxy 56 - specimens have been tested. The water sorption effect on interfacial adhesion quality has been studied. Two different types of damage induced by laser shock have been observed: resin cracks appear only for high laser intensity levels, and specific cone-shaped interfacial damage appears for lower intensity values. The reproducibility of the threshold value evaluation has been demonstrated for the two resins. A numerical simulation by finite elements has also been performed to enhance the understanding of laser shock wave propagation in such samples. These preliminary results demonstrate the ability of the laser shock test to study and quantify the mechanical quality of yarn/matrix interface, which is needed to help design of such composites.     

High strain rate out-of-plane compression properties of aramid fabric reinforced polyamide composite

The composite-structure protective systems in head-on collision with objects are largely subjected to dynamic compression load along the thickness of composite structure. A typical plain weave aramid fabric reinforced polyamide (PA) composite, which is defined as one of single polymer composites (SPCs), is addressed in this paper. Firstly, in the process of sample preparation, processing characteristics of the single polymer composites are skillfully achieved and discussed using differential scanning calorimetry (DSC) and capillary rheometer. Secondly, the out-of-plane compression properties of the composite are studied on Split Hopkinson Pressure Bar (SHPB) apparatus in the strain rate range of 400–1200s⁻¹. Effects of fiber content and strain rate on dynamic off-plane compression properties are investigated and quasi-static properties are obtained on a universal testing machine as a comparison. Results provide a basis for selecting composite composition and lay-up for designing armor with improved impact resistance. Additionally, penetration of the resin through the fabric is observed by the digital microscope and the internal damage of the laminates is qualitatively predicted by the microstructure of the internal fabric yarns.     

Solution-based Preparation of High Sulfur Content Sulfur/Graphene Cathode Material for Li-S Battery

Practical Li-sulfur batteries require the high sulfur loading cathode to meet the large-capacity power demand of electrical equipment.However,the sulfur content in cathode materials is usually unsatisfactory due to the excessive use of carbon for improving the conductivity.Traditional cathode fabrication strategies can hardly realize both high sulfur content and homogeneous sulfur distribution without aggregation.Herein,we designed a cathode material with ultrahigh sulfur content of 88%(mass fraction)by uniformly distributing the water dispersible sulfur nanoparticles on three-dimensionally conductive graphene framework.The water processable fabrication can maximize the homogeneous contact between sulfur nanoparticles and graphene,improving the utilization of the interconnected conductive surface.The obtained cathode material showed a capacity of 500 mA·h/g after 500 cycles at 2.0 A/g with an areal loading of 2 mg/cm2.This strategy provides possibility for the mass production of high-performance electrode materials for high-capacity Li-S battery.     

Electrochemical method for precise determination of wall shear rate

The convective diffusion problem near small electrodes is solved numerically using finite volume method (direct problem). The results obtained are first used to define the limits of the quasi-steady state Leveque solution for a rectangular and circular probe. After, the algorithm is integrated to an inverse sequential method in order to obtain the wall shear rate from the measurements of the limiting diffusion currents. The results are compared with the classical techniques of calculation of wall shear rate as the quasi-steady solution, transfer function methods and the Leveque solution with transient correction. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 470–481. The text was submitted by the authors in English.     

Full rate constant matrix contraction method for obtaining branching ratio of unimolecular decomposition

The branching ratio of unimolecular decomposition can be evaluated by solving the rate equations. Recent advances in automated reaction path search methods have enabled efficient construction of the rate equations based on quantum chemical calculations. However, it is still difficult to solve the rate equations composed of hundreds or more elementary steps. This problem is especially serious when elementary steps that occur in highly different timescales coexist. In this article, we introduce an efficient approach to obtain the branching ratio from a given set of rate equations. It has been derived from a recently proposed rate constant matrix contraction (RCMC) method, and termed full‐RCMC (f‐RCMC). The f‐RCMC gives the branching ratio without solving the rate equations. Its performance was tested numerically for unimolecular decomposition of C₃H₅ and C₄H₅. Branching ratios obtained by the f‐RCMC precisely reproduced the values obtained by numerically solving the rate equations. It took about 95 h to solve the rate equations of C₄H₅ consisting of 234 elementary steps. In contrast, the f‐RCMC gave the branching ratio in less than 1 s. The f‐RCMC would thus be an efficient alternative of the conventional kinetic simulation approach. © 2016 Wiley Periodicals, Inc.     

Pervaporation, a novel technique for the measurement of vapor transmission rate of highly permeable films

The moisture vapor transmission rate (MVTR) of poly(ether-block-amide) breathable films were measured with a set-up based on the ASTM E96 E and BW methods. These methods led to reliable MVTR for films of low breathability, but not for films of high breathability. The latter shows MVTR values varying over a large range when the operating conditions are changed. An analysis of the mass and the heat transfers pointed out the crucial role of the transfer resistances in the external phases adjacent to the film. The pervaporation technique was designed to minimize these mass and heat transfer resistances using a powerful stirring of the upstream chamber and a good vacuum applied on the downstream chamber. The MVTR was determined from the weight of vapor condensed in a cool trap. The MVTR of films of high breathability were reliably determined by this method; their value was much higher than those obtained with the ASTM E96 BW method for the same films. The obtained intrinsic MVTR data suggest that (i) the film structure is more ordered at lower thickness, and (ii) the activation energy for water permeation is low, probably due to the high flexibility of polyether segments. The technique was successfully used for the measurement of a very high MVTR film made of poly(vinylalcohol), ca. 120 kg day⁻¹ m⁻², and for the measurement of the permeation rate of ethylacetate through a silicone rubber film.     

A new method for testing polymer gear wear rate and performance

This paper provides details of a new test rig design and methodology intended for, and successfully applied to, measuring the gear wear rate and performance of polymer composite gears under both dry and lubricated conditions. One of its unique contributions is that it continuously measures the gear wear rate, a feature essential for understanding polymer gear behaviour. While sharing some concepts with the traditional back-to-back test configuration used for steel gears, the new method introduces a rotary freedom to the block supporting the polymer gears under test. This block rotates if the gear tooth thickness is reduced, which aids control of the test load. The gear surface wear rate is recorded continuously by using a capacitance transducer to measure the pivot block motion. A second unique contribution of the new test method involves splitting the support block so that controlled misaligned gear engagements (not reported in other designs) can be introduced and subsequent changes to wear behaviour studied. The paper first outlines the test rig concepts and design before discussing in more detail the gear wear rate measuring principles, the methods of centre distance adjustment and the achievement of virtually constant gear loading. Finally, a selection test results are presented in summary to further validate the new test method and illustrate potential applications.     

High loading Pt nanoparticles on ordered mesoporous carbon sphere arrays for highly active methanol electro-oxidation

Three-dimensionally (3D) ordered mesoporous carbon sphere arrays (OMCS) are explored to support high loading (60 wt%) Pt nanoparticles as electrocatalysts for the methanol oxidation reaction (MOR). The OMCS has a unique hierarchical nanostructure with ordered large mesopores and macropores that can facilitate high dispersion of the Pt nanoparticles and fast mass transport during the reactions. The prepared Pt/OMCS exhibits uniformly dispersed Pt nanoparticles with an average size of 2.0 nm on the mesoporous walls of the carbon spheres. The Pt/OMCS catalyst shows significantly enhanced specific electrochemically active surface area (ECSA) (73.5 m² g^-1) and electrocatalytic activity (0.69 mA cm^-2) for the MOR compared with the commercial 60 wt% Pt/C catalyst.     

A spot test for ammonium ion by the color band formation method

Removing nutrients from wastewaters is important in controlling eutrophication. Processes for removing nutrients require accurate control of operational conditions, and it is necessary to monitor nutrient concentrations during the removal process. For this purpose, a simple and accurate analytical method is especially important for small-scale wastewater treatment facilities. Here, we report a simple colorimetric method for determining NH₄⁺-N in wastewater. The method is to detect NH₄⁺-N by a color band length formed in a minicolumn, and similar methods for heavy metals detection were reported by Morosanova et al. In this study, the length of the color band of indonaphthol dye trapped on an adsorbent in a minicolumn was linearly correlated with NH₄⁺-N concentration in the range 1-10 mg NH₄⁺-N l⁻¹ under optimized conditions. This methods was developed on the basis of our previously reported color band methods for orthophosphate and nitrite determination, but the adsorbent used in this work consisted of an admixture of synthetic hydrotalcite particles and poly(vinyl chloride) particles coated with equal amounts of benzylcetyldimethylammonium chloride and biphenyl. When the method was applied to actual wastewaters, the results corresponded well with the results obtained by the standard method, and suspended solids (SS) and dissolved organic pollutants did not interfere with detection.     

Moment theory for the analytical determination of rate constants for solute permeation at the interface of spherical molecular aggregates

Moment equations were developed on the basis of the Einstein equation for diffusion and the random walk model to analytically determine the rate constant for the interfacial solute permeation from a bulk solvent into molecular aggregates (k_in) and the inverse rate constant from the molecular aggregates to the bulk solvent (k_out). The moment equations were in good agreement with those derived in a different manner. To demonstrate their effectiveness in one concrete example, the moment equations were used to analytically determine the values of k_in and k_out of three electrically neutral solutes, i.e. resorcinol, phenol, and nitrobenzene, from the first absolute (μ_1A) and second central (μ_2C) moments of their elution peaks, as measured by electrokinetic chromatography (EKC), in which the sodium dodecyl sulfate (SDS) micelles were used as a pseudostationary phase. The values of k_in and k_out should be determined with no chemical modifications and no physical action with the molecular aggregates because they are dynamic systems formed through weak interactions between the components. The moment analysis of the elution peak profiles measured by EKC is effective to unambiguously determine k_in, k_out, and the partition equilibrium constant (k_in/k_out) under appropriate experimental conditions.     

Novel evaluation method for degradation rate of polymer electrolytes in fuel cells

A simple and new method has been developed to evaluate the degradation rate of polymer electrolytes caused by the cross-leakage of H₂ or O₂ in PEFCs. Mixed gas of H₂ and air with a constant composition was supplied to a sample powder suspended in water, e.g., consisting of Pt supporting carbon black coated with a perfluorosulfonated acid electrolyte. Fluoride ion released from the electrolyte into the water was quantitatively analyzed as a function of time. The electrolyte was decomposed only when H₂, O₂, and Pt coexisted. The present method enables to compare the durability of different electrolyte polymers directly under the same controlled environment within a short period.     

Gas chromatographic method for studying the rate of photodegradation of some nitrogen-containing pesticides

Summary The photodegradation behaviour of 12 nitrogen-containing herbicides (atrazine, cyanazine, terbuthylazine, terbutryn, EPTC, buthylate, molinate, cycloate, vernolate, fenuron, chloroxuron, and methabenzthiazuron) has been examined. The compounds were degraded completely when exposed to a mercury-vapour lamp; the degradation process was followed by consecutive GC measurements. All the compounds studied had measurable photochemical activity, although actual and average degradation rates varied significantly. All the compounds except terbutryn furnished more than one major degradation product, in different ratios. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Correlation of molecular parameters,strain hardening modulus and cyclic fatigue test performances of polyethylene materials for pressure pipe applications

Currently, several testing methods are under development to understand the resistance of polyethylene pipe materials to slow crack growth over comparably short time periods without using aggressive chemicals to accelerate the time to brittle failure. Strain hardening and crack round bar tests have recently been developed and published as ISO testing methods. However, a better understanding of these testing methods is still required with respect to the molecular parameters of the materials. Comparative studies with existing slow crack growth testing methods such as the notched pipe test are of significant interest to the industry. This study discusses correlations of molecular weight, molecular weight distribution, short chain branching and rheological properties of different polyethylene materials with their slow rack growth resistances obtained from the strain hardening and crack round bar tests and their correlations with notched pipe tests.