Chemical toughening of epoxies. II. Mechanical, thermal, and microscopic studies of epoxies toughened with hydroxyl-terminated poly(butadiene-co-acrylonitrile)

Diglycidyl ether–bisphenol-A-based epoxies toughened with various levels (0–12%) of chemically reacted liquid rubber, hydroxyl-terminated poly(butadiene-co-acrylonitrile) (HTBN) were studied for some of the mechanical and thermal properties. Although the ultimate tensile strength showed a continuous decrease with increasing rubber content, the toughness as measured by the area under the stress-vs.-strain curve and flexural strength reach a maximum around an optimum rubber concentration of 3% before decreasing. Tensile modulus was found to increase for concentrations below 6%. The glass transition temperature Tg as measured by DTA showed no variation for the toughened formulations. The TGA showed no variations in the pattern of decomposition. The weight losses for the toughened epoxies at elevated temperatures compare well with that of the neat epoxy. Scanning electron microscopy revealed the presence of a dual phase morphology with the spherical rubber particles precipitating out in the cured resin with diameter varying between 0.33 and 6.3 μm. In contrast, a physically blended rubber–epoxy showed much less effect towards toughening with the precipitated rubber particles of much bigger diameter (0.6–21.3 μm).

Formation of shear bands in plane sheet

The formation of shear bands in plane sheet is studied, both analytically and experimentally, to enhance the fundamental understanding of this phenomenon and to develop a capability for predicting material failure. The evolution of voids is measured and its interaction with the process of shear banding is examined. The evolving dilatancy in plasticity is shown to have a vital role in analysing the shear-band type of bifurcation, and tremendously reduces the theoretical value of critical stresses. The analyses, referring to both localized and diffuse modes of bifurcation, fairly explain the corresponding observations obtained through testing a dual-phase steer sheet and provide a justification of the constitutive model used.

力学2000

本书收录关于力学领域的论文301篇。内容包括：回顾20世纪力学在中国的发展，描绘了2000年中国和世界在力学各主要领域的发展现状；展望力学在21世纪的发展方向，探论新世纪中可能面临的新的重大力学等问题。

Testing of a novel flexible concrete arch system

This paper describes the testing of a novel flexible masonry concrete arch system which requires no centering in the construction phase or steel reinforcement in the long-term. The arch is constructed from a 'flat pack' system by use of a polymer reinforcement for supporting the self-weight of the concrete voussoirs and behaves as a masonry arch once in the arch form. The paper outlines the construction of a prototype arch and load testing of the backfilled arch ring. Some comparisons to the results from analysis software have been made. The arch had a load carrying capacity far in excess of the current Highways Agency (United Kingdom) design wheel loads.

Unusually high differential attenuation at C band: Results from a two-year analysis of the French Trappes polarimetric radar data

The differential phase (ΦDP) measured by polarimetric radars is recognized to be a very good indicator of the path integrated by rain. Moreover, if a linear relationship is assumed between the specific differential phase (KDP) and the specific attenuation (AH) and specific differential attenuation (ADP), then attenuation can easily be corrected. The coefficients of proportionality, γH and γDP, are, however, known to be dependent in rain upon drop temperature, drop shapes, drop size distribution, and the presence of large drops causing Mie scattering. In this paper, the authors extensively apply a physically based method, often referred to as the “Smyth and Illingworth constraint,” which uses the constraint that the value of the differential reflectivity ZDR on the far side of the storm should be low to retrieve the γDP coefficient. More than 30 convective episodes observed by the French operational C-band polarimetric Trappes radar during two summers (2005 and 2006) are used to document the variability of γDP with respect to the intrinsic three-dimensional characteristics of the attenuating cells. The Smyth and Illingworth constraint could be applied to only 20% of all attenuated rays of the 2-yr dataset so it cannot be considered the unique solution for attenuation correction in an operational setting but is useful for characterizing the properties of the strongly attenuating cells. The range of variation of γDP is shown to be extremely large, with minimal, maximal, and mean values being, respectively, equal to 0.01, 0.11, and 0.025 dB °−1. Coefficient γDP appears to be almost linearly correlated with the horizontal reflectivity (ZH), differential reflectivity (ZDR), and specific differential phase (KDP) and correlation coefficient (ρHV) of the attenuating cells. The temperature effect is negligible with respect to that of the microphysical properties of the attenuating cells. Unusually large values of γDP, above 0.06 dB °−1, often referred to as “hot spots,” are reported for 15%—a nonnegligible figure—of the rays presenting a significant total differential phase shift (ΔϕDP > 30°). The corresponding strongly attenuating cells are shown to have extremely high ZDR (above 4 dB) and ZH (above 55 dBZ), very low ρHV (below 0.94), and high KDP (above 4° km−1). Analysis of 4 yr of observed raindrop spectra does not reproduce such low values of ρHV, suggesting that (wet) ice is likely to be present in the precipitation medium and responsible for the attenuation and high phase shifts. Furthermore, if melting ice is responsible for the high phase shifts, this suggests that KDP may not be uniquely related to rainfall rate but can result from the presence of wet ice. This hypothesis is supported by the analysis of the vertical profiles of horizontal reflectivity and the values of conventional probability of hail indexes.

Polydimethylsiloxane/polypyrrole stir bar sorptive extraction and liquid chromatography (SBSE/LC-UV) analysis of antidepressants in plasma samples

A new polymeric coating consisting of a dual-phase, polydimethylsiloxane (PDMS) and polypyrrole (PPY) was developed for the stir bar sorptive extraction (SBSE) of antidepressants (mirtazapine, citalopram, paroxetine, duloxetine, fluoxetine and sertraline) from plasma samples, followed by liquid chromatography analysis (SBSE/LC-UV). The extractions were based on both adsorption (PPY) and sorption (PDMS) mechanisms. SBSE variables, such as extraction time, temperature, pH of the matrix, and desorption time were optimized, in order to achieve suitable analytical sensitivity in a short time period. The PDMS/PPY coated stir bar showed high extraction efficiency (sensitivity and selectivity) toward the target analytes. The quantification limits (LOQ) of the SBSE/LC-UV method ranged from 20 ng mL(-1) to 50 ng mL(-1), and the linear range was from LOQ to 500 ng mL(-1), with a determination coefficient higher than 0.99. The inter-day precision of the SBSE/LC-UV method presented a variation coefficient lower than 15%. The efficiency of the SBSE/LC-UV method was proved by analysis of plasma samples from elderly depressed patients. (C) 2008 Elsevier B.V. All rights reserved.

Mechanochemical synthesis of nanoparticulate ZnO–ZnWO4 powders and their photocatalytic activity

In this study, mechanochemical reaction systems with H₂WO₄ as a precursor were investigated for the synthesis of nanoparticulate powders of WO₃, ZnWO₄, and dual-phase (ZnWO₄)_x(ZnO)_1–x. The objective was to establish whether mechanochemical processing can be used to manufacture high activity photocatalysts in the ZnO–WO₃ system. Milling and heat treatment of H₂WO₄ + 12NaCl was found to result in the formation of irregularly shaped platelets of a sodium tungstate rather than nanoparticles of WO₃. Powders of single-phase ZnWO₄ and dual-phase (ZnWO₄)_x(ZnO)_1–x were successfully synthesised by incorporating H₂WO₄ into the ZnCl₂ + Na₂CO₃ + 4NaCl reactant mixture. The photocatalytic activity of these powders was evaluated using the spin-trapping technique with electron paramagnetic resonance spectroscopy. It was found that the photocatalytic activity decreased with the ZnWO₄ content. This decrease in activity was attributed to the larger average particle size of the ZnWO₄ component compared to the ZnO, which reduced the surface area available for interfacial transfer of the photogenerated charge carriers.

Modeling of advanced high strength steels with the realistic microstructure–strength relationships

The objective of the work is to consider the first-order effects of the realistic microstructure morphology in the macroscale modeling of the multiphase Advanced High Strength Steels (AHSS). Instead of using constitutive equations at macroscale, the strength–microstructure relationship is studied in the forms of micromechanical and multiscale models that do not make considerable simplifications with regard to the microscale geometry and topology. The trade-off between the higher computational time and the higher accuracy has been offset with a stochastic approach in the construction of the microscale models. The multiphase composite effects of AHSS microstructure is considered in realistic microstructural models that are stochastically built from AHSS micrographs. Computational homogenization routines are used to couple micro and macroscale and resultant stress–strain relations are compared for models built with the simplified and idealized geometries of the microstructure. The results from this study show that using a realistic representation of the microstructure, either for DP or TRIP steel, could improve the accuracy of the predicted stress and strain distribution. The resultant globally averaged effective stress and strain fields from realistic microstructure model were able to accurately capture the onset of the plastic instability in the DP steel. It is shown that the macroscale mechanical behavior is directly affected by the level of complexities in the microscale models. Therefore, greater accuracy could be achieved if these stochastic realistic microstructures are used at the microscale models.

Conducting composite using an immiscible polymer blend matrix

Carbon black (CB) fillers were used to study the feasibility of achieving multiple percolation using an immiscible (polar) polymer blend matrix. By tailoring the morphology of the insulating dual phase matrix it has been shown that the percolation threshold (Ф_c) can be reduced over single-phase matrices. Cocontinuity in the polymer matrix is important in reducing Ф_c by either preferentially isolating the conducting filler at the interface of the two phases or within one particular continuous phase of the matrix thereby forming a continuous conducting network within a continuous network (multiple percolation). Actual melt processing time has been found to influence the dispersion of the fillers and hence Ф_c. Polarity of the matrix as well as the processing method has also been found to influence the dispersion of the filler within the host polymer.

Microstructure-property relationship of the high strength low alloy steels during tensile testing at high strain rates

Positive The influence of strain-rate on the room temperature mechanical properties of the Dual-Phase and Transformation Induced Plasticity (TRIP) steels was investigated.The results showed that both the plastic strain, and strength properties increased with increasing strain rates at high strain rates.At strain rates lower than approximateil 1s ~ (-1) the properties no longer have an advantageous proportionality to strain rate and remain strain rate neutral.Possible explanations are offered for trends exhibited, in terms of thermal and athermal considerations, in relation to the respective microstructures of the two steels

Efeito da temperatura e tempo de austenitização nas transformações de fase da liga 13Cr2Ni0,1C

New classes of martensitic stainless steels, with low carbon levels, have been developed aiming to meet the needs of the petroleum industry segment. However, their use has been restricted due to the fact it is a recent development and many of its properties are still under investigation. This work determines the values of initial and final temperatures for the austenitic transformation and the initial and final temperatures of martensitic formation for alloy 13Cr2Ni0,1C, by means of dilatometric tests under continuous cooling. Based on these results the optimized conditions for quench and temper heat treatments were obtained. The microstructural characterization of the alloys under coarse fusion condition was carried out by optical microscopy and the presence of delta-ferrite in the martensitic matrix was observed.

A simple, rapid method for the extraction of whole fire ant venom (Insecta: Formicidae: Solenopsis)

The invasive fire ant Solenopsis invicta is medically important because its venom is highly potent. However, almost nothing is known about fire ant venom proteins because obtaining even milligram-amounts of these proteins has been prohibitively challenging. We present a simple and fast method of obtaining whole venom compounds from large quantities of fire ants. For this, we separate the ants are from the nest soil, immerse them in dual-phase mixture of apolar organic solvent and water, and evaporate each solvent phase in separate. The remaining extract from the aqueous phase is largely made up of ant venom proteins. We confirmed this by using 2D gel electrophoresis while also demonstrating that our new approach yields the same proteins obtained by other authors using less efficient traditional methods. © 2013 Elsevier Ltd.

Caracterização microestrutural e mecânica de aços bifásicos de ultra-alta resistência como médio teor de carbono

Pós-graduação em Engenharia Mecânica - FEG

Multivisceral Transplantation for Diffuse Portomesenteric Thrombosis

Objective: To evaluate the clinical outcomes of multivisceral transplantation (MVT) in the setting of diffuse thrombosis of the portomesenteric venous system. Background: Liver transplantation (LT) in the face of cirrhosis and diffuse portomesenteric thrombosis (PMT) is controversial and contraindicated in many transplant centers. LT using alternative techniques such as portocaval hemitransposition fails to eliminate complications of portal hypertension. MVT replaces the liver and the thrombosed portomesenteric system. Methods: A database of intestinal transplant patients was maintained with prospective analysis of outcomes. The diagnosis of diffuse PMT was established with dual-phase abdominal computed tomography or magnetic resonance imaging with venous reconstruction. Results: Twenty-five patients with grade IV PMT received 25 MVT. Eleven patients underwent simultaneous cadaveric kidney transplantation. Biopsy-proven acute cellular rejection was noted in 5 recipients, which was treated successfully. With a median follow-up of 2.8 years, patient and graft survival were 80%, 72%, and 72% at 1, 3, and 5 years, respectively. To date, all survivors have good graft function without any signs of residual/recurrent features of portal hypertension. Conclusions: MVT can be considered as an option for the treatment of patients with diffuse PMT. MVT is the only procedure that completely reverses portal hypertension and addresses the primary disease while achieving superior survival results in comparison to the alternative options.