Hot compression and fracture toughness of HSS composed hot strip work rolls

The rolls in the finishing stands must have good resistance to both wear and fire cracks. The use of high-speed steel at the finishing stands has shown satisfactory results. The composition of this high-alloyed steel is an important parameter as the most significant change lays on the type, morphology, and volume fraction of the eutectics carbides. The heat treatment of these products consists of high temperature austenization followed by quenching and two temperings, as required in order to increase their overall hardness and to completely eliminate residual austenite. The influence of tempering temperatures on the mechanical properties of these products, determined using tensile, hot compression and fracture toughness tests, was studied in this research work. Their corresponding failure micromechanisms were defined by means of the analysis of fracture surfaces.     

Curing characteristics and internal stresses in epoxy coatings: Effect of crosslinking agent

The development of internal stresses in a series of epoxy coatings prepared using five different crosslinking agents have been studied. The crosslinking agents were: H1, 4,4 methylenedianiline (DDM); H2, diethylentriamine (DETA); H3, cycloaliphatic polyamine; H4, polyaminoimidazoline; and H5, polyamidoamine adduct. Four different post-cure treatments were applied and the dependence of internal stress on crosslinking agent and post-cure treatment was determined. Curing was followed by monitoring the FTIR epoxy band at 916 cm^{– 1} and the glass transition temperature was determined using DSC to assist interpretation of the measured values of internal stress. The internal stress was tensile in all of the materials at the end of each post-cure treatment. The stress magnitudes increased monotonically with post-cure temperature. The largest stresses were recorded with H1, H2 and H3 whereas the lowest stresses were recorded with H4 and H5, which both included a flexible aliphatic chain. The effects of ageing for extended periods in dry air and in humid air (52%RH and 97%RH) were also examined. Exposure to humid air almost always caused a reduction in the tensile stress and often produced compressive stresses, attributed to swelling due to water absorption. A comparison was made of the stresses formed in coatings applied to a thin substrate that was (i) free to bend during curing, post-curing and ageing, and (ii) prevented from bending (restrained substrate). The general trends in behaviour were in agreement but no simple relationship could be found between the stress magnitudes obtained by the two different test configurations.     

Etude de diverses roches au laboratoire par ondes ultrasonores

The wave propagation velocity in the rocks is a well known tool with many applications in their structure and conditions studies (porosity, microcracks, saturation) or for the relationship with their mechanical properties (R_c, dynamic modulus, ...). In this paper, the interest of the signal shape study is pointed out for a better characterization of the porous medium. An examination of the transmitted frequencies looks particularly promising for materials quality determination.     

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.     

Synergism Effect of Montmorillonite and Cellulose Whiskers on the Mechanical and Barrier Properties of Natural Rubber Composites

A series of nanocomposite films based on natural rubber (NR), Na⁺‐montmorillonite (MMT), and cellulose whiskers (W) was prepared, keeping a total filler content equal to 5 wt.‐%. In the binary NR/MMT system, small stacks of intercalated montmorillonites were homogeneously dispersed within the polymer matrix whereas they were clearly lying in the vicinity of cellulose whiskers in the ternary NR/MMT/W blends. The effects of MMT and W on mechanical and gas barrier properties of the nanocomposite films were investigated. A significant increase of the rubbery modulus was obtained upon filler addition. The reinforcing effect was particularly important for the nanocomposite film reinforced with 1 wt.‐% MMT and 4 wt.‐% W. The improvement of the gas barrier properties observed upon filler addition was explained by a tortuosity effect. The calculated tortuosity values indicated that the simultaneous use of MMT and W could greatly slow down the gas diffusion rate in NR. Formation of MMT‐W subassembly should be responsible for this synergism effect.

     

Beta zeolite supported sol-gel TiO2 materials for gas phase photocatalytic applications

Beta zeolite supported sol-gel TiO(2) photocatalytic materials were prepared according to a sol-gel route in which high specific surface area Beta zeolite powder was incorporated into the titanium isopropoxide sol during the course of the sol-gel process. This led to an intimate contact between the zeolite surface and the TiO(2) precursors, and resulted in the anchorage of large amounts of dispersed TiO(2) nanoparticles and in the stabilization of TiO(2) in its anatase form, even for high TiO(2) wt. contents and high calcination temperatures. Taking the UV-A photocatalytic oxidation of methanol as gas phase target reaction, high methanol conversions were obtained on the Beta zeolite supported TiO(2) photocatalysts when compared to bulk sol-gel TiO(2), despite lower amounts of TiO(2) within the photoactive materials. The methanol conversion was optimum for about 40 wt.% TiO(2) loading and calcination temperatures of 500-600°C.     

Numerical modelling for simulation and treatment planning of prostate thermal therapy

A 2D transmission line matrix model is used to study thermal transfer in living tissues exposed to laser energy. Damage size because of thermal coagulation in thermal treatment of benign prostate hyperplasia is determined quantitatively. Results show a quasilinear dependency of blood perfusion on temperature at the beginning of coagulation. Immediately thereafter, blood perfusion decreases considerably until it shuts down when the tissue under investigation has been coagulated. Increase in perfusion rate (ω) leads to high values of t₁₀₀, which is the time required to reach a primary zone temperature of about 100 °C, and reflects the increased cooling created by perfusion. The transmission line matrix numerical model predicts the coagulation damage contours; that way, it has a clinical interest in therapy as an aid for clinicians because damage cannot be easily measured within patients. Results are validated through comparison with other researches. Copyright © 2014 John Wiley & Sons, Ltd.     

Amoxicillin Magadiite Derivatives: Advanced Materials for Antibacterial and Drug Delivery Applications

Silicon - Herein, a pure and well crystallized Na-magadiite was synthesized by hydrothermal method. It was then used as a host matrix to prepare hybrid materials by intercalation of zwitterionic...