1,724,931 research outputs found
Onset of reversal and chaos thermally driven cavity flow
No full textWe investigate the onset of chaotic reversals of thermal convection cell in a two–dimensional square cavity using direct numerical simulation. To our knowledge, the chaotic reversal motion at the lowest Rayleigh number is related to the unicellular motion in this system. As Rayleigh number increases, the two antisymmetric attractors, which arise from the supercritical Hopf bifurcation, approach each other. However, because the basin boundaries of these attractors have multiple unstable directions, the behavior of the global changes seems to be complex for the small range of Rayleigh number around the onset of the chaotic reversal. On the other hand, period–doubling cascade from periodic reversal solutions leads to chaotic reversal as Rayleigh number decreases. At the conference we will report observation about the beginning of reversal and the quantities of the chaotic attractor
An Improved Torsional Method for Determining the Fracture Toughness of Stiff Materials and of Adhesive Joints
No full textA simple modification is described of the Outwater torsion test method for determining the fracture energy of stiff materials and of adhesive joints. It permits large torsions to be applied and the corresponding torque to be simultaneously monitored. The modified test method can be used with specimens of simple rectangular shape and having a wide range of stiffness. As an example, the fracture energy is determined for molded rectangular bars of polystyrene having a wide range of thickness and of width.
A simple modification is described of the Outwater torsion test method for determining the fracture energy of stiff materials and of adhesive joints. It permits large torsions to be applied and the corresponding torque to be simultaneously monitored. The modified test method can be used with specimens of simple rectangular shape and having a wide range of stiffness. As an example, the fracture energy is determined for molded rectangular bars of polystyrene having a wide range of thickness and of width.11Nsciescopu
Adhesion between Polystyrene and Polymethyl methacrylate
No full textMeasurements have been made of the energy required to break through unit area of polystyrene (PS), polymethylmethacrylate (PMMA), and joints prepared by molding the two polymers in contact. The results were: 1.23 ± 0.5 kJ/m2 (PS), 0.46 ± 0.10 kJ/m2 (PMMA), and 0.22 ± 0.04 kJ/m2 for the bonded joint. Thus, the interface was significantly weaker than either adherend, but surprisingly strong for two incompatible materials. Microscopy and selective dyeing revealed that fracture took place at the interface itself, with no appreciable transfer of material from one side to the other. It is concluded that Van der Waals interactions are sufficient to create relatively strong bonds.117Nsciescopu
Nanoparticle-induced enhancement in fracture toughness of highly loaded epoxy composites over a wide temperature range
No full textThe fracture toughness of an epoxy molding compound (EMC) has been enhanced over a wide temperature range by the addition of a very low volume fraction of silica nanoparticles to the EMC filled with micro-silica particles, which induces macroscopic crack deflection and plastic deformation in front of the crack tip. To evaluate the fracture toughness (G(IC)) of these materials, the single edge notched bending (SENB) test was performed for a wide range of temperatures (from ambient temperature to 230 degrees C). The fracture toughness of the nano-silica filled EMCs was found to be improved in this temperature range by as much as a factor of two. Investigation of the fracture surfaces revealed that the micro-silica particles are covered with deformed matrix materials, which implies that the silica nanoparticles induced the crack to move into the interface between the micro-silica particles. Fractography results suggest that the silica nanoparticles act as surface modifiers of the micro-silica particles, which results in crack deflection and plastic deformation. (c) 2006 Springer Science + Business Media, Inc.X1148sciescopu
Pattern formation in ultrathin films of a novel dimethylsiloxane-acrylate triblock copolymer
No full textX1133sciescopu
Effect of solvent type on formation of PVC-solvent complex
No full textThe effect of solvent type on the structural features of PVC gels prepared from the solutions of dibutyl phthalate(DBP) and butyl benzoate(BB) were investigated. The influence of solvent type, i.e., diester solvent or monoester solvent, on the mechanical responses was characterized by dynamic viscoelastic measurements as a function of temperature, aging time, and PVC concentration. In the case of PVC/DBP aged gels, the transition phenomenon appeared close to 50 degreesC, whereas no such transitions were observed for PVC/BB aged gels. This transition is considered to be associated with polymer-solvent complex which can be accounted for electrostatic interaction between C=O bond of solvent and H-C-CI part of PVC. While ED solvent molecules can not form polymer-solvent complex due to no capacity to act as a bridge between PVC molecular chains. FT-IR spectroscopy and DSC investigation on either PVC/DBP gels or PVC/BB gels was reported and discussed together with the mechanical behavior. Electron micrographs of the dried gel prepared from the critical point drying technique reveal that the gel morphology consists of well developed three dimensional fibrous network structure independent of solvent type.X114sciescopu
Surface Modification Effects of Core-Shell Rubber Particles on the Toughening of Poly(butylene terephthalate)
No full textWe toughened poly(butylene terephthalate) (PBT) by loading core-shell number CSR) type impact modifiers, consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shall. To optimize the dispersion of CSR particles into the PBT matrix during melt compounding, the shell surface was modified with different grafting ratios of glycidyl methacrylate (GMA) reactive with PBT chain ends. In PBT blends with a 20 wt % CSR loading, the dispersed rubbery phases showed discernible shapes depending on the grafted GMA content, from predetermined spheres with 0.25 +/- 0.05 mu m diameters to their aggregates in the 2-3 mu m diameter range. As a result, the interparticle spacing (tau) could be controlled from 0.25 to 4.0 mu m in the PBT blends containing the fixed rubber loading. The Izod impact strengths of these samples increased significantly below tau = 0.4 mu m. Additional thermal and morphological analyses strongly Supported the hypothesis that the marked increase in toughness of the blends was related to less ordered lamellar formation of the PBT matrix under the confined geometry. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1948-1957, 2010X11610sciescopu
Effect of molecular weight between cross-links on the abrasion behavior of rubber by a blade abrader
No full textThe effect of molecular weight between cross-links on the abrasion behavior of rubber was investigated using acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), and natural rubber (NR) with a blade abrader. The rate of abrasion was found to be almost constant irrespective of the cross-link density of rubber at low frictional input work, whereas it decreased to a minimum and increased again as frictional input work increased. For rubbers with high cross-link density, it was found that the rate of abrasion increased slowly below the critical frictional input work and increased abruptly above the critical frictional input work. A similar phenomenon was also found in the fatigue test. The values of critical input work in the abrasion test and fatigue test were very close to the fracture energies of rubber. Thus, mechanical fatigue was the major abrasion mechanism below the critical frictional input work and the abrasion mechanism changed from mechanical fatigue to direct tearing at the critical frictional input work. As cross-link density decreased, the critical point in the frictional input work was not observed due to the high fracture energy of rubber. In this range, the abrasion mechanism was the mechanical fatigue, which was confirmed by the fatigue test. However, the critical frictional input work was observed at high test-temperature due to the lowering of the fracture energy. For rubbers with very low cross-link density, a rolling-type abraded surface occurred as a result of the thin surface layer peeling away by abrasion. (C) 1999 Elsevier Science Ltd. All rights reserved.X118sciescopu
Layered silicate-induced enhancement of fracture toughness of epoxy molding compounds over a wide temperature range
No full textThe fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro-silica particles. Layered silicate-EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o-cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above T. of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 degrees C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.X1118sciescopu
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