Search Results - (Author, Cooperation:K. H. Wei)

2015-08-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1572-8935

Montmorillonite ; Nanocomposites ; Polyurethane ; Thermal transitions

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Abstract The hard-segment phase thermal transitions and heat-resistance of benzidine-modified-montmorillonite (BZD-Mont)/polyurethane nanocomposites of different hard segment contents were found to be affected by a small amount of BZD-Mont. In particular, the presence of less than 5 wt% layered silicates from BZD-Mont can result in hard segments not only having a more thermally stable long-range order and a higher melting temperature, but also showing a loss of crystallinity of the hard segment in polyurethane. Additionally, the degradation temperature of BZD-Mont/polyurethane nanocomposite was slightly higher than that of pure polyurethane.

Electronic Resource

0032-3888

Chemistry ; Chemical Engineering

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

A numerical method is described for calculating the stress a viscoelastic melt exhibits in a flow, based on approximate kinematics. The method assumes that the kinematics are reasonably close to those of a shear-thinning fluid such as the Carreau model. The strain history of a given flow and the resulting stress are calculated via a tracking method from finite element kinematics. Fullfield flow birefringence experiments were done for lowdensity polyethylene and polystyrene flowing past a thin plate divider in a 1.254-mm planar slit die. By digitally analyzing birefringence photographs of the flow field, the birefringence was measured over two dimensions. These birefringence results are in good agreement with birefringence fields calculated from the numerical simulations and the stress-optical law. The flow fields were most highly oriented in a region surrounding the weld interface just downstream of the plate divider. This orientation relaxed farther downstream, with polystyrene relaxing faster than low-density polyethylene.

12 Ill.

Electronic Resource

0032-3888

Chemistry ; Chemical Engineering

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

The kinematics of ideal welding flows generated by a thin-plate divider, a cylinder, or a slab in a slit channel are studied by using a finite element analysis. The analysis includes simulations of Newtonian and Carreau fluids. There are two flow configurations. First, a single plate-divider or an obstacle was positioned symmetrically in a slit channel with no-slip at the walls. In the second, an infinite number of plate-dividers or obstacles were positioned in parallel, and the boundary walls were infinitely far away. It was found that extensional flow dominates the region near the stagnation points of obstacles and plate-dividers, and that the fluid elements near the weld interfaces have a strain history of both high stretching and shearing. The thickness of the elongated region is reduced as the thickness of the plate-divider increases. Shear-thinning tends to increase the rate of extension. However, its influence on the flow field tends to lessen as the width of the flow channel or the obstacle size increases. A no-slip condition at walls causes slightly stronger elongational flow in the weld interface than does the symmetric condition of perfect slip at walls.

15 Ill.

Electronic Resource