Shear Flows and Shear Viscosity in a Two-Dimensional Yukawa System (Dusty Plasma)

The shear viscosity of a two-dimensional liquid-state dusty plasma was measured experimentally. A monolayer of highly charged polymer microspheres, with a Yukawa interaction, was suspended in a plasma sheath. Two counter-propagating Ar laser beams pushed the particles, causing shear-induced melting of the monolayer and a shear flow in a planar Couette configuration. By fitting the particle velocity profiles in the shear flow to a Navier-Stokes model, the kinematic viscosity was calculated; it was of order 1 mm^2/s, depending on the monolayer's parameters and shear stress applied.Comment: all 3 figures are combined in a separate pdf fil

The accuracy of approximate solutions in the analysis of fracture of composites

This paper concerns the accuracy of three related mathematical models (developed by Hedgepeth, Eringen and Sendeckyj and Jones) used in the stress analysis and in fracture studies of continuous-fiber composites. These models have particular application in the investigation of fiber and matrix stresses in unidirectional composites in the region near a crack tip. The interest in such models is motivated by the desire to be able to simplify the equations of elasticity to the point that they can be solved in a relatively easy manner

Errors in particle tracking velocimetry with high-speed cameras

Velocity errors in particle tracking velocimetry (PTV) are studied. When using high-speed video cameras, the velocity error may increase at a high camera frame rate. This increase in velocity error is due to particle-position uncertainty, which is one of two sources of velocity errors studied here. The other source of error is particle acceleration, which has the opposite trend of diminishing at higher frame rates. Both kinds of errors can propagate into quantities calculated from velocity, such as the kinetic temperature of particles or correlation functions. As demonstrated in a dusty plasma experiment, the kinetic temperature of particles has no unique value when measured using PTV, but depends on the sampling time interval or frame rate. It is also shown that an artifact appears in an autocorrelation function computed from particle positions and velocities, and it becomes more severe when a small sampling-time interval is used. Schemes to reduce these errors are demonstrated.Comment: 6 pages, 5 figures, Review of Scientific Instruments, 2011 (In Press

Micro-mechanical analysis of damage growth and fracture in discontinuous fiber reinforced metal matrix composites

The near-crack-tip stresses in any planar coupon of arbitrary geometry subjected to mode 1 loading may be equated to those in an infinite center-cracked panel subjected to the appropriate equivalent remote biaxial stresses (ERBS). Since this process can be done for all such mode 1 coupons, attention may be focused on the behavior of the equivalent infinite cracked panel. To calculate the ERBS, the constant term in the series expansion of the crack-tip stress must be retained. It is proposed that the ERBS may be used quantitatively to explain different fracture phenomena such as crack branching

Fracture behavior of unidirectional boron/aluminum composite laminates

An experiment was conducted to verify the results of mathematical models which predict the stresses and displacements of fibers and the amount of damage growth in a center-notched lamina as a function of the applied remote stress and the matrix and fiber material properties. A brittle lacquer coating was used to detect the yielding in the matrix while X-ray techniques were used to determine the number of broken fibers in the laminate. The notched strengths and the amounts of damage found in the specimens agree well with those predicted by the mathematical model. It is shown that the amount of damage and the crack opening displacement does not depend strongly on the number of plies in the laminate for a given notch width. By heat-treating certain laminates to increase the yield stress of the alumina matrix, the effect of different matrix properties on the fracture behavior was investigated. The stronger matrix is shown to weaken the notched laminate by decreasing the amount of matrix damage, thereby making the laminate more notch sensitive