2,734 research outputs found
Results of ASTM round robin testing for mode 1 interlaminar fracture toughness of composite materials
The results are summarized of several interlaboratory 'round robin' test programs for measuring the mode 1 interlaminar fracture toughness of advanced fiber reinforced composite materials. Double Cantilever Beam (DCB) tests were conducted by participants in ASTM committee D30 on High Modulus Fibers and their Composites and by representatives of the European Group on Fracture (EGF) and the Japanese Industrial Standards Group (JIS). DCB tests were performed on three AS4 carbon fiber reinforced composite materials: AS4/3501-6 with a brittle epoxy matrix; AS4/BP907 with a tough epoxy matrix; and AS4/PEEK with a tough thermoplastic matrix. Difficulties encountered in manufacturing panels, as well as conducting the tests are discussed. Critical issues that developed during the course of the testing are highlighted. Results of the round robin testing used to determine the precision of the ASTM DCB test standard are summarized
Surface-sampled simulations of turbulent flow at high Reynolds number
A new approach to turbulence simulation, based on a combination of large-eddy
simulation (LES) for the whole flow and an array of non-space-filling
quasi-direct numerical simulations (QDNS), which sample the response of
near-wall turbulence to large-scale forcing, is proposed and evaluated. The
technique overcomes some of the cost limitations of turbulence simulation,
since the main flow is treated with a coarse-grid LES, with the equivalent of
wall functions supplied by the near-wall sampled QDNS. Two cases are tested, at
friction Reynolds number Re=4200 and 20,000. The total grid node count
for the first case is less than half a million and less than two million for
the second case, with the calculations only requiring a desktop computer. A
good agreement with published DNS is found at Re=4200, both in terms of
the mean velocity profile and the streamwise velocity fluctuation statistics,
which correctly show a substantial increase in near-wall turbulence levels due
to a modulation of near-wall streaks by large-scale structures. The trend
continues at Re=20,000, in agreement with experiment, which represents
one of the major achievements of the new approach. A number of detailed aspects
of the model, including numerical resolution, LES-QDNS coupling strategy and
sub-grid model are explored. A low level of grid sensitivity is demonstrated
for both the QDNS and LES aspects. Since the method does not assume a law of
the wall, it can in principle be applied to flows that are out of equilibrium.Comment: Author accepted version. Accepted for publication in the
International Journal for Numerical Methods in Fluids on 26 April 201
Quantitative Flow Field Imaging about a Hydrophobic Sphere Impacting on a Free Surface
This fluid dynamics video shows the impact of a hydrophobic sphere impacting
a water surface. The sphere has a mass ratio of m* = 1.15, a wetting angle of
110 degrees, a diameter of 9.5 mm, and impacts the surface with a Froude number
of Fr = 9.2. The first sequence shows an impact of a sphere on the free surface
illustrating the formation of the splash crown and air cavity. The cavity grows
both in the axial and radial direction until it eventually collapses at a point
roughly half of the distance from the free surface to the sphere, which is
known as the pinch-off point. The second set of videos shows a sphere impacting
the free surface under the same conditions using Particle Image Velocimetry
(PIV) to quantify the flow field. A laser sheet illuminates the mid-plane of
the sphere, and the fluid is seeded with particles whose motion is captured by
a high-speed video camera. Velocity fields are then calculated from the images.
The video sequences from left to right depict the radial velocity, the axial
velocity, and the vorticity respectively in the flow field. The color bar on
the far left indicates the magnitude of the velocity and vorticity. All videos
were taken at 2610 fps and the PIV data was processed using a 16 x 16 window
with a 50% overlap.Comment: American Physical Society Division of Fluid Dynamics 2008 Annual
Meeting Replaced previous version because abstract had LaTex markup and was
too long, missing periods on middle initial of first two name
Park and Armisteads\u27 Nevertheless She Leads: Postcolonial Women\u27s Leadership for the Church (book review)
Use of Phosphoric Acid and Furfuryl Alcohol for Soil Stabilization
This paper presents results of an investigation of the effects of phosphoric acid and furfuryl alcohol on the resistance and strengths of a clayey soil and of a sandy soil. Results indicate that greater water resistance and higher strengths can be obtained with both soils by using the admixtures. For the sandy soil, a certain optimum amount of phosphoric acid gives the maximum strengths for all furfuryl alcohol contents. The stabilization mechanism for the clayey soil is thought to be a combination of the formation of phosphoric gels and of a resin product of a furfuryl alcohol polymerization reaction. The mechanism for the sandy soil is the formation of the polymerization resin product
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