21,444 research outputs found
Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components
Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels
Buckling behavior of Rene 41 tubular panels for a hypersonic aircraft wing
The buckling characteristics of Rene 41 tubular panels for a hypersonic aircraft wing were investigated. The panels were repeatedly tested for buckling characteristics using a hypersonic wing test structure and a universal tension/compression testing machine. The nondestructive buckling tests were carried out under different combined load conditions and in different temperature environments. The force/stiffness technique was used to determine the buckling loads of the panel. In spite of some data scattering, resulting from large extrapolations of the data fitting curve (because of the termination of applied loads at relatively low percentages of the buckling loads), the overall test data correlate fairly well with theoretically predicted buckling interaction curves. Also, the structural efficiency of the tubular panels was found to be slightly higher than that of beaded panels
The muon g-2 discrepancy: errors or new physics?
After a brief review of the muon g-2 status, we discuss hypothetical errors
in the Standard Model prediction that could explain the present discrepancy
with the experimental value. None of them looks likely. In particular, an
hypothetical increase of the hadroproduction cross section in low-energy e^+e^-
collisions could bridge the muon g-2 discrepancy, but is shown to be unlikely
in view of current experimental error estimates. If, nonetheless, this turns
out to be the explanation of the discrepancy, then the 95% CL upper bound on
the Higgs boson mass is reduced to about 130 GeV which, in conjunction with the
experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass
of this fundamental particle.Comment: 4 pages. Invited talk at 16th International Conference on
Supersymmetry and the Unification of Fundamental Interactions (SUSY08), June
16-21 2008, Seoul, Kore
Application of Finite Viscoelastic Theory to the Deformation of Rubberlike Materials I. Uniaxial Stress Relaxation Data
In this report the constitutive equation for finite viscoelastic materials will be postulated as the sum of equilibrium terms and integral terms which describe the viscoelastic behavior of the materials and vanish when the equilibrium state is reached or when the materials have
always been at rest. It is also our purpose i) to show how the twelve relaxation functions are reduced to two independent ones in the case that
the material has Mooney-Rivlin elastic behavior and that all the relaxation functions depend only on time, ii) to display the mechanics of evaluating the two non-zero relaxation functions from data obtained from uniaxial
stress relaxation tests
Development and application of a Ni–Ti interatomic potential with high predictive accuracy of the martensitic phase transition
Microelectronic bioinstrumentation systems
The possibility of using RF fields to power biologically implanted transmitters used in biomedical experiments was investigated. This approach would be especially useful when animal subjects are strapped in chairs or confined in cages. A telemetry system using an external source of energy has the additional advantage of not being limited in operation by battery lifetime and can therefore operate for virtually infinite lengths of time. A description of a system based on this principle is given. Progress in the development of battery-driven transmitters is also reported, including an ingestible temperature telemetry system and a resistance-to-pulse frequency convertor for implantable temperature telemetry systems
The locally covariant Dirac field
We describe the free Dirac field in a four dimensional spacetime as a locally
covariant quantum field theory in the sense of Brunetti, Fredenhagen and Verch,
using a representation independent construction. The freedom in the geometric
constructions involved can be encoded in terms of the cohomology of the
category of spin spacetimes. If we restrict ourselves to the observable algebra
the cohomological obstructions vanish and the theory is unique. We establish
some basic properties of the theory and discuss the class of Hadamard states,
filling some technical gaps in the literature. Finally we show that the
relative Cauchy evolution yields commutators with the stress-energy-momentum
tensor, as in the scalar field case.Comment: 36 pages; v2 minor changes, typos corrected, updated references and
acknowledgement
Synthesis of BaTiO3-TiO2-Graphene Nanocomposites and Kinetics Studies on their Photocatalytic Activity
BaTiO3-TiO2 nanoparticles were fabricated by a wet-chemical method using barium chloride dihydrate (BaCl2·2H2O), titanium dioxide (TiO2), and oxalic acid (C2H2O4) as precursors. BaTiO3-TiO2-graphene nanocomposites were obtained by heating the BaTiO3-TiO2 nanoparticles with graphene in an electric furnace at 700 °C for 2 h. X-ray diffraction analysis revealed that the resulting products were BaTiO3-TiO2-graphene nanocomposites. Scanning electron microscopy revealed the morphology of the nanocomposites. UV-vis spectrophotometry was used to analyze the photocatalytic degradation of several organic dyes using the BaTiO3-TiO2-graphene nanocomposites as a photocatalyst under ultraviolet irradiation at 254 nm
Fundamental Studies Relating to the Mechanical Behavior of Solid Propellants, Rocket Grains and Rocket Motors
During the past three years, the mechanical testing of solid
propellants, solid rocket grains, and solid rocket motors under idealized conditions has been receiving increased attention. Today it is not uncommon to see a multitude of new techniques and analyses being investigated. One may expect to see dummy propellant prepared with
glass bead filler to observe its dilatation to rupture; to ink circles, rectangular g rids at various critical areas on a grain surface, and to observe the distortion of these grids as a result of thermal cycling and/or slump; to subj e ct rectangular parallel-opipedal-shaped specimens
to both torsion and biaxial tension as well as hydrostatic compression and parallel-plate tension; to apply theories of large elastic strain, and non-linear viscoelasticity; to search for an isotropic failure criterion
as well as a crack propagation criterion. In short the mechanics of propellant behavior from small deformation all the way to fracture initiation and propagation has become quite sophisticated. Gradually the results of this testing and their thinking are being integrated in a
logical scheme of analysis which is being passed along to the engineer and being used in predicting performance of rocket motors.
This particular program will pertain to four areas:
1) The characterization of polyurethane propellant behavior
out to fracture initiation in terms of large strain theory.
2) The development of a failure criterion and crack propagation criteria for said materials.
3) The generation, where possible, of macroscopic mechanical
parameters in terms of molecular parameters.
4} The solution of certain stress problems, in both linear and non-linear theory, which are prerequisite to engineering
applications.
As such it is part of a continuing research study of structural integrity problems in solid propellant rocket motors being conducted under the general direction of Dr. M. L. Williams in the Guggenheim Aeronautical
Laboratory.
This preliminary report is intended as an interim working document to be circulated for the purpose of stimulating discussion
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