53,334 research outputs found
Damage prediction in cross-plied curved composite laminates
Analytical and experimental work is detailed which is required to predict delamination onset and growth in a curved cross plied composite laminate subjected to static and fatigue loads. The composite used was AS4/3501/6, graphite/epoxy. Analytically, a closed form stress analysis and 2-D and 3-D finite element analyses were conducted to determine the stress distribution in an undamaged curved laminate. The finite element analysis was also used to determine values of strain energy release rate at a delamination emanating from a matrix crack in a 90 deg ply. Experimentally, transverse tensile strength and fatigue life were determined from flat 90 deg coupons. The interlaminar tensile strength and fatigue life were determined from double cantilevered beam specimens. Cross plied curved laminates were tested statically and in fatigue to give a comparison to the analytical predictions. A comparison of the fracture mechanics life prediction technique and the strength based prediction technique is given
Daze fasteners
A daze fastener system for connecting two or more structural elements wherein the structural elements and fastener parts have substantially different coefficient of thermal expansion physical property characteristics is employed in this invention. By providing frusto-conical abutting surfaces between the structural elements and fastener parts any differences in thermal expansion/contraction between the parts is translated to sliding motion and avoids deleterious thermal stresses in the connection. An essential feature for isotropic homogeneous material connections is that at least two sets of mating surfaces are required wherein each set of mating surfaces have line element extensions that pass through a common point
Dielectric response effects in attosecond time-resolved streaked photoelectron spectra of metal surfaces
The release of conduction-band electrons from a metal surface by a
sub-femtosecond extreme ultraviolet (XUV) pulse, and their propagation through
the solid, provokes a dielectric response in the solid that acts back on the
photoelectron wave packet. We calculated the (wake) potential associated with
this photoelectron self-interaction in terms of bulk and surface plasmon
excitations and show that it induces a considerable, XUV-frequency-dependent
temporal shift in laser-streaked XUV photoemission spectra, suggesting the
observation of the ultrafast solid-state dielectric response in contemporary
streaked photoemission experiments.Comment: 4 pages and 4 figures, submitted to PR
Daze fasteners
A daze fastener system for connecting two or more structural elements wherein the structural elements and fastener parts have substantially different coefficient of thermal expansion physical property characteristics is employed in this invention. By providing frusto-conical abutting surfaces between the structural elements and fastener parts any differences in thermal expansion/contraction between the parts is translated to sliding motion and avoids deleterious thermal stresses in the connection. An essential feature for isotropic homogeneous material connections is that at least two sets of mating surfaces are required wherein each set of mating surfaces has line element extensions that pass through a common point
Random Walkers with Shrinking Steps in d-Dimensions and Their Long Term Memory
We study, in d-dimensions, the random walker with geometrically shrinking
step sizes at each hop. We emphasize the integrated quantities such as
expectation values, cumulants and moments rather than a direct study of the
probability distribution. We develop a 1/d expansion technique and study
various correlations of the first step to the position as ti me goes to
infinity. We also show and substantiate with a study of the cumulants that to
order 1/d the system admits a continuum counterpart equation which can be
obtained with a generalization of the ordinary technique to obtain the
continuum limit. We also advocate that this continuum counterpart equation,
which is nothing but the ordinary diffusion equation with a diffusion constant
decaying exponentially in continuous time, captures all the qualitative aspects
of t he discrete system and is often a good starting point for quantitative
approximations
Practical theories for service life prediction of critical aerospace structural components
A new second-order theory was developed for predicting the service lives of aerospace structural components. The predictions based on this new theory were compared with those based on the Ko first-order theory and the classical theory of service life predictions. The new theory gives very accurate service life predictions. An equivalent constant-amplitude stress cycle method was proposed for representing the random load spectrum for crack growth calculations. This method predicts the most conservative service life. The proposed use of minimum detectable crack size, instead of proof load established crack size as an initial crack size for crack growth calculations, could give a more realistic service life
Finding the way forward for forensic science in the US:a commentary on the PCAST report
A recent report by the US President’s Council of Advisors on Science and Technology (PCAST) [1] has made a number of recommendations for the future development of forensic science. Whereas we all agree that there is much need for change, we find that the PCAST report recommendations are founded on serious misunderstandings. We explain the traditional forensic paradigms of match and identification and the more recent foundation of the logical approach to evidence evaluation. This forms the groundwork for exposing many sources of confusion in the PCAST report. We explain how the notion of treating the scientist as a black box and the assignment of evidential weight through error rates is overly restrictive and misconceived. Our own view sees inferential logic, the development of calibrated knowledge and understanding of scientists as the core of the advance of the profession
The alloy with a memory, 55-Nitinol: Its physical metallurgy, properties, and applications
A series of nickel titanium alloys (55-Nitinol), which are unique in that they possess a shape memory, are described. Components made of these materials that are altered in their shapes by deformation under proper conditions return to predetermined shapes when they are heated to the proper temperature range. The shape memory, together with the force exerted and the ability of the material to do mechanical work as it returns to its predetermined shape, suggest a wide variety of industrial applications for the alloy. Also included are discussions of the physical metallurgy and the mechanical, physical, and chemical properties of 55-Nitinol; procedures for melting and processing the material into useful shapes; and a summary of applications
Theoretical progress for the associated production of a Higgs boson with heavy quarks at hadron colliders
The production of a Higgs boson in association with a pair of top-antitop or
bottom-antibottom quarks plays a very important role at both the Tevatron and
the Large Hadron Collider. The theoretical prediction of the corresponding
cross sections has been improved by including the complete next-to-leading
order QCD corrections. After a brief introduction, we review the results
obtained for both the Tevatron and the Large Hadron Collider.Comment: 3 pages, 6 figures, uses svjour.cls. Talk given by L. Reina at the
HEP2003 Europhysics Conference in Aachen, Germany (EPS 2003), July 17-23,
200
Cryogenic Insulation System
This invention relates to reusable, low density, high temperature cryogenic foam insulation systems and the process for their manufacture. A pacing technology for liquid hydrogen fueled, high speed aircraft is the development of a fully reusable, flight weight cryogenic insulation system for propellant tank structures. In the invention cryogenic foam insulation is adhesively bonded to the outer wall of the fuel tank structure. The cryogenic insulation consists of square sheets fabricated from an array of abutting square blocks. Each block consists of a sheet of glass cloth adhesively bonded between two layers of polymethacrylimide foam. Each block is wrapped in a vapor impermeable membrane, such as Kapton(R) aluminum Kapton(R), to provide a vapor barrier. Very beneficial results can be obtained by employing the present invention in conjunction with fibrous insulation and an outer aeroshell, a hot fuselage structure with an internal thermal protection system
- …