11,959 research outputs found
Optimizing the Post Sandvik Nanoflex material model using inverse optimization and the finite element method
This article describes an inverse optimization method for the Sandvik Nanoflex steel in cold forming\ud
processes. The optimization revolves around measured samples and calculations using the Finite Element\ud
Method. Sandvik Nanoflex is part of the group of meta-stable stainless steels. These materials are characterized\ud
by a good corrosion resistance, high strength, good formability and crack resistance. In addition, Sandvik\ud
Nanoflex has a strain-induced transformation and, depending on austenising conditions and chemical composition,\ud
a stress-assisted transformation can occur. The martensite phase of this material shows a substantial aging\ud
response. The inverse optimization is a sub-category of the optimization techniques. The inverse optimization\ud
method uses a top down approach, as the name implies. The starting point is a prototype state where the current\ud
state is to converge on. In our experiment the test specimen is used as prototype and a calculation result as\ud
current state. The calculation is then adapted so that the result converges towards the test example. An iterative\ud
numerical optimization algorithm controls the adaptation. For the inverse optimization method two parameters\ud
are defined: shape of the product and martensite profile. These parameters are extracted from both calculation\ud
and test specimen, using Fourier analysis and integrals. An optimization parameter is then formulated from\ud
the extracted parameters. The method uses this optimization parameter to increase the accuracy of ”The Post”\ud
material model for Sandvik Nanoflex. [1] The article will describe a method to optimize material models, using\ud
a combination practical experiments, Finite Element Method and parameter extraction
Infrared backscatter climatology and MACAWS
During FY91 NOAA's research activities funded under NASA's RTOP program were centered on two areas: (1) infrared backscatter climatology; and (2) MACAWS
Maxwell's theory on a post-Riemannian spacetime and the equivalence principle
The form of Maxwell's theory is well known in the framework of general
relativity, a fact that is related to the applicability of the principle of
equivalence to electromagnetic phenomena. We pose the question whether this
form changes if torsion and/or nonmetricity fields are allowed for in
spacetime. Starting from the conservation laws of electric charge and magnetic
flux, we recognize that the Maxwell equations themselves remain the same, but
the constitutive law must depend on the metric and, additionally, may depend on
quantities related to torsion and/or nonmetricity. We illustrate our results by
putting an electric charge on top of a spherically symmetric exact solution of
the metric-affine gauge theory of gravity (comprising torsion and
nonmetricity). All this is compared to the recent results of Vandyck.Comment: 9 pages, REVTeX, no figures; minor changes, version to be published
in Class. Quantum Gra
Clinical presentation, treatment and outcome in 31 dogs with presumed primary colorectal lymphoma (2001-2013)
Semirelativistic stability of N-boson systems bound by 1/r pair potentials
We analyze a system of self-gravitating identical bosons by means of a
semirelativistic Hamiltonian comprising the relativistic kinetic energies of
the involved particles and added (instantaneous) Newtonian gravitational pair
potentials. With the help of an improved lower bound to the bottom of the
spectrum of this Hamiltonian, we are able to enlarge the known region for
relativistic stability for such boson systems against gravitational collapse
and to sharpen the predictions for their maximum stable mass.Comment: 11 pages, considerably enlarged introduction and motivation,
remainder of the paper unchange
Constitutive modelling of Sandvik 1RK91
A physically based constitutive equation is being developed for the maraging\ud
stainless steel Sandvik 1RK91. The steel is used to make precision parts. These parts are formed through multistage forming operations and heat treatments from cold rolled and annealed sheets. The specific alloy is designed to be thermodynamically unstable, so that deformation even at room temperatures can bring about a change in the phase of face centred cubic austenite to either hexagonal closed packed martensite and/or, body centred cubic martensite. This solid state phase change is a function of the strain path, strain, strain rate and temperature. Thus, the fraction of the new phase formed depends on the state of stress at a given location in the part being formed. Therefore a set of experiments is being conducted in order to quantify the stress-strain behavior of this steel under various stress states, strain, strain rate as well as temperature. A magnetic sensor records the fraction of ferromagnetic martensite formed from paramagnetic austenite. A thermocouple as well as an infra red thermometer is used to log the change in temperature of the steel during a mechanical test. The force-displacement data are converted to stress-strain data after correcting for the changes in strain rate and temperature. These data are then cast into a general form of constitutive equation and the transformation equations are derived from Olson-Cohen type functions
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