4,636 research outputs found
Creep-rupture reliability analysis
A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep
Gravitational radiation from pulsar glitches
The nonaxisymmetric Ekman flow excited inside a neutron star following a
rotational glitch is calculated analytically including stratification and
compressibility. For the largest glitches, the gravitational wave strain
produced by the hydrodynamic mass quadrupole moment approaches the sensitivity
range of advanced long-baseline interferometers. It is shown that the
viscosity, compressibility, and orientation of the star can be inferred in
principle from the width and amplitude ratios of the Fourier peaks (at the spin
frequency and its first harmonic) observed in the gravitational wave spectrum
in the plus and cross polarizations. These transport coefficients constrain the
equation of state of bulk nuclear matter, because they depend sensitively on
the degree of superfluidity.Comment: 28 page
Study of the stress intensity factors in the bulk of the material with synchrotron diffraction
ArtĂculo de Proceedings de Congreso Internacional Fatigue2017In this work we present the results of a hybrid experimental and
analytical approach for estimating the stress intensity factor. It uses the
elastic strains within the bulk obtained by synchrotron X-ray diffraction
data. The stress intensity factor is calculated using a multi-point overdeterministic
method where the number of experimental data points is
higher than the number of unknowns describing the elastic field
surrounding the crack-tip. The tool is tested on X-ray strain
measurements collected on a bainitic steel. In contrast to surface
techniques the approach provides insights into the crack tip mechanics
deep within the sample.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech. The authors are grateful to the ESRF for ID15 beamtime awarded under MA-1483. Financial
support of Universidad de Malaga through Plan Propio, Junta de AndalucĂa through Proyectos de
Excelencia grant reference TEP-3244, Campus de Excelencia Internacional del Mar (CEIMAR)
and Ministerio de Economia y Competitividad through grant reference MAT2016-76951-C2-2-P is
also acknowledged. PJW acknowledges an ERC advanced grant
Modeling Wood Moisture Sorption Hysteresis Based on Similarity Hypothesis. Part II. Capillary-Radii Approach
The applicability of Mualem's capillary-radii model to wood moisture sorption hysteresis is evaluated. The model further simplifies the prediction of sorption hysteresis in that scanning curves can be obtained from the moisture content and relative humidity data of the boundary isotherms, with no other intermediate parameters needed. A comparison of predicted moisture contents with actual experimental data points for yellow-poplar (Liriodendron tulipifera) indicates that the model consistently underestimates the primary desorption scanning isotherms, with errors ranging from -0.01 to -1.31. These prediction errors are slightly larger than those obtained from an earlier model based on Mualem's direct similarity hypothesis
I-V curves of Fe/MgO (001) single- and double-barrier tunnel junctions
In this work, we calculate with ab initio methods the current-voltage
characteristics for ideal single- and double-barrier Fe/MgO (001) magnetic
tunnel junctions. The current is calculated in the phase-coherent limit by
using the recently developed SMEAGOL code, combining the nonequilibrium Green
function formalism with density-functional theory. In general we find that
double-barrier junctions display a larger magnetoresistance, which decays with
bias at a slower pace than their single-barrier counterparts. This is explained
in terms of enhanced spin filtering from the middle Fe layer sandwiched in
between the two MgO barriers. In addition, for double-barrier tunnel junctions,
we find a well defined peak in the magnetoresistance at a voltage of V=0.1 V.
This is the signature of resonant tunneling across a majority quantum well
state. Our findings are discussed in relation to recent experiments
Terahertz photoconductivity and plasmon modes in double-quantum-well field-effect transistors
Double-quantum-well field-effect transistors with a grating gate exhibit a sharply resonant, voltage tuned terahertz photoconductivity. The voltage tuned resonance is determined by the plasma oscillations of the composite structure. The resonant photoconductivity requires a double-quantum well but the mechanism whereby plasma oscillations produce changes in device conductance is not understood. The phenomenon is potentially important for fast, tunable terahertz detectors
Divergence-type 2+1 dissipative hydrodynamics applied to heavy-ion collisions
We apply divergence-type theory (DTT) dissipative hydrodynamics to study the
2+1 space-time evolution of the fireball created in Au+Au relativistic
heavy-ion collisions at 200 GeV. DTTs are exact hydrodynamic
theories that do no rely on velocity gradient expansions and therefore go
beyond second-order theories. We numerically solve the equations of motion of
the DTT for Glauber initial conditions and compare the results with those of
second-order theory based on conformal invariants (BRSS) and with data. We find
that the charged-hadron minumum-bias elliptic flow reaches its maximum value at
lower in the DTT, and that the DTT allows for a value of
slightly larger than that of the BRSS. Our results show that the differences
between viscous hydrodynamic formalisms are a significant source of uncertainty
in the precise extraction of from experiments.Comment: v4: 29 pages, 12 figures, minor changes. Final version as published
in Phys. Rev.
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