1,722,174 research outputs found
Theoretical and Experimental Analysis of an Externally Pressurized Porus Gas Thrust Bearings
No full textThis paper presents a fast modified three-dimensional flow model deduced from the Darcy equation and the modified Reynolds equation. The finite element method is used to discretize both equations so that only one nonlinear final set of equations is to be solved for finding the pressures in the gas film and porous matrix instead of two nonlinear sets of equations in the literature. In general, the time required by the present analysis on VAX 3100 is only about 30% of the time required by the classical three-dimensional flow model. For a circular porous thrust pad, the results from the present model agree well with the experimental result. It may also be observed that the analytical analysis and the one-directional flow model are not precise for the large values of R/H and small value of the film thickness h
Multi-cycles deformation modeling of hot forming tools under creep-fatigue regime
No full textHot forming processes (extrusion, die ca
sting and forging) allow the production
of a wide variety of products, both in terms
of worked material and achievable shapes.
However, critical working conditions are involved for the tools subjected to severe thermo-
mechanical loads, thus requiring an accurate design. Among the different classifications
proposed in literature for hot forming die failures, one focus on separating manufacturing
and in service failures. The latter category is additionally split, as proposed by the authors,
in static failure, damage and deformation/deflec
tion failures. Static failure appears after e
reduced number of extruded billets as a consequence of an overload or of a poor initial die
design. Damage and deflection failures are ind
eed induced by the synergic detrimental
action of creep and fatigue phenomenon. In disc
riminating the relative dominant role of
creep and fatigue in leading to the final die discard, the level of temperature and of the
applied load as well as of the dwell-time are d
ecisive. In extrusion, the latter is the time in
which a constant load acts on the die and represents the time required to extruded each
single billet function of both ram speed and billet length. Fatigue and creep can be seen as
limit cases with zero and infinite
dwell-time. A novel model is proposed for the prediction
of the deformation undergone by hot forming t
ools in the creep-fatigue regime after
multiple cycles. The model is presented as applied to extrusion dies and is based on a
modified version of a simple creep law already
implemented in all the FE codes. The model
is validated against small scale dies used
in physical experiments and then against
industrial extrusion dies
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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