123,471 research outputs found
Presentazione di Migrazioni al femminile
No full textLa previsione sull'andamento nei prossimi anni delle migrazioni verso l'Italia ci dicono che le caratteristiche principali dei migranti saranno la giovane età e la prevalenza della componente femminile. Spesso le storie personali delle protagoniste femminili delle migrazioni sono state occultate in una sostanziale invisibilità. Il numero monografico della rivista muove dall'intento di dar voce a queste protagoniste, di promuovere una più corretta e aggiornata conoscenza del fenomeno della migrazione femminile, dei risvolti economici dell'attività delle donne, dell'incontro scontro tra patrimoni culturali diversi di cui le donne sono portavoci e attive trasformatrici
Creep modelling of 316H stainless steel over a wide range of stress
No full textInvestigation of material creep behaviour in the diffusion controlled creep regime is often unfeasible because of the long duration associated with low stress levels. On the other side, extrapolation from higher creep rates usually provides inaccurate results because of the sharp change in the data trend as a result of the change in the governing deformation mechanism from dislocation to diffusion type controlled creep. Similarly, extrapolation based on creep models, which have been formulated and validated mainly for dislocation type creep (such power law creep with the creep exponent ranging from 6 to 9), underestimates the actual creep rate significantly. Recently, Bonora and Esposito (2010) developed a mechanism-based model (BE model) capable to account for deformation and damage mechanism occurring in creep. In this work the BE model was applied to AISI 316H stainless steel for which considerable creep data in both dislocation and diffusion temperature/stress controlled regime were available. Using the same data set, the predictive capabilities of several models were compared
Modeling of multiaxial stress effects on the creep resistance of high chromium steel
No full textMaterials creep resistance is usually determined under uniaxial constant load condition while the state of stress in real components is multiaxial in general. How to correlate multiaxial creep behavior to uniaxial creep data is still an open issue. Most of the theories available in the literature are phenomenological in nature and limited to few classes of metals and stress triaxiality ranges. From the computational point of view, stress field relaxation depends on the creep model formulation. Therefore, it is necessary to use a refined creep model capable to reproduce the effective state of stress in the material. In the present work, a mechanism based creep model proposed by Bonora and Esposito [1] was used to predict creep life of P91 high chromium steel under multiaxial state of stress. This creep model is capable to reproduce all creep stages and was validated for different classes of metals and alloys. The performance of different reference stress definitions (i.e. the principal facet stress, skeletal stress and a new formulation) was investigated. Results were compared with available creep life data obtained on round notched samples at different temperatures
Ormetica bonora
No full text<i>Ormetica bonora</i> (Schaus, 1905) <p> <i>Automolis bonora</i> Schaus, 1905: 219.</p> <p> <i>Ormetica bonora</i> – Watson 1971: 17.</p> <p> <i>Automolis ochreomarginata</i> Joicey & Talbot, 1918: 267, n. syn.</p> <p> <i>Ormetica ochreomarginata</i> – Watson 1975: 84.</p> <p>ARGUMENTAIRE TAXONOMIQUE</p> <p> <i>Automolis bonora</i> Schaus, 1905 est décrit sur un mâle unique provenant de Cayenne. <i>Automolis ochreomarginata</i> Joicey &Talbot, 1918 est décrit sur un mâle unique provenant de Saint-Jean-du-Maroni en Guyane. Dans leur publication, Joicey & Talbot (1918) comparent leur nouvelle espèce uniquement à <i>Ormetica sicilia</i> Druce, 1884 d’Amérique centrale, visiblement n’ayant pas connaissance de <i>O. bonora</i>. Pourtant les deux espèces ont manifestement des habitus identiques. Nous proposons donc cette synonymie.</p>Published as part of <i>Vincent, Benoît & Laguerre, Michel, 2013, Changements nomenclaturaux chez les Arctiinae nÉotropicales (Insecta, Lepidoptera, Erebidae); seconde partie, pp. 425-455 in Zoosystema 35 (3)</i> on page 437, DOI: 10.5252/z2013n3a5, <a href="http://zenodo.org/record/5165260">http://zenodo.org/record/5165260</a>
CDM modeling of ductile failure in ferritic steels: Assessment of the geometry transferability of model parameters
No full textOne of the most important features of micromechanical models, with respect to other global approaches to fracture, is that progressive damage and failure can be described only by parameters characteristic of the material and not of the geometry. In spite of the large number of papers on micromechanical modeling presented in literature, a detailed assessment the geometry transferability of model parameters has been addressed in a limited number of works. In most of the cases, the model parameters transferability is analyzed only for one geometrical configuration other than that - usually a uniaxial tensile bar - on which the parameters set has been identified. In this paper, the continuum damage mechanics approach, as proposed by [Bonora, N., 1997. A non-linear CDM model for ductile failure. Engineering Fracture Mechanics 58, 11-28] is used to model ductile damage processes in ferritic steels. The geometry transferability of the damage parameters is demonstrated both in the range of low and high stress triaxiality. The possibility to accurately predict constraint effects on material crack resistance curve is demonstrated
J. Lhuillier, N. Boroffka (éds), A Millennium of History. The Iron Age in southern Central Asia (2018)
No full textBonora G.L. J. Lhuillier, N. Boroffka (éds), A Millennium of History. The Iron Age in southern Central Asia (2018). In: Topoi, volume 22/2, 2018. pp. 693-704
A model for steady stage III creep regime at low-high stress/temperature range
No full textAlthough diffusional flow creep is often considered out of practical engineering applications, the need for a model capable to account for the resulting action of both diffusional and dislocation type creep is justified by the increasing demands of reliable creep design for very long lives (exceeding lOO.OOOh), high stress-low temperatures and high temperature-low stress regimes. In this paper, a creep model formulation, in which the change of the creep mechanism has been accounted for through an explicit dependence of the creep exponent "n" on stress and temperature, has been proposed. An application example of the proposed approach to high purity aluminum is given
Mechanism Based Creep Model Incorporating Damage
No full textThe increasing demand of reliable creep design for very long lives (exceeding 100.000 h), as those for high stress-low temperatures and high temperature-low stress regimes, requires a model formulation capable to account for the nonlinearity in the stress dependence of the logarithm of the creep rate as a result of the combination of both diffusional and dislocation type creeps. In this paper, a creep model, where the effect of mechanism change has been accounted for through an explicit dependence of the creep exponent n on stress, has been proposed. The model has been also extended, incorporating damage processes and characteristics of tertiary creep stage, adopting a time independent damage formulation proposed by the authors. An application example of the proposed approach to high purity aluminum is given
Mechanism based unified creep model incorporating damage
No full textAlthough it is often said that diffusional flow creep is out of the practical engineering applications, the need for a unified model capable to account for the resulting action of both diffusional and dislocation type creep is justified by the increasing demands of reliable creep design for very long lives (exceeding 100.000h), high stress-low temperatures and high temperature-low stress regimes. In this paper, a unified creep model formulation, in which the change of the creep mechanism has been accounted for through an explicit dependence of the exponent n on stress and temperature, has been proposed. The model has been also extended incorporating damage processes, characteristics of creep stage IV, adopting a time independent damage formulation proposed by the authors. An application example of the proposed approach to high purity aluminum is given
New time-independent formulation for creep damage in polycrystalline metals and its specialisation to high alloy steel for high-temperature applications
No full textIn this work, a new time-independent, micromechanism based, creep damage formulation, derived in the framework of the continuum damage mechanics (CDM) approach to creep proposed by Bonora et al., has been developed and specialized for high chromium steel grades. One of the major features of the proposed formulation is that the kinetic law of creep damage evolution depends only on the accumulated inelastic strain and stress triaxiality and not on time needed to reach a given creep deformation level. The effects associated with the microstructure evolution during high-temperature service, such as the nucleation, growth and coarsening of secondary phases, have been also taken into account through the definition of an evolution law for damage-model parameters. A procedure for the identification of the damage-model parameters using short-duration creep-test data (<10,000 h) has been developed. Long-term creep lives, up and beyond 50,000 h, in the temperature range 550-650 degrees C have been successfully predicted for ASTM steel grade 92 with high degree of accuracy
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