196,431 research outputs found
Towards a Reliable Uncertainty Quantification in Residual Stress Measurements with Relaxation Methods: Finding Average Residual Stresses is a Well-Posed Problem
No full textBackground: In a previous work, the problem of identifying residual stresses through relaxation methods was demonstrated to be mathematically ill-posed. In practice, it means that the solution process is affected by a bias-variance tradeoff, where some theoretically uncomputable bias has to be introduced in order to obtain a solution with a manageable signal-to-noise ratio.
Objective: As a consequence, an important question arises: how can the solution uncertainty be quantified if a part of it is inaccessible? Additional physical knowledge could—in theory—provide a characterization of bias, but this process is practically impossible with presently available techniques.
Methods: A brief review of biases in established methods is provided, showing that ruling them out would require a piece of knowledge that is never available in practice. Then, the concept of average stresses over a distance is introduced, and it is shown that finding them generates a well-posed problem. A numerical example illustrates the theoretical discussion.
Results: Since finding average stresses is a well-posed problem, the bias-variance tradeoff disappears. The uncertainties of the results can be estimated with the usual methods, and exact confidence intervals can be obtained.
Conclusions: On a broader scope, we argue that residual stresses and relaxation methods expose the limits of the concept of point-wise stress values, which instead works almost flawlessly when a natural unstressed state can be assumed, as in classical continuum mechanics (for instance, in the theory of elasticity). As a consequence, we are forced to focus on the effects of stress rather than on its point-wise evaluatio
Analysis of the contact between cubic profiles
Get PDFThe contact between cubic profiles with continuous relative curvatures has been analyzed and solutions in closed form were obtained for both symmetric and non-symmetric conditions. Analytical solutions have allowed a complete parametric study to be performed, showing the effects of the gradient of relative curvature. The accuracy of approximate 'equivalent' Hertzian solutions has been verified
Fine increment hole-drilling method for residual stress measurement, proposal of a calibrating apparatus
No full textHole drilling is one of the most widely used technique for residual stress measurements, due to its precision and low cost. Standard ASTM E 837 is limited to the uniform distribution of residual stresses, whereas it is well known that residual stresses usually feature high gradient along the depth, particularly if residual stresses are induced by surface treatments such us shot peening. The incremental hole-drilling method can be used to evaluate the not-uniform residual stress distribution as shown by Schajer. The strain measurement is repeated at different hole depths to achieve information on the residual stress gradient, from relaxed surface strain. Influence functions for the incremental hole drilling are proposed by Beghini and Bertini by which the relaxed strain can be evaluated analytically if the residual stress distributions are known for any kind of rosette, hole diameter and elastic material. Valentini has developed an apparatus able to produce fine increment hole drilling, by means of a high speed air turbine drill automatically controlled. Valentini et al. used the appartatus to experimentally show the effects on residual stresses measurement by the hole drilling such as eccentricity and sequence of increments steps
An application of the weight function technique to inclined surface cracks under rolling contact fatigue, assessment and parametric analysis
Get PDFThis paper proposes the use of the weight function technique to calculate mode I and mode II stress intensity factors for a shallow surface crack typical of rolling contact fatigue, that experiences the detrimental effects of the pressurization of lubricating fluid. The weight function technique was able to easily take the pressurization into account just by adding the pressure term to the nominal stress component which is then integrated. The crack closure was also modeled by introducing an assumption for the distribution of the contact pressure on the crack face. The results were validated with the literature data and finite element analyses. Parametric simulations were performed showing that mode I and mode II stress intensity factors strongly depend on the crack angle with respect to the surface, and almost linearly on the size of the crack. In addition, the proposed algorithm was able to include any residual stress distribution. Compressive residual stress hinders pressurization and promotes the crack closure. This effect was parametrically investigated and it was found that cracks, and especially small ones, can even remain closed, with the opening effect of the pressurization completely suppressed
Nunc age . . . expediam: A Didactic Introductory Construction in Virgil’s Poetry
No full textThe present paper analyses a didactic three-part construction (henceforth D3C), composed of nunc, age and a first person singular commissive and metacommunicative
verbum dicendi. The D3C is present three times in Virgil’s poetry: once
in the Georgics and twice in the Aeneid. This study aims to consider each element from a linguistic, sociolinguistic, and pragmatic point of view, paying special attention to context and genre. Moreover, the D3C and its variants are studied in a comparative perspective along the literary and non-literary testimonia both latina and graeca of Antiquity, in order to identify possible literary models
CORTE DI GIUSTIZIA DELL’UNIONE EUROPEA, IV SEZIONE, 27 MARZO 2014, CAUSA C-565/12 (PRE- SIDENTE DI SEZIONE L. BAY LARSEN; GIUDICI M. SAFJAN; J. MALENOVSKÝ, A. PRECHAL, RELATO- RE K. JÜRIMÄE - LCL LE CRÉDIT LYONNAIS SA - AVV. C. VEXLIARD) - FESIH KALHAN.
Get PDFIl commento alla sentenza si propone di illustrare la tematica del merito creditizio e le conseguenze previste per la sua violazione sul profilo degli interessi. In particolare, si ha riguardo all'obbligo precontrattuale del creditore di valutare la solvibilità del debitore consultando una banca dati pertinente. L'attenzione è all'ordinamento francese che disciplina tale aspetto nel codice monetario e finanziario
Mechanical energy dissipation due to the propagation of elastic waves during the lateral impact of elastic cylinders
Get PDFThe lateral impact between elastic cylinders is studied using two dynamic models. We propose
an elementary example to justify the mechanical energy dissipation in a pure elastic contact
and to define the parameters needed for its quantification. A finite element model is presented
as the theoretical basis for the quantification of the mechanical energy dissipation produced
by the propagation of elastic waves in continuous deformable impacting cylinders. The results
are exploited to build an accurate and more numerically efficient dynamic lumped parameter
model. The models are applied to the lateral impact of identical cylinders with various diameters
and different impact speeds. The impact of the cylinders with a different mass and radius
is also analyzed. The calculation of the coefficient of dissipation enables the global loss of
mechanical energy to be quantified, and an equivalent damping ratio associated with the impact
is calculated. The obtained damping values can be used as a reasonable underestimate of the
dissipation produced in the engagement of spur gears, thus allowing a conservative prediction
of the dynamic overloads of the system in resonant conditions
Prefazione a 'La città come bene comune'
No full textIl contributo mira a proporre una peculiare prospettiva di analisi del tema dei beni comuni: per un verso, il tema è declinato specificamente in relazione alla dimensione della città; per altro verso, è favorito un approfondimento multidisciplinare, che valorizzi tanto i profili giuridici quanto quelli economici. Nell'insieme, si ricava un quadro critico caratterizzato dalla profonda messa in discussione di tante categorie giuridiche - consegnateci dalla tradizione - che si collegano all’antica idea della monoliticità del diritto dominicale
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