Resistenza a fatica di strutture in leghe di alluminio: normative a confronto e verifica sperimentale

Le problematiche relative all’utilizzo delle normative nell’ambito della progettazione a fatica di strutture in leghe di alluminio sono state di recente affrontate in numerosi lavori che hanno messo in luce sia le difficoltà legate al passaggio da normative oramai obsolete ad altre di nuova concezione, ma di caratteristiche e struttura completamente diverse, che la sostanziale carenza anche all’interno delle più recenti normative europee, quale l’Eurocodice 9, di molti risultati e metodi sviluppati in anni di ricerca scientifica e ormai indiscutibilmente consolidati. Il presente lavoro si propone di approfondire entrambe le tematiche tramite il confronto tra risultati sperimentali tratti da letteratura e le corrispondenti curve di resistenza proposte rispettivamente dalla normativa italiana UNI 8634, di recente ritirata, e dall’Eurocodice 9. In questo modo verranno messe in luce le differenze tra i valori di resistenza proposti dalle due norme e verrà illustrata sia la corrispondenza a volte poco soddisfacente con i risultati sperimentali che le conseguenze dovute alla mancata applicazione di assodati risultati teorici

Analysis of the fatigue strength under two load levels of a stainless steel based on energy dissipation

In this paper the fatigue behaviour of a stainless steel AISI 304L is analysed. In the first part of the work the results obtained under constant amplitude fatigue are presented and synthesised in terms of both stress amplitude and energy released to the surroundings as heat by a unit volume of material per cycle, Q. Then some specimens have been fatigued in variable amplitude, two different load level tests: the first level was set higher while the second was lower than the constant amplitude fatigue limit. The Q values, evaluated during the second part of the fatigue test, have been compared with those calculated under constant amplitude fatigue at the same load level. The comparison allowed us to notice that the Q parameter is sensitive to the fatigue damage accumulated by the material during the first part of the fatigue test

Towards trajectory anonymization: A generalization-based approach

Trajectory datasets are becoming,popular,due,to the massive,usage,of GPS and,location- based services. In this paper, we address privacy issues regarding the identification of individuals in static trajectory datasets. We first adopt the notion of k-anonymity,to trajectories and propose,a novel generalization-based approach,for anonymization,of trajectories. We further show,that releasing anonymized,trajectories may,still have,some,privacy,leaks. Therefore we propose,a randomization based,reconstruction,algorithm,for releasing anonymized,trajectory data and,also present how,the underlying,techniques,can be adapted,to other anonymity,standards. The experimental,results on real and,synthetic trajectory datasets show,the effectiveness of the proposed,techniques

The potential of metabolomics in the diagnosis of thyroid cancer

Thyroid cancer is the most common endocrine system malignancy. However, there is still a lack of reliable and specific markers for the detection and staging of this disease. Fine needle aspiration biopsy is the current gold standard for diagnosis of thyroid cancer, but drawbacks to this technique include indeterminate results or an inability to discriminate different carcinomas, thereby requiring additional surgical procedures to obtain a final diagnosis. It is, therefore, necessary to seek more reliable markers to complement and improve current methods. “Omics” approaches have gained much attention in the last decade in the field of biomarker discovery for diagnostic and prognostic characterisation of various pathophysiological conditions. Metabolomics, in particular, has the potential to identify molecular markers of thyroid cancer and identify novel metabolic profiles of the disease, which can, in turn, help in the classification of pathological conditions and lead to a more personalised therapy, assisting in the diagnosis and in the prediction of cancer behaviour. This review considers the current results in thyroid cancer biomarker research with a focus on metabolomics

Effetto delle dimensioni del cordone di saldatura sulla resistenza a fatica dei giunti a croce

La scelta della dimensione da assegnare al cordone di saldatura nel caso di giunzioni saldate a croce può presentarsi problematica, specie quando gli spessori delle lamiere che formano il giunto sono differenti tra loro. Le normative di tipo tecnologico suggeriscono in genere di prevedere uno spessore del cordone di saldatura inferiore al minimo spessore della lamiera da collegare, mentre le normative di tipo strutturale non prevedono una dipendenza della resistenza del giunto, sia statica che a fatica, dalle dimensioni del cordone di saldatura, a meno che queste non siano tanto ridotte da portare a rotture che si inneschino e si propaghino non più nella lamiera base ma nel cordone di saldatura. Scopo del presente lavoro è la verifica, teorica e sperimentale, della variazione della resistenza a fatica al variare del rapporto tra lo spessore del cordone di saldatura e quello minimo delle lamiere da saldare

Resistenza a fatica di strutture in leghe di alluminio: normative a confronto e verifica sperimentale

Le problematiche relative all’utilizzo delle normative nell’ambito della progettazione a fatica di strutture in leghe di alluminio sono state di recente affrontate in numerosi lavori che hanno messo in luce sia le difficoltà legate al passaggio da normative oramai obsolete ad altre di nuova concezione, ma di caratteristiche e struttura completamente diverse, che la sostanziale carenza anche all’interno delle più recenti normative europee, quale l’Eurocodice 9, di molti risultati e metodi sviluppati in anni di ricerca scientifica e ormai indiscutibilmente consolidati. Il presente lavoro si propone di approfondire entrambe le tematiche tramite il confronto tra risultati sperimentali tratti da letteratura e le corrispondenti curve di resistenza proposte rispettivamente dalla normativa italiana UNI 8634, di recente ritirata, e dall’Eurocodice 9. In questo modo verranno messe in luce le differenze tra i valori di resistenza proposti dalle due norme e verrà illustrata sia la corrispondenza a volte poco soddisfacente con i risultati sperimentali che le conseguenze dovute alla mancata applicazione di assodati risultati teorici

Drag Assessment for Boundary Layer Control Schemes with Mass Injection

The present study considers uniform blowing in turbulent boundary layers as active flow control scheme for drag reduction on airfoils. The focus lies on the important question of how to quantify the drag reduction potential of this control scheme correctly. It is demonstrated that mass injection causes the body drag (the drag resulting from the stresses on the body) to differ from the wake survey drag (the momentum deficit in the wake of an airfoil), which is classically used in experiments as a surrogate for the former. This difference is related to the boundary layer control (BLC) penalty, an unavoidable drag portion which reflects the effort of a mass-injecting boundary layer control scheme. This is independent of how the control is implemented. With an integral momentum budget, we show that for the present control scheme, the wake survey drag contains the BLC penalty and is thus a measure for the inclusive drag of the airfoil, i.e. the one required to determine net drag reduction. The concept of the inclusive drag is extended also to boundary layers using the von Karman equation. This means that with mass injection the friction drag only is not sufficient to assess drag reduction also in canonical flows. Large Eddy Simulations and Reynolds-averaged Navier-Stokes simulations of the flow around airfoils are utilized to demonstrate the significance of this distinction for the scheme of uniform blowing. When the inclusive drag is properly accounted for, control scenarios previously considered to yield drag reduction actually show drag increase

Aerodynamic Effects of Uniform Blowing and Suction on a NACA4412 Airfoil

We carried out high-fidelity large-eddy simulations to investigate the effects of uniform blowing and uniform suction on the aerodynamic efficiency of a NACA4412 airfoil at the moderate Reynolds number based on chord length and incoming velocity of Rec= 200 , 000. We found that uniform blowing applied at the suction side reduces the aerodynamics efficiency, while uniform suction increases it. This result is due to the combined impact of blowing and suction on skin friction, pressure drag and lift. When applied to the pressure side, uniform blowing improves aerodynamic efficiency. The Reynolds-number dependence of the relative contributions of pressure and friction to the total drag for the reference case is analysed via Reynolds-averaged Navier–Stokes simulations up to Rec= 10 , 000 , 000. The results suggest that our conclusions on the control effect can tentatively be extended to a broader range of Reynolds numbers