NUMERICAL-EXPERIMENTAL METHOD FOR THE ANALYSIS OF RESIDUAL STRESSES IN COLD-EXPANDED HOLES

Hole cold expansion is a technique widely used to improve the fatigue life of components with holes, e.g. bolted or riveted joints. As it has been demonstrated in literature by analytical, numerical and experimental analyses carried out by several authors, the compressive residual stresses introduced by the hole cold expansion have a beneficial influence on both the static and the fatigue strength of the treated component, because they reduce significantly the typical stress peaks around the hole due to stress concentration. In the literature, various analyses of the residual stresses introduced by the hole cold expansion have been performed by using several methods such as X-ray diffraction, neutron diffraction and the modified Sachs method. Unfortunately, all these method are affected by some limitations: low measurement depth (X-ray method), complex measurement procedure (neutron diffraction method) and approximate formulation (Sachs method). In order to overcome such drawbacks, in this study a new mechanical method, based on an innovative extension of the “rectilinear groove method” associated with the classical “integral method” calculation procedure, is proposed. Experimental assessment of the proposed method has been performed by using aluminum 5083 H321 specimens with holes subjected to various levels of cold expansion

Analysis and optimization of hybrid double lap aluminum-GFRP joints

In this paper a systematic investigation of the mechanical performance of hybrid double-lap Al-GFRP bonded-bolted joints, has been carried out by using experimental analyses and numerical simulations. In order to detect the optimal geometric configuration, as well as to highlight the contribution of adhesive and bolts, the results relative to hybrid joints have been compared with those of simply adhesively bonded and simply bolted joints. The experimental and numerical results have shown that by using the minimum overlap length provided from theory, the bolt leads to a significant decreasing of both the maximum shear and the maximum peel stresses in the adhesive layer and, consequently, the hybrid joint exhibits a static tensile strength that is in practice equal to the sum of the relative values corresponding to the simply bonded joint and the simply bolted joint. Moreover, the so configured hybrid joint, exhibits an energy absorption and a fatigue strength higher than twice those of the simply adhesively bonded joint that are, in turn, higher than those of the simply bolted joint. © 2014 Elsevier Ltd

OTTIMIZZAZIONE DI GIUNTI IBRIDI HBB A DOPPIA SOVRAPPOSIZIONE GFRP-ALLUMINIO

In order to exploit the advantages of both mechanical joints and adhesively bonded joints, in the last year a noticeable research activity has addressed to the so called hybrid joints (Hybrid Bonded Bolted joint, HBB) that consist in combining a classical mechanical joint (bolted, riveted joint, etc..) to a traditional bonded joint or a co-cured joint. The present work shows the results of experimental and numerical analyses of double-lap HBB joints, carried out to detect the geometric configuration that permits to distribute the applied load between the two coexisting junctions and then to optimize their mechanical performance. The studied joint consists of an internal adherent made by GFRP and external adherents made by aluminum type 2024-T6, connected by using an adhesive bonding and a M6 bolt. The optimization is detected by varying various influence parameters such as the geometry of the lip and the shape of the washer, which influences the distribution of the bolt preload. After the experimental tests, various numerical analyses are carried out to obtain a better understanding of the static behavior of the joint, as well as to define reliable criteria for the strength prediction under various operating conditions

Sviluppo di procedimenti di saldatura LASER e LASER arco per pannelli AFS (Aluminum Foam Sandwich)

2008 - 2009La tesi presenta l’attività di ricerca condotta presso il laboratorio LASER del centro di ricerca ENEA - Trisaia (MT) per lo sviluppo di un procedimento di saldatura, ancora poco diffuso a livello industriale, che è la saldatura ibrida LASER-arco. Inoltre, la novità del lavoro riguarda anche i materiali oggetto di indagine consistenti in estrusi di lega di alluminio, saldati a formare una struttura portante, a cui sono stati collegati pannelli sandwich di schiuma di alluminio (AFS), con una giunzione continua tale da garantire un collegamento strutturale. Considerate alcune problematiche, rilevate dal lavoro di ottimizzazione dei parametri della saldatura LASER-MIG, è stata verificata la possibilità di superare questi problemi (ad esempio la mutua influenza di parametri LASER e di quelli MIG) con l’impiego di un altro tipo di tecnologia LASER-arco basata su generatori a caratteristica cadente di tipo TIG e materiale d’apporto sotto forma di filo freddo. Per questa parte, il lavoro è stato mirato fondamentalmente alla progettazione del nuovo sistema e alla realizzazione di un primo prototipo che ha permesso di evidenziare alcuni importanti risultati. Nella prima parte del lavoro si sono analizzate le prove di saldatura ibrida LASER-MIG tra AFS e profilati di lega di alluminio. Dall’analisi delle prove è emerso che la saldatura ibrida, applicata a materiali altamente riflettenti alla radiazione LASER CO2 come la lega AA6060 T6, permette la saldatura con adeguati fili d’apporto, al contrario della saldatura LASER stand alone. Infatti, questo tipo di lega, di cui sono costituite anche le pelle dei pannelli AFS, riflette fortemente la radiazione LASER CO2 inibendo l’innesco del processo di saldatura keyhole anche con potenze specifiche di 4 x 106 W/cm2. Tale problematica è influenzata molto dall’impostazione dei parametri geometrici LASER-MIG, in particolare il posizionamento relativo delle sorgenti e, più in generale, permette una variabilità molto limitata nell’impostazione dei parametri geometrici, elettrici, delle velocità di saldatura e la quantità di filo d’apporto. Per limitare il problema della mutua interazione fra LASER ed arco, poiché il processo MIG non permette una regolazione della quantità di filo indipendente dalla erogazione della potenza, nella parte finale delle attività si è descritta l’analisi dei componenti necessari, le scelte progettuali, la progettazione di componenti specifici per l’implementazione di una stazione di saldatura ibrida LASER –TIG. Si è realizzato un prototipo con il quale si sono fatti dei test preliminari. Con il prototipo, se pur limitante per quanto riguarda le regolazioni possibili rispetto alle attrezzature definitive progettate, si sono eseguite alcune prove di penetrazione su acciaio inossidabile e leghe di nichel, per le quali erano già noti i benchmark, in termini di velocità massima di processo, alla massima potenza del LASER per ottenere la piena penetrazione, sulla stazione di lavorazione ND:YAG del C.R. ENEA - Trisaia. Da queste prove è emerso chiaramente che la saldatura ibrida, in termini di produttività, è molto più vantaggiosa della saldatura con il solo LASER poiché si sono riscontrati, su tali materiali, aumenti di velocità variabili tra il 60% e il 70% (a parità di potenza LASER). Chiaramente trattandosi di prove esplorative i valori devono intendersi solo indicativi, ma comunque superiori al 20%-30% che normalmente la letteratura riporta come dato. [a cura dell'autore]VIII n.s

Synthetic biology: Novel approaches for microbiology

In the past twenty years, molecular genetics has created powerful tools for genetic manipulation of living organisms. Whole genome sequencing has provided necessary information to assess knowledge on gene function and protein networks. In addition, new tools permit to modify organisms to perform desired tasks. Gene function analysis is speed up by novel approaches that couple both high throughput data generation and mining. Synthetic biology is an emerging field that uses tools for generating novel gene networks, whole genome synthesis and engineering. New applications in biotechnological, pharmaceutical and biomedical research are envisioned for synthetic biology. In recent years these new strategies have opened up the possibilities to study gene and genome editing, creation of novel tools for functional studies in virus, parasites and pathogenic bacteria. There is also the possibility to re-design organisms to generate vaccine subunits or produce new pharmaceuticals to combat multi-drug resistant pathogens. In this review we provide our opinion on the applicability of synthetic biology strategies for functional studies of pathogenic organisms and some applications such as genome editing and gene network studies to further comprehend virulence factors and determinants in pathogenic organisms. We also discuss what we consider important ethical issues for this field of molecular biology, especially for potential misuse of the new technologies. [Int Microbiol 2015; 18(2):71-84]Keywords: synthetic biology · genetic engineering · genomics · pathogenesis · bioethics · artificial cells · astrobiolog

Redescoberta de Dendropsophus tintinnabulum (Anura: Hylidae) na bacia do Alto Rio Negro (Amazonas, Brasil) com a descrição do canto de anúncio e da morfologia externa

Dendropsophus tintinnabulum is one of six species of the genus unassigned to any group. Voucher specimens and recordings of this taxon obtained during field work in the municipality of São Gabriel da Cachoeira and elsewhere in the district of Cucuí in Amazonas state, Brazil, permit a description of the advertisement call and external morphological features. Based on overall similarities in size, dorsal color, body shape, advertisement call, and preliminary genomic results, D. tintinnabulum is tentatively assigned to the D. microcephalus GroupDendropsophus tintinnabulum é uma das seis espécies de Dendropsophus que ainda não foi atribuída a nenhum dos grupos de espécies atualmente aceitos. Espécimes-testemunhos e gravações desse táxon obtidos durante trabalho de campo no município de São Gabriel da Cachoeira e no distrito de Cucuí, estado do Amazonas, Brasil, permitem a descrição do canto de anúncio e de caracteres da morfologia externa. A partir de todas as similaridades em relação ao tamanho corporal, padrão de coloração, formato do corpo, canto e dados genômicos preliminares, alocamos tentativamente D. tintinnabulum no grupo de D. microcephalu

Desarrollo y puesta en marcha de una nueva línea de negocio en una empresa del sector de tecnologías de información, para la ejecución e implementación de una herramienta informática dirigida al sector de músicos independientes

Ingeniero (a) IndustrialPregrad

Masked stereolithography of wollastonite-diopside glass-ceramics from novel silicone-based liquid feedstock

Silicate bioceramics, including systems based on the simultaneous presence of wollastonite (CaSiO3) and diopside (CaMgSi2O6), are of great interest in bone tissue engineering applications, especially in form of variously shaped three-dimensional scaffolds, as determined by application of several additive manufacturing technologies. In this framework, silicone resins, properly modified with CaO- and MgO-based fillers and blended with photocurable acrylates, are attractive both as precursors and as feedstock for additive manufacturing technologies, including stereolithography. The use of powder fillers, however, may lead to issues with homogeneity or with printing resolution (owing to light scattering). The present paper aims at presenting the first results from a new concept of incorporation of CaO and MgO, relying on salts dispersed in emulsion within a photocurable silicone/acrylate blend. Direct firing at 1100 °C of printed scaffolds successfully produced wollastonite-diopside glass-ceramic scaffolds, with a very fine crystal distribution. The strength-to-density was tuned by operating either on the topology of scaffolds or on the firing atmosphere (passing from air to N2)