Studio della propagazione della frattura in polibutene per tubi

Il Polibutene-1 isotattico (i-PB1) è un materiale polimerico usato per la produzione di tubi per il trasporto di fluidi in pressione. In questo lavoro si sono studiati due tipi di i-PB1 prodotti da Basell che differiscono per grado di isotatticità. Si sono condotte prove di frattura a diverse temperature e velocità di spostamento imposte. Si è utilizzata una configurazione di flessione su provini con singolo intaglio (SENB) unitamente a quella di doppia trave a sbalzo (DCB), quest’ultima limitatamente allo studio della fase di propagazione. Al fine di individuare con precisione l’innesco della frattura e la velocità di propagazione della stessa si è fatto ricorso a metodi ottici. Dal punto di vista fenomenologico durante la propagazione si assiste alla formazione di zone in cui il materiale risulta fortemente stirato. La frattura in esse avanza con una lacerazione continua che si alterna a salti repentini in occasione del brusco cedimento di queste zone, associato a conseguenti cadute del carico. Questa parziale instabilità è stata osservata sui due materiali per entrambe le configurazioni di prova. I risultati ottenuti sono stati interpretati seguendo l’approccio della meccanica della frattura e applicando uno schema di riduzione di tipo tempo-temperatura che ha permesso di descrivere il comportamento viscoelastico del materiale su un intervallo temporale di diverse decadi. I risultati hanno permesso di applicare un modello analitico per la previsione della vita utile di tubi in pressione. Il modello si è mostrato in buon accordo con i dati sperimentali disponibili da prove condotte su tubi dello stesso materiale

Chemical Hazard in FRP Pleasure boats' Manufacturing

The work aims to discuss measures to reduce risks associated with the workers’ exposure to harmful chemical agents in FRP manufacturing processes. Data on workers’ exposure were collected directly on the site plant of a manufacturer of fiberglass pleasure boats. Work focuses on various stages of progressive study: I) study of the molding manufacturing process, workplace, structures, tools, materials and plants in the company; II) statistical study of the use of Personal Protective Equipment; III) environmental and personal sampling campaign. The study phase I is preliminary to the following. It allowed us to identify, for each operators category, the risk factors to which each category is most exposed. Styrene and other VOCs are the main chemical risk factor on which attention has been paid for resins and gelcoat workers. The phase study II about the use of PPE leads to define evolution models in the use of PPE in relationship with room temperature and referring to Behaviour-Based Safety techniques to increase the percentage of use of PPE. The phase study III leads to define what the critical exposure moments are for workers, specially the processes when resin or gelcoat are sprayed. From this stage, intervention proposals arise measured to reduce risks

Sustainability in Aquaponics: Industrial Spirulina Waste as a Biofertilizer for Lactuca sativa L. Plants

Aquaponics represents an alternative to traditional soil cultivation. To solve the problem of nutrient depletion that occurs in this biotechnological system, the application of a spirulina-based biofertilizer was assessed. The microalgal waste used in this study came from industrial processing. Four different dilutions of the supernatant portion of this waste were sprayed on lettuce plants cultivated in an aquaponics system installed at the Botanical Gardens of the Tor Vergata University of Rome. The biofertilizer was characterized to evaluate its amount of macro- and micronutrients. The analysis conducted on the plants involved both morpho-biometric aspects and qualitative–quantitative measurements. The experiments showed that the spirulina extract had a positive effect on the growth and nutraceutical content of the lettuce plants; the obtained results highlighted that a dilution of 75% was the best for treatment. The use of the proposed organic and recycled fertilizer could increase the sustainability of crop cultivation and promote the functioning of aquaponics systems

tetraxial textiles assessment of mesoscale mechanical modelling by experimental measurements

Tetraxial technical textiles were recently manufactured by a new loom developed to weave yarns in four directions. The textile has warp, weft, and two diagonal yarns oriented at symmetrical angles (typically ±45°) with respect to the warp direction. The peculiar yarns distribution could enhance the mechanical response of the textile in multiple directions aiming to almost isotropic in-plane behaviour. For the prediction of the mechanical performance of such tetraxial textiles, a reliable and accurate predictive model is of relevant importance. The present investigation aims to adopt the finite element numerical approach at the mesoscopic scale to predict the mechanical response for any in-plane loading of tetraxial textiles. An accurate modelling of the constitutive behaviour of the fibrous yarns was adopted considering a hyperelastic model. The modelling of the tetraxial unit cell allowed to have the mechanical behaviour for uniaxial and biaxial tensile and for shear loading conditions. The assessment of the accuracy of the numerical model was performed considering a huge experimental campaign dedicated to several hybrid tetraxial textiles. The comparison highlights the accuracy of the numerical model to predict the nonlinear behavior of the fabric for any loading condition and to provide the proper mechanical model for further optimization of tetraxial textiles supposed for different industrial applications

ccdc80-l1 Is Involved in Axon Pathfinding of Zebrafish Motoneurons

Axon pathfinding is a subfield of neural development by which neurons send out axons to reach the correct targets. In particular, motoneurons extend their axons toward skeletal muscles, leading to spontaneous motor activity. In this study, we identified the zebrafish Ccdc80 and Ccdc80-like1 (Ccdc80-l1) proteins in silico on the basis of their high aminoacidic sequence identity with the human CCDC80 (Coiled-Coil Domain Containing 80). We focused on ccdc80-l1 gene that is expressed in nervous and non-nervous tissues, in particular in territories correlated with axonal migration, such as adaxial cells and muscle pioneers. Loss of ccdc80-l1 in zebrafish embryos induced motility issues, although somitogenesis and myogenesis were not impaired. Our results strongly suggest that ccdc80-l1 is involved in axon guidance of primary and secondary motoneurons populations, but not in their proper formation. ccdc80-l1 has a differential role as regards the development of ventral and dorsal motoneurons, and this is consistent with the asymmetric distribution of the transcript. The axonal migration defects observed in ccdc80-l1 loss-of-function embryos are similar to the phenotype of several mutants with altered Hedgehog activity. Indeed, we reported that ccdc80-l1 expression is positively regulated by the Hedgehog pathway in adaxial cells and muscle pioneers. These findings strongly indicate ccdc80-l1 as a down-stream effector of the Hedgehog pathway

TECNOLOGIE E PROPRIETA’ DEI MATERIALI COMPOSITI

I contenuti di questo libro sono indirizzati principalmente agli studenti di ingegneria che si avvicinano per la prima volta al mondo di questi materiali tecnologicamente avanzati. Esso contiene però anche interessanti spunti per chi già lavora nel settore e vuole approfondire qualche argomento o razionalizzare le sue competenze. I contenuti dei primi Capitoli sono del tipo “di base” e sono quindi adatti anche a lettori che, pur non avendo solide conoscenze tecniche di tipo ingegneristico, siano mossi dalla semplice curiosità di approcciare questo mondo. I Capitoli relativi al comportamento meccanico richiedono invece una conoscenza seppure elementare di meccanica dei materiali e delle strutture. Di particolare interesse poi l’ultimo Capitolo che affronta la tematica dell’economia circolare, molto attuale in questo periodo, in modo semplice e divulgativo. Il testo presentato non può e non vuole ovviamente essere completamente esauriente: nella parte di bibliografia sono però citati riferimenti utili per approfondire i diversi argomenti

Long-Term Performance of a Polymer Composite Repair System for Gas Pipelines

Predictions were made of the long-term behavior of a new repair system for gas pipelines, which involves the wrapping of a polymer composite tape coated with a pressure-sensitive adhesive on the damaged pipe. The time- and temperature-dependent behavior of the tape and the adhesive was experimentally evaluated using constant strain rate tests. A theoretical model was developed for the winding, taking into account the nonisothermal viscoelastic behavior of the materials. A good agreement was found between theoretical predictions and full-scale experimental results