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Through a systematic experimental analysis, the impact characterization of carbon-aramid hybrid composites, typically used in the automotive sports field, has been performed. CFRP laminates object of this study have been produced by adding a hybrid foil obtained using a fabric of twill type, so-called carbon-kevlar. In order to highlight the effects of hybridisation, that is, the different properties of kevlar fibre with respect to carbon, a comparative analysis was also carried out considering a CFRP laminate with the same lay-up. The analysis of the experimental results obtained through preliminary tensile tests and subsequent low-velocity drop-weight impact tests integrated with x-ray tomography, showed that although the hybrid composite has a lower static strength than the simple CFRP, it has an increase in impact strength of up to 50%, combined with an appreciable increase in maximum impact force and mainly in resistance to surface damage.

In order to comply with the recent regulations in terms of environmental protection, biocomposites reinforced with natural fibers are increasingly used in the automotive sector, for the replacement of synthetic materials in semi-structural applications as panels, filling material, coating, dashboards, etc. The good mechanical performances of these materials, mixed with low weight and low cost, also make it possible to minimize the weight of the vehicle, and therefore consumption, but also the relative production costs. These are composites with random short fiber appreciated for their good stiffness, generally well above that of the matrix alone. Due to the peculiar "transverse" damage phenomena, often also influenced by debonding and pull-out phenomena related to the limited fiber-matrix adhesion, the mechanical, static and fatigue resistance of these materials is instead generally comparable to that of the matrix alone. This prevents their use in more mechanically demanding applications. For this reason, several chemical treatments on the fibers have been proposed in the literature by various authors, although still not fully satisfactory results have been obtained in terms of improving resistance. Taking into account the positive effects of the nanotubes on the fatigue resistance of structural polymeric adhesives and polymer matrix composites reinforced with synthetic fibers, in this work the effects of nanotubes on the fatigue resistance of biocomposites reinforced with agave fibers are analyzed, the fibers are obtained with a special compression molding process. The tests carried out on green epoxy matrix biocomposites in which nanotubes with different concentrations in volume were previously dispersed, showed that the static strenght is significantly influenced by the presence of nanotubes, although more appreciable improvements are found in the fatigue performance.

Data la crescente attenzione nei confronti dell’ambiente, le sempre più restrittive norme in materia di salvaguardia ambientale e di riciclo dei materiali hanno portato ad un notevole interesse dei ricercatori verso i biocompositi, materiali costituiti da rinforzi di origine naturale e matrici a basso impatto ambientale. Nonostante molteplici studi siano stati indirizzati a tali materiali innovativi, allo stato attuale poche ricerche hanno riguardato l’analisi della tenacità alla frattura di laminati biocompositi. Il presente lavoro propone pertanto uno studio sperimentale del comportamento alla frattura translaminare in modo I di laminati biocompositi in fibre di agave e matrice epossidica green, valutando in particolare l’effetto della variazione percentuale volumetrica del rinforzo e della sequenza di impacchettamento (unidirezionali, cross-ply, angle-ply ecc.). Le prove di resistenza alla frattura a trazione in modo I sono state eseguite su campioni con configurazione Compact Tension (CT) al fine di determinare sia il fattore critico di intensificazione delle tensioni, sia la Critical Strain Energy Release Rate (CSERR). In particolare, i diversi provini CT sono stati ottenuti attraverso laminazione manuale e successivo processo di compression-moulding, a partire da tessuti unidirezionali di tipo stitched appositamente prodotti in laboratorio. Al fine di individuare il metodo ottimale per una accurata valutazione sperimentale della CSERR, sono stati confrontati i risultati ottenuti con diversi metodi tra cui l’Area Method ed il Compliance Calibration The recent attention toward the environmental protection, as well as to the restrictive regulations in term of material recycling, have led to a noticeable interest of the scientific research for biocomposites, i.e. materials constituted by natural fibers and eco-friendly matrix. Although various research works have been focused on such innovative materials, only a few articles have been devoted to the their fracture strenght (thoughness). The present work regards the experimental study of the translaminar fracture behavior (in mode I) of biocomposite laminates constituted by green epoxy matrix reinforced by optimized agave sisalana fibers, varying the main influence parameters as the fiber concentration and the lay-up (unidirectional, cross-ply, angle-ply etc.). The fracture tests in mode I, have been performed by using Compact Tension (CT) specimens, in order to determine both the critical Stress Intensity Factor (SIFc) and the so called Critical Strain Energy Release Rate (CSERR). In more detail, several CT specimens have been manufactured by hand lay-up and successive compression-moulding process whose parameters have been optimized in previous study of the same authors. To this aim proper stitched fabrics have been previously manufactured in laboratory. In order to detect the optimal method for an accurate experimental analysis of the CSERR, the results provided by the Area Method and the Compliance Calibration, have been compared.

The growing attention on environmental issues has led to a recent research interest in eco-sustainable and renewable materials, among which biocomposites play an important role. Biocomposites are materials consisting of a matrix with low environmental impact or renewable, reinforced with natural fibres. Several research activities reported in literature, deal mainly with the static mechanical properties. Just few works are instead devoted to the assessment of their dynamic properties, such as fatigue strength, impact strength, etc. In order to give a contribution to the knowledge of the impact behaviour of green epoxy matrix biocomposites reinforced with agave fibres, in this paper a systematic study is carried out to evaluate the impact strength of different laminates (single layer, cross-ply, quasi-isotropic), by low velocity impact test. The various selected laminates, allowed to assess the effects of the main influence parameters as fibre distribution (unidirectional and random), fibre concentration and lay-up.

La crescente sensibilità nei riguardi dell'inquinamento ambientale e le nuove disposizioni legislative in materia di protezione dell'ambiente, hanno portato negli ultimi anni ad una crescente attenzione verso i cosiddetti biocompositi, cioè verso materiali compositi ecocompatibili e/o rinnovabili, ottenuti da biopolimeri rinforzati da fibre naturali come lino, kenaf, agave ecc. Il presente lavoro intende dare un contributo alla comprensione del comportamento meccanico ed alla efficiente progettazione di performanti biocompositi, ottenuti attraverso una oculata scelta di matrici termoindurenti e termoplastiche, rinforzate con fibre di agave. Dopo avere indagato sulle peculiari proprietà delle fibre di agave, attraverso prove di trazione e prove di pull-out su singola fibra, nonché sulle effettive proprietà delle matrici selezionate, si propongono modelli teorici e di micromeccanica che descrivono correttamente il comportamento meccanico di tali biocompositi. Verifiche sperimentali, eseguite su biocompositi a fibre corte e lunghe hanno consentito di correlare le proprietà meccaniche ai particolari meccanismi di danneggiamento, confermando la bontà dei modelli teorici proposti.

Le giunzioni ibride, ottenute dalla sovrapposizione di una giunzione meccanica e di una incollata, sono sempre più utilizzate in diversi campi della produzione industriale in quanto consentono, se correttamente configurate, di ottenere performance meccaniche superiori a quelle che si possono ottenere con le giunzioni semplici. La corretta configurazione delle giunzioni ibride necessita di opportuni studi teorici, numerici e sperimentali finalizzati ad individuare la combinazione ottimale dei principali parametri di influenza (lunghezza di sovrapposizione, rigidezza degli aderendi, sbilanciamento del giunto, posizione dei bulloni/rivetti, tipo di adesivo, ecc.) e quindi la correlazione tra parametri e prestazioni. Per dare un contributo alla conoscenza del comportamento meccanico delle giunzioni ibride tra aderendi in alluminio e CFRP, nel presente lavoro è stato condotto uno studio numerico-sperimentale su giunzioni bullonate a semplice sovrapposizione tra una lamina di alluminio AW 6082 T6 e un laminato CFRP a matrice epossidica. Nel lavoro è esaminato in dettaglio il comportamento del giunto al variare della sequenza di laminazione, delle modalità di giunzione, del tempo di polimerizzazione dell’adesivo strutturale e dell’entità del precarico applicato al bullone.

The Dystrophin-Glycoprotein Complex (DGC) is a large multisubunit complex that plays a crucial role in maintaining the structural integrity and physiology of muscle fibers. Dystrophin has been reported to be absent in the pyloric muscle of infantile hypertrophic pyloric stenosis (IHPS) patients. The present study was designed to investigate the other two patterns of DGC (dystroglycan and sarcoglycan complexes) in normal pyloric muscle and their possible modifications in IHPS patients.Ten pyloric muscle biopsies were obtained from babies operated for IHPS and five control pylorus biopsy taken at autopsy from cases without gastrointestinal disease. The DGC sub-complexes (beta-dystroglican and beta, delta- sarcoglycans) were localized immunohistochemically using specific monoclonal antibodies. The results were evaluated using a confocal laser scanning microscope.Positive immunolocalization of the two DGC sub complexes was demonstrated in the smooth muscle cells (SMCs) of the pyloric region of control patients. Similarly, a positive immune expression of beta-dystroglican was observed in the pyloric SMCs of IHPS patients. On the other hand a negative immunoreaction for sarcoglycans was recorded within the full thickness of the pyloric SMCs of these patients.The absence of sarcoglycans within the hypertrophied pyloric muscle may be a predisposing factor in the pathogenesis of IHPS since it could alter the normal physiology of SMCs through the modifications of structural integrity of sarcolemma and signaling between the extracellular and intracellular compartment.