Toward high performance renewable agave reinforced biocomposites: Optimization of fiber performance and fiber-matrix adhesion analysis

The increasing sensitivity toward the environmental pollution and the recent laws on the environmental protection, have led to an increasing attention to the so called biocomposites, i.e. to ecofriendly or renewable composite materials, obtained from biopolymers reinforced by natural fibers. Although the contribution of various works reported in literature, focused on biocomposites reinforced by agave fibers, such materials are still exclusively used in the automotive industry for non-structural applications, and the implementation of high performance biocomposites for semi-structural and structural applications, is an expected, but not yet reached objective. Therefore, the present work aims to give a contribution to reach such an objective, by means of a proper selection of the fiber, in terms of variety, age and position, as well as by the implementation of a new ecofriendly fiber extraction method that allows the user to obtain fibers with improved mechanical performance. In more detail, it is shown that the agave marginata, widespread in the Mediterranean area, provides fiber with performance higher than the agave sisalana commonly considered in literature, and its performance can be furtherly improved by proper optimization of the main influence parameters and the extraction process. On the basis of these optimized fibers, as well as of thermoplastic and thermosetting matrixes, particularly suitable for the manufacturing of high performance ecofriendly biocomposites, an accurate theoretical-experimental analysis on the fiber-matrix adhesion has allowed first to confirm the good adhesion of the agave with epoxy and PLA matrixes, as well as to detect the actual influence of the mercerization treatments and the significant effects of the stiffness of the coupled materials on the potential pull-out and/or debonding damage mechanisms

fatigue delamination experiments on gfrp and cfrp specimens under single and mixed fracture modes

Abstract This paper deals with the experimental analysis of the delamination phenomena in composite materials under different loading conditions. Quasi-static and fatigue tests are performed on specimens made of glass-fibre (GFRP) and carbon-fibre (CFRP) reinforced plastic. In particular, experiments have been carried out under single fracture modes I and II (using standard DCB and ENF test configurations) and mixed modes I+II (using the MMB test configuration) with several mode mixtures. Results obtained for the two materials have been compared paying attention on the relationship between the parameters that describe the fatigue behaviour and the mode mixture acting during the crack propagation

STUDIO NUMERICO-SPERIMENTALE DI GIUNZIONI IBRIDE A SEMPLICE SOVRAPPOSIZIONE ALLUMINIO-CFRP

Le giunzioni ibride, ottenute dalla sovrapposizione di una giunzione meccanica e di una incollata, sono sempre pi\uf9 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 \ue8 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 \ue8 esaminato in dettaglio il comportamento del giunto al variare della sequenza di laminazione, delle modalit\ue0 di giunzione, del tempo di polimerizzazione dell\u2019adesivo strutturale e dell\u2019entit\ue0 del precarico applicato al bullone

Influence of the Resin Layer Thickness at the Interface of Hybrid Metal-composite Co-cured Joints

As discussed in literature, the accurate analysis of the modern co-cured joints between composite materials or between a metal and a composite material (hybrid joints) is complicated by the influence of the interface resin layer on the interface singular stress field. In such joints, in fact, there is not a proper adhesive layer and the thickness of the resin layer, that plays the role of the adhesive, is not constant due to the presence of the reinforcing fibers in the composite adherent. For this reason several authors assume that a generic co-cured joint can not be studied as a simple bi-material joint, without considering the particular characteristics of the actual resin layer. This problem is also involved into the development of reliable design methods able to give accurate predictions of the joint efficiency. In this work, by theoretical analyses performed by using the Lekhnitskii theory, numerical simulations carried out by means of the boundary element method and experimental investigations based on the combined use of the generalized Dundurs parameters and digital photoelasticity, the influence of the resin layer on the singular stress field at the interface of a generic hybrid metal-composite joint, has been investigated.\ua9 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM1

Numerical model for the characterization of biocomposites reinforced by sisal fibres

Abstract Although several works have been recently published in literature about biocomposites, i.e. on innovative and ecofriendly polymer matrix composites reinforced by natural fibers, there are not studies on the influence of the waviness that various natural fiber present after their extraction. In order to give a contribution to the knowledge of the effects of the fiber waviness on the main mechanical properties of biocomposites, as the longitudinal Young modulus, in the present study a systematic numerical analysis has been carried out by using parametric models properly developed, that let the user to consider the effects of the key influence parameters as the fiber concentrations and the fiber curvature. Successive experimental studies have allowed to corroborate the accuracy of the numerical results, as well as to highlight the local effects due to the fiber waviness, that in some cases can become more significant than the global effects analyzed by the numerical approach

Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions

Eruptive solar flares were predicted to generate large-scale vortex flows at both sides of the erupting magnetic flux rope. This process is analogous to a well-known hydrodynamic process creating vortex rings. The vortices lead to advection of closed coronal loops located at peripheries of the flaring active region. Outward flows are expected in the upper part and returning flows in the lower part of the vortex. Here, we examine two eruptive solar flares, an X1.1-class flare SOL2012-03-05T03:20 and a C3.5-class SOL2013-06-19T07:29. In both flares, we find that the coronal loops observed by the Atmospheric Imaging Assembly in its 171\,\AA, 193\,\AA, or 211\,\AA~passbands show coexistence of expanding and contracting motions, in accordance with the model prediction. In the X-class flare, multiple expanding/contracting loops coexist for more than 35 minutes, while in the C-class flare, an expanding loop in 193\,\AA~appears to be close-by and co-temporal with an apparently imploding loop arcade seen in 171\,\AA. Later, the 193\,\AA~loop also switches to contraction. These observations are naturally explained by vortex flows present in a model of eruptive solar flares.Comment: The Astrophysical Journal, accepte

Implementation of eco-sustainable biocomposite materials reinforced by optimized agave fibers

Although several works have recently been published in literature about biocomposites, i.e. about composites with polymeric matrix reinforced by natural fibers, only a few articles have been devoted to the implementation of high performance biocomposites for structural and semi-structural applications. The present study aims to give a contribution by considering biocomposites obtained by using an eco-friendly partially bio-based epoxy (green epoxy) and sisal (agave sisalana fibers) obtained by a proper optimization process. Through a systematic experimental analysis, three different types of biocomposites obtained with a suitable manufacturing process, such as random short fiber biocomposites, random discontinuous fibers biocomposite obtained through the preliminary manufacture of MAT fabrics, and unidirectional long fibers biocomposites obtained through the preliminary manufacture of unidirectional \u201cstitched\u201d fabrics, have been studied

OTTIMIZZAZIONE DI UNA GIUNZIONE INCOLLATA A DOPPIA SOVRAPPOSIZIONE PER SANDWICH IN COMPOSITO

Grazie alle peculiari performances meccaniche, quali soprattutto l\u2019elevata resistenza a flessione unita ad un basso peso specifico, le strutture sandwich in composito sono sempre pi\uf9 frequentemente utilizzate nella moderna progettazione industriale. Nel presente lavoro, considerando un composito sandwich con skins in vetroresina e core in PVC espanso, \ue8 stato eseguito uno studio numerico e sperimentale al fine di individuare la configurazione ottimale di una giunzione incollata a doppia sovrapposizione avente quali aderendi esterni le stesse skins del sandwich e aderendo interno costituito da un inserto in metallo o in composito. In dettaglio, previa preliminare ottimizzazione teorica della geometria della giunzione, eseguita tenendo conto delle propriet\ue0 dell\u2019adesivo e del materiale costituente l\u2019aderendo interno, la configurazione ottimale \ue8 stata individuata attraverso sistematiche prove sperimentali di trazione e flessione al variare dei principali parametri di influenza. Successive analisi numeriche eseguite in ambiente Ansys APDL, hanno evidenziato i particolari meccanismi di danneggiamento interlaminare