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

Satellite observations of reconnection between emerging and pre-existing small-scale magnetic fields

We report multi-wavelength ultraviolet observations taken with the IRIS satellite, concerning the emergence phase in the upper chromosphere and transition region of an emerging flux region (EFR) embedded in the unipolar plage of active region NOAA 12529. The photospheric configuration of the EFR is analyzed in detail benefitting from measurements taken with the spectropolarimeter aboard the Hinode satellite, when the EFR was fully developed. In addition, these data are complemented by full-disk, simultaneous observations of the SDO satellite, relevant to the photosphere and the corona. In the photosphere, magnetic flux emergence signatures are recognized in the fuzzy granulation, with dark alignments between the emerging polarities, cospatial with highly inclined fields. In the upper atmospheric layers, we identify recurrent brightenings that resemble UV bursts, with counterparts in all coronal passbands. These occur at the edges of the EFR and in the region of the arch filament system (AFS) cospatial to the EFR. Jet activity is also found at chromospheric and coronal levels, near the AFS and the observed brightness enhancement sites. The analysis of the IRIS line profiles reveals the heating of dense plasma in the low solar atmosphere and the driving of bi-directional high-velocity flows with speeds up to 100 km/s at the same locations. Furthermore, we detect a correlation between the Doppler velocity and line width of the Si IV 1394 and 1402 \AA{} line profiles in the UV burst pixels and their skewness. Comparing these findings with previous observations and numerical models, we suggest evidence of several long-lasting, small-scale magnetic reconnection episodes between the emerging bipole and the ambient field. This process leads to the cancellation of a pre-existing photospheric flux concentration of the plage with the opposite polarity flux patch of the EFR. [...]Comment: 4 pages, 2 figures, to be published in "Nuovo Cimento C" as proceeding of the Third Meeting of the Italian Solar and Heliospheric Communit

Progettazione efficiente di Biocompositi Rinforzati con fibre di Agave

La crescente sensibilit\ue0 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, cio\ue8 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 propriet\ue0 delle fibre di agave, attraverso prove di trazione e prove di pull-out su singola fibra, nonch\ue9 sulle effettive propriet\ue0 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 propriet\ue0 meccaniche ai particolari meccanismi di danneggiamento, confermando la bont\ue0 dei modelli teorici proposti

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

Plasma flows and magnetic field interplay during the formation of a pore

We studied the formation of a pore in AR NOAA 11462. We analysed data obtained with the IBIS at the DST on April 17, 2012, consisting of full Stokes measurements of the Fe I 617.3 nm lines. Furthermore, we analysed SDO/HMI observations in the continuum and vector magnetograms derived from the Fe I 617.3 nm line data taken from April 15 to 19, 2012. We estimated the magnetic field strength and vector components and the LOS and horizontal motions in the photospheric region hosting the pore formation. We discuss our results in light of other observational studies and recent advances of numerical simulations. The pore formation occurs in less than 1 hour in the leading region of the AR. The evolution of the flux patch in the leading part of the AR is faster (< 12 hour) than the evolution (20-30 hour) of the more diffuse and smaller scale flux patches in the trailing region. During the pore formation, the ratio between magnetic and dark area decreases from 5 to 2. We observe strong downflows at the forming pore boundary and diverging proper motions of plasma in the vicinity of the evolving feature that are directed towards the forming pore. The average values and trends of the various quantities estimated in the AR are in agreement with results of former observational studies of steady pores and with their modelled counterparts, as seen in recent numerical simulations of a rising-tube process. The agreement with the outcomes of the numerical studies holds for both the signatures of the flux emergence process (e.g. appearance of small-scale mixed polarity patterns and elongated granules) and the evolution of the region. The processes driving the formation of the pore are identified with the emergence of a magnetic flux concentration and the subsequent reorganization of the emerged flux, by the combined effect of velocity and magnetic field, in and around the evolving structure.Comment: Accepted for publication in Astronomy and Astrophysic

The 2013 February 17 sunquake in the context of the active region's magnetic field configuration

© 2017. The American Astronomical Society. All rights reserved. Sunquakes are created by the hydrodynamic response of the lower atmosphere to a sudden deposition of energy and momentum. In this study, we investigate a sunquake that occurred in NOAA active region 11675 on 2013 February 17. Observations of the corona, chromosphere, and photosphere are brought together for the first time with a nonlinear force-free model of the active region's magnetic field in order to probe the magnetic environment in which the sunquake was initiated. We find that the sunquake was associated with the destabilization of a flux rope and an associated M-class GOES flare. Active region 11675 was in its emergence phase at the time of the sunquake and photospheric motions caused by the emergence heavily modified the flux rope and its associated quasi-separatrix layers, eventually triggering the flux rope's instability. The flux rope was surrounded by an extended envelope of field lines rooted in a small area at the approximate position of the sunquake. We argue that the configuration of the envelope, by interacting with the expanding flux rope, created a “magnetic lens” that may have focussed energy on one particular location of the photosphere, creating the necessary conditions for the initiation of the sunquake

ERROR AND UNCERTAINTY ANALYSIS OF RESIDUAL STRESS EVALUATION BY USINGTHE RING-CORE METHOD

The Ring-Core Method is a technique used for the experimental analysis of the residual stresses in mechanical components. For uniform and non-uniform residual stresses estimation, the use of the method leads in general to accurate results but, unfortunately at present the user does not have appropriate procedures to correct the obtained results from systematic errors as well as to estimate the uncertainty due to random errors. In order to overcome such drawbacks, in the present work, the procedures for the correction of the effects of the main error sources and for the stress uncertainty estimation, are proposed. The practical application of such procedures allow the user to highlight the relative magnitude of the error and stress uncertainty associated with the main influence parameters