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In the last years, bistable composite structures are finding interest in several aeronautical applications such as power harvesting devices or morphing applications on very small aircraft/drones, not needing servo-activated control systems. Residual stresses, developed upon cooling after curing, leads to warped the composite laminates. Several batches of unsymmetrical and unbalanced [0°/90°] laminates were cured in an autoclave according to a standard temperature cycle, following the pre-preg supplier suggested curing cycle. In order to increase the thermal stresses (and hence the bistability phenomenon), these laminates were removed from the autoclave immediately after the curing reaction and rapidly cooled down at room temperature not applying the indicated cool rate between 2 and 5 °C min−1. During storage at room temperature, thermal stresses changed over time, indicating that asymptotic stress relaxation occurs. The first part of this work looks at residual stress characterization of bistable composite plates measuring the changes of shape observed during room temperature annealing. Rectangular plates were produced and the bistable geometric shapes were accurately assessed using a laser scanner system over several days, in order to monitor the curvature changes due to stress relaxation. Then phenomenological viscoelastic predicting models were proposed for a quick estimate for the strain/stress relaxation phenomenon. The loss of bistability was demonstrated with the help of numerical simulation and experimental testing. The final goal was to gain a better knowledge of the relation between processing and final shape of bistable laminates, in order to make them suitable for application on small air vehicles.

Composite materials, in addition to the high specific mechanical properties, have properties enabling their applications in high-pressure, high-temperature (HPHT) and corrosive environment as occurs in deep water. Their use for manufacturing pipelines and offshore risers can provide relevant performance advantages over steel such as lower weight, improved fatigue capacity, corrosion resistance and higher strain limits. However, composite materials are more complex to use in design than metallic materials due to their anisotropic properties and lack of accurate failure prediction models. Thus, a continuous in-situ and in real-time Structural Health Monitoring (SHM) of composite components would be necessary and useful to promote their use in a wider range of operational conditions. In this work, an FRP pipe sample was instrumented with Piezoelectric Wafer Active Sensors (PWAS) used either as passive receivers or as transmitters of guided waves for active health monitoring in pitch-catch configuration. The propagation properties of guided waves in glass fibres reinforced composites were studied by developing MATLAB scripts, running FE simulation and experiments. The numerical and experimental signals were post-processed in MATLAB by Short Time Fourier Transform (STFT) in order to evaluate their frequency and time-frequency content. Furthermore, the guided waves were used to detect artificial defects imposed on the structure identifying their location. Several testcases were studied to find out the limitations and the most suitable conditions of using guided waves for defects monitoring in a composite pipe. The work proposes effective methods for pipe structural health evaluation by non-destructive techniques and ultrasonic guided waves.

Heritage buildings worldwide are primarily masonry construction. Over the centuries, these structures have demonstrated a high vulnerability in seismic events. The seismic protection and retrofitting of these historical structures require an effective structural solution, without compromise, cover or loss of architectural and artistic value. For these scenarios, the use of Fiber Reinforced Polymers (FRPs) is discouraged since removability of the intervention is often a mandatory requirement, and the polymeric adhesives bond the fiber to the masonry substrate, eliminating the possibility of preserving the underlying material during a replacement operation. In FRP-strengthening, the force transfer from the substrate to the FRP occurs by means of bond stresses. However, in the case of column confinement, while full bond is nevertheless developed through the adhesive, it is not necessary for the effectiveness of the confinement. Instead, the confining pressure is applied by the FRP when transversal dilatation of the column is mobilized. Thus, with the exception of the overlapping regions, an FRP retrofit for column confinement works due to a contact phenomenon instead of bond. In this context, new FRP-confinement techniques, based on contact rather than adhesion, can be developed. This paper presents research on fully-reversible contact-based techniques for FRP-confinement. Three different techniques were developed and demonstrated by the authors. Each technique was experimentally evaluated through compression tests of small-scale limestone cylinders. The reversibility of each technique was verified through comparison of the substrates before the FRP-confinement and after the testing. The effectiveness of each technique was evaluated by comparing the compressive strength and the deformability with those obtained for unconfined specimens. The concepts show promise as effective and reversible strengthening techniques.

The role of deposition fluxes on the mercury cycle at Concordia station, on the high Antarctic plateau have been investigated over the Austral summer between December 2017 to January 2018. Wet/frozen deposition was collected daily from specially sited tables, simultaneously with the collection of surface (0-3 cm) and subsurface (3-6 cm) snow and the analysis of Hg-0 in the ambient air. Over the course of the experiment the atmospheric Hg-0 concentrations ranged from 0.58 +/- 0.19 to 1.00 +/- 0.33 ng m(-3), surface snow Hg concentrations varied between (0-3 cm) 0.006 +/- 0.003 to 0.001 +/- 0.001 ng cm(-3) and subsurface snow (3-6 cm) concentrations varied between 0.001 +/- 0.001 to 0.003 +/- 0.002 ng cm(-3). The maximum daily wet deposition flux was found to be 23 ng m(-2) d(-)(1). Despite the low temporal resolution of our measurements combined with their potential errors, the linear regression of the Hg deposition fluxes against the snow accumulation rates allowed us to estimate the mean dry deposition rate from the intercept of the graph as -0.005 +- 0.008 ng m(-2) d(-1). From this analysis, we conclude that wet deposition accounts for the vast majority of the Hg deposition fluxes at Concordia Station. The number of snow events, together with the continuous GEM measurements have allowed us to make a first estimation of the mean snow scavenging factor at Dome C. Using the slope of the regression of mercury flux on snow accumulation we obtained a snow scavenging factor that ranges from 0.21 to 0.22 +/- 0.02 (ng(Hg)/g (snow))/(ng(Hg)/m(3) (air)). Our data indicate that the boundary layer height and local meteorological effects influence Hg-0 reemission from the top of (0-3 cm) the snowpack into the atmosphere and into the deeper snowpack layer (3-6 cm). These data will help constrain numerical models on the behaviour of mercury in Antarctica.

Continuous induction welding for thermoplastic matrix composites requires an accurate modeling of the temperature distribution in the laminates, depending on the electromagnetic field. In this work, a transient three-dimensional finite element (FE) model was developed in order to study the heat transfer phenomena, and melting and crystallization in the welding area during the continuous induction welding of carbon fiber reinforced Poly(ether ether ketone) (CF/PEEK) laminates. The multiphysics problem was solved by coupling electromagnetic and heat transfer equations considering matrix melting and crystallization behavior. The model was able to simulate the continuous process along a linear path at a constant speed. The computed temperatures were in good agreement with experimental measurements. Several numerical simulation were used for selecting a processing window as a function of coil speed and current, for the welding of CF/PEEK joints. The results of welding experiments were evaluated by single lap shear tests and morphology characterization of the welded interfaces and fracture surfaces. Keywords: Carbon fiber, Finite element analysis, Joining, Heat treatment, Induction welding, Thermoplastic resin

The Col Margherita (MRG) Observatory is a high-altitude background station located in the Eastern Italian Alps. Its elevation and distance from major anthropogenic and natural sources make it ideal for monitoring baseline mercury levels and investigating its geochemical cycles. In this work, total gaseous mercury (TGM), ozone (O3) and meteorological variables were studied to investigate seasonal and diurnal variability of TGM measurements from March 2018 to May 2019. We found that the year-round mean TGM concentration was 1.8 times higher than the annual atmospheric mercury measurements previously reported during the GMOS project at the same measurement site. The seasonal variation of TGM was characterized by high values in spring and summer and lower values in winter. A systematic diel pattern of TGM was obtained, with low concentrations during the daytime and higher concentrations in the late evening. Spatial patterns and temporal changes in TGM, back- trajectories (BTs) and planetary boundary layer (PBL) analysis showed that total gaseous mercury levels were influenced by local meteorology, as well as regional and long-range transport of air masses. The lowest TGM concentrations in winter are associated with high wind speeds, low boundary layer height and cleaner air masses originating from the Western sector. Conversely, the highest TGM concentrations in spring and summer were attributed to polluted air masses passing over North-eastern and Continental Europe and were probably favoured by the higher PBL height. During the snow cover season, investigation of TGM peak events also demonstrated the potential influence of re-emission processes of previously reactive mercury deposition over snow surfaces.

This work is aimed to the development and property optimization of cardanol derived plasticizers. To this purpose, different plasticizers were produced though different epoxidation routes, characterized by low toxicological and environmental impact. The plasticizers are characterized by different yield of epoxidation of the alkyl chain double bonds. The properties of the cardanol derived plasticizers were compared to the properties of commercial plasticizers, either phthalates or natural derived. Mechanical properties of soft PVC plasticized by cardanol derivatives were shown to be comparable to those of PVC with commercial plasticizers. The plasticizing efficiency of cardanol derivatives was significantly improved by increasing the yield of epoxidation. Also, mechanical properties performed after ageing showed the excellent stability of the properties of the cardanol derived plasticizer characterized by the higher yield. Evaluation of the property retention index after ageing indicated that such plasticizers showed an improved stability of properties compared to other commercial plasticizer. The results obtained highlight the relevance of an high conversion of the double bonds into epoxies in order to produce high quality plasticizers.

This work is aimed to study the suitability of a bio based compound, cardanol acetate (CA), as plasticizing agent of poly(lactic acid) (PLA). Compared to other natural derived plasticizers, cardanol acetate is not obtained from food crops but as a by product of cashew nut extraction. In addition, the cardanol derived plasticizers can be obtained by the use of non toxic and low environmental impact reagents. The plasticizing effectiveness of cardanol acetate was confirmed by the decrease of the glass transition temperature and flexural modulus, which were comparable to those obtained by the use of conventional oil based plasticizers, such as diethylhexyl phthalate (DEHP). In addition, calorimetric analysis revealed that the addition of the plasticizer, both cardanol derived and phthalate, involves a significant increase of the crystallization kinetics. An analysis of the flexural strength and deformation at break indicated that the increase of the crystallization kinetics has more dramatic effects compared to the decrease of the glass transition, particularly at low plasticizer content, finally leading to a decrease of the ductility. At higher plasticizer content, an increase of the ductility is observed, and PLA plasticized by 10% of CA showed a significant higher deformation at break than PLA plasticized by DEHP. In addition, plasticizer migration tests showed a lower weight loss of PLA plasticized by CA compared to DEHP plasticized PLA, which indicates the potential higher stability of properties of the cardanol derived plasticizer.

Bioactive food-preserving materials are based on the use of a natural antimicrobial compound loaded in a carrier material, which is able to trigger its release when requested and to modulate the rate of release, thus using either toxic or inhibitory properties against pathogens or bacteria due to food decomposition. In this study, the Schiff base formation for chitosan functionalization was achieved by the reaction of chitosan with cinnamaldehyde at different concentrations. Cinnamaldehyde is an aromatic α,β-unsaturated aldehyde, and the major component in essential oils from some cinnamon species. It has been shown to exert antimicrobial action against a large number of microorganisms including bacteria, yeasts, and mould. The formation of the Schiff base is reversible under suitable conditions, and this might allow the release of the active cinnamaldehyde from chitosan, used as the carrier. The reaction kinetics was investigated by means of rheological measurements, while infrared spectroscopy was used to assess the efficacy of the functionalization. The addition of nanometric graphene stacks to the cinnamaldehyde-functionalized chitosan films was evaluated with the aim to increase the mechanical properties of the film. Finally, the films were tested for antifungal properties with bread slices against a selected mould line.

This paper is aimed to study the morphology of intercalated nanocomposites, by coupling experimental permeability data with different analytical models. X-Ray diffraction provided the reference morphological features of the nanocomposite, including gallery thickness and aspect ratio of the lamellar stacks. Afterward, the water permeability of two intercalated nanocomposites was used for the calculation of the nanofiller aspect ratio, following different approaches. The obtained results indicate that an assumption of impermeable stacks involves a significant over-estimation of the nanofiller aspect ratio. Further, when the morphological features determined in the assumption of impermeable particles are used for estimation of the nanocomposite diffusivity by the use of the Fricke model, results do not show a satisfactory agreement with experimental data. On the other hand, fitting experimental permeability data with an analytical model accounting for intra-stack diffusion provided an estimation of the nanofiller aspect ratio in excellent agreement with that obtained by XRD. Further, applying the Fricke equation with the morphological features determined by the permeable stack model, an excellent agreement to the experimental data was obtained. The results indicate the relevance of intra-stack diffusion in intercalated nanocomposite, and the need to account for it when modeling mass transfer in nanocomposites.

Dust found in polar ice core samples present extremely low concentrations, in addition the availability of such samples is usually strictly limited. For these reasons the chemical and physical analysis of polar ice cores is an analytical challenge. In this work a new method based on low background instrumental neutron activation analysis (LB-INAA) for the multi-elemental characterization of the insoluble fraction of dust from polar ice cores is presented. Thanks to an accurate selection of the most proper materials and procedures it was possible to reach unprecedented analytical performances, suitable for ice core analyses. The method was applied to Antarctic ice core samples. Five samples of atmospheric dust (μg size) from ice sections of the Antarctic Talos Dome ice core were prepared and analyzed. A set of 37 elements was quantified, spanning from all the major elements (Na, Mg, Al, Si, K, Ca, Ti, Mn and Fe) to trace ones, including 10 (La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu) of the 14 natural occurring lanthanides. The detection limits are in the range of 10 −13 –10 −6 g, improving previous results of 1–3 orders of magnitude depending on the element; uncertainties lies between 4% and 60%.

This work is aimed to the study of the thermal and UV stability of Poly Vinyl Chloride (PVC) plasticized by cardanol derivatives. To this purpose, soft PVC obtained by cardanol derivatives, as well as by commercial plasticizers, were subjected to different sources of degradation, i.e. thermal treatments and UV weathering, and characterized by means of the tensile tests. Analysis of variance (ANOVA) was used to highlight the statistical significance of the type of plasticizer and treatment of soft PVC on the mechanic properties. In particular, estimation of the retention index of different plasticizers to different sources of degradation allowed highlighting the better performances of PLACARD compared to the other commercial plasticizers. In absence on any relevant loss of plasticizer during thermal treatment or UV weathering, the change in mechanical properties was attributed to change in the chemical structure of PVC homopolymer, which was studied by FTIR analysis. It was shown that the better retention of property of soft PVC plasticized by PLACARD is due to a lower amount of thermal or UV activated degradation. Therefore, the results highlight that PLACARD plasticizer can also act as an efficient thermal and UV stabilizer, which could increase soft PVC durability and recyclability, and contribute to a reduction of the amount of thermal and UV stabilizers, with additional relevant effects on the toxicological and environmental impact of soft PVC.

The structural behaviour of bolted joints of composite laminates for aerospace applications was modelled comparing the shape, amplitude and phase of stress–strain cycles. This study proposes a model for the bolted joints resulting in a typical load–displacement curve, under cyclic loading, significantly affected by hysteretic effects. From the data gathered through the experimental activities, a constitutive relationship between strain and stress was proposed, starting from simple physical models. The assumption of a rigid shift between the laminates was used to correlate load and displacement curves in the different phases of the load cycle. The hysteretic behaviour was attributed to friction phenomena and interpreted using damping coefficients characterizing the global dynamic response of the structural joint.

In this work the architectural anisotropy of short fiber reinforced polymers (SFRPs) has been characterized using X-ray computed micro-tomography (micro-CT) with four different morphometric methods: Mean Intercept Length (MIL), Volume Orientation (VO), Star Length Distribution (SLD) and Star Volume Distribution (SVD). The fabric tensor obtained from micro-CT analysis provided information on the fiber orientation, indicating that fibers were partially aligned in the injection direction. The fiber length and orientation obtained from optical microscopy and from the morphometric analysis in 3D, respectively, has been used to determine the mechanical properties of the composite sample, using a model based on micro and macromechanics. This approach leads to the prediction of the elastic constants of the component for any possible composite morphology resulting from injection, representing a key need for the design of SFRP components.

The need for reconstructing complex bone defects in the maxillofacial region as a result of trauma, tumor surgery or congenital malformation has become a hot topic in the field of tissue engineering. Tools such as 3D computer aided design (CAD) systems and rapid prototyping (RP) machines can be exploited to fabricate custom made bone scaffolds. RP techniques allow the construction of complex physical models based on 3D clinical images elaborated by suitable software and CAD systems. Hydroxyapatite (HA) is one of the most commonly used materials for bone reconstruction because of its close similarity in composition to human bone and teeth. Thus, producing a custom-made scaffold from a ceramic material directly by RP represents an exciting challenge. The aim of this paper is the development of a suspension of HA powder dispersed in an UV curable epoxy based resin, suitable for stereolithography (SLA). The influence of different HA concentrations within the ceramic suspension on the kinetics of the photochemical reaction was firstly investigated. The rheological behavior of the same ceramic suspensions was also analyzed by verifying the effect of HA on the viscosity and the stability of the suspensions as a function of the shear rate and the time from preparation. After the selection of a suitable suspension, simple green ceramic bars built by stereolithography and sintered with an appropriate thermal cycle, were built and characterized, showing good mechanical properties. A complex prototype, starting from a CAD model, was finally built by a SLA apparatus. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The strong influence of graphite oxide (GO) nanofiller on the glass transition temperature ( T g ) of epoxy resins, generally attributed to restricted molecular mobility of the epoxy matrix by the nanofiller or to the crosslinking of GO layers via the epoxy chains, is investigated. The study confirms that large increases of the glass transition temperature of the nanocomposite can be observed in presence of GO. However, similar T g increases are observed, when the filler is a high-surface-area graphite (HSAG), lacking oxidized groups. Moreover, these T g differences tend to disappear as a consequence of aging or thermal annealing. These results suggest that the observed T g increases are mainly due to a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine), rather than to reaction of the epoxide groups with functional groups of GO. This hypothesis is supported by investigating the catalytic activity of graphite-based materials on reactions between analogous monofunctional epoxide and amine compounds.

This work is aimed to study the use of pultruded profiles for the selective reinforcement of linear low density polyethylene (LLDPE) parts produced by rotational molding. A preliminary screening on different types of pultruded profiles was performed, highlighting the relevance of adhesion to LLDPE in order to prevent debonding of the reinforcing pultruded profiles. As expected, high density polyethylene (HDPE) matrix pultruded tapes are characterized by a very high adhesion to rotomolded LLDPE. Therefore, HDPE matrix pultruded tapes, fastened on the inner surface of the mold, are incorporated into LLDPE during rotomolding. Plate bending tests performed on reinforced rotomolded plates and pressurization tests performed on the box shaped prototypes showed a significant increase of the stiffness with a negligible amount of reinforcement and increase of the weight of the component.

The aim of this work is to study the effect of an organically modified clay on the structural relaxation behavior of an amorphous thermoplastic matrix. Differential scanning calorimetry (DSC) and pressure–volume–temperature (PVT) analysis were used in order to calculate the relaxation enthalpy and specific volume of the neat matrix and the nanocomposite during ageing below the glass transition region. Stress relaxation experiments were used to measure the characteristic relaxation time of the materials at different temperatures below glass transition. DSC and PVT analysis both revealed that relaxation phenomena are more relevant for the nanocomposite compared to the neat matrix. This result was confirmed by stress relaxation measurements, which indicates that below the glass transition the relaxation times of the nanocomposite are lower than those of the neat matrix. The enhanced relaxation behavior of the nanocomposite compared to the neat matrix was attributed to the presence of the organic modifier, which, acting as a plasticizer for the matrix, enhances its molecular mobility. The presence of low glass transition portions in the matrix was also evidenced by DSC and dynamic mechanical analysis.

The dynamics of spontaneous and sensory-evoked up-states have been recently compared, in multi-site recordings in vivo and found to have similarities and differences. Also in vitro , this is evident because we here describe a novel computational method to classify into statistically different states the spontaneous reverberating activity recorded from long-term (12–18 days- in vitro) cultured cortical neurons (from 60-site m ulti- e lectrode a rrays, MEA). State classification was performed by s pike n umber t ime h istograms (SNTH, or other burst features) of excitatory and inhibitory neuron clusters and revealed that in novel identified states the number of engaged neurons or up-state duration can change. To improve the characterization of each state we also computed the f iring s pike h istograms (FSH) which revealed a new facet of the firing probability of clusters. In exemplary functional experiments we show that: (i) up to 6–7 states can be safely categorized during several hours of recordings without observing spike rate changes, (ii) they disappear after a short pharmacological stimulation being replaced with novel states active and living up to 6–8 h, (iii) antagonists in the nM range can split the activity of a homogeneous network into the chronological coexistence of 2 states, one completely different and one not significantly different from control state. In conclusion, we believe that this novel procedure better characterizes the number of functional states of a network and opens up the possibility of predicting the elementary “vocabulary” used by small networks of neurons.