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Electromechanical sensing devices, based on resins doped with carbon nanotubes, were developed by digital light processing (DLP) 3D printing technology in order to increase design freedom and identify new future and innovative applications. The analysis of electromechanical properties was carried out on specific sensors manufactured by DLP 3D printing technology with complex geometries: a spring, a three-column device and a footstep-sensing platform based on the three-column device. All of them show a great sensitivity of the measured electrical resistance to the applied load and high cyclic reproducibility, demonstrating their versatility and applicability to be implemented in numerous items in our daily lives or in industrial devices. Different types of carbon nanotubes—single-walled, double-walled and multi-walled CNTs (SWCNTs, DWCNTs, MWCNTs)—were used to evaluate the effect of their morphology on electrical and electromechanical performance. SWCNT- and DWCNT-doped nanocomposites presented a higher Tg compared with MWCNT-doped nanocomposites due to a lower UV light shielding effect. This phenomenon also justifies the decrease of nanocomposite Tg with the increase of CNT content in every case. The electromechanical analysis reveals that SWCNT- and DWCNT-doped nanocomposites show a higher electromechanical performance than nanocomposites doped with MWCNTs, with a slight increment of strain sensitivity in tensile conditions, but also a significant strain sensitivity gain at bending conditions.

The incorporation of graphene nanoplatelets (GNPs) as a coating on glass fibre fabrics for strain monitoring applications was analysed. Non-functionalized and functionalized GNPs were used in order to study the effect of the functionalization in the morphology of the coating and the electrical behaviour of the material. In contrast with non-functionalized GNPs, when NH 2 -functionalized GNPs were used, the nanoparticles adapted to the surface of the fibres causing a major effectiveness of the electrical network created along the fibres, achieving an electrical conductivity in the order of 10 −2 S/m. The sensitivity values, obtained under tensile loads, reached values in the order of 840 up to 16400.

A historical research is presented about the foundation and evolution of the Cuban subsidiary of clinical pathology in Cienfuegos, contextualized in antecedents, development and present situation of the clinical laboratories in the province. The most complex and important tasks which were developed by the members of the scientific society from its foundation to the current period are stated, so as future challenges.

La presente investigación tiene por objetivo demostrar, que la investigación policial en el delito de lavado de activos puede vulnerar los derechos fundamentales de los investigados si no se lleva a cabo con la observancia de los estándares internacionales mínimos del proceso penal garantista. Esto supone la comparación entre la labor policial realizada en el marco del proceso penal de naturaleza inquisitiva, donde la Policía Nacional del Perú dirigía la investigación y el Fiscal hacía suyo el atestado policial, y la investigación policial llevada a cabo dentro del proceso penal de corte acusatorio, propio del Nuevo Código Procesal Penal, donde la Policía Nacional del Perú es una entidad auxiliar del Ministerio Público, quien es el que dirige la investigación.

The mechanical and crack sensing capabilities of CFRP-metal Mode-II coupons and skin-stringer T-joints under bending conditions with carbon nanotube (CNT) doped adhesive films are explored. Different surface treatments of the aluminium substrate are tested (grit blasting and sandpaper brushing). Mode-II energy fracture slightly increases with CNT addition due to the nanoparticle toughening effect when the surface treatment is adequate. However, in the case of brushed specimens, the enhanced lubricant properties of CNTs leads to the promotion of weak interfaces between adhesive and metal substrate. The electrical resistance increases with the load nose displacement with a good correspondence to the crack length. A crack opening effect is herein noticed in the last stages of the Mode-II tests due to the difference between the stiffness of metal and CFRP adherents, which is reflected in a sudden increase of the electrical resistance. These results have been also validated by theoretical analysis. Electromechanical response of T-joints shows a similar behaviour with an increasing sensitivity when placing a CFRP stringer, due to a more prevalent crack opening observed in this type of specimens. Therefore, crack sensing capabilities are demonstrated at both coupon and sub-element level.

The strain-sensing, self-curing and self-heating capabilities of a 3D printed circuit made of a graphene nanoplatelet and carbon nanotube reinforced resin, have been widely explored. These materials exhibit high Joule’s heating effect capabilities that can be used for post-curing processes. More specifically, the values of glass transition temperature reached by Joule’s heating post-curing were very similar to those obtained by conventional oven heating. The temperature profile along each individual ribbon was relatively homogeneous, being an indicative of a good nanoparticle dispersion, confirmed by field emission gun scanning electron microscope analysis. Furthermore, the proposed printed circuits showed excellent strain-sensing capabilities with a much higher strain sensitivity, with a gauge factor of 6–8, in comparison to conventional metallic gauges or bulk nanocomposites, with a gauge factor of around 2, showing also good linearity. In addition, the breakage of individual ribbons can be easily detected by the strain-sensing system as a sharp increase of the electrical resistance. Finally, temperature compensation tests showed that, in case of printed ribbon breakage, it is possible to keep constant the average temperature of the circuit by raising the applied voltage to avoid ice accretion. Thus, with none to two broken ribbons, the 3D printed circuit can act as an efficient anti-icing and de-icing system.

A performance mapping of GNP/epoxy composites was developed according to their electromechanical and electrothermal properties for applications as strain sensors and Joule heaters. To achieve this purpose, a deep theoretical and experimental study of the thermal and electrical conductivity of nanocomposites has been carried out, determining the influence of both nanofiller content and sonication time. Concerning dispersion procedure, at lower contents, higher sonication times induce a decrease of thermal and electrical conductivity due to a more prevalent GNP breakage effect. However, at higher GNP contents, sonication time implies an enhancement of both electrical and thermal properties due to a prevalence of exfoliating mechanisms. Strain monitoring tests indicate that electrical sensitivity increases in an opposite way than electrical conductivity, due to a higher prevalence of tunneling mechanisms, with the 5 wt.% specimens being those with the best results. Moreover, Joule heating tests showed the dominant role of electrical mechanisms on the effectiveness of resistive heating, with the 8 wt.% GNP samples being those with the best capabilities. By taking the different functionalities into account, it can be concluded that 5 wt.% samples with 1 h sonication time are the most balanced for electrothermal applications, as shown in a radar chart.

This paper studies the development and characterization of 3D printed conductive circuits based on epoxy inks doped with carbon nanotubes (CNTs) and/or graphene nanoplatelets (GNPs), which could be used in applications such as electronic circuits, heated seats, Anti-icing and De-Icing Systems (ADIS) or Structural Health Monitoring (SHM) systems, among others. A design of experiments (DOE) has been carried out by the Taguchi method to develop and optimize an ADIS based on a 3D printed circuit, using a conductive ink doped with CNTs/GNPs to achieve Joules heating. The target of the DOE is based on reaching the highest average temperature, which was measured by infrared thermographic analysis, taking also into account the quality of the 3D printed circuits. The DOE factors were the CNT and GNP content, the voltage applied to the circuit and its geometry, proposing two alternative designs. Finally, a de-icing test was carried out with the optimal parameters obtained from the DOE. Results evince the viability of the system developed, being able to melt an ice layer of 2.5 mm thick in 3 min and 30 s.

Many studies were performed to improve CNT dispersion into epoxy using different mechanical dispersion methods as well as CNT functionalization. In this study, a novel method is introduced to enhance CNT dispersion using 2D nanoclay as a secondary filler. Hence, this study was aimed to investigate the effect of nanoclay platelets on electrical, mechanical, and piezoresistive characteristics of the SWCNTs doped epoxy nanocomposites. Two different types of nanocomposites were prepared for comparison including binary (SWCNT/epoxy) and hybrid (SWCNT-nanoclay/epoxy) states. CNT content of 0.1 wt% was used for the binary and hybrid states while two different nanoclay loadings (0.5 wt% and 1.0 wt%) were employed in the hybrid nanocomposites. Tensile and mode I fracture tests were performed for the mechanical and electromechanical characterization using two probe techniques while electron microscopy and X-ray diffraction were used for microstructural analysis. Results showed severe CNT agglomeration in the binary state whilst a homogenous CNT dispersion was achieved in the ternary states. The binary nanocomposite showed weak performance in terms of electrical, mechanical and piezoresistive properties caused by severe CNT aggregates. On the other hand, addition of nanoclay into CNTs doped epoxy manifested a significant increase in the electrical, mechanical and piezoresistive-sensitivity performance of the hybrid nanocomposites compared to the binary one. The best performance was achieved at 0.5 wt% nanoclay loading where electrical conductivity increased by six orders of magnitude, UTS increased by 37%, KIC and GIC increased by 34% and 64%, respectively, with respect to the binary nanocomposite. Crack-pinning and crack deflection were accounted for the fracture toughness increase in ternary composites. Nonlinear piezoresistivity resulting from the predominate effect of tunneling resistance ruled piezoresistivity in the hybrid nanocomposites. A sensitivity of 2.1 and 2.0 at strain of 0.01 were obtained for 0.5 wt% and 1.0 wt% nanoclay contents, respectively, whereas no sensitivity was achieved for the binary composite.

The present study investigates, through experimental and numerical approaches, the incorporation effect of different weight concentrations of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of epoxy. Tensile and mode I fracture tests were performed to investigate the effect of the addition of MWCNTs on Young’s modulus, Ultimate Tensile Strength (UTS), critical stress intensity factor (KIC) and critical strain energy release rate (GIC). Different carbon nanotubes (CNTs) contents were employed to compare the effect of the resulting microstructures (well-dispersed and agglomerated CNTs) on the mechanical properties. Field Emission Scanning Electron Microscopy (FESEM) and Scanning Electron Microscopy (SEM) were used for microstructural analysis and fractography. Experimental results showed that UTS was improved (28%) by incorporation of MWCNTs while the KIC and GIC were substantially increased by 192% and 614%, respectively. CNT pullout and crack bridging were the main contributing mechanisms in toughening the epoxy at low CNT contents (0.1 and 0.25 wt%). In contrast, a combination of crack bridging and crack branching was responsible for the resin toughening in the case of 0.5 wt% loading. The significant increase for KIC and GIC demonstrated the excellent performance of the dispersion approach used in this study. Finite Element modelling was used to provide a more robust analysis of the effect of CNT incorporation in tension tests and of the toughening mechanism of the nanocomposites in mode-I fracture tests.

Carbon fibers reclamation from waste composites by pyrolysis is developing fast. Pyrolysis allows the reclamation of the fibers by thermal decomposition of the polymeric resin, but the material value of these resins is not yet recovered. In this research work, the possibility of obtaining high-value gaseous fractions by treating the vapors generated in the decomposition of a poly(benzoxazine) containing carbon fiber waste composite has been studied. The experiments have been carried out in a lab-scale facility consisting of two reactors in series. In the first reactor, the pyrolysis of the waste is carried out at 500 °C, while in the second reactor the vapors coming from the first reactor are treated at 900 °C. Such treatment enables to triple the amount of gas in comparison to conventional pyrolysis. Besides, this gas contains 56% by volume of H2, which means the recovery of approximately 60% of the hydrogen contained in the resin. On the other hand, clean carbon fibers with mechanical properties within commercial values have been also obtained.

The influence of dispersion procedure and nanofiller geometry on thermal and electrical properties of graphene nanoplatelet (GNP) based composites has been investigated. A theoretical model, based on the contacts between adjacent nanoparticles, has been proposed aiming to connect thermal and electrical properties. It has been observed that GNP overlapping (type I) induces a decrease on thermal conductivity. Its effect on electrical conductivity is more complex and depends on the areas of overlap and in-plane contacts (type II). A higher type I area in comparison to type II implies an increase of electrical conductivity with overlapping whereas the opposite effect is found when type II area is higher than type I. The predicted results of the theoretical model fitted experimental measurements at different GNP contents and three roll milling processing conditions, giving a better overview of the influence of GNP geometry and interactions on electrical and thermal properties of nanocomposites.

Carbon nanotubes (CNT) were added to epoxy/polycaprolactone (PCL) blends in order to get electrically conductive blends. As it was expected, an increase of CNT content promotes a higher electrical conductivity due to the creation of more electrical pathways. Furthermore, it was observed that the enhancement is also observed with increasing PCL content, reaching values of around 0.2 S/m for 0.2 wt % CNT and 20 wt % PCL samples, due to its effect on rheological properties of the mixture, which affect positively to the CNT dispersion process, thus leading to more homogeneous and well dispersed nanocomposites, as observed by microstructural analysis. Thermal conductivity also increases with CNT content but decreases with PCL addition due to its insulating properties. A study of the voltage required to reach the above-mentioned self-healing temperature for each material has been performed by thermography monitoring. It has been observed that the samples with the highest amount of both CNT and PCL, have the best resistive heating capabilities due to a higher thermoresistive efficiency of the electrical network, reaching temperatures above 100 °C, at voltages below 150 V.

The electrical behaviour and mechanical properties of functionalized graphene nanoplatelets (GNPs) reinforced epoxy-based composites were evaluated. These properties were analysed scaling up from the nanocomposite to the multiscale composite material. The electrical conductivity of 12 wt % GNPs reinforced nanocomposites was in the order of 10 −4 S/m, in contrast to the in-plane conductivity of multiscale composite materials with the same GNPs content, which was found to be ∼10 −3 S/m. This was attributed to microstructural features that also provoke the electrical conductivity through the thickness diminish down to ∼10 −4 S/m in multiscale composites. Additionally, mechanical properties were enhanced by the dispersion of GNP in nanocomposites but experienced a reduction in glass fibre composites because of the formation of a weak interface between the GNPs filled matrix and fibres.

The addition of graphene nanoplatelets (GNPs) into the epoxy adhesives has been studied in order to increase their thermal conductivity. Thermally conductive adhesives are often used as thermal interface materials (TIMs). The incorporation of 8 and 10 wt% GNPs reinforcement caused a thermal conductivity enhancement of ~206 and ~306%, respectively. The wettability seems to decrease with low GNPs content (2–3 wt%) in comparison with the neat epoxy adhesive but the contact angle remains constant for higher GNPs contents. Lap shear strength remains constant for neat adhesives and resins doped with GNPs. The lack of enhancement of adhesive properties of doped resins is due to a weak interface reinforcement-matrix. In fact, the joint failure is in the adhesive except for high GNPs content (10 wt%) where a cohesive failure mode is observed.

Fabrication of multiscale composites by the addition of CNT in epoxy matrices as previous step to the impregnation process leads to several manufacturing difficulties associated to filtration effects and viscosity increments. These effects have been analyzed finding a relation between the type of CNT and the dispersion degree with the change in the rheological behavior and the heterogeneity of the mechanical properties. This heterogeneity is associated to filtration effects of the nanoreinforcement. Modification of the carbon fibers by a nanoreinforced sizing has been presented as an alternative, obtaining homogeneous composites and avoiding the filtration effects. These multiscale composites have higher electrical and interlaminar mechanical properties.

The study carried out analyses the strain sensor capability of nanocomposites reinforced with different graphene nanoplatelets (GNPs) contents. Nanocomposites with GNPs content around the percolation threshold have shown high gauge factor values, around 65 at high strain. The dominant mechanism of the sensors, based on changes induced in the tunnel and contact resistance, was evaluated. Monitored GNP/epoxy based sensors have shown to be capable of discriminating between tensile and flexural strain modes as the configuration of the GNPs during the tests behaves differently. Flexural strains makes possible the creation of new electrically conductive paths meaning an apparent lower sensitivity while strain produced in a tensile test provokes the breakage of the tunnel or contact based conductive paths.

The reversibility and failure detection and localization capabilities of sensors based on graphene nanoplatelets (GNPs) were tested. Results have shown that the strain sensing capability is reversible presenting no hysteresis and has been demonstrated to endure up to 50 cycles. It was elucidated that if a stationary load is applied, normalized electrical resistance increases and remains mainly constant while load is maintained. Once this load has been completely removed, the structure recovers the initial electrical resistance what reinforced the reversibility of the sensor. Additionally, developed GNP/epoxy sensors were demonstrated to detect and locate damage in the sample due to a breakage of the electrical network when failure occurs that could be differentiated from changes due to strain as they caused an abrupt increase.

Context Hamelia patens Jacq. (Rubiaceae) is traditionally used to treat wounds, inflammation and diabetes. However, there is still a lack of scientific evidence to support these applications. Objective The objective of this study is to evaluate the anti-inflammatory, antioxidant and antidiabetic activities of Hamelia patens, and identify its bioactive compounds. Materials and methods Four extracts were obtained by maceration and liquid-liquid extraction: HEX, DCM-EtOAc, MeOH-EtOAc and MeOH-Aq. The anti-inflammatory effect was evaluated orally on rat paw carrageenan-induced oedema over 6 h (50, 200 and 500 mg/kg), and topically in mouse ear oedema induced by 12-tetradecanoylphorbol-13-acetate (TPA) after 4 h (0.5 and 1 mg/ear). We also evaluated myeloperoxidase levels in ear tissue, 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability, and in vitro α-glucosidase inhibition. The chemical compounds were separated by column chromatography and identified by spectroscopic analysis. Results We found that the oral administration of the HEX extract at 500 and 200 mg/kg significantly decreased the carrageenan-induced inflammation after 1 and 3 h, respectively. The MeOH-EtOAc extract significantly inhibited myeloperoxidase activity (83.5%), followed by the DCM-EtOAc extract (76%), β-sitosterol/stigmasterol (72.7%) and the HEX extract (55%), which significantly decreased oedema induced by TPA at both doses, giving a similar effect to indomethacin. We also found that the MeOH-EtOAc, MeOH-Aq and DCM-EtOAc extracts showed good DPPH scavenging activity (IC50 values of 18.6, 93.9 and 158.2 μg/mL, respectively). The HEX extract showed the lowest α-glucosidase inhibition (an IC50 value of 26.07 μg/mL), followed by the MeOH-EtOAc extract (an IC50 value of 30.18 μg/mL), β-sitosterol/stigmasterol (IC50 34.6 μg/mL) and compound A ((6E,10E,14E,18E)-2,6,10,14,18,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene, an IC50 value of 114.6 μg/mL), which were isolated for the first time from Hamelia patens. Discussion and conclusion Hamelia patens possesses anti-inflammatory, antioxidant and α-glucosidase inhibitory activities, which support its traditional use. These effects can be attributed to the identified compounds.

To date, most analytical models used to calculate electrical conductivity in carbon nanotube (CNT) reinforced nanocomposites are not able to predict electrical properties for contents much higher than the percolation threshold. This is because these models do not take into account many critical factors, such as nanotube waviness, dispersion state and process parameters. In the present paper, a novel analytical model based on an equivalent percolation threshold concept, valid for all CNT contents, is developed for this approach. To achieve this, the influence of all these factors has been investigated and several experimental tests have been conducted in order to validate the model. The electrical conductivity varies by several orders of magnitude depending on the value of these parameters, increasing with carbon nanotube content and aspect ratio and decreasing with its waviness. From experimental data, it is found that the waviness increases with carbon nanotube content. Besides, functionalization also causes a local distortion of CNTs, producing more entanglement. When comparing two different dispersion procedures, calendering and toroidal milling, it is noticed that the first method has a greater stretching effect because the shear forces induced are much higher, causing the breakage of carbon nanotubes.

A new manufacturing process based on applying weak magnetic field during the curing treatment is reported in order to induce a selective mobility and alignment of the carbon nanotubes on epoxy resins. Depending on experimental conditions, this procedure allows manufacturing different materials: (a) anisotropic composites with aligned carbon nanotubes and (b) composites with selected nanoreinforced areas and neat epoxy areas. Different composites have been manufactured, such as dielectric materials with insulating inside and electrically doped surfaces, or doped composites with insulating ring. The procedure basically consists on the anchorage of magnetite nanoparticles in the surface of carbon nanotubes and the application of magnetic field during the curing treatment. The mobility of nanofillers can be directly observed through the appearance of black and transparent areas on the composites, while the alignment of carbon nanotubes is analyzed by scanning electron microscopy of high resolution. The anisotropy and different behavior of selected areas for the manufactured composites have been determined by electrical measurements.

RESUMENObjetivoComparar la precisión marginal de cofi as de zirconia elaboradas empleando dos sistemas CAD/CAM Cerec InLab (Sirona®) y Zirkonzahn (Zirkonzahn®) y un sistema pantográfi co Zirkograph 025 ECO (Zirkonzahn®). Material y métodos: Se elaboró un muñón maestro de Cr-Co con preparación para corona de zirconia de un premolar superior. Se fabricaron 10 cofi as de zirconia por grupo siguiendo los parámetros de cada sistema. El grupo control consistió en 10 cofias metálicas. Se ejecutó una técnica de réplica, utilizando polivinilsiloxano elite HD+ (Zhermack®). Mediante observación estereomicroscópica con aumento de 50x, se determinó en micras la discrepancia marginal absoluta y el espesor marginal de un punto por cara de cada cofi a. El análisis estadístico se ejecutó con el software IBM SPSS®. Para comparar los datos obtenidos se realizó el test t. Resultados: La discrepancia marginal absoluta media y el espesor marginal fue 92.14 ± 38.59 y 78.62 ± 31.33 μm para el sistema CAD/CAM Cerec InLab (Sirona®), 38.71 ± 12.62 y 36.91 ± 13.56 μm para el sistema CAD/CAM Zirkonzahn (Zirkonzahn®), 77.92 ± 38.01 y 69.42 ± 33.23 μm para el sistema pantográfico Zirkograph 025 ECO (Zirkonzahn®) y 44.11 ± 15.36 y 43.74 ± 15.70 μm para el grupo control. Existieron diferencias estadísticamente significativas entre los sistemas Cerec InLab (Sirona®) y Zirkograph 025 ECO (Zirkonzahn®) en comparación con el grupo control para la discrepancia marginal absoluta y el espesor marginal. No existieron diferencias estadísticamente significativas entre los sistemas CAD/CAM Zirkonzahn (Zirkonzahn®) y el grupo control. El nivel de significancia fue p > 0.001.ConclusionesEl sistema más preciso fue CAD/CAM Zirkonzahn (Zirkonzahn®). El sistema que mostró menor precisión marginal fue Cerec InLab (Sirona®).ABSTRACTObjectiveTo compare marginal fit of zirconia copings manufactured following two different systems: CAD/CAM Cerec InLab (Sirona®) and Zirkonzahn (Zirkonzahn®) as well as a Zirkograph 025 ECO (Zirkonzahn®) pantograph system. Material and methods: A master Cr-Co model stump was manufactured; it was prepared for the zirconia crown of an upper premolar. Ten zirconia copings were manufactured for each group following manufactureŕs instructions. Control group consisted on ten metallic copings. A replication technique was followed using elite HD+ polyvinyl siloxane (Zhermack®). Measurements were taken using a stereomicroscope at 50x magnification so as to obtain marginal width in microns and thus determine absolute marginal discrepancy of each coping. Statistical analysis was conducted using IBM SPSS® software. T-test study was conducted in order to compare obtained data. Results: Mean marginal absolute discrepancy and marginal width were as follows: 92.14 ± 38.59 and 78.62 ± 31.33 μm for Cerec InLab (Sirona®) CAD/CAM system, 38.71 ± 12.62 and 36.91 ± 13.56 μm for Zirkonzahn (Zirkonzahn®) CAD/CAM system, 77.92 ± 38.01 and 69.42 ± 33.23 μm for Zirkograph 025 ECO (Zirkonzahn®) pantograph system. Control group made of metal copings exhibited 44.11 ± 15.36 and 43.74 ± 15.70 μm. With respect to absolute marginal discrepancy and marginal width, significant differences were observed when comparing Cerec InLab (Sirona®) and Zirkograph 025 ECO (Zirkonzahn®) with control group. Nevertheless, no significant differences were observed between Zirkonzahn (Zirkonzahn®) CAD/CAM system and the control group. Overall level of statistical significance was p > 0.001.ConclusionsZirkonzahn® CAD/CAM system was the most accurate system of all. CAD/CAM Cerec InLab system (Sirona®) proved to be the less precise system.

Standard Mode-I and skin-stringer sub-elements were manufactured using novel adhesive films reinforced with carbon nanotubes. Peeling tests were conducted to analyse the different crack propagation mechanisms. In this context, the influence of manufacturing methods and artificial defects is deeply explored. It was observed that the electrical resistance increased with crack length due to a breakage of electrical pathways, depending on manufacturing and induced defects. Co-bonded specimens showed a more stable behaviour due to a better interface between the adhesive and substrate than joints manufactured by secondary bonding. Moreover, by analysing the influence of artificial defects, it was observed that larger discontinuities induced more unstable electromechanical behaviours as there is a more prevalent breakage of electrical pathways. In this regard, samples with Teflon inserts showed sharper increases of electrical resistance than those previously treated with a liquid agent simulating a kissing bond. Therefore, the proposed technique shows a high potential and applicability for Structural Health Monitoring (SHM) of integrated composite structures.

The electromechanical performance and reversibility of sensitive GNP/epoxy strain sensors were experimentally and theoretically analyzed. Under tensile loads, the strain sensors showed lower sensitivity and more linearity than bulk sensors, behavior attributed to a slight preferential orientation of the GNPs along the in-plane direction. The Gauge Factor (GF) obtained was 9.1 ± 0.9 and 11 ± 1 for strain values up to 0.005 mm mm−1 and above 0.015 mm mm−1, respectively. In contrast, the electromechanical response when subjected to compressive strain is more complex and three different regions are distinguished: (I) diminution, (II) stabilization and (III) increase of the normalized electrical resistance. Here, GF under compressive loads was negative at low strain values (region I), being −13 ± 2, and positive at high strain (region III), with a value of 8 ± 1. Theoretical analysis revealed that at low strain, there is prevalence of in-plane tunneling mechanisms whereas at higher strain, the out of plane mechanisms dominate, explaining the apparently anomalous behavior at compressive loads. Additionally, strain sensors showed high reversibility with cyclic load in the electromechanical response, but under compressive forces, the loading-unloading electrical resistance curve was asymmetric due to the opening and closing of microcavities and defects in the vicinities of the GNPs.

Polycaprolactone (PCL) is being researched as a self-healing agent blended with epoxy resins by several reasons: low melting point, differential expansive bleeding (DBE) of PCL, and reaction induced phase separation (RIPS) of PCL/epoxy blends. In this work, PCL/epoxy blends were prepared with different PCL ratios and two different epoxy networks, cured with aliphatic and aromatic amine hardeners. The curing kinetic affects to the blend morphology, varying its critical composition. The self-healing behavior is strongly affected by the blend morphology, reaching the maximum efficiency for co-continuous phases. Blends with dispersed PCL phase into epoxy matrix can also show high self-healing efficiency because of the low PCL domains that act as reservoir of self-healing agent. In this last case, it was confirmed that the most efficient self-healable blends are one whose area occupied by PCL phase is the largest. These blends remain the good thermal and mechanical behavior of epoxy matrix, in contrast to the worsened properties of blends with bicontinuous morphology. In this work, the self-healing mechanism of blends is studied in depth by scanning electron microscopy. Furthermore, the influence of the geometry of the initial surface damage is also evaluated, affecting to the measurement of self-healing efficiency.

Mechanical and strain sensing behavior of polycaprolactone (PCL) epoxy blends reinforced with carbon nanotubes (CNTs) has been studied. It was observed that glass transition temperature generally decreases with PCL content while the effect of CNT is more complex, leading to an initial increase and then a sudden decrease when comparing to neat PCL/epoxy samples. It is explained by the increasing miscibility of PCL in the epoxy system, being more significant in presence of properly dispersed nanofillers, promoting a decrease of cross-linking degree. Concerning the mechanical behavior, CNT addition does not have an effective reinforcing effect, as expected, because of the increasing miscibility of PCL. In addition, PCL nanocomposites have a linear electrical response to applied strain, showing a high potential as sensors. Moreover, electrical sensitivity decreases with PCL content due to a higher deformation of PCL in comparison to epoxy matrix, corroborated by in situ microstructural characterization during mechanical tests, leading to a reduction in the tunneling distance between adjacent CNTs.

In the present study, a numerical model was built using LS-DYNA® to investigate the static and dynamic fracture behaviours of neat epoxy. Fracture and Izod tests were conducted experimentally for validation. The applicability of different numerical methods, i.e., finite element method and meshfree methods (element-free Galerkin, and smoothed particle Galerkin), was investigated considering different loading conditions (static and dynamic). When compared with the experimental data, the meshfree methods were found to replicate the dynamic fracture behaviour more precisely, while all the methods provided comparable results under static loading conditions. Besides, to foster the development of more accurate numerical methods focussed on the fracture mechanism in epoxy resin, the effects of pre-crack length and strain rate on modelling were investigated by exploiting the results from the fracture tests and Izod tests, respectively. The results showed that the pre-crack length had a strong influence on the fracture toughness obtained, while incorporating the strain rate effect in a material model noticeably influenced the damage caused by the impactor and the final value of energy absorbed.

In this study, the hydrothermal resistance of an epoxy resin (aircraft quality) reinforced with graphene is analyzed. Different geometries and aspect ratios (thickness and lateral dimensions) of graphene nanoplatelets were studied. The addition of these graphene nanoplatelets induces important advantages, such as an increase of the glass transition temperature and stiffness and an enhancement of barrier properties of the epoxy matrix, in spite of the excellent behavior of pristine resin. The effectiveness of graphene nanoplatelets increases with their specific surface area while their dispersion degree is suitable. Thinner nanoplatelets tend to wrinkle, decreasing their efficiency as nanofillers. Graphene used as reinforcement not only reduces the absorbed moisture content but also decreases its effect on the thermal and mechanical properties related to the matrix.

Single lap shear tests are carried out at the joints of similar and dissimilar materials, and their electrical resistance through thickness is monitored to evaluate their sensing capabilities. Al-Al and carbon fibre reinforced polymer (CFRP)-Al joints are manufactured with two types of surface treatments of the Al substrates: brushing (B) and grit blasting (GB). The lap shear strength (LSS) is higher with grit blasting due to the optimum surface roughness and the creation of an active surface. Carbon nanotube (CNT)-doped samples are detrimental to the LSS in Al-Al joints compared to the neat adhesive, while a slight increase in LSS for CFRP-Al and CFRP-CFRP is observed due to a better CNT-CFRP interaction and good load transfer between the substrates. Electrical monitoring tests are strongly influenced by the surface treatment with better adhesive-substrate interfaces leading to a more stable response and higher sensitivity, proving the high applicability of the proposed technique.

La empresa Vertical es una empresa de aviación general de transporte aéreo no regular, comprometida con el sector defensa, petroleros, logísticos y gubernamentales. Durante actividades de transporte de materiales para la construcción de torres eléctricas del proyecto hidroituango, un helicóptero MI-17 que pernoctó en cercanías del área urbana del municipio de Toledo, fue objeto de un acto terrorista que generó pérdida total de la aeronave. Identificadas las vulnerabilidades en las políticas de comunicación y coordinación internas, así como con las autoridades militares y de Policía, se establecieron las políticas de seguridad que permitirán reducir al mínimo los riesgos y amenazas en posteriores eventos. Tabla de contenido Introducción 4 Marco Teórico 5 Planeamiento del Caso 8 Discusión o Reflexión Final 12 Preguntas de Discusión 14 Lista de Referencias 15 Vertical company is a general aviation company of non-regular air transport, committed to the defense sector, oil, logistics and government. During activities to transport materials for the construction of electric towers of the hydroituango project, an MI-17 helicopter that spent the night near the urban area of ​​the municipality of Toledo was object of a terrorist act that caused the total loss of the aircraft. Once the vulnerabilities in internal communication and coordination policies were identified, as well as with the military and police authorities, security policies were established to minimize the risks and threats in subsequent events.

In recent years, the interest in monitoring the damage of composite materials by measuring the variation of electrical resistance is increasing because deformations and cracks generated in the structure produce changes in the electrical conductivity of the material. In this work, the structural integrity of glass fiber composite materials with epoxy matrix doped with graphene nanoparticles is evaluated under in plane tests (interlaminar shear tests and fracture propagation tests in mode I and II). The results demonstrated the ability of graphene nanoparticles to form conductive networks in the epoxy resin with auto-detection capability of deformation and damage. In the interlaminar shear tests, permanent changes in resistance were associated to strain and delamination produced during the test. In the case of fracture tests in mode I and II, the electrical resistance increased as the crack grew. The use of multiple electrodes has also allowed locating the area of damage generation in the material. Finally, the electrical response of discontinuities generated out of plane of the laminate was analyzed by means of cuts through the material.

The proposal that the respiratory complexes can associate with each other in larger structures named supercomplexes (SC) is generally accepted. In the last decades most of the data about this association came from studies in yeasts, mammals and plants, and information is scarce in other lineages. Here we studied the supramolecular association of the F1FO-ATP synthase (complex V) and the respiratory complexes I, III and IV of the colorless alga Polytomella sp. with an approach that involves solubilization using mild detergents, n-dodecyl-β-D-maltoside (DDM) or digitonin, followed by separation of native protein complexes by electrophoresis (BN-PAGE), after which we identified oligomeric forms of complex V (mainly V2 and V4) and different respiratory supercomplexes (I/IV6, I/III4, I/IV). In addition, purification/reconstitution of the supercomplexes by anion exchange chromatography was also performed. The data show that these complexes have the ability to strongly associate with each other and form DDM-stable macromolecular structures. The stable V4 ATPase oligomer was observed by electron-microscopy and the association of the respiratory complexes in the so-called "respirasome" was able to perform in-vitro oxygen consumption.

A novel nanoreinforced adhesive film has been developed to detect adhesive deformation and crack propagation along the bonding line by means of the electrical response of the material. Adhesive films were doped by spraying an aqueous dispersion of carbon nanotubes (CNTs) over the surface. To determine the sensitivity of bonded joints, single lap shear (SLS) and mode-I fracture energy tests have been carried out while their electrical response has been measured. It has been found that CNT-doped adhesive films are able to detect adhesive deformation and final failure for SLS specimens and crack initiation and propagation along the bonding line for mode-I specimens with a high sensitivity. Sudden increases on electrical resistance are correlated to a rapid growing of the crack length due to instability on crack propagation in a tick-slip case, whereas specimens with a more uniform crack propagation are linked to a steadier increase on electrical resistance, and both of them are properly correlated to the mechanical response. By analyzing more in detail the electrical response and comparing with theoretical approaches, the stick-slip behavior is associated with the presence of porosity and lack of adhesives because of possible manufacturing issues such as adhesive overflowing. These statements are also validated by microstructural analysis. Therefore, the potential and applicability of the proposed adhesive films for evaluating the structural integrity has been demonstrated.

A structural analysis demonstrating how the manufacturing method of graphene nanoplatelets (GNPs) into a polymer matrix can strongly modify the GNPs morphology and, consequently, their properties, was carried out. Three different methods based on sonication and high shear forces were used to elucidate defects induction and possible size diminution. Manufacturing methods including high shear forces caused the extension of the GNPs while sonication induces wrinkling of the sheets. Residual stresses are induced in the nanoplatelets structure showing an increase in the Raman intensities ratios ID/IG and ID′/IG when a major cycles number of calendering are applied.

In this work the wear behaviour of epoxy matrix composites with different types and percentages of multiwalled carbon nanotubes (MWCNTs) has been studied. Three different types (NC3100, NC3150 and NC3152) and percentages (0.1 and 0.5 wt%) of MWCNTs were dispersed into an epoxy resin by a calendering process. The tribological properties of epoxy-MWCNTs nanocomposites were investigated using “pin-on disc” wear testing machine under different conditions (counterpart material, distances and sliding speeds test). Scanning electron microscopy and 3D optical profilometer were used to observe the worn surfaces of the samples. Compared with neat epoxy, the composites with MWCNTs showed a lower mass loss, friction coefficient and wear rate, and these parameters decreased with the increase of MWCNT percentage. Also, the results demonstrated that the epoxy composites with 0.5 wt% of amino-MWCNT (NC3152) have the best tribological properties.