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Hybrid composite samples with different carbon and glass fiber layers arrangement were produced by resin transfer molding (RTM) in an attempt to disclose the effects of low temperature on their flexural and low velocity impact behavior. Flexural tests were carried out at T = −50°C and the failure modes were examined, while impact tests, always at T = −50°C, were performed at penetration and at indentation in the range from 10 J to 30 J. The damage extension was accurately evaluated by ultrasonic non-destructive testing. The results were then compared with the room temperature ones obtained in a previous paper to highlight the influence of the temperature. The compression after impact tests were carried out at room temperature for samples previously impacted at both room and low temperature to assess the damage tolerance of the different hybrid configurations. Stacking sequence was found to govern both the flexural and impact behavior of laminates. At low temperature, the flexural strength and modulus values improved over the corresponding room temperature values irrespective of the stacking sequence, while an easier damage propagation and less residual strength were detected in dynamic loading.

We here characterize the response to the extremely low-frequency (ELF) magnetic field (MF, 50 Hz, 1 mT) of SH-SY5Y human neuroblastoma cells, cultured in a three-dimensional (3D) Alvetex® scaffold compared to conventional two-dimensional (2D) monolayers. We proved that the growing phenotype of proliferating SH-SY5Y cells is not affected by the culturing conditions, as morphology, cell cycle distribution, proliferation/differentiation gene expression of 3D-cultures overlap what reported in 2D plates. In response to 72-h exposure to 50-Hz MF, we demonstrated that no proliferation change and apoptosis activation occur in both 2D and 3D cultures. Consistently, no modulation of Ki67, MYCN, CCDN1, and Nestin, of invasiveness and neo-angiogenesis-controlling genes (HIF-1α, VEGF, and PDGF) and of microRNA epigenetic signature (miR-21-5p, miR-222-3p and miR-133b) is driven by ELF exposure. Conversely, intracellular glutathione content and SOD1 expression are exclusively impaired in 3D-culture cells in response to the MF, whereas no change of such redox modulators is observed in SH-SY5Y cells if grown on 2D monolayers. Moreover, ELF-MF synergizes with the differentiating agents to stimulate neuroblastoma differentiation into a dopaminergic (DA) phenotype in the 3D-scaffold culture only, as growth arrest and induction of p21, TH, DAT, and GAP43 are reported in ELF-exposed SH-SY5Y cells exclusively if grown on 3D scaffolds. As overall, our findings prove that 3D culture is a more reliable experimental model for studying SH-SY5Y response to ELF-MF if compared to 2D conventional monolayer, and put the bases for promoting 3D systems in future studies addressing the interaction between electromagnetic fields and biological systems.

In this article, a holistic technique for sensing damage initiation, as well as damage progression in composite plates, is presented combining linear and nonlinear ultrasonic techniques. For this investigation, multiple sets of composite plate specimens made of two different composite materials were fabricated to check if the proposed technique works for different types of specimens. The specimens were damaged by impact loading and then inspected by propagating Lamb waves through them. Different failure mechanisms, such as fiber breaks, matrix cracking, debonding, and delamination, cause composite damage. Two groups of composite specimens that were fabricated and damaged were glass fiber–reinforced polymer composite and basalt fiber–reinforced polymer composite. A chirp signal excited by PZT (lead zirconate titanate) transducer was propagated through undamaged and damaged specimens to investigate the effects of varying degrees of damage on the recorded signals. Both linear and nonlinear ultrasonic parameters were extracted from the recorded signals and analyzed. The change in the linear ultrasonic parameters such as the wave speed and attenuation with damage progression were recorded. A new nonlinear ultrasonic parameter, the sideband peak count or sideband peak count-index, is also introduced and calculated from the recorded signals. It is observed that the nonlinear ultrasonic parameter can monitor the early stage of damage progression better than the linear ultrasonic parameters, while some linear ultrasonic parameters are more effective than the nonlinear ultrasonic parameter for monitoring the advanced stage of damage. Therefore, a combination of linear ultrasonic and nonlinear ultrasonic analyses is ideal for the holistic monitoring of the composite panels from the crack nucleation stage to the structural failure stage.

Fiber-reinforced laminar composite structures are widely used in several industrial sectors like aerospace and automotive due to their extraordinary peculiarities. This work deals with the influence of the impactor mass on the behaviour of carbon/vinylester woven laminates subjected to low velocity impact (LVI) events, very common in the cited fields. Samples with two different thicknesses were tested with a drop weigh machine using three nominal impact energy values and three different impactor masses. To highlight any influence of the impactor mass, the impact behaviour and the evolution of the damage suffered by the specimen examined were systematically analyzed through confocal microscope inspections and ultrasound investigations. Results also discussed in terms of strain rate sensitivity and mass of the specimen emphasized the prevalence of dissipative interlaminar phenomena and a more marked influence of the impactor mass on the thinnest laminates.

An improved technique for sensing damage initiation and progression in thermoplastic resin composite plate specimens is presented in this study. The composite plate specimens are investigated by using a nonlinear ultrasonic (NLU) technique called S ideband P eak C ount I ndex or SPC-I. The technique presented in this paper is an improvement from the previous SPC-I technique. This improved technique provides more reliable and consistent results and can monitor the damage progression over a wide range. In this paper the narrow band SPC-I technique is introduced to replace the conventional wide band SPC-I technique. The method implemented here is improved in three ways. First and foremost the narrow band SPC-I technique is introduced. Secondly, the non-permanently adhered gel coupled Lead-Zirconate-Titanate (PZT) transducers are used to reduce inconsistency in transducer adhesion and manufacturing. Lastly, higher sampling rate equipment is used for better signal resolution and peak counting. The experiments are performed on 4 sets of composite plate specimens fabricated using two composite fiber materials (Glass and Basalt) that have increasing levels of damage. The composite plate specimens were damaged by a falling weight impact machine with increasing impact energy (0 J, 10 J, 20 J and 30 J). The composite plate specimens were examined by propagating a narrow band chirp signal through the specimens using gel coupled transducers in a transmission mode setup. The received signals were recorded and analyzed using the NLU SPC-I technique. The modified SPC-I technique proposed in this paper can reliably and consistently detect both initiation and progression of damage in the composite plate specimens.

In this study, the effects of surface treatment of a low-temperature atmospheric oxygen plasma on basalt/epoxy composites were investigated to improve the hydrophobility of the composite surface. After the plasma treatment, the unmodified and surface treated composite laminates have been experimentally characterized by performing contact angle measurements, low-velocity impact tests and indentation depth on the impacted laminates. Results have showed a dependence of such composite properties on the plasma coating deposition and on the treatment parameters outlining the need to optimize both the plasma power and exposition time to plasma in order to assess the efficiency of the plasma treatment and establish the optimal processing conditions.

n this work, carbon fiber‐reinforced composites (CFRP), respectively, based on a vynilester and epoxy resin were loaded under low‐velocity impact condition to highlight the influences of different matrices and temperature on their dynamic response. In particular, measurements were performed at room and the low temperature of −25°C on samples simply supported by air to exactly simulate the incidental impact during the structure service and having the same thickness. Impact tests were carried out at penetration to obtain the complete load–displacement curve and to measure the penetration energy, and at different energy levels, 5, 10, and 20 J, to investigate the influence of the matrix on the damage start and propagation. After the impact tests, the specimens were nondestructively investigated by the ultrasound technique to measure the delamination. The interesting results obtained on carbon fiber laminates impacted at room and lower temperature are here reported and compared. In general, better behavior was noted for vinyl ester‐based composites, extensively used in the naval field, thanks to their low absorption for humidity. POLYM. ENG. SCI., 2019. © 2019 Society of Plastics Engineers

In the field of impact response of thermoplastic reinforced composites, several investigations about material behaviour in terms of delamination, indentation and fracture mechanism were conducted. Although a significant influence of the polymer temperature on the overall material impact response is expected, a limited number of studies are available in this regard. Most of the available scientific evidence concerns thermosetting composites and thermoplastic composites response only at room temperature. In particular, the purpose of this contribution is to better understand the dissipation mechanisms involved in thermoplastic reinforced composite under impact conditions for different temperatures. Starting from the few available literature data about the modelling of the problem, the aim of the present work is the development of a numerical approach able to reproduce the experimentally tested conditions. An experimental campaign on hot pressed polyamide 6 /basalt plain fabric laminates impact was selected as the benchmark for the numerical approach. The laminates impact response at increasing values of impact energy between 5J and 30J were simulated under three temperature conditions set around the polymer transition temperature (40°C, 80°C and 100°C). By validating the overall numerical model response on the room temperature experiment, considerations about the magnitude of viscous dissipation and its influence, for the different tested temperatures and in function of the adopted lamination technology, were made.

Low velocity impact tests at different impact energies were performed on basalt fibre reinforced plastic laminates, varying laminate thickness, stacking sequence, support dimensions and indenter diameter. A previous modified analytical model for the prediction of the indentation as a function of the impact energy, valid for carbon and glass fibre reinforced plastic laminates, was applied: a different behaviour was observed denoting an other damage mechanisms of the basalt fibre laminates. About the prediction of the penetration energy, the previous model largely applied in the literature showing the importance of the total fibre content was adopted, and a good agreement between the theoretical predictions and the experimental results was found. In analysing previous experimental data, in comparison to those of carbon fibre reinforced plastics, higher impact energy was found to be necessary to penetrate the basalt laminates whereas the indentation depth at the same impact energy was lower. A larger number of tests were carried out to validate a preliminary work done by the authors.

Among the several additive manufacturing techniques, fused filament fabrication (FFF) is a 3D printing technique that is fast, handy, and low cost, used to produce complex-shaped parts easily and quickly. FFF adds material layer by layer, saving energy, costs, raw material costs, and waste. Nevertheless, the mechanical properties of the thermoplastic materials involved are low compared to traditional engineering materials. This paper deals with the manufacturing of composite material laminates obtained by the Markforged continuous filament fabrication (CFF) technique, using an innovative matrix infilled by carbon nanofibre (Onyx), a high-strength thermoplastic material with an excellent surface finish and high resistance to chemical agents. Three macro-categories of samples were manufactured using Onyx and continuous carbon fibre to evaluate the effect of the fibre on mechanical features of the novel composites and their influence on surface finishes. SEM (Scanning Electron Microscopy) analysis and acquisition of roughness profile by a confocal lens were conducted. Tensile and compression tests, thermogravimetric analysis and calorimetric analysis using a DSC (differential scanning calorimeter) were carried out on all specimen types to evaluate the influence of the process parameters and layup configurations on the quality and mechanical behaviour of the 3D-printed samples.

The paper deals with the mechanical degradation of composite material components in seawater at room temperature. In particular, this study compares quasi-static and dynamic behaviour of carbon fiber/vinyl ester components, dry and water saturated in a saline environment at 3% to simulate the seawater exposition. At this regard, short-beam shear, flexural and low-velocity impact tests were systematically performed before and after the conditioning of the material under examination. Finally, the damage of the impacted specimens was carefully analyzed by visual inspections and ultrasound investigations. Despite a very low water absorption, the analyses allow to highlight different phenomena, reflecting on variations in the mechanical properties and in the extent of the damage of the investigated samples.

The low-velocity impact behavior of polyester glass fiber composite laminates has been investigated under different clamping conditions, by wetting the specimens surface with fluids having different densities. Unidirectional composite laminates, based on polymer resin and fibers of naval interest, with different thicknesses have been manufactured by resin transfer molding process in order to have a high control of the final properties and a high fiber volume fraction. Impact tests in air have been, first, performed up to penetration on all manufactured composites having four different thicknesses to get information on the material impact behavior. The effect of the clamping conditions and the interaction of the laminates with two fluids different in density, i.e., water and paraffin oil, have been investigated, then, only on the thickest laminates that showed a lower tendency to impact damage. In particular, the impact tests have been performed by impacting the front surface of the sample and by wetting the back surface of the composite samples under unclamped and clamped conditions, replicating the boundary constraints suggested by ASTM D7136 Standard for the conventional impact tests. Experimental results showed a lower initial rigidity, higher absorbed energy and deflection for specimens exposed to liquids with respect to those exposed to air, confirming the need of taking into account the fluid interaction in the case of marine composite applications.

The widespread additive manufacturing technology for producing components having complex geometries has increased the attention towards new reinforced materials, whose internal structure can be designed ad hoc on the required mechanical performance. Moreover, fused deposition modelling (FDM) technology allows the building of continuous fibre-reinforced thermoplastic composites. Due to this innovative technology, there is a lack of knowledge mainly about the impact behaviour of these materials, also considering that the main demand comes from the transportation field (automotive, aircraft, etc.), where the impact event is always possible. Thus, the aim of this research is the investigation of the impact behaviour of specimens obtained by continuous fiber fabrication technique, where Onyx and nylon white filaments were used as matrices and glass fibres for reinforcement. Onyx is a nylon mixed with short carbon fibres. An extensive non-destructive evaluation was performed on the specimens subjected to impact tests to assess the impact damage tolerance of these materials and to measure the damage extension as well. Nevertheless, considering that different non-destructive techniques were employed, the research aims also to suggest the most suitable and reliable technique to detect damage, mainly by on-site inspection.

In the last decades, a new class of polymer composites has attracted the attention of research activities and has driven the development of new materials with interesting potential in many industrial fields. The idea of these new materials, better known as single polymer composites (SPCs) or self-reinforced polymeric composites (SRPCs), arises from the observation that the same polymer shows different melting points depending on the form in which it is available (eg powder, fibre or film). In other words, it is possible to obtain innovative composites by combining matrices and reinforcements made of the same polymer ensuring, among other things, products with perfect interfacial adhesion and recyclability . In this work, self reinforced laminated samples based on a technical polyamide 66 (PA66) fabric were manufactured by hot-compaction technique and compared with compression molded plaques based on commercial polyamide 66, neat and filled with 30 wt% of glass fibres, taken as the reference materials. Preliminary calorimetric analyses made possible to establish the most appropriate process conditions. With the awareness of a narrow window of processability of the raw materials, plates from the PA66 fabric were produced by considering two cooling protocols. The calorimetric analysis and the mechanical tests carried out in quasi-static, dynamic and impulsive modalities have highlighted distinctions between the 2 types of self-reinforced composites essentially due to the different structural features promoted by the applied process conditions. The results were systematically validated with morphological investigations of the fractured surfaces coming from the impact tests. Analysis of micrographs , among other things, made it possible to identify the main damage mechanisms characterizing the failure of the new self reinforced materials.

Static magnetic fields created by superconducting magnets have been proposed as an effective solution to protect spacecrafts and planetary stations from cosmic radiations. This shield can deflect high-energy particles exerting injurious effects on living organisms, including plants. In fact, plant systems are becoming increasingly interesting for space adaptation studies, being useful not only as food source but also as sink of bioactive molecules in future bioregenerative life-support systems (BLSS). However, the application of protective magnetic shields would generate inside space habitats residual magnetic fields, of the order of few hundreds milli Tesla, whose effect on plant systems is poorly known. To simulate the exposure conditions of these residual magnetic fields in shielded environment, devices generating high-intensity static magnetic field (SMF) were comparatively evaluated in blind exposure experiments (250 mT, 500 mT and sham -no SMF-). The effects of these SMFs were assayed on tomato cultures (hairy roots) previously engineered to produce anthocyanins, known for their anti-oxidant properties and possibly useful in the setting of BLSS. Hairy roots exposed for periods ranging from 24 h to 11 days were morphometrically analyzed to measure their growth and corresponding molecular changes were assessed by a differential proteomic approach. After disclosing blind exposure protocol, a stringent statistical elaboration revealed the absence of significant differences in the soluble proteome, perfectly matching phenotypic results. These experimental evidences demonstrate that the identified plant system well tolerates the exposure to these magnetic fields. Results hereby described reinforce the notion of using this plant organ culture as a tool in ground-based experiments simulating space and planetary environments, in a perspective of using tomato ‘hairy root’ cultures as bioreactor of ready-to-use bioactive molecules during future long-term space missions.

Understanding the response of water-backed panels to impact loading is of paramount importance in the design of marine and aerospace structures. In this theoretical study, we propose a modeling framework to investigate the two-dimensional, nonlinear hydroelastic response of thin structures. Within Euler–Bernoulli beam theory, we account for nonlinear stiffening due to membrane stretching. We demonstrate a closed-form solution for the fluid potential flow, which affords the exact computation of the hydrodynamic loading. The Galerkin discretization is used to cast the governing nonlinear integro-differential equation into a set of nonlinear ordinary differential equations. Two different semi-analytical solutions are established, by using the in-vacuum linear mode shapes of the beam and Hermitian finite element basis functions. Results are verified against full two-dimensional finite element simulations. We conduct a parametric study to elucidate the role of the beam thickness and the functional form of the impact loading. Our results indicate that the water-backing has a critical role on the structural dynamics, which is stronger for thin beams subject to rapid pulses. The model fills a significant gap in the technical literature, holding promise to inform the design of experimental setups and assist in the analysis of observations on water-backed panels.

The aim of this work is to present a preliminary investigation on the propagation of electromagnetic fields generated by wireless technologies inside a nuclear facility or power plant. First, a survey of currently proposed wireless technologies for nuclear facilities and plants has been carried out. Then, for selected scenarios, the electromagnetic field propagation has been studied by means of electromagnetic simulation tools, and the presence of the nuclear environment has been simulated by properly modeling environmental parameters and engineered barriers. The choice of the proper simulation techniques and tools is mandatory in order to simulate the effect of the realistic environment on the propagation. Accordingly, the feasibility of wireless technologies application at nuclear facilities can be assessed on the basis of results achieved from simulated scenarios. The goal is to analyze, for selected scenarios, possible issues due to the propagation of an electromagnetic field in the presence of simplified barriers mimicking the real nuclear environment. This approach can provide indications on how to deploy potential benefits of wireless technologies in a nuclear environment, evaluating pros and cons of the investigated technologies.

This paper aims to investigate the ability of ultrasonic and electronic speckle pattern interferometry to analyse the low-velocity impact internal damage mechanisms on basalt composite laminates and to provide information on the shape and the extent of the delamination in non-destructive way. Basalt/epoxy composites with different thicknesses have been realised and characterised by mechanical tests to investigate both fibre-dominated (tensile and flexural behaviour) and matrix-dominated properties (interlaminar shear strength). Specimens were impacted at penetration and at increasing energy values, to explore the damage onset and propagation. The results showed that the damage was concentrated under the impactor–material contact point and that the composite with intermediate thickness had the best balance between the different kinds of impact damages: delamination and indentation. Further, a good agreement was found between the overall data obtained by the two non-destructive techniques, confirming the capability of both techniques to examine the composite impact damage.

Literature reports several works concerning the impact response of thermoplastic composites reinforced with woven fibres and involved dissipation mechanisms. However, although a significant temperature effect is expected on the impact behaviour of these materials, to the best of our knowledge, a limited number of experimental studies are focused on this aspect, and the most of them concern thermosetting composites. For this purpose, this research deals with experimental tests performed on a polyamide 6/woven basalt fibers composite specimens by a drop weight-testing machine, at four different temperatures (room temperature, 40°C, 80°C and 100°C), selected around the glass transition temperature (Tg) of the matrix. It was verified that the temperature influences the impact behaviour of the basalt composite even if a value of threshold seems to be achieved at T=80° C. This probably happens because the Tg of the tested composite matrix has been exceeded. Furthermore, dynamic-mechanical tests conducted on specimens from both the reference composite laminates and plates with equal thickness of the pure matrix, these latters obtained under optimal hot pressing of stacked PA6 films, demonstrated outstanding improvements in terms of moduli as well as superior damping ability of the composite structure.

Microwave thermal ablation treatments induce coagulation necrosis of diseased tissue through the absorption of an electromagnetic field at microwave frequencies. In particular, the electromagnetic field absorbed by the tissue induces a temperature increase that, in turn, produces an almost instantaneous cell death. The electromagnetic field is radiated by a minimally invasive antenna located in the centre of the diseased area. Temperatures close to 60°C are needed to induce thermal ablation, so that very high temperatures values (up to 100°C or higher) can be achieved close to the radiating antenna. To develop reliable interventional protocols, numerical tools able to correctly predict the temperature increase are needed. In this work, values recently measured of the thermal conductivity as a function of the temperature have been introduced into the numerical model to evaluate their influence on the calculated data.

In this work, the evaluation of damaged areas due to low velocity impact tests at different impact energy values on Carbon Fibre (CF) laminates with 3D fabric, made by infusion technology and reinforced with epoxy resin, were investigated by NDI (Non-destructive Investigation) technique based on speckle interferometry. Composites are characterized by several interacting failure modes such as matrix breakage, fibre failure and delaminations, which can be simultaneously induced by low velocity impacts. It can be very difficult to detect by visual inspections of the structures such phenomena. The aim of this study is to evaluate the damaged area due to an impact event. CF composite laminates were impact damaged with four energy levels (5, 10, 20, 30J) at room temperature, by drop weight impact machine. The results showed that ESPI technique was able to identify barely visible low-velocity impact damages.

Guided acoustic wave techniques have been found to be very effective for damage detection. In this investigation Lead Zirconate Titanate (PZT) transducers are used to generate guided acoustic waves for structural health monitoring of a variety of composite specimens. Multiple sets of composite plate specimens are inspected for impact induced damage detection using PZT transducers. Composite samples are divided into two groups for comparative studies i.e. glass fiber composites and basalt fiber composites. They are damaged by impactors having different levels of impact energy. A chirp signal is excited and propagated through the specimens in a single sided excitation/detection setup to investigate the damages induced by impacts of varying intensity. Signal processing of the recorded signals for damage analysis involved both linear and nonlinear analyses. Linear ultrasonic analysis such as change in the time-of-flight of the propagating waves, Fast Fourier Transform and S-Transform of the recorded signals were tried out while the nonlinear ultrasonic analysis involved the Sideband Peak Count or the SPC technique.

Hydrophobic surfaces are highly desired for several applications due to their exceptional properties such as self-cleaning, anti-icing, anti-friction and others. Such surfaces can be prepared via numerous methods including plasma technology, a dry technique with low environmental impact. In this paper, the effect of a one-step sulfur hexafluoride (SF6) plasma treatment upon the low velocity impact behavior of basalt/epoxy composites has been investigated by using several characterization techniques. A capacitive coupled radiofrequency plasma system was used for the plasma surface treatment of basalt/epoxy composites, and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the water droplet contact angle of treated specimens. The contact angle measurements showed that treating with SF6 plasma would increase the hydrophobicity of basalt/epoxy composites, moreover, the impact results obtained on reinforced epoxy basalt fiber showed damage in a confined area and higher impact resistance for plasma-treated basalt systems.

The results of orthogonal cutting tests on unidirectional carbon and glass fibre reinforced plastics are presented. The specimens were under shape of rectangular plates, circular disks and cylinders with different fibre architectures and a milling machine, a lathe machine and a five-axis high-speed vertical machining centre, were used for the experimental tests. The cutting speed was varied. During the tests, performed at low cutting speed, avoiding thermal effects, and high speed, to investigate about the effect of the cutting velocity on the cut quality, the fibre orientation respect to the cutting direction, the tool rake angle and the depth of cut were varied to investigate their influence on the phenomenon. A high speed steel tool in different geometries, was used. The mechanisms of chip formation and the cutting quality were investigated. A tentative to correlate the mechanisms of chip formation and cutting forces signals was done. Since the anisotropy, the mechanisms of chip formation consists of different failure modes occurring simultaneously and their identification, on the basis of the cutting force evolution, is very complex. Only in particular conditions, the features of cutting forces allow a precise identification of the chip development and detachment. The results indicated that the fibre orientation respect to the cutting direction determines the mechanisms of chip formation and influences the cutting quality. It was noted that for fibre orientation higher than 60°, the quality of the surface was revealed unacceptable. These conclusions were obtained independently of the particular shape of specimen tested and of the speed adopted. © 2017 The Authors. Published by Elsevier B.V.

Epoxy based laminates reinforced with woven basalt fibres have been manufactured and characterized by quasi-static mechanical tests and low-velocity impact tests. Samples were prepared by infusion of 16 plies of basalt under pre-optimized conditions. All the interlaminar shear strength, flexural and impact tests were carried out at room temperature, −25 °C and −50 °C to investigate the effect of temperature on the mechanical characteristics and the impact damage onset and propagation. Ultrasonic technique were adopted to provide information on the shape and the extent of the internal damage. The final aim was to be able to predict impact energy and delamination under different temperature conditions and to assess the influence of the resin matrix stiffening at low temperature on the composite behaviour. Results show that at low temperature due to the stiffening of the resin matrix, the composite tested is more resistant and less deformable. It is interesting since, at low temperatures, it is more straightforward the damage propagation. In particular, ILSS and flexural tests show a maximum increase of 39% and 12.78% respectively at T = −50 °C compared to the value at room temperature. A delamination area increase of wholly 40% at T = −50 °C, is detected.

Basalt-epoxy laminates are establishing gradually in engineering sectors due to increasing attention toward environmental matters. Some properties should be improved to extend their applications and the cold spray (CS) metallization provides a potential solution. Unfortunately, the fragile nature of thermosetting polymers makes it difficult the CS coating formation and grow-up. Therefore, this research work aims to study an innovative solution able to enhance the adhesion mechanisms between the cold sprayed metal particles and the thermosetting polymer-based substrates. For this purpose, an original manufacturing method that provides the surface PLA treatment for thermosetting samples was developed. AlSi10Mg particles were cold sprayed on the treated surface, and the low-velocity impact behaviour of the metallised hybrid structures was analysed in details. The outcomes prove the effectiveness of the method proposed on the deposition process and the beneficial effects of metallization on impact damage mechanisms.

The low-velocity impact behaviour of novel composite structures, made of a polymer matrix composite with a superficial 3D printed metallic layer, was studied. The metallic layer was produced through cold spray deposition which is a relatively new additive coating technique allowing for the deposition of metallic coatings on thermal-sensitive substrates, such as the polymeric materials. Micron-sized aluminium particles were used to metallise the surface of basalt-nylon 6 (PA6) laminates manufactured by the compression moulding technique. Three different energy levels (10 J, 20 J, 30 J) were set for the impact tests. The results obtained pointed out the beneficial contributions of the metallic coating on the energy absorbing modes of the polymeric substrates; the positive effects on the damage mechanisms as well as the crack propagation were detected by plastic deformation analyses and ultrasonic damage controls.

International audience; In this work, the influence of a tensile preload on the impact behavior of thin woven composite laminates is investigated. These kinds of laminates are usually parts of more complex structures, for example, skins of structural sandwich panels or helicopter blades. These structures are generally subjected to external loads, and can also be impacted in operation. The objective of this study is to identify a correspondence between the preload of the structure and the resulting impact damage. This preliminary work is a first step of a more global study that aims at predicting impact damage in structural composites in order to optimize the design process. Experimental tests are carried out on carbon/epoxy and glass/epoxy mixed thin laminates and on sandwich structures. The samples are loaded uniaxially using a specially designed test rig. The effect of the preload on the impact damage size and shape and the peak load is experimentally quantified and discussed.

Recently, the growing attraction to the development of new eco-sustainable composite materials is driving the research interest toward the replacement of synthetic reinforcing fibres with natural ones and exploiting the inherent recyclability of thermoplastic resins even for uses in which thermosetting matrices are well consolidated (e.g. naval and aeronautical fields). Among the natural fibres, a growing interest of the research is addressed to basalt fibres. Focusing the attention on thermoplastic composites, many experimental findings already available in literature highlight the outstanding mechanical properties of composite materials including basalt fibres and their potentiality concerning glass ones. On the other hand, some issues are related to the surface properties of the bio-laminates: in particular, the wear ones, the flame resistance and the aesthetic appearance have to be improved to extend the application fields of these materials. Aiming to these goals, this paper deals with the study of the deposition ofaluminium coating through cold spray process on polypropylene/basalt fabric composite laminates. The specimens were obtained by film stacking, and compression moulding technology and their performances were studied in terms of low-velocity impact behaviour, considering the influence of the surface modification with the aluminium coating. The results obtained from the reference laminates and the coated ones are compared in terms of impact parameters: the aluminium deposition seems to affect the damage mechanism propagation even if the impact response seems to be similar in both conditions.

In this work, the evaluation of damage area due to low-velocity impact tests at different impact energy values and different temperatures on glass fiber-reinforced plate laminates was investigated by two nondestructive evaluation (NDE) techniques, electronic speckle pattern interferometry (ESPI) and ultrasound testing (UT). Composites are characterized by several interacting failure modes such as matrix breakage, fiber failure and delaminations, which can be simultaneously induced by low-velocity impacts and can be different depending on the temperature. It can be complicated to detect by visual inspections of the structures for such phenomena. This paper aims to investigate the dependence of the damaged area with respect to temperature variation on glass fiber composite laminates. GF composite laminates were impacted with three energy levels (5, 10, 20 J) and at different temperatures (room temperature, − 25, − 50 °C) by a drop weight impact machine. The results show that at decreasing temperature, a decrease in the damage extension was observed, which is more evident at increasing impact energy. Moreover, as expected, the results confirm UT and ESPI techniques are able to identify the barely visible low-velocity impact damage. However, some limitations for detection were found in ESPI. Nonetheless, the ESPI technique can be considered as one of the useful NDE methods if the calibration and the post-processing methods are improved. © 2019, ASM International.

With the aim of simulating the real conditions during the navigation, in this framework, impact tests were performed by loading CFRP laminates immersed in the water from the front side. The specimens, made by vinyl ester matrix because of the lower moisture absorption compared to the other epoxy systems, are in the presence of the water to accurately simulate the incidental impact on the hull of the vessel, immersed or partially immersed, during the navigation. It can be caused by the ice in the Arctic Ocean, by a projectile due to a terroristic attack or by debris from an explosion. The results are compared with the ones obtained by loading the laminates in pure traditional impact tests in the air. The influence of the clamping device has been tested too. The exciting results obtained on carbon fiber laminates in the air (pure traditional impact tests), water-backed (with water on the back side) and waterfront (water only on the front side) conditions at room temperature are here reported and compared. They highlighted the critical role played by the complex fluid–structure interaction.

Composite laminates reinforced by woven basalt fibers and based on different polymer matrices were prepared and mechanically characterized, in static and dynamic conditions, to compare the results and evaluate the influence of the matrix type. In this regard, a thermoplastic resin, polyamide 6 (PA6), and two thermosetting matrices, vinyl ester and epoxy grades, commonly used for high-performance applications, were considered. Indentation depth measurements carried out by a confocal microscope and ultrasound analyses performed on specimens subjected to falling dart tests at levels of impact energies lower than the perforation one permitted to evaluate the extent of plastic deformations and of subjected delaminations, respectively. These data have provided useful information about the involved damage mechanisms and highlighted interesting perspective of use for the eco-friendly thermoplastic sample.

Basalt fibre reinforced plastic laminates in vinyl ester resin were obtained by overlapping plain woven fabrics by resin infusion technique. Rectangular specimens, 100 mm × 150 mm, were cut from the original panels and impacted at penetration and increasing energy values, at two different temperatures (room and −50 °C). The final aim was to investigate the damage onset and propagation to study the dynamic behaviour in extreme conditions of basalt laminates, correlating the absorbed energy to the impact one and to evaluate the possibility to replace the traditional carbon and glass laminates in fields where the temperature plays an important role.

The effect of stacking sequence on the impact damage mechanisms and the matrix-fiber dependent properties, such as flexural and interlaminar strength , of epoxy hybrid basalt/flax composites has been experimentally investigated. The basalt and flax fabrics have been appropriately selected with approximately the same areal weight and stacked in the same number in three different symmetrical analysed configurations to manufacture composites with comparable conditions regarding fibre content by weight. No influence of fibre sequence was observed for the flexural modulus , whereas some differences were exhibited by the flexural and the interlaminar shear strength depending on the resin content. The impact tests were carried out at penetration and different energy levels. After impact, indentation measurements have been performed by a confocal microscope to get information on the damage propagation and characteristics that resulted affected by the hybridisation type and by the impact energy. The results evidenced the relevance of the stacking sequence in the composite design to meet specific requirements.

The aim of this work is to show a preliminary investigation on the propagation of electromagnetic fields generated by wireless technologies inside a nuclear facility or power plant. First, a survey of currently proposed wireless technologies for nuclear facilities and plants has been carried out. Then, for selected scenarios, the electromagnetic field propagation has been studied by means of electromagnetic simulation tools, and the presence of the nuclear environment has been simulated by properly modeling environmental parameters and engineered barriers. The choice of the proper simulation techniques and tools is mandatory in order to simulate the effect of the realistic environment on the propagation. Accordingly, the feasibility of wireless technologies application at nuclear facilities can be assessed on the basis of results achieved from simulated scenarios. The goal is to analyze, for selected scenarios, possible issues due to the propagation of an electromagnetic field in presence of simplified barriers mimicking the real nuclear environment. This approach can provide indications on how to deploy potential benefits of wireless technologies in a nuclear environment, evaluating pros and cons of the investigated technologies. Copyright İ 2018 ASME

The aim of this work is the study of the influence of a large notch damage in a stiffened aeronautical panel. In particular, the damage onset and evolution due to a cut-out located in the bay of an omega stiffened composite panel subjected to a compressive load is investigated. Three different cut-outs are considered: parallel, normal, and 45° oriented respect to the load. The effects of such configurations are compared in terms of fibre and matrix failures, in order to better understand which configuration is the most sensitive to these type of damages.

The present experimental investigation is aimed at modeling the falling weight impact properties of thermosetting composites produced using a partially bio-based vinylester resin with flax and basalt fibers and using them both in a hybrid configuration, therefore obtaining three different types of laminates, fabricated by hand lay-up and resin infusion. Cure processes were accelerated and controlled by applying heat and pressure in autoclave. After acquiring tensile and flexural data, falling weight impact tests were carried out at several energies of up to 40J, so to induce penetration, but also to have information on the evolution and the different characteristics of damage produced. Modeling analysis was mainly based on the study of impact hysteresis cycles, which correlate the mode of energy absorption, whether quasi-elastic or producing irreversible damage and the rebound characteristics, in case the energy is not sufficient to produce penetration, from the patterns of force vs. displacement curves obtained during impact loading.

Woven basalt fiber composite laminates based on epoxy and polypropylene (PP) resins were dynamically loaded by a falling weight machine, by using a cylindrical impactor with a hemispherical nose. Laminates with the same thickness were investigated to compare their dynamic response. Impact tests were carried out at penetration to obtain the complete load-displacement curve and to measure the penetration energy, and at different energy levels to study the influence of the matrix on the damage start and propagation. A general better behavior of epoxy basalt fibre reinforced plates (BFRP) was noted while, surprisingly, the polypropylene based laminates didn’t show any penetration even at high impact energy highlighting the importance of this study.

Directive 2013/35/EU lays down minimum health and safety requirements regarding the exposure of workers to electromagnetic fields, including those present in Magnetic Resonance Imaging (MRI) facilities. For what concerns the Static Magnetic Field (SMF), the Directive follows a "flexible approach" introduced by the 2009 ICNIRP guidelines, which is based on the distinction between sensory and health effects, thus allowing in some circumstances exposed workers to possibly experience unpleasant sensory effects. In addition, the Directive provides for the possibility of derogating from the health exposure limits, explicitly referring to the case of MRI. However, protection issues related to effects associated with movements of workers in the SMF are not completely addressed by EU limits. ICNIRP has published a guideline on this matter in 2014, but it has not yet been transposed into the Directive. Measurements were performed of low frequency switched gradient magnetic fields and of the magnetic flux density experienced as variable by workers moving in the SMF of 1.5 T, 3 T and 7 T MRI scanners. In the latter case, three different metrics were applied to process the collected data and compare them with the EU Directive Exposure Limit Values (ELVs) for SMF, the ICNIRP basic restrictions (BRs) aimed at preventing vertigo effects and the ICNIRP reference levels (RLs) intended to prevent stimulation effects. Regarding movement in the SMF, reported values of the peak magnetic flux density, of its variation in 3 s and of the weighted-peak indices for stimulation effects show several cases of non-compliance with the corresponding ICNIRP BRs and RLs even when EU Directive ELVs are complied with. Results of exposure to low frequency magnetic fields are being processed.

A study was conducted to investigate the impact strength of basalt fibres in vinyl ester resin, a composite laminate material used for the design of marine vessels. The basalt/vinyl ester laminate material was dynamically loaded with a Ceast/Instron falling weight machine, using a 3.6 kg cylindrical impactor with a 19.8 mm diameter hemispherical nose. Impact tests were conducted at various energy levels—up to complete penetration—to obtain the full load–displacement curve, identify the material’s penetration energy, and investigate damage initiation and propagation. After the impact tests, the internal damage of each specimen was evaluated using the non-destructive Ultra Sound technique.

The growing demand for more convenient and reliable means to recharge the battery of electric vehicles (EVs) has stimulated scientific efforts toward wireless power transfer (WPT) technology, demonstrating the feasibility of its application through the realization of various prototypes and some products already present on the market. The long-term goal is to dynamically power EVs moving on road. The dynamic wireless charging (DWC) is based on the inductive magnetic coupling between an electrified track on the road and a pickup coil mounted on the EV. In this paper, a new DWC system of coupled coils (named DD coils due to their shape) has been numerically designed and simulated in the perspective of a future prototype. A preliminary analysis of exposure to the stray magnetic fields emitted by the system has been performed by numerical simulations, in order to assess the compliance to the reference level for general public exposure of the European Council Recommendation 1999/519/EC. Results from simulations evidence that the reference level for magnetic field is exceeded at a distance of 30 cm from the DD coils pair. Results from preliminary numerical dosimetry, performed in a homogeneous phantom, show that exposure to the stray magnetic fields emitted by the DD coils pair can also lead to non-compliance with the basic restriction defined by the European Recommendation. Further numerical dosimetry will be carried out on human anatomical models, to assess compliance to the basic restriction. © Institution of Engineering and Technology.All Rights Reserved.

The adoption of composite materials is becoming increasingly attractive in many aeronautical applications. The improved endurance and corrosion resistance are few of the advantages they can offer, compared to the conventional alloy solutions. Due to the extraordinary mechanical property of carbon nanotubes (CNTs), they can be considered as an effective reinforcement treatment for composites. Multifunctional materials are designed so as to meet specific requirements through tailored properties. These materials, employed both for general aviation and very light class, allow to be readily modified with extra upgrading treatments during the lay-up manufacturing phase, thanks to their physical constitution. Particularly, in aerospace applications, the potential implementations of these advanced materials have been predicted to have a large impact on future aircraft vehicles, mainly due to their distinct features, which include greater mechanical, thermal and electrical characteristics. In such framework, different vibro-acoustic tests have been performed on a fiber-reinforced panel, representative of an aeronautical shell, for the characterization of the damping as well as the transmission loss properties related to such micro-handling treatment. The spectral excitation has been provided by an acoustic source, simulating in such a way the aerodynamic pressure load agent on the structure. Significant studies have been carried out to investigate and improve the vibro-acoustic properties of filled or reinforced polymer composites: the authors showed that the use of nano-particles such as CNTs can really improve the dynamic performance of standard laminates.

Polyamide 6 (PA6) and vinyl ester (VE) basalt fabric composite laminates were prepared and analyzed in terms of flexural and low velocity impact properties in order to compare the results and evaluate the influence related to the matrix type. The BS/PA6 exhibits superior flexural performances and a higher rigidity in all tests. It is also interesting to note a particular behavior of the vinyl ester samples that can be related to the damage mechanism. After the impact tests, the specimens were non destructively investigated by a ultrasound technique to evaluate the delamination extent. These data, complemented by morphological inspections and indentation depth measurements, have provided useful information about the involved damage mechanisms.

Composite laminates with different stacking sequences of woven carbon and glass fibre layers in hybrid configurations were manufactured by vacuum resin infusion. The effect of stacking sequence and hybridisation on the flexural properties and impact damage mechanisms were widely studied. The performances were also studied to investigate the effect of the stacking sequence and the hybridisation in an attempt to compare the results from the literature on traditional composite laminates. Bending tests were carried out in three-point configuration, and the failure mechanism was investigated by visual inspection. Impact tests were carried out at penetration and different energy values to study the impact behaviour by evaluating the external and internal damage evolution. At this scope, indentation measurements were carried out by a confocal microscope, whereas the UltraSound technique investigated the delamination. The data obtained from the different configurations were compared at the aim to individuate the best one. The results were then compared with traditional composite laminates to highlight the advantages of the hybridisation. A strong relevance of the stacking sequence in the design to meet specific requirements was observed in both impact and flexural behaviour.