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Additive manufacturing has revolutionised the field of manufacturing, allowing for the production of complex geometries with high precision and accuracy. One of the most promising applications of additive manufacturing is in the production of composites, which are materials made by combining two or more substances with different properties to achieve specific functional characteristics. In recent years, the use of Continuous Filament Fabrication (CFF) in additive manufacturing has become increasingly popular due to its ability to produce high-quality composite parts which have fibres with a complex orientation and high curvature. This paper aims to investigate the influence of fill pattern and stacking sequence on the open-hole tensile strength of composites manufactured using CFF and made of an innovative matrix composed of nylon and short carbon fibres, i.e., Onyx, and with continuous carbon fibre as reinforcement. By systematically varying the fill pattern and stacking sequence, we aim to identify the optimal combination that can achieve the highest open-hole tensile strength in these composites. The results of this study will provide valuable insights into the design and manufacture of high-strength composites using additive manufacturing. Open-hole strength and elastic properties are strongly influenced by the infill strategy and stacking sequences adopted, and show different failure modes. The results also point out a technological issue characterising the process and indicate some guidelines for designing and manufacturing 3D printing composites.

Green composites have gained increasing attention in recent years as a sustainable alternative to traditional materials used in marine structures. These composites are made from biodegradable and renewable materials, making them environmentally friendly and reducing the subsequent carbon footprint. This review aims to provide a comprehensive overview of green composites materials and their applications in marine structures. This review includes a classification of the potential fibres and matrixes for green composites which are suitable for marine applications. The properties of green composites, such as their strength and Young’s modulus, are analysed and compared with those of traditional composites. An overview concerning current rules and regulations is presented. The applications of green composites in marine structures are reviewed, focusing on both shipbuilding and offshore applications. The main challenges in a wider application of green composites are also highlighted, as well as the benefits and future challenges.

Additive Manufacturing (AM) techniques have recently attracted the attention of scientists for the development of prototypes with complex or particular geometry in a fast and cheap way. Among the different AM processes, the Fused Deposition Modelling process (FDM) offers several advantages in terms of costs, implementation features and design freedom. Recently, it has been adopted to realise auxetic structures, which are characterised by negative Poisson ratio, enhanced mechanical properties, and a higher compression resistance than conventional structures. This review outlines the use of AM processes, in particular FDM, to design and obtain auxetic structures, with the final aim to exploit their applications in different fields. The first part of this work presents a brief classification of auxetic structures and materials. Subsequently, a summary of additive manufacturing processes is presented, focusing on the use of FDM and its limitations. Finally, the studies on the use of additive manufacturing to produce auxetic structures are shown, evidencing the potential of the concurrent combination of a fast prototyping technique such as FDM and the characteristics of polymer- and/or composite-based auxetic structures. Indeed, this new technological field opens the possibility of realising novel structures with integrated smart behaviour, multifunctional properties, compression resistance, and a tailored microstructure and shape.

Laminated composite structures are subjected to impact damage during maintenance and manufacturing operations and their life service. Driven by the necessity to value damage tolerance and durability of composite materials, an analysis of multi-hit impact is conducted to reproduce the real service conditions. Despite many studies in the literature investigated the properties of composites at low impact velocity, in contrast the behavior of the hybrid configuration, especially at repeated impacts, result still little known. This work presents an experimental and numerical study of the dynamic behavior at the repeated low-velocity impact of a carbon and glass fibers hybrid composite laminate.

Low velocity impact behaviour of laminates made of different reinforcements and matrices was studied in this paper. Impact tests were carried out up to penetration and at increasing energy values on glass fibre reinforced phenolic resin laminates, with different configurations (quasi-isotropic and orthotropic) and thicknesses, in order to correlate the indentation depth with the impact energy. Impact results obtained on basalt fibre reinforced epoxy resin laminates with different thicknesses were compared too. The stacking sequence of the glass fibre specimens was found to have no influence on the penetration energy but revealed lower indentation for the quasi-isotropic ones, under the same impact energy, for all the thicknesses tested. Moreover, basalt laminates showed lower indentation depths, compared to the data from this research and present in literature on other material systems. Finally, the results from the impact tests were used to validate existing semi empirical laws for the evaluation of the indentation and the penetration energy, in which the fibre content assumes the most relevant role.

Environmentally friendly composite plates intended for load-bearing applications were prepared and systematically characterized in terms of mechanical performances and morphological features. Sample plates combining two extrusion grades of bio-polyamide 11, one of which is plasticized, and two basalt fiber fabrics (plain weave and twill architectures) were obtained by film stacking and hot pressing, and their mechanical properties were investigated by quasi-static flexural and low-velocity impact tests. The comparative analysis of the results, also interpreted by the bending damage analysis, through optical microscope observations, and impact damage analysis through visual inspection and indentation measurements demonstrate that, besides interfacial adhesion issues, the mechanical performance of the laminates need to be optimized through a careful selection of the constituents in the light of the final application. In particular, if the goal is a gain in impact strength, the use of the plasticized matrix is beneficial, but it brings about a loss in stiffness and strength that can be partially compensated by properly selecting a more performing fiber fabric architecture. The latter must also be easily permeated by the matrix to enhance the efficiency of stress transfer from the matrix. Overall, our results can be exploited for the development of bio-composites for particularly demanding applications.

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.

Glass fiber composite materials in epoxy resin with different content of a nitrile rubber modified hybrid resin were manufactured by infusion with two different rubber concentrations. SX 10 epoxy resin was modified to improve the response of the laminates under impact loads. At the aim to test the improvement of the impact resistance over the conventional epoxy resin system, the rectangular specimens 100∗150 mm2 were dynamically loaded in the center by a falling weight machine, Ceast Fractovis, using a cylindrical impactor with a hemispherical nose 19,8 mm in diameter and a total mass of 3.6 kg. Impact tests were carried out at penetration to obtain the complete load-displacement curve useful to measure the penetration energy and to highlight the characteristics points for the increasing energies evaluation, 5J, 10J and 20J, to investigate the damage start and propagation. After the impact tests, the specimens were observed by visual inspection to investigate the delamination extension whereas a confocal microscope was used for the indentation measurements. The obtained results on the modified epoxy system were compared to neat GFRP laminates impact performances. No significant impact performance difference was recorded between samples with different nitrile rubber modifier content. A higher indentation was recorded on the modified samples related with a lower delamination extension. It could represent a good practical results since from a simple external damage measurement it can be possible to obtain information about a low internal delamination. © 2016 The Authors.

An experimental activity, in order to assess the impact behavior at room and low temperature, of carbon fiber in vinylester resin laminates used in the shipbuilding industry, was conducted. The conditions, which simulate the impact of a tool that drop on the panel mounted on a boat hull in contact with water, were reproduced. This is a condition named water backing, in the middle between the pure impact (air backing) and the hull slamming, and not already tested before. An innovative equipment was designed and realized at University of Naples “Federico II,” to reproduce the real dynamic material behavior in the presence of water, at the aim to investigate the influence of the water backed on the response of laminates under impact conditions. The results were obtained impacting the laminates placed between the cylindrical steel impactor and a bag containing water. A falling weight machine, equipped with a thermal chamber, was adopted for the experimental tests. The simulated test condition is completely new since no similar research is possible to find in literature. The impact behavior in hostile environments was compared to the room conditions, and the data obtained by the water backed loading tests were compared with the results by the pure impact tests. In the latter case, a completely different behavior was observed between the two different loading conditions, in terms of both load–displacement curve and the internal damage. The effect of the impact load on the laminates has been analyzed through the delamination and the indentation. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

The purpose of this work is to evaluate the influence of the manufacturing technology on the mechanical behaviour of composite laminates from commingled fabrics consisting of glass and polypropylene fibers. In this regard, non-isothermal and isothermal moulding technologies were used for manufacturing flat laminates with different thicknesses and stacking sequences. The laminates were characterized by flex and impact tests up to complete penetration; the data of penetration energy were also used to estimate the goodness of fit of a prediction model present in literature. The results obtained from the mechanical tests show the effectiveness of the isothermal moulding technology compared to the non-isothermal one, which is extremely important considering that the preheating phase is avoided with the first technology, saving on equipment and processing times.