Dynamic Response and Failure of Composite Materials

This work uses three-dimensional (3D) continuum models on the explicit finite element (FE) basis to simulate interlaminar delamination of a carbon fiber reinforced plastics (CFRP) laminate at a high strain rate. The high strain rate experiments have been performed using the Split Hopkinson Pressure Bar (SHPB) system. The 3D FE simulations, including both CFRP and the entire experimental setup, were carried out by taking into account the highly dynamic nature of the tests. The delamination propagation was modelled using the Virtual Crack Closure Technique (VCCT). The modelling cases covered I) layer-by-layer models; and II) homogenized orthotropic laminate models. A comparison between the experimental and numerical results indicates a good accuracy of the laminate simulation with homogenization. The simulated data shows that the time step selection significantly affects the prediction of the rapid delamination onset and growth at high strain rates.

The aviation industry aims to reduce costs in aircraft design, manufacturing, and maintenance. Structural Health Monitoring (SHM) is a key technique for monitoring the health of aircraft structures, providing valuable data throughout their operational life. This data can enhance design techniques, production control, real-time structural health evaluations, and maintenance plans, improving reliability and safety.This study examines the effectiveness of distributed fiber optic sensors in detecting impact damage on a full-scale composite wing. The sensors track changes in strain distribution caused by controlled impacts at predefined locations. A specific algorithm developed by CIRA identifies the position and size of the damage without relying on reference systems of the undamaged structure. Through structural tests under load, the SHM system’s accuracy in detecting damage was experimentally validated.Funded by the Clean Sky 2 Joint Undertaking under the EU Horizon 2020 program, this research advances SHM techniques for aeronautical applications and presents an alternative to traditional Non-Destructive Inspection (NDI) methods.

Interlaminar damages are a key challenge that limits the widespread use of composite materials in aircraft primary structural parts. Although years have already passed since the introduction of these materials, unstable propagation of delamination damage is still the base for evaluating the durability and reliability of structures made of composite laminates. In this paper, the unsteady and sudden propagation of skin-stringer debonding in a typical aircraft composite panel is investigated. Experimental tests and advanced finite element simulations have been performed to assess the evolution of debonding under compressive loading conditions. Fibre-reinforced composite panels, reinforced with a single T-shape stringer and characterized by artificial debonding at the interface between skin and stringer, have been experimentally tested and numerically analysed. The test output has revealed unstable growth of the debonding, with implications for the structural stability of the panels. The experimental results have been then compared with numerical simulations performed by using the Virtual Crack Closure Technique based SMart-time XB numerical procedure and excellent correlation have been found in terms of strain measurements against compressive load.

Inconel 718, one of the most employed nickel-based superalloys, proved to be efficiently processable through Wire-Arc Additive Manufacturing (WAAM), including Cold Metal Transfer Technology (CMT). Nevertheless, a multi-step heat treatment is still necessary to control the microstructure and the mechanical properties of this complex alloy. This work aimed to compare the effects on microstructure, tensile properties, Vickers microhardness and chemical composition of two heat treatments performed on Inconel 718 parts produced through CMT, namely: i) the heat treatment used for conventionally processed Inconel 718 parts, defined by the AMS5662 and AMS5663 standards; ii) a custom heat treatment that reduces the number of steps included in the previous case. The experiments were performed on prismatic CMT-produced parts, subsequently machined to extract the test specimens, considering both the aforementioned heat treatment conditions as well as the as-deposited material. The results suggested that comparable results were achieved for the selected heat treatments, however, a complete recrystallization of the fine grains never occurred for all the investigated conditions, thus retaining the typical microstructural anisotropy deriving from the CMT process. Moreover, the heat-treated parts showed, in any case, comparable properties to those of the conventionally cast alloy, opening a new scenario in the context of industrial production of semi-finished parts with huge costs and time savings.

Auxetic structures with negative values of Poisson’s ratio attract attention due to their surprising deformation response, durability under long-term loading and energy absorption properties. In this work, different 3D-printed specimens with the internal auxetic structure were investigated in real time during flexural tests by means of shearography.The 3D printed specimens have been mechanically characterized by performing flexural tests according to the ASTM D790 standard in order to investigate the effect of the new manufacturing process on the flexural strength and modulus. The lateral face of the specimens was monitored in real time during the test. The preliminary results showed the points of greatest stress where the specimens starts to fail. This information can be useful to understand the behaviour of the investigated structures in order to improve geometries and printing processes.

SMC composites, comprising chopped fiber bundles within a matrix material, offer the potential to create lightweight structures with high strength and stiffness, serving as viable substitutes for heavier metal components. The complex task of designing SMC composites with optimized performance characteristics is compounded by their inherently localized anisotropic behavior and the presence of various interacting forms of damage. Consequently, simulating the performance of SMC in crash-worthy applications necessitates a comprehensive characterization of the material’s mechanical properties through tailored experimental tests. In this study, an experimental study has been conducted on a commercial SMC material, with the primary objective of comprehensively comprehending its behavior and deriving specific parameters essential for numerical simulations. Employing ESI-VPS, the crashworthiness of flat components was simulated and successfully achieved a favorable correlation between the obtained results and the experimental data.

Composite materials are common in industries like aerospace, automotive, construction, and wind energy. Understanding the behavior of composite bolted joints is crucial but challenging due to fiber anisotropy and stress concentration. Factors influencing joint efficiency include washer size, bolt torque, and hole-to-edge distance. Studies suggest that higher clamping pressure improves bearing strength and affects failure mechanisms in composites.Additive Manufacturing (AM), particularly using continuous fibers, has enabled new customized composites with enhanced mechanical properties. Fused Filament Fabrication (FFF) is a key method, but there is limited research on the bearing behavior of FFF composites and the role of geometric parameters.While joint failure modes are well studied, data on the effect of torque on bolted joints in additively manufactured composites is scarce. This study investigates the mechanical behavior of these joints under various torques, focusing on bearing behavior, strain fields, and deformation.

This study aims to present a novel approach for composite panel inspection to identify Barely Visible Impact Damage (BVID) and Visible Impact Damage (VID), using computer vision algorithms. A new methodology for visual inspections was developed using computer vision algorithms is based on the YOLO - You Only Look Once architecture about the aircraft composite components, that use digital optics and deep learning techniques to identify and classify damages. Computer vision algorithms are used as instruments for automating the process of surface inspection and damage detection, increasing productivity and safety for maintenance operators (in the case of inspection of remote areas of aircraft). An overview of the problems, methods, and recent developments in deep learning algorithms used for general damage detection is provided. Data for Convolutional Neural Network (CNN) training were collected using a high-quality acquisition system. The database was populated by collecting images with damages from many composite panels, previously damaged by different impactors. Each defect has been photographed under different lighting conditions (bright or dark), resolution, and lighting angles to accurately simulate the environmental conditions of an aircraft maintenance hangar.

Carbon fiber-reinforced polymers (CFRPs) are widely used in transportation applications for structural components due to their outstanding lightweight and crashworthiness properties. Unlike metals, these composites fail through a combination of different failure mechanisms that contribute to the energy absorption capability of the final structure. In this study, the crash absorption capability of flat and C-shaped CFRPs, specifically carbon/epoxy composites, under dynamic conditions was investigated both experimentally and numerically. Initially, Charpy impact tests were conducted at different impact velocities using a three-point bending procedure. Subsequently, a finite element model was developed and simulated using LS-DYNA software. The numerical results closely replicated the outcomes of the physical experiments and exhibited a strong correlation with the experimental data, thereby validating the effectiveness of the designed model. Furthermore, the model successfully reproduced the observed damage mechanisms occurring during the physical tests, demonstrating its capability to accurately capture the composite behavior under the prescribed impact loading conditions.

Several industries make an extensive use of sandwich structures in structural design, especially in the aerospace and automotive Engineering fields.Sandwich structures are characterised by two thin layers (skins) with a thick, but light, core in the middle, for increased stiffness to bending. The use of additive manufacturing allows us to adopt very light and geometrically complex cores based on the lattice structures concepts. Lattice structures performances are strongly affected by geometrical factors such as the array configuration, the unit cell shape or topology and the relative density.The research presented in this paper is aimed at adopting hybrid sandwich structures with lattice cores to develop structural engineering solutions characterised by high energy absorption properties and low weight for occupant protection in transportation.Actually, these kind of hybrid shock absorbers have been already demonstrated to be a good compromise between crashworthiness performances and weight efficiency.To improve the shock absorbers designs presented in [1], the additive manufacturing technology has been used to produce three different sandwich panels based on a Body Centred Cubic (BCC) unit cell type, such as a Waved Body Centred Cubic (WBCC) unit cell. The Direct Metal Laser Sintering (DMLS) technology has been adopted by using the EOS M290 3D Printer for metals.The shock absorbers’ configurations have been numerically designed by modifying the core unit cell topology starting from a linear shape to a curved shape with two different orientation.

Aeronautical structures, often, experience impacts with foreign objects in service and during maintenance operations. Foreign Objects Impacts (FOI) can lead to critical damages and can compromise the overall performances of structural components. Indeed, among the others, composite components can exhibit various interacting post impacts damage mechanisms, including fiber breakage, matrix fracture, and interlaminar damages, such as delamination between different layers of the laminates. Delamination represents the most critical failure mechanisms, as it is, often, undetectable by visual inspections and it may, unstably and silently, develop within the component. This Phenomenon may be amplified under cyclic loading conditions, as the residual strength and stiffness can decrease rapidly after a certain number of cycles, potentially leading to structural collapse [1]. Unstable propagation of delaminations is particularly critical, since it, actually, can take place without the need of increasing the load acting on the structure. This phenomenon, which is very dangerous for the structural integrity of components, can be very challenging to be predicted, under fatigue loading conditions, by the standard geometrically non-linear Finite Elements Methodologies (FEM) which use a sequence of simulations under force control to mimic the fatigue behaviour of composite materials. Actually, FEM simulations under controlled force levels lead to convergence issues when predicting the highly dynamic behaviour of the unstable growth of delaminations under fatigue loading conditions.The research activity, presented in this paper, is aimed to develop an alternative efficient methodology able to mimic the unstable delamination propagation under cyclic loading conditions in composite structures by non-linear static analyses. This new methodology has been demonstrated to be able to correctly consider the fast variation of delamination size associated to decrease in loading during the unstable growth phenomenon under cyclic loading conditions. To achieve this objective, the Paris Law [2, 3] approach has been implemented in the ANSYS FEM code together with an enhanced Virtual Crack Closure Technique (VCCT) based method.

In recent years, the advancement of new manufacturing technologies has greatly influenced engineering applications. Among these, the additive manufacturing technology has been progressively applied to aircraft structures design and production, as it allows the effective optimization of the strength and the outstanding reduction of the weight in structural components. The research activity presented in this paper is focused on the static and dynamic numerical verification of the horizontal tail of an UAV, entirely Designed for Additive Manufacturing (DfAM) with Technopolymers. A proper selection of a variable internal infill has been introduced to reduce the overall weight of the structural component, while static and dynamic numerical analyses, simulating low-speed impacts, have been adopted to evaluate the structural strength and the ability of the proposed configuration to withstand damage onset and evolution due to in-service loads and impact events. The obtained numerical results indicate that the structural components Designed for Additive Manufacturing can be considered effective in terms of weight reduction and they are characterised by stresses significantly below the failure limits of the proposed techno Polymer. They also demonstrate good resistance of the proposed structural components to low-speed impacts without compromising the overall structural performance of components selves. This study provides solid bases for increasing the use of Additive Manufacturing technologies in the aviation industry.

Carbon Fiber Reinforced Polymer (CFRP) composites are well established in aircraft, aerospace and automotive industry due to their lightweight structure and robustness. Generally, in uni-directional (UD) composite laminates the mechanical properties depend of fiber orientation, the number and the thickness of the plies and the stacking sequence [1], Fig. 1. In continuous fiber laminates the prediction of failure is dependent on the fiber orientation and the failure criteria that are adopted.

The use of composite and sandwich materials in civil engineering applications can be an efficient and sustainable alternative to the traditional materials. The design of a composite sandwich panel for applications in roofing systems such as the canopies on the platforms of train stations, made up of glass fiber reinforced polymer (GFRP) skins and a PET foam core, is herein presented, as a case study. The main advantages compared to traditional steel/concrete systems are: a high strength-to-weight ratio, durability, lightness, limited interference on railway traffic thanks to reduced installation times, factory production which reduces dangerous activities carried out on construction sites and the sustainability provided by the possibility of using recycled materials.The design approach, developed on the recommendations provided by UNI CEN/TS 19101, an extensive experimental activity carried out on specimens and full-scale elements to characterize the mechanical and physical properties and the durability of the materials, and numerical models having different level of details developed to assess internal stressed and deformations, are critically presented and discussed. From the results, it emerges that the geometrical characteristics, i.e. the thickness of the panel, are mainly defined by the fulfilment of the limitations imposed to deformation in operational conditions, while the selection of the materials and, therefore, their mechanical and physical properties, are mainly determined by durability and fire reaction requirements.

The structures presented in this paper demonstrate that large (8′ × 2′ × 1′), lightweight, and strong structures are indeed manufacturable through industrial large scale polymer additive manufacturing. The production experiments done to manufacture these structures resulted in process defects that were identified and documented. Processing failures during manufacturing prompted the modification of several process control parameters (layer height, material choice, bed temperature) and post-processing techniques (annealing). This yielded five specimens, each with a unique treatment modification combination.This paper describes an experimental setup for analyzing the effect of these various processing treatments on large-scale additively manufactured thermoplastic structures. Specifically, it presents and compares the uniaxial compression performance results of ABS chopped fiber composite structures made with different processing treatments.Force-displacement experiments were conducted to determine and compare the effects of such processing modifications on the uniaxial compression performance of the different specimens. The data are also analyzed for transient behavior related to plastic deformation and creep. These data indicate that the large additively manufactured polymer composite structural specimens are stiff and strong in bulk. However, the authors do not draw significant conclusions about the effects of the individual processing treatments themselves. The experimental setup and process of identifying and characterizing significant performance effects of manufacturing modifications are generally useful and applicable to other large scale additively manufactured structural products.

The prefabricated pile footing structures presented in this paper demonstrate that large (3’ × 2’ × 1’), mostly hollow structures are indeed manufacturable through industrial large scale polymer additive manufacturing (ILSPAM). Additionally, this work identifies manufacturing process defects which resulted from the production of such structures. Processing failures during manufacturing prompted the modification of process control parameters (layer height, material choice). This yielded four specimens, each with a unique treatment modification combination.This paper utilizes an experimental setup [1] for analyzing the effect of various processing treatments on large-scale additively manufactured thermoplastic structures. Specifically, it presents and compares the uniaxial compression results of layer height and material treatments on pile footings made with virgin and recycled glass fiber reinforced PETg (PETg-GF) using cyclic loading experiments.Force-displacement experiments were conducted to determine and compare the effects of such modifications on the uniaxial compression performance of the different specimens. The authors note that the data supports the hypothesis that increasing layer height will decrease the stiffness of additively manufactured structures. Furthermore, the cyclic uniaxial compression experiments conducted on the pile footings validate the applicability of the related experimental setup for multiple large-scale additively manufactured structural products. Finally, the authors recommend further experiments and analysis to determine the effect of material choice, as well as experiments with smaller specimens to address the limitations of measuring large-scale structures.

The study analyzes the development of analytical models for the reinforcement of structures using nanomaterials. Initially, it introduces the “Surface stress” phenomenon within the context of composite materials. In fact, nanocomposites show distinct characteristics compared to traditional composites due to the high surface-to-volume ratio at the nanoscale, which significantly influences the mechanical properties. Secondly, the research explores the Eshelby Tensor for a homogeneous solid with inclusions. Thirdly, various homogenization methods are compared, such as the Mori-Tanaka method, the self-consistent method with Eshelby Tensor and the refined Mori-Tanaka method for determining the effective stiffness tensor of nanocomposites. Fourthly, the introduction of “interface stress” between matrix and nanomaterials is analyzed. All the models are compared based on values of experimental results; moreover, a comparison with traditional composite techniques is performed. Overall, this work provides a detailed analytical framework for understanding and predicting the behavior of nanocomposites, integrating advanced mathematical models to account for the unique effects observed at the nanoscale.

This work aims to explore efficient and accurate structural design methods for orthotropic plates. The design challenges are addressed by introducing a novel Continuum Sensitivity Analysis (CSA) technique capable of managing multiple design variables and constraints. CSA has demonstrated superior accuracy and efficiency compared to traditional numerical sensitivity analysis methods, particularly in shaping high-performance air vehicles, even with numerous design variables. This study extends CSA to orthotropic plates for the first time and establishes an efficient simulation framework for high-fidelity structural shape optimization. The CSA approach facilitates the calculation of shape derivatives with respect to multiple design variables at a minimal computational time. Furthermore, this method is non-intrusive and compatible with black-box programs like NASTRAN, providing more accurate high-fidelity sensitivities than those currently available from the software.

Structural batteries (SBs) are multipurpose devices that can store energy while also supporting structural loads. The focus was on anticipating internal short circuits and their consequences caused by mechanical abuse while doing Multiphysics Simulations with the commercial solver LS-DYNA. The available numerical strategies are detailed, as are the results of experimental experiments.A typical abuse load scenario (executed using a hemi-spherical dart) on structural batteries is simulated, both with and without their incorporation in a composite laminate. The acquired findings are contrasted and analyzed, emphasizing the use of Multiphysics-based design tools in the creation of safer multifunctional structures.

Lightweight structures with a high stiffness-to-weight ratio are crucial for reducing aerospace weight. Lattice infilled structures have proven superior to conventional ones, offering better stiffness, strength, and lower weight. Additive manufacturing (AM) enables the production of these complex lattice structures, overcoming traditional manufacturing challenges. Composite materials, known for their exceptional properties, especially in different environmental and flight conditions, are increasingly replacing metallic parts. Combining metallic lattice structures with composite skins offers an optimal solution for aircraft wing design, improving performance and reducing weight. This study assesses the feasibility of metallic and hybrid (metal-composite) lattice infilled wing for a drone compared to traditional spar-rib design using finite element analysis. A comprehensive design framework for AM was developed using nTop tool. Iterative simulations were conducted to find the optimal type and size of lattice unit cells under level flight loading conditions. The process involved Python coding for iterative simulations, resulting in significant weight reduction, lower stress, and reduced wing tip deflection for lattice structures. A comparative study also examined the replacement of metallic skins with composite skins for further weight reduction and enhanced performance. The findings highlight the potential of innovative lightweight hybrid wing designs for aerospace applications.

The aviation industry is increasingly turning to composite materials for manufacturing high-performance components, necessitating efficient methods to optimize the design of composite laminates. Initially used to replace metals, composites are now being further optimized to enhance performance and reduce weight. This involves adjusting the number and orientation of plies, with approaches such as Double-Double (DD) laminates proving effective for improving strength and reducing weight, regardless of symmetry or orientation. Crashworthiness evaluation remains crucial for assessing the performance of composite aircraft structures, particularly in optimized components such as fuselages. In this work, the crashworthiness performance of a composite fuselage barrel section has been investigated when a new design based on the Double-Double laminates is considered for the skin. Accordingly, a detailed numerical model of the fuselage barrel section structure have been developed in the finite element software Ls-Dyna to simulate a drop test phenomenon. An Anthropomorphic Tesh Device has been placed on the seat to analyze loads experienced during the impact when the skin design changes. A comparison of the lumbar load recorded by the dummy in both configurations has been performed with the aim to prove the effectiveness of the proposed Double-Double design for the skin for ensuring aircraft passengers safety.

In the present paper, the design and the evaluation of the environmental and economic impacts of a CFRP tubular structural component, employed for supporting passenger seats of commercial aircraft, realized with the innovative FW process, were performed. At first, a simulation of the winding process was conducted to realize the component layers, and then a FEM analysis was performed to identify the optimal layering of the tubular structure to support the defined loads. Then, Life Cycle Assessment and Life Cycle Costing methodologies were employed to assess the environmental and economic impacts, with a “from cradle to grave” approach: all life cycle phases of the analysed component were included (from raw materials extraction to the disposal phase). A comparison between the CFRP tubular structure and traditional aluminium alternative was investigated to identify the most sustainable solution. From the analysis emerged that the CFRP tubular beam resulted in lower environmental impacts than the traditional alternative, mainly due to the reduced weight. However, the cost evaluation identified the CFRP beam alternative as the most expensive solution.

The tiltrotor wing structure is one of the most critical and thoroughly investigated components in aircraft design due to the interactions between the wing, pylon, and rotor systems, which are crucial for ensuring aeroelastic stability. In this context, composite materials are essential for meeting structural requirements while also minimizing weight. The reference aircraft for this study is the Next-Generation Civil Tiltrotor Technological Demonstrator (NGCTR-TD), developed by Leonardo Helicopters within the Clean Sky 2 research program. An innovative wing box configuration featuring three spars, including one curved spar, was designed and manufactured. Given the uniqueness of this tailored solution, it is crucial to ensure that the manufactured assembly meets the design requirements. In the field of structural dynamics, experimental modal analysis is essential for determining experimental modal parameters to satisfy these requirements. Several experimental tests on lab-scale demonstrators and incomplete full-scale mockups were conducted to validate the test setup and approach. Finally, preliminary vibration testing activities have been performed on the full-scale test article, thus validating the test setup in view of the final test.

The current work is focused on Bullet Impact Threat, that consists of the prediction the energetic response inside a pyro component when hit by a 12,7 AP bullet, in accordance with the test procedures described in design standardization documents. Reaction of a munition to the bullet impact stimulus occurs because there is either direct shock initiation or ignition of damaged energetic material as the bullet passes through or lodges in the material. The starting point of the work was the collection of the various NATO publications to understand which tests are carried out, how and the various definitions. Then moved on to a study through literature research of the way in which to describe the reaction grade of the Energetic Material subject to the shock initiation, so a specific equation of state called “Ignition and growth of reaction in HE”. The analysis has been carried out exploiting the capabilities of the commercial hydrocode LS-DYNA, widely used in Aerospace and Defense fields. Different scenarios have been evaluated let varying the velocity of the bullet, all in accordance with the test requirements prescribed by NATO publications. To compare the results and then define the reaction grade can be used a customized analytical tool called Split-X, an expert system for the design and assessment of fragmenting warheads.

Structural components of aircraft, civil and marine structures are prone to deterioration and require complex and costly maintenance activities. In recent years, much effort has been put into shifting from a preventive maintenance model, based on statistically scheduled interventions, to a predictive one, based on monitoring the actual health of the structure. The development of DIMOSS® (DIsplacement MOnitoring using Strain Sensors) software fits this context. DIMOSS® is a structural monitoring software for reconstructing fundamental quantities to assess the health of a structure, displacements and stresses. The software relies on strain sensors and it is based on the inverse Finite Element Method (iFEM). The software integrates iFEM and all the tools needed to design and operate a monitoring system. This paper introduces the theoretical background and the design approach of DIMOSS®. Moreover, it presents two successful experimental applications of the software: the monitoring of a stiffened composite wing-shaped panel and the live monitoring of an aluminium beam through the realisation of a structural digital twin.

Structural Batteries (SB) are considered a promising new technology for the next generation of hybrid electric airliners made of composite materials. The introduction of this type of embedded batteries into the aircraft industry presents new challenges involving the current manufacturing processes applied to composite aircraft components, certification issues, design methods, integration matters and accessibility considerations, up to issues related to the connection to on-board electrical systems.This work provides an assessment of the feasibility of the structural batteries at aircraft level for different categories of aircraft. It has been carried out as part of the SOLIFLY project, funded by the Clean Sky 2 Joint Undertaking (JU) under grant agreement No. 101007577. This project has identified the pros and cons, technology gaps and recommendations for the integration of this type of batteries in commercial aircraft for short-, medium- (2035) and long-term (2050) applications. The current and predicted performance parameters of the SB concepts, developed in the SOLIFLY project, have been used in this work to analyze the effectiveness of their applicability on some existing configurations of different commercial aircraft. The results of this study show that SB concepts certainly represent an innovative technology for the aviation decarbonization and they appear very promising for weight savings.

The article begins by presenting the hybrid version of Dardo Aircraft by CFM Air, a full composite material aircraft, whose hybrid version has been designed to meet the following requirements: 1) Takeoff with only one of the two engines (electric or piston) 2) One hour of hybrid cruise with at least 10% of mechanical power supplied by the electric motor 3) Maximize the range 4) Limited modifications to the propulsion system and structure 5) Wing-mounted batteries.In the second part of the work, the effectiveness of introducing surface protection methods based on nanotechnologies is evaluated. Three application areas have been identified. It investigates the anticorrosive and potential increase in fatigue life of metal joints like Al-2024-T3 aluminum alloy, the enhanced cleaning for composite and plexiglass parts, and the possible thermal protection effect for application on plexiglass and composite parts.

An extensive implementation of electric and hybrid-electric propulsion is one of the ambitions of the European Commission to achieve a sustainable aviation. Current mature developments of electric aircraft are using architectures with battery packs, with the Pipistrel Velis Electro being the first electric aircraft, and still the only one in the world, to receive full type-certification. In addition, aircraft structures are inspected in scheduled maintenance on ground, while early detection of overstress of the structure during flight can reduce the sizing factors for damage tolerance and ease inspections. Addressing the previous topics, multifunctional structural batteries satisfy three functions simultaneously: energy storage, monitoring electrical and structural performance, and loads bearing. This technology can reduce weight penalty compared to conventional batteries and improve the health monitoring of the structure. MATISSE project implements this technology in an aeronautic component, i.e. a composite wingtip of a light aircraft, reaching a technology readiness level (TRL) 4 in 2025 by performing full-scale ground structural and functional tests. This paper will overview how smart structural batteries can contribute to reducing emissions and make electric and hybrid-electric aircraft more efficient.

Modifications of material surface properties due to interactions with ambient atomic oxygen have been observed on space structures surfaces facing the orbital direction in Low Earth Orbits (LEO). Some effects are very damaging to surface optical properties because LEO atomic oxygen possesses sufficient energy to break most organic polymer bonds and sufficient flux to cause oxidative erosion of polymers. At a certain energy level, atomic oxygen triggers chemical and physical reactions with materials, leading to surface degradation. The extent of degradation depends on factors such as spacecraft altitude, orientation, orbital inclination, mission duration, and solar activity variations. Atomic oxygen can also oxidize silicones and silicone contamination, resulting in non-volatile silica deposits. Such contaminants are commonly found on LEO missions and can pose a threat to the performance of optical surfaces. This work concerns the definition of a numerical model to study the erosion depth on the typically employed spacecraft material with fixed orbit parameters and mission duration. The Finnie model was chosen, and a limited number of parameters were considered to better understand and test the dynamics of the phenomenon. The results show the erosion depth of exposed materials over a 1-year simulation to highlight its magnitude and the potential impact on mission failure.

The development of multi-stage launch vehicle is the most affordable response to increase the competition and efficiency of complex systems for space access. Nevertheless, each subcomponent has to be designed to exploit any possible weight reduction without compromising the structural performance. In this framework CIRA worked on a new composite structural architecture for space applications, like the inter-stages for space launch systems, named ANISO-GRID structure [1–5]. Thanks to this technology, it is possible to realize the entire main structure in a unique part and, successively partition it into more than one sub-part in order to match the assembly requirements [6]. Generally, each sub structure is connected to the adjacent structural component by means of metallic massive interconnection flanges. The present work aims to design novel interconnecting flanges based on exploiting the benefit of additive manufacturing technologies.

In the current global scenario, sustainability is a crucial issue influencing decision across various sectors. Sustainable manufacturing is essential for long-term benefits, with composite materials playing a key role. Green composites, made with natural fibers, represent a significant advancement in sustainability due to their biodegradability and low specific weight. However, there are several open points concerning the variability in fiber properties and sensitivity to moisture. These challenges currently limit their applicability mostly to non-structural applications. Few studies address these issues, and this experimental study aims to fill this knowledge gap by investigating the mechanical properties of an interply flax-basalt woven fabric reinforced with epoxy resin SR GreenPoxy 56, through static and dynamic tests The laminate was characterized through tensile, flexural, and low-velocity impact tests, including Charpy and drop tower tests.

FRPs composites are currently used for several civil, marine and industrial applications due to their interesting specific properties, such as low weight, high stiffness resistance to weight ratio and high chemical resistance. In general, their mechanical performance, especially for conventional composites based on synthetic fibers (i.e. glass or carbon) under common environmental conditions are known to the scientists and engineers. However, there is a lack of knowledge on the mechanical properties and durability of novel composites, based on mineral or natural fibers, exposed to harsh environmental conditions. Among innovative FRPs, basalt-based composites are attracting the attention of researchers as potential substitutes for glass fibers composites, that overcome the corrosion problems of metals and are currently adopted for many marine applications where the water intake can lead to swelling and plasticization of the polymer matrix, fiber/matrix interface deterioration and debonding. In this work, epoxy/basalt twill woven fabric composites have been manufactured by vacuum infusion process and experimentally characterized to investigate the effect of fresh and saline water on their mechanical performance. In particular, to reduce the water absorption, after infusion and curing, the external lower and upper surfaces of composite laminates were covered with polylactic acid (PLA) layers, while an acrylic coating was applied along the cut edges of the samples. Then, both uncoated and coated composites were immersed for 30, 60, and 120 days in freshwater and a proper salt solution at environmental temperature. Five samples of each batch were regularly weighed and used to perform flexural tests.

Fiber-reinforced composite materials are usually adopted for transportation applications, where the impact behavior is crucial for vehicle safety and protection. Therefore, since composites are characterized by low toughness and consequent poor damage resistance, several authors have investigated different approaches to improve the impact resistance, such for example the addition of rubber particles to the polymer matrix or the reinforcement hybridization to obtain a new material by exploiting the benefits of all its constituents. Hybridization gives the possibility to realize composites with more balanced and tailored properties by lowering the costs too. In this work, the low-velocity impact behavior of hybrid composites has been numerically and experimentally investigated. In particular, epoxy-based laminates based on only 16 basalt twill, only 16 flax twill, and 16 flax/basalt layers, alternatively stacked have been realized by the vacuum infusion process. Basalt and flax fibers can be both considered green fibers, having the first ones a mineral origin and the second one a natural source. Thus, their adoption combines the impact resistance of basalt fibers and the actual environmental sustainability issues. The experimental results showed the advantage of fiber hybridization and evidenced better impact performances for the hybrid composites than those of pure basalt and pure flax laminates. In addition to the experimental tests, to implement and optimize a predictive tool for the impact resistance behavior of composite laminates, Finite Element (FE) models were developed by using the LS-DYNA solver. The model consisted of 16 shell layers connected by cohesive elements to better reproduce the delamination phenomenon. The boundary conditions applied were the same as for the physical tests. It is known that, in the definition of numerical models, some parameters cannot be experimentally determined or are not available from the tests; therefore, a trial-and-error approach was properly used to select them. The numerical results showed a good reproduction of the experimental trend and can therefore be considered as a valid and capable tool for the impact behavior simulation of other hybrid solutions or different stacking sequences.

This work is a preliminary study investigating the issues related to the preparation and characterisation of green composites with a biodegradable matrix (PLA) and a natural filler typical of the Mediterranean area, sourced from alien/invasive plants (Chamaerops humilis). Additive manufacturing has been chosen as the primary technique to produce these bio-composites, leveraging its ability to produce complex geometries with precision. The choice of Chamaerops humilis is motivated by the fact that these plants are non-edible and abundant in the Mediterranean area, aligning with the new design guidelines inspired by the circular economy and “zero waste” principles. This paves the way for the creation of a new generation of green and sustainable materials. Using this plant as a filler for green composites is expected to enable the biodegradation of the composites in marine environments while providing remarkable mechanical properties. Starting from the selected materials, filaments will be manufactured for 3D printing components made of polymeric material with different filler percentages (10% wt and 20% wt). Mechanical and chemical-physical analyses will be conducted to evaluate the process parameters and assess their printability. The effect of fillers and their different percentages on the mechanical performance of the filaments will also be evaluated.

The study investigates the mechanical response and damage tolerance of 3D-printed cornstalk-inspired structures (porous, lightweight) manufactured using Acrylonitrile Butadiene Styrene (ABS) material. Specimens were subjected to localised impact (dynamic indentation tests) with a conical-shaped indenter at 90 J impact energy. The base polymeric material (ABS) was characterized across varying strain rates using Shimadzu® Universal Testing Machine and Split Hopkinson Pressure Bar. A homogeneous (uniform density) specimen was prepared to compare the damage resistance of cornstalk-like geometry using a drop-weight impact test. The results demonstrated that the homogeneous specimen weighed ~39% more than the bio-inspired specimen and exhibited ~28% lower energy-absorbing capability. Damage characteristics of the damaged specimens were interrogated through X-ray CT scans and provided detailed failure modes associated with conical indenter. Further, finite element simulations (using LS-DYNA) were undertaken to compare the experimental results and validate the identified mechanical properties of ABS polymer. These lightweight structures have the potential to be used in the sports industry, i.e., protection helmets.

Thick sandwich beam structures are commonly used in various engineering applications due to their lightweight and high-stiffness properties. However, their distinct material compositions often result in pronounced transverse shear deformations and in the case of thicker beams, additional transverse normal deformations. The recently developed mixed-higher-order en-RZT for plates is here applied to numerically evaluate the dynamic properties of symmetric thick sandwich beams. In this experimental-numerical study, a series of sandwich beam specimens of different thicknesses, made of ERGAL face-sheets and Rohacell® WF110 core, are dynamically investigated using a Laser Doppler Vibrometry (LDV). The experimental modal parameters (natural frequencies and modal shapes) obtained from LDV measurements are compared with the theoretical predictions for the flexural modes based on a finite element beam model developed on the mixed-Refined Zigzag Theory ( $${\text{B - RZT}}_{{\{ 3,2\} }}^{(m)}$$ B - RZT { 3 , 2 } ( m ) ).

The use of full-metal sandwich structures in transportation industry represents a promising way to address key challenges such as weight reduction, improved fuel efficiency, reduced emissions, and use of more sustainable materials. This research evaluates the possibility of replacing common marine sandwich structures with aluminium honeycomb sandwich structures (AHS) with equal flexural stiffness. As aluminium is a versatile, environmentally friendly and recyclable material, AHS structures are one of the most promising solutions. Quasi-static perforation (QS) and low-velocity impact (LVI) tests carried out with a conical indenter and allowed the crashworthiness assessment of the analysed materials. The crashworthiness of the structures was evaluated by calculating the total energy absorption (TEA) and specific energy absorption (SEA). Comparisons were performed between the energy absorption capacity of AHS and conventional sandwich structures (GFRP-PVC and GFRP-balsa). The results of the research activity show that aluminium sandwich structures are valid alternatives, in terms of energy absorption properties, to the composite structures currently used in the transport industry.