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The innovative approach used for the design and fabrication of a UAV tails through additive manufacturing (AM) completely changes the concept of designing and manufacturing products through conventional methods. AM based processes can reduces costs, lead times, and increases design freedom, allowing parts to be tailored to specific needs. A key benefit of AM processes is the ability to produce optimized designs with reduced mass and without compromising structural effectiveness. This is possible thanks to the combination of high‐performance AM materials and the extraordinary manufacturing capability of AM technologies combined with an appropriate design‐for‐additive manufacturing (DfAM) approach, overcoming traditional manufacturing techniques. This article presents the development process of a UAV tails, based on a Design for Additive Manufacturing (DfAM) approach in order to reduce structural mass and guarantee safe operation under service loads. Therefore, by replacing the metallic component of the UAV with a techno‐polymeric one, several configurations have been developed. The optimal additive configuration achieved a weight reduction of 60% compared to a metal configuration of equivalent volume, without loss of mechanical properties. In conclusion, a feasibility study of the proposed configuration was carried out by 3D printing the vertical tail redesigned. Highlights: An innovative approach by combining DfAM processes with FFF technology.Metal replacement of UAV tails with advanced technopolymers.Efficient Weight Reduction about 60% compared to metal structure.Single‐piece design simplifies assembly and manufacturing.UAV redesigned tails with enhanced efficiency, adaptability, and feasibility. [ABSTRACT FROM AUTHOR]

The passive safety in aircraft concerns all measures able to protect the passengers and crew in the event of an accident or emergency. In this context, an important role is played by the design adopted for components inside the passengers' cabin, such as the seats and the interior lining. An effective approach in design of passive safety system is provided by anthropomorphic test devices. In this work, a new design of the interior lining of the fuselage wall has been introduced and its crashworthiness features have been studied through a side impact of an unbelted window‐side passenger. The new proposed interior lining is made with a hybrid sandwich‐based design with a polypropylene honeycomb core able to ensure passive safety for passengers and thermal and acoustic insulation. [ABSTRACT FROM AUTHOR]

The use of additive manufacturing techniques in the development of aerospace components is gaining ground. These innovative methodologies facilitate the proposal of new designs for components with weight reduced features without compromising their mechanical properties. This results in lower fuel consumption and emissions. The present paper focuses on a metal replacement process in a UAV's vertical tail, using a Design for Additive Manufacturing (DfAM) strategy and making use of the lightweight, high‐strength engineering polymer known as carbon PA. By comparing the results achieved through numerical simulations conforming to certification standards between the metal and carbon PA vertical tail model, this work points out the possibility of decreasing the structural mass of the component by up to 48% while maintaining structural integrity. This reduction is achieved by matching materials, design concepts, and manufacturing capabilities. [ABSTRACT FROM AUTHOR]

Numerically predicting the mechanical behavior of additively manufactured sandwich structures, particularly those produced through filament extrusion, poses a significant challenge. Existing collapse mechanisms, including interlayer debonding, lack comprehensive numerical formulation. This paper presents an improved finite element (FE) modeling approach for filament‐based additive processes. Utilizing the cohesive zone model (CZM), it incorporates a cohesive‐type contact to simulate critical layer interactions, such as the core‐face sheet interface. Validation against a literature‐referenced composite sandwich structure with designed for additive manufacturing honeycomb core demonstrates good agreement between the proposed numerical approach and experimental test data in compression and bending. [ABSTRACT FROM AUTHOR]

Supersonic aircraft is defined as aircraft that can travel at speeds above the speed of sound (M > 1). For these aircraft, correct dimensioning is essential to enable them to withstand the high aerodynamic loads they face. This study evaluates the impact of internal architecture, boundary conditions, and material on the dimensioning of the vertical tailplane when subjected to a gust load. The optimal configuration is the one that achieves a balance between weight and structural performance. Titanium alloy Ti 6AI‐4 V and carbon/carbon composites are selected as the most suitable materials for this application due to their known high‐temperature resistance. The best configuration, although it weighs 20% times more than the composite configuration, manages to achieve a reduction in tip displacement of 80%, significantly improving strength and instability performance. [ABSTRACT FROM AUTHOR]

Lightweight structures with a high stiffness-to-weight ratio always play a significant role in weight reduction in the aerospace sector. The exploration of non-conventional structures for aerospace applications has been a point of interest over the past few decades. The adaptation of lattice structure and additive manufacturing in the design can lead to improvement in mechanical properties and significant weight reduction. The practicality of the non-conventional wing structure with lattices infilled as a replacement for the conventional spar–ribs wing is determined through finite element analysis. The optimal lattice-infilled wing structures are obtained via an automated iterative method using the commercial implicit modeling tool nTop and an ANSYS workbench. Among five different types of optimized lattice-infilled structures, the Kelvin lattice structure is considered the best choice for current applications, with comparatively minimal wing-tip deflection, weight, and stress. Furthermore, the stress distribution dependency on the lattice-unit cell type and arrangement is also established. Conclusively, the lattice-infilled structures have shown an alternative innovative design approach for lightweight wing structures. [ABSTRACT FROM AUTHOR]

Increasing the impact resistance properties of any transport vehicle is a real engineering challenge. This challenge is addressed in this paper by proposing a high-performing structural solution. Hence, the performance, in terms of improvement of the energy absorbing characteristics and the reduction of the peak accelerations, of highly efficient shock absorbers integrated in key locations of a minibus chassis have been assessed by means of numerical crash simulations. The high efficiency of the proposed damping system has been achieved by improving the current design and manufacturing process of the state-of-the-art shock absorbers. Indeed, the proposed passive safety system is composed of additive manufactured, hybrid polymer/composite (Polypropylene/Composite Fibres Reinforced Polymers—PP/CFRP) shock absorbers. The resulting hybrid component combines the high stiffness-to-mass and strength-to-mass ratios characteristic of the composites with the capability of the PP to dissipate energy by plastic deformation. Moreover, thanks to the Additive Manufacturing (AM) technique, low-mass and low-volume highly-efficient shock-absorbing sandwich structures can be designed and manufactured. The use of high-efficiency additively manufactured sandwich shock absorbers has been demonstrated as an effective way to improve the passive safety of passengers, achieving a reduction in the peak of the reaction force and energy absorbed in the safety cage of the chassis' structure, respectively, up to up to 30 kN and 25%. [ABSTRACT FROM AUTHOR]

A strong increase in the use of composite materials has been observed in all the industrial fields, related to manufacturing of lightweight load‐bearing components. However, despite the excellent mechanical properties that characterize such innovative materials, uncertainties still exist on their complex failure mechanisms. Hence, the use of non‐destructive techniques and experimental tests is needed to increase the understanding of composite materials damage evolution. This paper deals with the use of the Digital Image Correlation (DIC) technique to investigate the failure mechanisms of delaminated composite panels under compressive loading conditions, accounting for the complex phenomena related to unstable delamination growth due to buckling snap‐through. The panels have been produced by tuning manufacturing parameters to test their influence on toughening mechanisms such as fiber bridging. The main aim is to understand how to improve laminate out‐of‐plane performance and delay the delamination growth phenomenon. The obtained data in terms of strain and displacements distributions has been used to assess the phenomenon of delamination propagation related to local delamination and global panels' instabilities. [ABSTRACT FROM AUTHOR]

Vehicle frames can be considered the main stiffening component being, at the same time, functional hubs for all the other components assembly. Frames' main goal is to absorb the static and dynamic loads acting on the vehicle, ensuring passengers' safety. In this paper a feasibility study on an innovative modular frame concept is presented. An attempt has been made to design a modular frame by using customized additive manufacturable steel joints. Actually, standard frame structures are manufactured by welding separated tubes, making access to some internal areas of the vehicle very difficult where not impossible. Consequently, some maintenance operations become also challenging. The modular configuration solves these maintenance problems enabling, at the same time, to start thinking about multi‐purposes vehicle configurations, which can be switched by simply changing the modules connected to a central cell. Reinforced panels have been, also, integrated into the modular frame, which contribute to torsional stiffness with an overall mass reduction. The concept of a modular frame with collaborating reinforced panels, has been preliminary demonstrated by means of numerical simulations within the ABAQUS FEM environment. Certification torsional loads have been applied to the modular reinforced frame and the obtained numerical results contributed to prove the feasibility and the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

The use of nanomodified epoxy resins can potentially increase composites application to aeronautical structural components, thanks to the potential enhancement, in terms of physical and mechanical properties, when compared to the neat epoxy matrix. In this work, the effects of silica nanoparticles (NPs) on the fracture toughness and, consequently, the crack growth resistance of fiber‐reinforced polymers (FRPs) have been numerically investigated. The skin‐stringer debonding initiation and growth have been studied by a tailored innovative numerical procedure considering an aeronautical panel reinforced with a single T‐shape stringer, made of carbon fibers/epoxy resin material, and subjected to compressive load. An analytical model has been used to evaluate the Mode I fracture toughness value of the nanomodified resin, and the Virtual Crack Closure Technique methodology has been employed to assess the delamination growth in the frame of a Finite Elements (FE) analysis performed in the Ansys FE environment. Numerical results presenting the comparison between charged and neat configurations have been assessed to provide a first understanding of the influence of nanoparticles on the static delamination growth in geometrically complex composite structures. [ABSTRACT FROM AUTHOR]

Featured Application: Shock absorbing systems for aerospace applications developed through additive manufacturing. In this work, a preliminary numerical assessment on the application of an additive manufactured hybrid metal/composite shock absorber panels to a military seat ejection system, has been carried out. The innovative character of the shock absorber concept investigated is that the absorbing system has a thickness of only 6 mm and is composed of a pyramid-shaped lattice core that, due to its small size, can only be achieved by additive manufacturing. The mechanical behaviour of these shock absorber panels has been examined by measuring their ability to absorb and dissipate the energy generated during the ejection phase into plastic deformations, thus reducing the loads acting on pilots. In this paper the effectiveness of a system composed of five hybrid shock absorbers, with very thin thickness in order to be easily integrated between the seat and the aircraft floor, has been numerically studied by assessing their ability to absorb the energy generated during the primary ejection phase. To accomplish this, a numerical simulation of the explosion has been performed and the energy absorbed by the shock-absorbing mechanism has been assessed. The performed analysis demonstrated that the panels can absorb more than 60% of the energy generated during the explosion event while increasing the total mass of the pilot-seat system by just 0.8%. [ABSTRACT FROM AUTHOR]

Featured Application: Numerical investigation on the damage behavior of CFRP laminates subjected to low velocity impacts. Composite laminates are characterized by high mechanical in-plane properties and poor out-of-plane characteristics. This issue becomes even more relevant when dealing with impact phenomena occurring in the transverse direction. In aeronautics, Low Velocity Impacts (LVIs) may occur during the service life of the aircraft. LVI may produce damage inside the laminate, which are not easily detectable and can seriously degrade the mechanical properties of the structure. In this paper, a numerical-experimental investigation is carried out, in order to study the mechanical behavior of rectangular laminated specimens subjected to low velocity impacts. The numerical model that best represents the impact phenomenon has been chosen by numerical–analytical investigations. A user defined material model (VUMAT) has been developed in Abaqus/Explicit environment to simulate the composite intra-laminar damage behavior in solid elements. The analyses results were compared to experimental test data on a laminated specimen, performed according to ASTM D7136 standard, in order to verify the robustness of the adopted numerical model and the influence of modeling parameters on the accuracy of numerical results. [ABSTRACT FROM AUTHOR]

• The combination of innovations in manufacturing and materials makes the development of compact and high-performance shock absorbers possible. • The manuscript analyses an engineering product starting from the design up to the manufacturing and to the testing phases. • The manuscript analyses an engineering product manufactured by machines which are the state of the art of additive manufacturing techniques. • Mechanical responses of different sandwich shock absorbers was compared and a minimum-mass configuration that maximises energy absorption was identified. • A correlation between numerical and experimental data was performed. The capability to guarantee passenger safety is a core feature of any transportation system. For this reason, a considerable effort is being committed, by researchers, to the study of innovative shock-absorbing devices able to increase the safety performance. According to this topic of great interest, this paper presents a numerical/experimental study on a new effective shock absorber concept achievable by means of the Additive Manufacturing technology. Indeed, additive technologies exhibit some fundamental advantages, such as the possibility to produce complex microstructures, with superior impact energy absorption capabilities, which cannot be made with standard manufacturing processes. Hence, this manufacturing technique could be preferred for the development of high-efficiency shock absorbers cores. In the present work, to achieve shock absorbers high mechanical efficiency while limiting mass and volume, an innovative sandwich shock absorber concept is introduced, which uses additive manufactured solutions for the core by combining the advantages offered by thermoplastics (polypropylene), such as their ability to absorb energy through plasticisation and their recyclability, to those offered by fibre-reinforced thermoset composites (Carbon Fibre Reinforced Polymers), i.e. high stiffness/mass and strength/mass factors. First, numerical low-velocity impact analyses have been carried out to compare the mechanical response of several shock absorber configurations, Designed for Additive Manufacturing (DfAM), characterised by a polypropylene (PP) honeycomb core and CFRP composite external skins. These PP-CFRP sandwich configurations have been compared to full polypropylene configurations (with polypropylene skins and core PP-PP). Comparisons have shown that the PP-CFRP configurations are characterised by better overall crashworthiness performances (energy absorption and peak-force smoothing). Finally, an experimental activity, including ASTM D7136 based impact tests, have been carried out on the best performing investigated PP-CFRP configuration, to preliminary validate the numerical results. [ABSTRACT FROM AUTHOR]

Increasing transportation safety can be observed as one of the biggest engineering challenges. This challenge often needs to be combined with the need to deliver engineering solutions that are able to lower the environmental impact of transportation, by reducing fuel consumption. Consequentially, these topics have attracted considerable research efforts. The present work aims to address the previously cited challenges by maximizing the energy absorption capabilities of hybrid aluminum/composite shock absorbers with minimal thickness and mass. This engineering solution makes it possible to lighten vehicles and reduce fuel consumption, without compromising safety, in terms of crashworthiness capabilities. A numerical sensitivity study is presented, where the absorbed energy/mass (AE/m) and the absorbed energy/total panel thickness (AE/Htot) ratios, as a consequence of low-velocity impact simulations performed on six different shock absorbers, are compared. These hybrid shock absorbers have been numerically designed by modifying the core thickness of two basic absorbers' configurations, characterized, respectively, by a metallic lattice core, intended to be produced through additive manufacturing, and a standard metallic honeycomb core. This work provides interesting information for the development of shock absorbers, which should be further developed with an experimental approach. Indeed, it demonstrates that, by integrating composite skins with a very light core producible, by means of additive manufacturing capabilities, it is possible to design shock absorbers with excellent performance, even for very thin configurations with 6 mm thickness, and to provide a significant increase in AE/m ratios when compared to the respective equal volume standard honeycomb core configurations. This difference between the AE/m ratios of configurations with different core designs increases with the growth in volume. In detail, for configurations with a total thickness of 6 mm, the AE/m increases in additive manufacturing configurations by approximately 93%; for those with a total thickness of 10 mm, the increase is 175%, and, finally, for those with a total thickness of 14 mm, the increase is 220%. [ABSTRACT FROM AUTHOR]

This work evaluates the effectiveness of commonly adopted local damage evolution methods and failure criteria in finite element analysis for the simulation of intralaminar damage propagation in composites under static loading conditions. The proposed numerical model is based on a User Defined Material subroutine (USERMAT) implemented in Ansys. This model is used to predict the evolution of damage within each specific lamina of a composite laminate by introducing both sudden and gradual degradation rules. The main purpose of the simulations is to quantitatively assess the influence of the adopted failure criteria in conjunction with degradation laws on the accuracy of the numerical predictions in terms of damage evolution and failure load. The mechanical behavior of an open hole tension specimen and of a notched stiffened composite panel under shear loading conditions have been numerically simulated by Progressive Damage Models (PDM). Different failure criteria have been implemented in the developed Ansys USERMAT, together with sudden and gradual degradation rules based on the Continuum Damage Mechanics (CDM) approach. Numerical results have been validated against experimental data to assess the effects of the different failure criteria and damage evolution law on the global mechanical response and local damage predictions in composite laminates. [ABSTRACT FROM AUTHOR]

In this work, an analytical procedure for the preliminary design of shape memory alloy spring-based actuators is investigated. Two static analytical models are considered and interconnected in the frame of the proposed procedure. The first model, based on the works from An, is able to determine the material properties of the SMA components by means of experimental test data and is able to size the SMA component based on the requirements of the system. The second model, based on a work from Spaggiari, helps to design and size an antagonist spring system that allows one to obtain the geometric characteristics of springs (SMA and bias) and the mechanical characteristics of the entire actuator. The combined use of these models allows one to define and size a complex SMA actuator based on the actuation load requirements. To validate the design procedure, static experimental tests have been performed with the entire SMA actuator. [ABSTRACT FROM AUTHOR]

This work provides a feasibility and effectiveness analysis, through numerical investigation, of metal replacement of primary components with composite material for an executive aircraft wing. In particular, benefits and disadvantages of replacing metal, usually adopted to manufacture this structural component, with composite material are explored. To accomplish this task, a detailed FEM numerical model of the composite aircraft wing was deployed by taking into account process constraints related to Liquid Resin Infusion, which was selected as the preferred manufacturing technique to fabricate the wing. We obtained a geometric and material layup definition for the CFRP components of the wing, which demonstrated that the replacement of the metal elements with composite materials did not affect the structural performance and can guarantee a substantial advantage for the structure in terms of weight reduction when compared to the equivalent metallic configuration, even for existing executive wing configurations. [ABSTRACT FROM AUTHOR]

Composite materials, like metals, are subject to fatigue effects, representing one of the main causes for component collapse in carbon fiber-reinforced polymers. Indeed, when subject to low stress cyclic loading, carbon fiber-reinforced polymers exhibit gradual degradation of the mechanical properties. The numerical simulation of this phenomenon, which can strongly reduce time and costs to market, can be extremely expensive in terms of computational effort since a very high number of static analyses need to be run to take into account the real damage propagation due the fatigue effects. In this paper, a novel cycle jump strategy, named Smart Cycle strategy, is introduced in the numerical model to avoid the simulation of every single cycle and save computational resources. This cycle jump strategy can be seen as an enhancement of the empirical model proposed by Shokrieh and Lessard for the evaluation of the fatigue-induced strength and stiffness degradation. Indeed, the Smart Cycle allows quickly obtaining a preliminary assessment of the fatigue behavior of composite structures. It is based on the hypothesis that the stress redistribution, due to the fatigue-induced gradual degradation of the material properties, can be neglected until sudden fiber and/or matrix damage is verified at element/lamina level. The numerical procedure has been implemented in the commercial finite element code ANSYS MECHANICAL, by means of Ansys Parametric Design Languages (APDL). Briefly, the Smart Cycle routine is able to predict cycles where fatigue failure criteria are likely to be satisfied and to limit the numerical simulation to these cycles where a consistent damage propagation in terms of fiber and matrix breakage is expected. The proposed numerical strategy was preliminarily validated, in the frame of this research study, on 30° fiber-oriented unidirectional coupons subjected to tensile–tensile fatigue loading conditions. The numerical results were compared with literature experimental data in terms of number of cycles at failure for different percentage of the static strength. Lastly, in order to assess its potential in terms of computational time saving on more complex structures and different loading conditions, the proposed numerical approach was used to investigate the fatigue behavior of a cross-ply open-hole composite panel under tension–tension fatigue loading conditions. [ABSTRACT FROM AUTHOR]

This paper introduces a numerical tool developed for the design and optimization of axial-symmetrical hybrid composite/metal structures. It is assumed that the defined structures are produced by means of two different processes: Additive Layer Manufacturing (ALM) for the metallic parts and Filament Winding (FW) for the composite parts. The defined optimization procedure involves two specific software: ANSYS and ModeFrontier. The former is dedicated to the production of the geometrical and FE models, to the structural analysis, and to the post-process, focusing on the definition of the Unit Cells for the modelling of the metal part. The latter is dedicated to the definition of the best design set and thus to the optimization flow management. The core of the developed numerical procedure is the routine based on the Ansys Parametric Design Language (APDL), which allows an automatic generation of any geometrical model defined by a generic design set. The developed procedure is able to choose the best design, in terms of structural performance, changing the lattice metallic parameters (number of unit cells and their topology) and the composite parameters (number of plies and their orientation). The introduced numerical tool has been used to design several hybrid structures configurations. These configurations have been analysed in terms of mechanical behaviour under specific boundary conditions and compared to similar conventional metal structure. [ABSTRACT FROM AUTHOR]

In this paper, the skin–stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin–stringer separation can be influenced by the fibre bridging phenomenon at the skin–stringer interface, in this study, comparisons among three different material systems with different fibre bridging sensitivities have been carried out. Indeed, a reference material system has been compared, in terms of toughness performance, against two materials with different degrees of sensitivity to fibre bridging. A robust numerical procedure for the delamination assessment has been used to mimic the skin–stringer separation. When analysing the global compressive behaviour of the stiffened panel, intra-laminar damages have been considered in conjunction with skin–stringer debonding to evaluate the effect of the fibre and matrix breakage on the separation between the skin and the stringer for the three analysed material systems. The latter are characterised by different toughness characteristics and fibre bridging sensitivities, resulting in a different material toughness. [ABSTRACT FROM AUTHOR]

The presence of cut-outs within thin-walled shell structures is unavoidable, holes being needed for the passage of electrical cables, fuel, or just to reduce the weight of the components. Nevertheless, the high stress concentration can lead to a premature collapse of the structure. For this reason, the preliminary design of cylindrical shell structures with holes needs a profound knowledge of the stress distribution for different loading conditions and constraints. In this paper, a parametric study of a fiber-reinforced composite shell cylinder with an elliptical cut-out has been performed. Three different loading conditions were analyzed: Tension, bending, and torsion. Ansys® script, capable of easily generating and analyzing different geometrical configurations, was used to study the dependence of the geometry on the stress distribution near the cut-out. Finally, graphical and analytical relationships were tentatively extrapolated from numerical results, aimed at linking the geometrical parameters of the cut-out to the maximum stress near the cut-out. [ABSTRACT FROM AUTHOR]