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One of the ongoing challenges in aeronautics is the development of increasingly lighter structures. This has become a crucial goal because structural lightening means improving aircraft performance in terms of speed, manoeuvrability, fuel efficiency, and at the same time reducing manufacturing and service costs. The aerospace industry continues to focus more and more on this goal and every improvement in technology and materials can bring significant advantages in performance, efficiency, and safety of aircraft. The present work is part of this framework, as it analyses the feasibility of achieving very high weight reduction in sandwich panels using a new manufacturing approach. It introduces an experimental limited sensitivity analysis on the mechanical responses of composite sandwich structures for shock-absorption applications lightened by appropriately setting a specific additive manufacturing process parameter: the infill value. The investigated sandwich structures are characterised by a core Designed for Additive Manufacturing (DfAM) in order to maximise their performance in terms of energy-to-weight ratio and damping of impact loads. The material chosen for the inner part of the sandwich structure (core and internal face sheets) is polypropylene (PP) while the external face sheets are in Carbon Fibre Reinforced Polymers (CFRP). By comparing the post-impact responses at 20 J impact of three sandwich configurations with the same external shape but different material layer densities related to different setting of the infill parameter in the frame of the printing process, the work proves that this approach leads to lightening of this specific sandwich structures by up to 28% and at the same time improves their structural effectiveness in terms of energy absorption characteristics. The comparison was made by relating specific absorption indices, force-time and force-displacement graphs and CT scans.

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%.

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.

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%.

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.

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.

The continuous demand of lightweight structures characterized by high load-carrying capabilities has led to an increasing use of composite materials. However, despite the outstanding properties of this kind of materials, uncertainties still exist on their complex damage behavior. For such a reason, extensive investigation, from both an experimental and numerical perspective, is mandatory. This work aims to investigate the damage behavior of delaminated composite specimens subjected to compressive load. The strain and displacement fields are monitored by using Digital Image Correlation (DIC), in order to obtain information on the delamination propagation during the experiment. The acquired data can be used, supported by Finite element analyses, to help the understanding of such complex phenomenon.

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.

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.

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.

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.

Commonly adopted shock absorbers and, in general, crashworthy structural components, based on sandwich structural concepts and/or complex dumping mechanisms, are, generally, characterized by high volumes and significant additional mass. This research activity is focused on the investigation of the feasibility and effectiveness of novel thin additive manufactured hybrid metal/composite lattice structures as lightweight shock absorbing devices for application to structural key components in impact events. These hybrid structures would represent a real step beyond the state of the art of shock absorbers being characterized by an additive manufactured metal lattice core, able to maximize the absorbed energy by plastic deformations and, at the same time, by a composite skin/cohesive coating, fully integrated with the internal metal lattice structure, able to lower the global weight and increase the stiffness and strength of the shock absorber. First, an extensive explicit numerical activity has been performed finalised to the assessment of the mechanical behaviour of basic lattice Unit Cells configurations under impact conditions in shock-absorbing panels. The variation of the geometrical characteristics of the lattice cells have been taken into account by adopting a parametric Python routine in ABAQUS with a simplified FEM formulation based on beam and shell elements. Once identified the key features maximizing the energy absorption capabilities of the metallic core, several complex models with 3d solid element formulation have been developed. A final comparison between the hybrid configurations and the state of the art shock absorbing panels, demonstrated the effectiveness of the proposed lightweight hybrid configuration based on additive manufacturing techniques in terms of mass reduction, mechanical and energy absorption performances .

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%.

In this work, an experimental characterization of Shape Memory Alloy (SMA) springs was carried-out to assess the efficiency of simple analytical procedure for a preliminary design of Shape Memory Alloy-based spring actuators. Two static analytical models were considered recursively, respectively to determine SMA material properties by accurate tensile experimental test and to identify the optimized geometrical characteristic of SMA-bias spring-based unit for a specific feasible mini-actuator for vehicle moveable part. The final extra-force and displacement of the actuator was validated at different temperature above transformation temperature to assess the limitation of the implemented procedure.

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.

The aim of this work is to investigate the effects of thermal loads on the elastic instability of jointed composite components. Fibre-reinforced composite materials, which are of great interest for aerospace structures, are characterised by anisotropic thermal expansion coefficients. This characteristic influences the elastic stability behaviour when thermal stresses applied on the component. Actually, the presence of thermal coefficients varying with direction, can generate interlaminar shear stresses related to specific stacking sequences and in general shear stresses between bonded composite subcomponents and/or hybrid metal/composite subcomponents. A numerical study, performed within the ABAQUS FE code environment, is presented here with the aim to provide a preliminary investigation on the effects of the thermal load on the elastic behaviour of the jointed composite structures representative of a civil aircraft fuselage component. The influence in terms of buckling load and mode variation has been investigated by comparing the numerical results with experimental data from ad ad-hoc thermo-structural test campaign.

In recent years, metallic lattice structures produced by means of the Selective Laser Melting (SLM) process have attracted a growing interest in the scientific community for their valuable stiffness/weight ratio and, consequently, wide range of possible applications. Indeed, additive manufacturing techniques are inherently capable to produce structural configuration with any geometric complexity fulfilling any topological optimization requirement, if compared to the common subtractive production techniques. There are many application fields for lattice structures, such as recoverable lattices, plate lattices or hierarchical lattice structures for applications ranging from heat exchangers, medical implants or acoustic dampers. In many applications, metal lightweight lattice structures are joined with carbon fibers reinforced polymers in order to improve the overall mechanical performances and decrease the weight of structural components. The research activity presented here is focused on the investigation of the feasibility and the effectiveness of hybrid metal/composite lattice structures shock absorbers manufactured by additive techniques. Firstly, an extensive modelling and analysis activity has been carried out focused on the assessment of different configurations of Unit Cells within the commercial FEM code Abaqus, by adopting a simplified Fem model with beam and shell elements formulation The Unit Cells, has been designed as a solid base model, represented by a metallic lattice Repetitive Volume Element and composite skins. Different configurations of metallic lattice structures with and without composite skins have been investigated in order to evaluate their energy absorbing capability under a 6J impact analysis. Once selected the best configuration in terms of energy absorption capability, a refined numerical model with 3D elements formulation and by discretising the composite at ply level has been defined. The mechanical behaviour under impact and the energy absorbing capability have been assessed in order to evaluate the applicability of this hybrid composite panels as multipurpose shock absorber.

In this paper, the damage mechanisms of reinforced composite panels subjected to symmetrical and asymmetrical flexural loading conditions have been investigated. The composite components are representative of a regional aircraft fuselage. Three-point bending tests numerical simulations have been used to assess the influence of the different test parameters on the damage behavior of the investigated component. Then, the most representative configuration has been selected for the experimental bending test. the outputs from the numerical simulations, in terms of stiffness and damage onset and propagation, has been employed, in combination with the experimental data, to accurately describe the damage mechanisms associated to the asymmetric application of the load.

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&ndash, 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.

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.

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&reg, 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.

This paper investigates the damage behavior of a reinforced composite panel under symmetrical and asymmetrical bending load. The examined reinforced composite structure is a curved CFRP panel and a co–cured CFRP omega stringer. It may be considered a typical stiffened skin section of a regional aircraft fuselage. The bending loading conditions have been simulated by means of three–point bending tests. The aim of the work is a numerical study, performed to study the influence of asymmetric bending loads on intra–laminar and inter–laminar damage, taking into account the different configurations of the panels and the different orientations of the rollers.

In this paper, the skin&ndash, stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin&ndash, stringer separation can be influenced by the fibre bridging phenomenon at the skin&ndash, 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&ndash, stringer separation. When analysing the global compressive behaviour of the stiffened panel, intra-laminar damages have been considered in conjunction with skin&ndash, 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.

The present work is focused on the study of the damage behaviour of a composite reinforced panel under quasi-static bending loading conditions. The investigated reinforced composite structure, consisting of a curved CFRP panel reinforced and a co-cured CFRP omega stringer, can be considered representative of a regional aircraft fuselage stiffened skin section. The bending loading conditions have been simulated by means of both 3-point and 4-point bending tests. A first numerical sensitivity study has been performed, in order to investigate the influence of boundary conditions (spacing span and size of the rollers, number of loading points, etc) on the flexural driven inter-laminar damage. Then, the damage behaviour of a representative selected test article has been deeply investigated by detailed numerical models able to take into account both the inter-laminar and intra-laminar damages onset and evolution. A first validation has been attempt by comparing the obtained numerical results for this selected specimen, in terms of stiffness and debonding area, with data taken from experimental tests and non-destructive inspections (NDI). Finally, the influence of the FE formulation on the accuracy of the numerical model and on the related computational costs has been assessed by comparing the results obtained with shell layered elements or ply by ply 3D elements formulations in order to attempt the definition of an effective modelling strategy for the investigated composite structural element.

The use of carbon fibers-reinforced plastic materials has progressively increased due to growing requirements of reduction in weight and high resistance. However, for this kind of materials, barely visible damages can become very critical for the carrying load capability during life cycle of primary components. This applies, especially for laminates subjected to impulsive loads such as low velocity impacts. In order to check the damage resistance and tolerance of composite panels subjected to low velocity impacts, compression after impact (CAI) tests are usually performed. In the present work, CAI tests have been carried out on composite plates laminated with plies characterized by two different material systems. According to CAI tests, the specimens have been subject, first, to a low velocity impact with a 20 J impact energy, then a compression test has been performed to assess their residual strength. The experimental results have been discussed and compared.

The sandwich composite panels, due to their highly specific mechanical properties, are widely used in many engineering fields (such as the aeronautical, railways and automotive). In this work, a numerical study is presented on the impact behavior of several sandwich composite panels configurations with polypropylene core, usually adopted for aerospace applications, with the aim to assess their mechanical properties and to make a selection of the best configurations taking into account their multifunctional characteristics. The existing limits in current aeronautical sandwich panels have been assessed and techniques/solutions able to improve (even through the utilization of micro and nano fillers) the multifunctional and structural properties have been explored. Indeed, resistance to fire and resistance to impact events have been selected as the main characteristics of interest for the presented study. Low-speed impact tests (according to the ASTM standards) on sandwich composite panels with polypropylene core have been simulated by means of the commercial FEM software “Abaqus”. Low velocity impacts can switch complex damage mechanisms (such as delaminations or large indentations) in composite panels. These damage mechanisms are of major concern from a structural point of view because they can suddenly reduce the loading carrying capability without being visible in programmed visual inspections. As a result of the performed simulations, the low velocity impact induced damage, in terms of delamination and indentation, has been evaluated for several sandwich panels with varying polypropylene core material composition. The outputs have been compared providing a first estimation of the capability to resist to impact event provided by several polypropylene core configurations. The resistance to impact events have been associated to the fire resistance capability of the analyzed material core configurations proving a comprehensive insight on the multifunctional behavior of sandwich composite panels with polypropylene core.