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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 paper aims to investigate the crashworthiness capability of a commercial aircraft metallic sandwich leading edge, subjected to bird strike events. A sensitivity analysis is presented, aimed to assess the influence of the skin parameters (inner and outer faces and core thicknesses) on the leading-edge crashworthiness and to determine, among the configurations able to withstand a bird strike event, the best compromise in terms of weight and structural performances. In order to easily manage the design parameters and the output data, the ModeFrontier code was used in conjunction with the FE code Abaqus/Explicit. A dedicated python routine was developed to define a fully parametric simplified leading-edge model. To fulfill the aerodynamic requirements, the external surfaces were considered fixed during the sensitivity analysis, and, thus, only the internal leading edge&rsquo, s components were modified to study their influence on the structural response. The total mass of the model, the maximum deformation and the energy dissipated due to material failure and the plastic deformations were monitored and used to compare and assess the behavior of each configuration.

This work is focused on the investigation of the structural behavior of a composite floor beam, located in the cargo zone of a civil aircraft, subjected to cyclical low-frequency compressive loads with different amplitudes. In the first stage, the numerical models able to correctly simulate the investigated phenomenon have been defined. Different analyses have been performed, aimed to an exhaustive evaluation of the structural behavior of the test article. In particular, implicit and explicit analyses have been considered to preliminary assess the capabilities of the numerical model. Then, explicit non-linear analyses under time-dependent loads have been considered, to predict the behavior of the composite structure under cyclic loading conditions. According to the present investigation, low-frequency cyclic loads with peak values lower than the static buckling load value are not capable of triggering significant instability.

Crashworthiness is defined as the capability of a structure to guarantee its occupants safety during a crash event. In the present work, the crashworthiness of a composite wing section, subjected to a bird strike event, has been investigated. Indeed, the mechanical behavior of the impacted wing section has been inspected by means of the FE code Abaqus/Explicit. The impact phenomenon has been numerically simulated with a coupled Eulerian–Lagrangian (CEL) approach. The impacted structure has been modeled considering a Lagrangian formulation, while a Eulerian one has been used to model the bird. Moreover, Eulerian–Lagrangian contacts are used for transfer the loads arising from the impact event to the Lagrangian structure. The proposed numerical model, capable to take into account the matrix and fiber traction and compression damages, uses a 3D finite element approach to better predict the deformations and the damages onset and propagation during the impact event. The numerical results, in terms of structural deformation and damage onset and propagation, have been obtained by considering different impact locations and different impact angles.

In the present work, a numerical study on the dynamic response of a composite fuselage barrel, in relation to crashworthiness, has been investigated. The aim of this work is to investigate the influence of the material fracture toughness on the capability of a composite fuselage barrel to tolerate an impact on a rigid surface. Three different material configurations with different intra-laminar fracture energy values were considered to take into account variations in material toughness. Indeed, the dynamic behaviour of the analysed fuselage barrel has been numerically simulated by means of the FE (Finite Element) code Abaqus/Explicit. The effects of intralaminar fracture energy variations on the impact deformation of the barrel has been evaluated comparing the numerical results in terms of displacements and damage evolution for the three analysed material configurations.

In this work, the crashworthiness of the floor subsection of the cargo area of a civil aircraft is investigated. The structural behaviour under dynamic loading conditions of a structural sub-floor component, made of carbon fibre-reinforced composite material, has been studied in detail from a combined experimental/numerical perspective. Indeed, numerical impact tests characterized by different impact energies have been performed, with advanced numerical tools, finalized to the full understanding of the damage onset and propagation during the impact event. Preliminary numerical quasi-static and dynamic analyses have been carried out on the single sub-components. Then, the impact behaviour of the entire subfloor component has been numerically simulated taking into account the inter-laminar and intra-laminar damages onset and propagation. The comparison between the numerical results and the experimental data from the entire subfloor component has allowed to fully characterize the damage evolution in the investigated component and to provide interesting information finalized to a crashworthy design.

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.

Bird impacts can be extremely critical events for the air transport safety. Since aircraft structures have become more and more complex components, the numerical prediction of the damage onset and evolution induced by a bird impact has become a very challenging task. The aim of this work is to provide a brief overview of the numerical techniques adopted for the prediction of the bird impact phenomenon on a leading edge of a regional aircraft wing. Smooth Particle Hydrodynamics (SPH), Rigid and Lagrangian models have been investigated and the results have been compared and critically assessed.

Crashworthiness is the ability of a structure to withstand a crash event ensuring the safety of its passengers. The aim of this work is to investigate the damage onset and evolution in a composite fuselage barrel undergoing a vertical drop test on a rigid surface. The mechanical behaviour of the barrel has been assessed by means of a Numerical-Experimental study. Indeed, the experimental data from a full scale barrel test, performed at the CIRA facilities, have been used in conjunction with numerical results, obtained by means of an advanced 3D FEM model, to investigate, in detail, the deformations and the damage development during the crash event. The adopted three-dimensional numerical model, based on an explicit FE formulation, uses Continuum Shell elements and CDM to take into account the onset and the evolution of the intra-laminar damages in each subcomponent of the investigated composite fuselage barrel. The obtained numerical results have been compared with experimental data in terms of accelerations, displacements and deformations to provide a preliminary validation of the adopted FEM model. A special attention has been given to sub-components which demonstrated to mainly influence the global mechanical behaviour of the investigated composite fuselage barrel during the experimental test.

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.

The work aims to investigate the capability of a vertical tail leading edge to withstand bird strike and to provide general considerations on the improvement of such capability with respect to the mass saving and to the required structural performances by considering different material systems. The assessment of the numerical models was ensured by a double check, and therefore considering the two test cases, aimed to calibrate and validate the numerical models against experimental data, coming from literature: 1) bird strike on metallic flat square plate; 2) bird strike on wing leading-edge with the skin made in metallic sandwich structure (both the honeycomb core and the outer and inner face was in aluminum). Finally, the crashworthy design of several leading-edge configurations, modifying the material and thickness of the skins and the central core of the leading edge, without changing its external geometrical shape, was investigated by adopting the numerical procedures used for the validation test cases. Actually, unidirectional fiber-reinforced composite material systems were considered for the outer and inner face of the skins, while different materials were adopted for the core. A comparison among the developed configurations, in terms of requirement fulfillment, global deformation parameters and weight, was performed.

Crashworthiness is defined as the capability of a structure to guarantee its occupants safety during a crash event. In the present work, the crashworthiness of a composite fuselage section has been preliminary investigated. Indeed, the mechanical behavior of the investigated fuselage section has been assessed by means of the FE code ABAQUS/Explicit, considering an impact event on a rigid surface. The proposed numerical model, capable to take into account the matrix and fiber traction and compression damages, uses a 3D Finite Element formulation to better predict the deformations and the damages onset and propagation during the impact event. Two numerical models have been introduced to study the effect of the passenger floor stiffening on the mechanical response to impact of the entire investigated fuselage barrel. The results in terms of displacements and qualitative deformations of the fuselage, for the analyzed numerical models, have been compared.

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

During its service life, an airplane can experience impact events with different foreign objects. In case of impact with a flying bird, the term “Bird Strike” is commonly adopted. Bird strike can be catastrophic, especially when small general aviation airplanes are involved. Indeed, the Federal Aviation Administration (FAA), to prevent catastrophic failures with casualties, obliges airplanes to be able to complete the flight after an impact with a medium dimensions bird. Hence, it is clear that, when designing aerospace components, the potential effects of the bird strike events must be taken into account to guarantee the structural integrity and, as a consequence, the passengers and the pilot safety. In order to optimize the costs, the experimental activity for certification purpose should be suitably prepared and driven by an extensive campaign of numerical simulations. Therefore, the accuracy and the effectiveness of the numerical models able to simulate the bird strike event and its consequences on the structural integrity become of major concern when designing aerospace components. In this paper, the numerical methodologies, commonly adopted for the simulation of the bird strike event, are presented and assessed focusing on their capability to predict the induced damage and the composite components’ residual strength .

Natural fibres have been adopted for long time as low-cost fillers in the plastic industry but, nowadays they are starting to replace glass fibres in composite structures thanks to their advantages in terms of weight, cost, and environmental (biodegradability) characteristics. Among the others, one of the most interesting application of natural fibre composites is related to the manufacturing of honeycomb cores for sandwich panels with an improvement in terms of weight saving as well as in mechanical properties and functional capabilities, such as vibration control, heat and energy dissipation. In this work, a numerical model, able to predict the impact behaviour of natural fibres honeycomb cores, has been proposed. An explicit impact analysis has been conducted and the results have been validated by comparisons with experimental data in terms of impact force as a function of impactor displacement. Furthermore, the numerical deformed shapes have been compared with experimental images taken during the impact test. The results have demonstrated the validity and the robustness of the proposed numerical model.

In this paper, the compressive behaviour of an omega stiffened composite panel with a large notch damage has been investigated. The influence of intra-laminar and inter-laminar damage onset and evolution on the compressive behaviour of a stiffened panel, characterised by a cut-out located in the middle bay and oriented at 45° with respect to the load direction, has been studied. A numerical model, taking into account delamination and fibre-matrix damage evolution, respectively, by means of cohesive elements and Hashin's failure criteria together with material degradation rules, has been adopted. By comparing the performed numerical analyses, taking into account intra-laminar and inter-laminar damages, the effects of the interaction between delaminations and fibre-matrix damage in the large notch area on the global compressive behaviour of the omega stiffened composite panel have been assessed and critically discussed.

The investigation of the mechanical response of fibre-reinforced composite laminates under impact loads can be very difficult due to the occurrence of simultaneous failure phenomena. Indeed, as a consequence of low velocity impacts, intra-laminar damages, like fibre and matrix cracking, and inter-laminar damages, such as delaminations, can take place simultaneously. These damage mechanisms can lead to significant reductions in strength and stability of the composite structure. In this paper a joint numerical-experimental study is proposed which, by means of non-destructive testing techniques (Ultra-sound and thermography) and non-linear explicit FEM analyses, aims to completely characterise the impact induced damage in composite laminates under low velocity impacts. Indeed the proposed numerical tool has been used to improve the understanding of the experimental data obtained by Non-Destructive Techniques. Applications on samples tested according to the AECMA (European Association of Aerospace Manufacturers) prEn6038 standard at three different impact energies are presented. The interaction between numerical and experimental investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the inter-laminar damage formation and evolution.

The mechanical response of reinforced composite structures under impact loads is particularly challenging owing to the rising of multiple and simultaneous failure phenomena. Indeed, low velocity impacts may produce intra-laminar damages, like fibre breakage and matrix cracking, and inter-laminar damages, such as delaminations and skin-stringer debonding. As already remarked, these failure phenomena often take place simultaneously, leading to a significant reduction in strength and stability of the composite components. In this paper, the behaviour of stiffened composite panels, with omega shaped stringers, under low velocity impacts is numerically investigated by means of non-linear explicit FEM analyses. Different impact energy levels are considered and correlation with experimental data is provided, in terms of impact force, displacement and energy. A sensitivity analysis has been performed to investigate the influence of numerical models’ approximations on the accuracy of the obtained numerical results. Models with an increasing level of damage simulation details have been adopted to study the effects of combined and separated intra-laminar and inter-laminar failures providing an interesting insight on the modelling requirements for an accurate simulation of the investigated phenomena.

Low velocity impacts induce concurring failure phenomena in unidirectional fiber reinforced composites. Hence a refined methodology able to predict the different failure modes and their interaction is mandatory to correctly predict the damage onset and evolution. Indeed, intra-laminar damage and inter-laminar damage often take place concurrently, causing a significant strength reduction up to composite structure collapse. In this paper, a numerical study is proposed which, by means of non-linear explicit FEM analysis, aims to completely characterize the composite reinforced laminates damage under low velocity impacts by introducing a user defined material model in the FEM code ABAQUS. The proposed 3-D numerical investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the damage formation and evolution.

The investigation of fiber-reinforced composite laminates mechanical response under impact loads can be very difficult due to simultaneous failure phenomena. Indeed, as a consequence of low velocity impacts, intra-laminar damage as fiber and matrix cracking and inter-laminar damage, such as delamination, often take place concurrently, leading to significant reductions in terms of strength and stability for composite structure. In this paper a numerical study is proposed which, by means of non-linear explicit FEM analysis, aims to completely characterize the composite reinforced laminates damage under low velocity impacts. The numerical investigation allowed to obtain an exhaustive insight on the different phases of the impact event considering the damage formation and evolution. Five different impact locations with the same impact energy are taken into account to investigate the influence on the onset and growth of damage.