1,720,998 research outputs found
A feasibility study on additive manufactured hybrid metal/composite shock absorbers
No full textCommonly 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
UAV Wing leading edge crashworthiness behaviour under bird strike events: The added value of CF/PA additive solutions versus traditional metallic wing structures
No full textIn recent years, an increasing interest in innovative solutions design of aircraft structural components has been raised through both research and industrial fields, aimed at optimising weight and enhancing the ability to withstand both static and dynamic loads. This study compares the structural response to a bird strike phenomenon of a vertical tail of a UAV in standard metallic configuration with the one obtained from an innovative solution, equal in volume but with an internally designed architecture for an additive approach and manufactured by employing a carbon fibre reinforced filament engineered for metal replacement applications (carbon fibre, CF/polyamide, PA). The additive solution proposes the use of a 10 % infill and a lattice structure that completely replaces the traditional aircraft structure concept. This approach leads to a significant weight reduction, approximately 45 % compared to the traditional metallic configuration. The investigation was conducted through explicit numerical simulations considering different impact angles. The numerical model of the bird strike has been assessed by numerical-experimental comparison, simulating the impact of a bird with a flat plate. For this study, the Coupled Eulerian-Lagrangian (CEL) approach has been adopted to perform the simulation. The results were compared in terms of stress distribution, failure analysis, displacements, and energy-time and force-time diagrams. The work demonstrated that using innovative manufacturing processes, such as additive manufacturing, can significantly improve the bird strike resistance of aerospace structures. This improvement is achieved though the production of lighter, structurally collaborative geometries, by reducing the load transferred to the rest of the UAV by about 47 % and decreasing the displacement on the impact area by 53 %
Experimental and numerical assessment of the impact behaviour of a composite sandwich panel with a polymeric honeycomb core
No full textThe 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
On the use of hybrid shock absorbers to increase safety of commercial aircraft passengers during a crash event
No full textthe passive safety of aircraft passengers is such an important aspect in the design of aircraft structures as strength and fatigue concerns. The development of methods and devices to prevent passenger injuries is the subject of continuous efforts. The mission is to minimize stresses and accelerations on passengers during a crash. Over the years, studies on crash phenomena have been focused on experimental tests, using full-scale structures and Anthropomorphic Test Devices (ATDs) to assess the consequences of impact phenomena on the human body. However, due to the high costs of experimental campaigns and the difficulty of controlling all relevant parameters, the need of efficient numerical models capable of validating experimental data has increased. This is specifically relevant for tests on ATDs. In the frame of this work, the side-impact of an aircraft passenger have been numerically investigated positioned on a window-side seat of an aluminium commercial aircraft fuselage a World SID-based dummy. An attempt to increase the aircraft crashworthiness was made placing in correspondence with the head and the shoulders of the dummy hybrid sandwich shock absorbers. In order to validate the considered dummy model, a lateral impact against a flat barrier has been carried out. The obtained numerical results have been cross-compared with literature experimental data. Then, the side-impact behaviour of the dummy within a fuselage section has been investigated, with the aim to verify the absorption capability of the shock absorbers and to quantify their effect on the safety of the dummy. The employment of the shock absorbers allowed to reduce the acceleration peaks experienced by the dummy's head up to 50%
A Numerical Study on the Influence of Nanosilica-Reinforced Epoxy Resin on the Delamination Behavior of Composite Laminates
No full textThe 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 Feasibility Study on Innovative Reinforced Modular Frames for Automotive Applications
No full textVehicle 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
On the effect of printing orientation on the surface roughness of an additive manufactured composite vertical tail
No full textAdditive manufacturing (AM) enables the production of customised and sophisticated components; Fused filament fabrication (FFF) is a widely used and cost-effective AM technique. Nevertheless, the use of FFF for aerospace and aeronautical applications is often impeded by the inadequate surface finish it imparts to the produced components. This work aims to demonstrate that, with careful calibration of process parameters and build orientation, FFF can produce aerospace components with low surface roughness. This could enable FFF to be used in aeronautics, allowing the benefits of lightweighting structures using metal replacement thermoplastics and variable infill to be exploited. In this study, rudder sections of a UAV tailplane were produced using FFF and lightened through variable internal infills, thin thicknesses, and a polymer for metal replacement. By setting different printing processes, such as infill percentage and orientation, a configuration with 10% of linear infill which results in a 97.5 g component was identified that exhibits suitable surface roughness for aerospace applications and a weight saving of approximately 50% compared to an equivalent metal volume
Development of a combined micro-macro mechanics analytical approach to design shape memory alloy spring-based actuators and its experimental validation
Full text linkIn 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
Metal Replacement in UAV Vertical Tails Using Additive Manufacturing
No full textThe 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
On the Use of a Hybrid Metallic-Composite Design to Increase Mechanical Performance of an Automotive Chassis
No full textThanks to the introduction of high-performance composite materials, 'metal replacement' approaches are successfully gaining ground even in the most challenging engineering applications. Among these, one of the most recent application challenges is improving the driving range of Battery Electric Vehicles (BEVs) by adopting innovative materials to lighten the mass of structural components, thus reducing energy requirements and enabling the use of smaller and less expensive batteries. Hence, in the present work, the employment of laminated composite panels in an electric minibus chassis is investigated as an effective way to reduce the global mass of the chassis’ structure and, at the same time, to increase its structural performances in terms of torsional stiffness and crashworthiness. By replacing specific steel tubulars with carbon-fiber-reinforced polymer (CFRP) laminated composite structures, different chassis configurations were numerically developed and detailed simulations to compare both masses and mechanical responses were carried out. The paper proves that with this approach it is possible to lighten the chassis up to 9%, while achieving a 7% increase in torsional stiffness and a 9% increase in Specific Energy Absorption (SEA)
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