High-Velocity Impact Behaviour of Prestressed Composite Plates under Bird Strike Loading

An experimental and numerical analysis of the response of laminated composite plates under high-velocity impact loads of soft body gelatine projectiles (artificial birds) is presented. The plates are exposed to tensile and compressive preloads before impact in order to cover realistic loading conditions of representative aeronautic structures under foreign object impact. The modelling methodology for the composite material, delamination interfaces, impact projectile, and preload using the commercial finite element code Abaqus are presented in detail. Finally, the influence of prestress and of different delamination modelling approaches on the impact response is discussed and a comparison to experimental test data is given. Tensile and compressive preloading was found to have an influence on the damage pattern. Although this general behaviour could be predicted well by the simulations, further numerical challenges for improved bird strike simulation accuracy are highlighted

Effects of fibre misalignment on the stability of double-curved composites

In the context of developing a novel technology for the automated production of continuously draped preforms, the effects of fibre misalignment on the stability of double-curved, unidirectional plies are investigated. The critical buckling stress as well as correlations with geometric parameters are analysed numerically using a parametric finite element model. For this purpose, a test program is conducted comprising various geometric configurations. The results provide a foundation for extending the investigation to laminates and indicate significant dependencies of the critical buckling stress on the curvature, length-to-thickness ratio and fibre angle

Representative structural element approach for assessing the mechanical properties of automated fibre placement-induced defects

In this paper, a 3D finite element modelling approach is presented to assess the effects of manufacturing defects within composite structures. The mesoscale modelling approach derives the stress-strain response of a composite structure from a representative structural element. A set of tensile and bending loads is used to compute its ABD-Matrix. The boundary conditions of the model are described in detail as is the extraction of the strain and curvature response. The derived stiffness from the presented modelling approach is compared to the classical lamination theory and the models' shortcomings are discussed. Finally, the influence of a gap, an overlap and two different-sized fuzzballs on the macroscopic mechanical properties of a composite structure are evaluated using the presented multiscale modelling approach, thereby providing stiffness matrices influenced by the defects for the use in global models of composite parts

Automated fiber placement: The impact of manufacturing constraints on achieving structural property targets for CFRP-stiffeners

The use of automated fiber placement (AFP) to manufacture integrated CFRP stiffening structures leads to a conflict between structural requirements and process limitations in early design stages. In order to avoid costly design iterations, the presented analytical approach enables the computation of tool geometries that are at the limit of theoretical manufacturability. The model is able to determine the profile of manufacturable omega stiffeners with high accuracy. It is shown that the maximum manufacturable profile parameters depend non-linearly on the properties of the AFP system and the profile itself. This allows prioritization of the profile parameters for the efficient definition of omega stiffeners that should meet distinct structural property targets. The results show that current, non-optimized AFP systems already have the potential to manufacture omega stiffeners with sufficiently high stiffness values when taking into account current aerospace applications

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools

Choc mou basse énergie sur composite interlock 3X: approche expérimentale et numérique

Dans ce travail, on s’intéresse aux mécanismes d’endommagement qui appa- raîssent lors d’un choc mou entre un impacteur déformable en caoutchouc et une plaque composite tissée 3D (interlock 3X). Des impacts basses énergies sont réalisés à l’aide d’une tour de chute. L’impacteur en caoutchouc est de forme hémisphérique. La cible, obtenue par procédé RTM, est en fibre de carbone et résine RTM 6. Plusieurs impacteurs de différentes duretés et de différents diamètres d’une part, et des tissus avec différents degrés de renfort 3D d’autre part, sont disponibles pour cette étude pour permettre une analyse de variabilité ultérieure. Dans ce papier, les résultats obtenus avec un impacteur de diamètre 40 mm sont présentés. L’accent est mis à la fois sur les moyens expérimentaux employés pour l’analyse des endommagements (Analyse par stéréo-corrélation d’images, Thermographie IR, Micro- graphie) et sur les développements numériques menés en parallèle (FEM) avec le logiciel Abaqus. Contrairement aux composites stratifiés UD, la notion de délaminage n’est plus appropriée pour ce type de composite tissé 3D. Des décohésions et ruptures de torons ainsi que des fissurations matricielles sont majoritairement identifiées.AN

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools

Hybrid Electric Propulsion Systems for Medium-Range Aircraft from a Maintenance Point of View

The use of a hybrid electric propulsion system for aircraft offers the potential to increase aircraft efficiency, reduce fuel consumption and thus reduce emissions. Design concepts, emission analysis and aircraft performance are being studied extensively. However, how future hybrid electric propulsion systems will change the maintenance, repair and overhaul (MRO) of an aircraft is also an important consideration. This paper examines the effects of hybridisation on a parallel hybrid electric propulsion system of a medium-range aircraft, the Airbus A320, powered by an IAE V2500 engine. The electric motor is powered by a battery and is used to assist the turbofan engine, mainly during the takeoff phase. The additional system components of the chosen hybrid electric propulsion system and their corresponding damage mechanisms are addressed from a maintenance point of view. Challenges for future maintenance are discussed and possible failure modes and failure possibilities are analysed. For this purpose, a Failure Mode and Effects Analysis and a Fault Tree Analysis will be carried out. The results of this analysis can be used to determine how the additional components need to be designed to maintain the overall safety of the propulsion system at the current level. This will also provide needs and ideas for a future design for maintenance