Tim
Bergmann and Sebastian Heimbs
Department of Structures Engineering, Production and Aeromechanics, EADS Innovation Works, Willy-Messerschmitt-Straße, 81663 Munich, Germany
The application of carbon fibre-reinforced plastic (CFRP) materials in aircraft structures is ever-expanding. Besides established utilisation in control surfaces or wing structures, the latest generation of commercial airliners also feature a fuselage made of carbon fibre composite material. Besides their well-known advantages in terms of weight-specific mechanical properties and fatigue tolerance, such structures are vulnerable against transversal impact loads, which can lead to undetectable internal damage and cracks that can reduce the strength and grow under load. Typical examples of such impact load cases with frequent occurrence are bird strike loads on composite wing leading edges or hard body impact loads from stones or runway debris being thrown against lower fuselage panels by the aircraft tires.
Most studies that have been performed so far to investigate the impact performance of composite laminates are based on unloaded structures. However, this simplification may be far off reality as the structure in flight may typically be under a state of prestress before impact. For example, the lower fuselage panels are typically exposed to compressive loads during takeoff, when stone impact is likely to occur. There is a strong interest in investigating the influence of preloads on the impact response of aeronautic structures.
An investigation on the effect of prestress on the high-velocity impact behaviour of laminated composite structures under soft body impacts has not been performed yet. This effect can be of great importance for bird strike analyses and bird-proof design of composite aircraft structures, though. There is a big difference between the spread contact area of soft body impact loads resulting from bird or hail strike compared to hard body impact loads, which are resulting from bird strike compared much more localised.
This study was based on an experimental test campaign in order to obtain a reliable data basis for model validations. 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.
Department of Structures Engineering, Production and Aeromechanics, EADS Innovation Works, Willy-Messerschmitt-Straße, 81663 Munich, Germany
The application of carbon fibre-reinforced plastic (CFRP) materials in aircraft structures is ever-expanding. Besides established utilisation in control surfaces or wing structures, the latest generation of commercial airliners also feature a fuselage made of carbon fibre composite material. Besides their well-known advantages in terms of weight-specific mechanical properties and fatigue tolerance, such structures are vulnerable against transversal impact loads, which can lead to undetectable internal damage and cracks that can reduce the strength and grow under load. Typical examples of such impact load cases with frequent occurrence are bird strike loads on composite wing leading edges or hard body impact loads from stones or runway debris being thrown against lower fuselage panels by the aircraft tires.
Most studies that have been performed so far to investigate the impact performance of composite laminates are based on unloaded structures. However, this simplification may be far off reality as the structure in flight may typically be under a state of prestress before impact. For example, the lower fuselage panels are typically exposed to compressive loads during takeoff, when stone impact is likely to occur. There is a strong interest in investigating the influence of preloads on the impact response of aeronautic structures.
An investigation on the effect of prestress on the high-velocity impact behaviour of laminated composite structures under soft body impacts has not been performed yet. This effect can be of great importance for bird strike analyses and bird-proof design of composite aircraft structures, though. There is a big difference between the spread contact area of soft body impact loads resulting from bird or hail strike compared to hard body impact loads, which are resulting from bird strike compared much more localised.
This study was based on an experimental test campaign in order to obtain a reliable data basis for model validations. 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.
No comments:
Post a Comment