Sebastian Heimbs

Dynamic testing and modelling of composite fuselage frames and fasteners for aircraft crash simulations

In crash simulations of composite aircraft fuselage sections, frame breaking, skin bending and failure of mechanically fastened joints can typically be identified as major contributors to crash energy absorption. In order to generate a database for model validations, corresponding static and dynamic tests have been performed on coupon and structural element level to characterise the rate-dependent failure behaviour and energy absorption. Skin-bending, frame-bending and joint-failure tests under pull-out, bearing and peeling loads were performed on 977-2/HTS carbon fibre/epoxy specimens. On the one hand, effects of loading rate on the frame-bending behaviour could be observed. On the other hand, fastener failure did not appear to be depending on loading rate for the test speeds up to 10 m/s involved in this study. Adequate modelling methods in Abaqus/Explicit were derived and validated, and finally applied to a global aircraft crash simulation model.

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.

Composite crash absorber for aircraft fuselage applications

A composite crash absorber element for potential use in z-struts of commercial aircraft fuselage structures was developed, which absorbs energy under crash loads by cutting the composite strut into stripes and crushing the material under bending. The design concept of this absorber element is described and the performance is evaluated experimentally in static, crash and fatigue test series on component and structural level under normal and oblique impact conditions. The physics of the energy absorption by high rate material fragmentation and delamination interactions are explained and numerical modelling methods in explicit finite element codes for the simulation of the crash absorber are assessed.

Hydrodynamic ram analysis of aircraft fuel tanks with different composite T-joint designs

Three different composite T-joint designs were investigated experimentally and numerically for application in fuel-filled wing tanks under hydrodynamic ram (HRAM) loads. The test campaigns covering 0° T-pull and 30° T-bending tests were conducted under quasi-static and high-rate dynamic conditions in order to assess potential strain rate effects on the failure behaviour. In addition to the experimental test campaign, numerical modelling with the explicit finite element code LS-Dyna was conducted with the models being validated against the test results and being applied to ballistic impact simulations of a composite fuelfilled tank structure. While the unreinforced baseline design showed a rather brittle behaviour and poor performance, significant residual strength improvements and structural integrity under HRAM loads could be obtained with a hybrid design with metallic, arrow-shaped z-reinforcements between the composite laminates of skin and spar. A promising macro modelling approach for an efficient representation of the T-joint failure behaviour in large models was derived and successfully applied to structural HRAM simulations.

High velocity impact on composite link of aircraft wing flap mechanism

This paper describes the numerical investigation of the mechanical behaviour of a structural component of an aircraft wing flap support impacted by a wheel rim fragment. The support link made of composite materials was modelled in the commercial finite element code Abaqus/Explicit, incorporating intralaminar and interlaminar failure modes by adequate material models and cohesive interfaces. Validation studies were performed step by step using quasi-static tensile test data and low velocity impact test data. Finally, high velocity impact simulations with a metallic rim fragment were performed for several load cases involving different impact angles, impactor rotation and pre-stress. The numerical rim release analysis turned out to be an efficient approach in the development process of such composite structures and for the identification of structural damage and worst case impact loading scenarios.

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.

Investigation and Improvement of Composite T-Joints with Metallic Arrow-Pin Reinforcement

Aiming at an increase in failure resistance and damage tolerance of composite T-joints, a novel reinforcement technique in through-thickness direction using metallic arrow-pins has been proposed by the authors in previous studies. In a recent investigation, different options for further improvement of the T-pull performance have been assessed. These include optimized arrow-pin configurations, filler and ply materials and thermoplastic interleaf layers. T-specimens have been manufactured and tested under quasi-static and high-rate dynamic loading conditions to quantify the influence of these measures. Additionally, FE models have been developed in LS-Dyna to predict the performance numerically. Model validation was conducted step by step using material coupon test data, dedicated single-pin pull-out tests and T-pull tests.

Rim release analysis: Impact of aircraft wheel flange fragment on wing flap mechanism

This paper describes the numerical investigation of the mechanical behaviour of a structural component of an aircraft wing flap support impacted by a wheel rim fragment. A simulation model of the support link made of composite materials was developed, incorporating intralaminar and interlaminar failure modes. Validation studies were performed using quasi-static and low velocity impact test data. Finally, high velocity impact simulations with a metallic rim fragment were performed for several load cases involving different angles, impactor rotation and pre-stress.