Efficient simulation of multiple impact on double-curved composite structures

Kurzfassung

Fibre-reinforced plastics are used for a wide variety of engineering applications due to their high stiffness and strength values at low weight. This makes them particularly suitable for aircraft structures, where the overall mass is an important factor, especially due to the increasing demands on CO-2 emissions. However, a major disadvantage is their vulnerability to impact damage caused by e.g. hail, ice shedding or runway debris. These impacts can lead to so-called BVIDs (Barely Visible Impact Damage). As a result, the damage may remain undetected until the next maintenance. Because of the random nature of such impact events (varying impact energies and positions), as well as the scatter of composite material properties, several simulation loops are necessary to capture the possibility space opened by these uncertainties. Since conventional high-fidelity finite element (FE) analyses are not feasible due to required computational effort, alternative approaches have to be provided. A simulation approach using contact laws to derive the resulting pressure distribution acting on the fuselage during the impact is developed. The approach is implemented as a FORTRAN library into the commercial FE program ABAQUS. The computational effort is further decreased by using a single layer of shell elements to discretize the impacted structure. The three-dimensional stress-state in each ply is recovered at the start of each increment, allowing the usage of modern three-dimensional failure criteria. The damage initiation is subdivided into fibre, matrix and delamination, and the damage evolution is described by a set of increment-wise linearized functions. The developed method is applied and results are compared to numerical and experimental data from literature. Additionally, the structure-mechanical response of a double-curved composite structure is evaluated with respect to different impact events and resulting damage accumulation over time. The complete approach is embedded into a simulation environment. This allows describing parameters like impact position and/or energy by probability density functions instead of deterministic values. Furthermore, computation steps are applied to analyse the residual properties of the impacted structure. The feasibility of the overall approach is presented and discussed by the example of a fuselage section. This work was supported by the European Commission Clean Sky 2 Programme under the rant H2020-CS2-CPW01-2014-01 within the ADEC project (ADVANCE ENGINE AND AIRCRAFT CONFIGURATIONS).