Aero-Engine Fastened Structural Components: An Investigation into Impact Induced Three-Dimensional Dynamic Fracture Mechanism 2024-26-0414

Fastener joints play a critical role within aircraft engine structures by connecting vital structural members and withstanding various load scenarios, including impact occurrences like foreign object damage (FOD) on engine nacelles. The precise modeling and simulation of fastener joint behavior under dynamic loads are pivotal to ensuring their structural integrity and functionality. Simulation is essential for minimizing costly experiments in evaluating the challenging design aspect of containing FOD. Prior investigations on fastener joints have predominantly focused on quasi-static or in-plane dynamic loads. This study introduces a comprehensive methodology to simulate the impact dynamics of fastener joints, accommodating both in-plane and out-of-plane loads. The approach employs a fully self-consistent 3D viscoplastic finite element formulation-based simulation using a newly developed code. We further investigate the significance of rate-dependent and three-dimensional stress effects, including some comparative investigations using a simplified sequential stress update formulation available in LS-DYNA to understand the implication of couple damage process leading to complex fracture mechanisms. Central to this investigation is capturing the intricate stress state and material behavior of fastener joints under high strain rates. The Johnson-Cook model is utilized to characterize viscoplastic deformation, incorporating damage evolution and crack initiation effects. A key challenge is determining parameters for this model, which is addressed through a consistent variational finite element formulation combined with coupon tests designed for encompassing varying stress triaxiality ratios considering pure and mixed-mode loading conditions. By synergizing experimental data and simulation techniques, this methodology extracts parameters under dynamic tension, compression, and shear loading, providing precise predictions of fastener joint behavior. The study offers insights into stress distribution, deformation patterns, damage progression, and crack initiation mechanisms through simulations. In summary, this research enhances the understanding of fastener joint responses under dynamic loads and informs predictive failure analysis, facilitating design improvements for FOD mitigation and containment strategies.