Application of phase field approach to predict fatigue crack link-up in a riveted lap joint

• Conducted fatigue testing on lap joint panels to study crack growth and link-up of multi-site damage. • Developed a phase field model excluding damage accumulation due to plastic deformation during unloading. • Validated the phase field model for predicting link up of multi-site damage. This article presents a study on fatigue crack growth and link-up behavior in riveted lap joint panels, representative of an aircraft fuselage, containing multi-site damage (MSD). Four sub-scale lap joint specimens were subjected to constant-amplitude sinusoidal fatigue testing with marker band loading sequences. Artificially induced damage sites were introduced to simulate MSD scenarios. An anti-bend fixture was used to assess the effect of secondary bending on fatigue crack initiation and growth. The experimental results showed that the anti-bend fixture significantly reduced secondary bending in the lap joints, leading to an overall improvement in fatigue life. Post-fatigue forensic analysis of the fracture surfaces was performed to track crack progression and determine crack growth rates. The forensic analysis results provided detailed measurements of crack progression and link-up behavior, enabling a clear characterization of the MSD progression observed in the tested lap joint specimens. A finite element-based framework, incorporating phase field approach, was developed to simulate fatigue crack growth and link-up behavior. An exiting phase field framework was adopted and modified by excluding plastic strain energy in the critical damage-driving term of total strain energy to address the crack growth characteristics during unloading phases. Simulation results showed good agreement with experimental data in terms of crack growth rate, crack path, and link-up behavior. These findings demonstrated the effectiveness of the phase field approach in capturing fatigue crack growth and link-up in aircraft fuselage lap joints, offering a robust tool for damage tolerance assessment and life prediction in aircraft structures.