Experimental and Predicted Crack Paths for Al-2024-T351 Under Mixed-Mode I/II Fatigue

Abstract

The aerospace industry has experience with a range of structural failures, oftentimes due to fatigue cracks in aircraft fuselage components that are exposed to relatively high stress levels during cyclic loading effects that lead to fatigue crack initiation at material defects and near stress concentrations. These aircraft components are under complex stress states. In this study, mixed mode I/II fatigue experiments and simulations are performed for an Arcan fixture and a 6.35 mm thick Al-2024-T351 specimen, a popular aerospace alloy. Experiments were performed for Arcan loading angles that gave rise to a range of Mode I/II crack tip conditions from 0 ≤ ΔKII/ΔKI ≤ ∞. Measurements include the crack paths, loading cycles, and maximum and minimum loads for each loading angle. Simulations were performed using three-dimensional finite element analysis (3D-FEA) with 10-noded tetrahedral elements via the custom in-house FEA code, CRACK3D. While modeling the entire fixture-specimen geometry, a modified version of the virtual crack closure technique (VCCT) with automatic crack tip re-meshing and a maximum circumferential stress criterion was used to predict the direction of crack growth. Results indicate excellent agreement between experiments and simulations for the measured crack paths during the first several millimeters of crack extension.