Characterization and modeling of ductile rupture with relationship of microstructures in 2198 Al-Li alloy for aeronautic application

Damage and fracture mechanisms of two 2198 Al-Li thin sheet alloys having different thicknesses (2 and 6 mm) are investigated. Two heat treatments are studied: T3 and T8. Mechanical tests are carried out on flat specimens including smooth tensile samples and U-notched specimens (with various notch radii). Test data are used to identify the parameters of constitutive equations describing plastic anisotropy. Crack initiation and stable propagation is studied using Kahn tear tests. The microscopic fracture surface of the different specimens is observed using SEM (Scanning Electron Microscopy). Smooth and notched samples exhibit a slant fracture surface. With increasing notch severity, the fracture mode changes significantly. Failure initiates at the notch root in a small triangular region, outside this zone, slant fracture is observed. Observations show two different failure mechanisms with respect to triangular and slant zones.