Quasi-Brittle Fracture of Lamellar γTiAl: Simulation Using a Cohesive Model with Stochastic Approach

Abstract

Quasi-brittle fracture of fully lamellar two phase (α2+γ)TiAl is investigated both experimentally and numerically. Fracture tests are conducted at room temperature, which fail in a quasi-brittle and unstable manner but exhibit significant variations in crack initiation and propagation prior to unstable failure. Fractographic investigations are performed which elucidate the micromechanical causes of the macroscopic behaviour. The observed deformation and fracture behaviours of the specimens are simulated by a finite element model containing cohesive elements for modelling the material separation. In order to capture the scatter of the macroscopic behaviour, a stochastic approach is chosen, in which local variations of cohesive parameters are taken into account. The model can describe and explain the physical phenomena of the specific material.

Fracture in lamellar TiAl simulated with the cohesive model

“…First results of an investigation of Kabir et al [30], as well done for γTAB, show an improvement of the predictions with respect to the experimental scatter with unstable fracture or pop-in events.…”

“…From bend specimens, still in the global elastic regime, they found an R-curve effect, i.e. increasing fracture toughness from initiation (K Ic ≈ 16 MPa√m) up to saturation of about [25][26][27][28][29][30] MPa√m. This increase is confined within small crack extension, less than 200 µm, i.e.…”

Simulation of local instabilities during crack propagation in the ductile–brittle transition region

“…For instance, the works of Tvergaard, Needleman and co-workers (Tvergaard and Needleman, 1993;Gao et al, 1996;Needleman and Tvergaard, 2000) or Kabir et al (2007) can be cited out of this group.…”