Tridimensional FE-analysis of stable crack growth in a CT-specimen of a structural steel

The crack growth in a plain sided Compact Tension specimen made of an annealed mild steel is simulated by a new tridimensional (3D) Finite Element analysis. The crack extension (Δa) is controlled by local Δa vs. load line displacement (ν_LL) curves originating from a multi-specimen J_IC-test. The results of the 3D-analysis fit excellently to the measured load (P) vs. displacement and J-integral (J) vs. Δa-curves. It is shown that the local crack tip opening displacement at the advancing tip, CTOD, reaches a steady state value after a short transition region. Further, a modified version of a two layer model (TLM), which was used in previous studies, is introduced. The TLM replaces the expensive 3D-analysis by two 2D-analyses, a plane strain analysis for the midsection region and a plane stress analysis for the near side surface region. The modified TLM uses two local Δa vs. ν_LL curves (for the midsection and the side surface) to control the crack extension in the two layers. The P-ν_LL- and J-Δa-curves of the modified TLM come very close to the results of the 3D-analysis.