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 (Aa) is controlled by local Aa vs. load line displacement (vll) curves originating from a multi-specimen Jic-test. The results of the 3D-analysis fit excellently to the measured load (P) vs. displacement and 7-integral (J) vs. Aa-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 tire near side surface region. The modified TLM uses two local Aa vs. vll curves (for the midsection and the side surface) to control the crack extension in the two layers. The P-vll- and J-Aa-curves of the modified TLM come very close to the results of the 3D-analysis.