Volume 9, Issue 3 (March 2012)
Evaluation of Fracture Toughness Test Data for Multilayer Dissimilar Joint Welds Using a Weibull Stress Model
Fracture behaviour of welded joints with dissimilar weld metals (WMs) has been investigated in this paper. A low-toughness WM and a high-strength WM with a moderate toughness were layered alternately in the thickness direction. Fracture tests were conducted with 3-point bend (3PB) specimen and tension plate with a through-thickness crack. The 3PB specimen showed a multistage fracture. The first fracture was originated from the low-toughness WM. On the other hand, no multistage fracture occurred in the tension plate, although the low-toughness WM was responsible for brittle fracture initiation in the same manner as in the 3PB specimen. The fracture toughness of the multilayer dissimilar joint was apparently larger than the welded joint made with the low toughness WM only. The weakest-link model has been applied for analyzing those toughness properties of the multilayer dissimilar joint. The estimated fracture toughness by the weakest-link model was not necessarily consistent with the toughness data, which was because of the local stress elevation in the low-toughness WM area close to the high-strength WM. Because of this, a modified Weibull stress model was used to estimate fracture toughness values for the multilayer dissimilar joint WM and to account for an active fracture zone length scale in the multilayer weld joint materials.