FRACTURE-MECHANICS IN CREEP SITUATION - INTERPRETATION OF RESULTS ON A TEST SPECIMEN

Fracture mechanics in creep situation is a difficult challenge for the 1990s. In France, CEA Saclay has conducted experimental tests on compact tension (CT) specimens at 650 degrees C in order to investigate crack initiation under creep situations. The constitutive material is the 316SPH austenitic stainless steel used for most LMFR structures. Numerical simulations using sus-rvs code and simplified method analysis were performed on one of the tests (CT specimen at 650 degrees C under constant load) to compare some parameters (notch opening, initiation time) with experimental values. The material constitutive law was represented by the complete elasto-viscoplastic CHABOCHE model for SYSTUS computation. Owing to geometrical characteristics such as thickness, the situation of the CT specimen was likely to be intermediate between plane stress and plane strain assumptions. From C* parameter, incubation time obtained using the R5 rule was conservative in comparison with the test result. The continuum damage model developed at Ecole des Mines de Paris has also been used to assess creep damage in the notch tip area. The crack initiation time has been deduced from critical damage at characteristic distance (X(c) = 0.05 mm). Considering critical damage specifically, for a CT specimen (D-c = 0.05), initiation time obtained was higher than the test result. The results of this study will contribute to the development of a methodology for nocivity analysis of cracks in creep situation.