Three-dimensional interpretation of cleavage fracture tests of cladded specimens with local approach to cleavage fracture

Electricite de France has conducted during these last years an experimental and numerical research programme in order to evaluate fracture mechanics analyses used in nuclear reactor pressure vessels integrity assessment, regarding the risk of brittle fracture. Two cladded specimens made of ferritic steel A508 C13 with stainless steel cladding, and containing shallow subclad flaws, have been tested in four point bending at very low temperature to obtain cleavage failure. The crack instability was obtained in base metal by cleavage fracture, without crack arrest. The tests have been interpreted by local approach to cleavage fracture (Beremin model) using three-dimensional finite element computations. After the elastic-plastic computation of stress intensity factor Kj along the crack front, the probability of cleavage failure of each specimen is evaluated using m, (sigma)u Beremin model parameters identified on the same material. The failure of two specimens is conservatively predicted by both analyses. The elastic-plastic stress intensity factor Kj in base metal is always greater than base metal fracture toughness K 1c. The calculated probabilities of cleavage failure are in agreement with experimental results. The sensitivity of Beremin model to numerical aspects is finally exposed.