Experimental and numerical studies of crack growth in cladded specimens

Behaviour of cracks at the inner surface of reactor pressure vessels cladded with a stainless steel layer is judged to be complicated due to differences in the properties of bases and cladding material. The scope of the present study is to form a methodology for analysis of such cracks. The J-integral was selected as a characterizing candidate for initiation and crack growth. The test material was of A533-B steel which clad layered using a commercial strip welding process. Two layers, the first of type 309 and the second of type 308 austenitic stainless steel were applied. In addition, cladding material was provided for fabrication of homogeneous specimens. The fracture resistance properties were developed independently for cladding and base material using homogeneous specimens of each material. Side-grooved bend specimens of type three-points-bending were used in the testing program. It was observed that the cladding was anisotropic with the lowest yield strength in the thickness direction. A fracture toughness between 175 to 184 MPa√m at 60 degree C was obtained for the cladding material. The transferability of fracture results between homogeneous and cladded specimens was studied in single edge notched bend specimens. Some cladded specimens were tested and the experimental data from one test were analyzed with the finite element method. The obtained 3D J-values were the compared with the J-values evaluated by using the measured crack extension in the cladded specimen and the JR-data of the respective material provided from homogeneous specimens. A reasonable good agreement was obtained in this comparison for a small amount of crack growth