The present FRACTESUS project aims to determine the effect of specimen size on the fracture toughness properties. Finite element models (FEM) are used to investigate the difference between large-size and miniature compact tension (MC(T)) specimens and quantitatively assess the resulting loss of constraint due to size reduction. The optimal range of usability of MC(T) specimens can therefore be determined and evidenced with experimental results. Large inter-laboratory testing is included in the FRACTESUS project in an attempt to prove the repeatability and reproducibility of the small-scale testing of fracture toughness properties. Various materials relevant for most of the available reactor pressure vessel materials and irradiation conditions are investigated.
The project has entered its last year and many preliminary data and interpretations are available. The main achievements so far are summarized by: i) a numerical round robin; ii) an experimental round robin on unirradiated materials; and iii) an experimental round robin on irradiated material.
The numerical round robin is completed by nine different laboratories to ensure that the different numerical tools and set-ups used by the different laboratories provide comparable and consistent results. Two specimen geometries, 1T-C(T) and MC(T), and two temperatures, -100 °C and 23 °C are considered. The specimen geometries, minimum meshing parameters around the crack tip, the material constitutive law and boundary conditions are prescribed. This allowed a free choice of the simulation software (ANSYS, Abaqus, Cast3M20, XPER r2465 and MSC.Marc) the number of elements and nodes and pin material. Both macroscopic results (load, J-integral, plastic volume and correction factor versus pin displacement) and microscopic results (mechanical field at the crack tip) are compared. It can be concluded that both macroscopic and microscopic results are coherent and comparable between the different laboratories.
The experimental round robins on unirradiated materials has been completed by 13 different laboratories (>480 fracture toughness tests). The reference temperatures T0 obtained from MC(T) specimens by the different laboratories are compared to the ones obtained from larger (mostly 1T C(T)) specimens for six different materials. The considered materials are relevant for the nuclear industry and consist of four base (15Kh2MFAA, A533B LUS, A533B JRQ, A508 Cl.3) and two weld (ANP-5 and 73W) materials.
The inter-laboratory round robin showed the equivalence between T0 obtained by MC(T) and larger specimens, except for A533B JRQ and 73W. The reasons for the deviations of A533B JRQ and 73W are under investigation. As a general comment, it can be stated that the results from MC(T) specimens often lead to material inhomogeneity as compared to the results from larger specimens. The small sampling volume combined with the weakest link theory interpretation means that local differences in the material may result in a large variation from one tested MC(T) specimen to another. Thus, rather than MC(T) specimens misinterpreting homogeneous materials as being inhomogeneous, MC(T) specimens could be more adept at identifying inhomogeneity than larger specimens.
The experimental round robin on the irradiated 73W weld material irradiated at 288 °C up to 1.5×1019 n/cm2 (E > 1 MeV) has been performed by seven different laboratories (>112 fracture toughness tests). All experiments have finished and the results will be analyzed in RP3.
