Experimental and numerical investigations on the miniaturization for fracture toughness characterization of RPV materials

Li Meng


Pardoen Thomas, (UCL), thomas.pardoen@uclouvain.be

SCK•CEN Mentor

Uytdenhouwen Inge
+32 14 33 31 71

SCK•CEN Co-mentor

Lambrecht Marlies
+32 14 33 30 13

Expert group

Structural Materials

PhD started


Short project description

The knowledge of mechanical properties for structural reactor materials is among the key points for producing reliable integrity assessments and accurate residual life predictions. The evaluation of mechanical properties, with the sole exception of hardness measurements, is by definition a destructive technique. In the nuclear field, the space available inside irradiation facilities is quite small and the exploitation of material has to be optimized. The optimum use of very limited irradiated materials becomes very critical in the perspective of long term operation (LTO). Thus the use of very small specimens becomes then very appealing, although they usually do not comply with existing requirements of the test standards. This triggered worldwide research efforts for developing miniature specimens that can be used for fracture mechanics testing with particular insight on the master curve application, where SCK.CEN has been very often at the fore-front of the developments [1, 2, 3, 4, 5].

Fracture toughness can be more or less directly transferred without any empirical correlation procedures such as used for the Charpy impact properties of reactor pressure vessel materials. SCK.CEN was the first one that selected the mini-CT specimen as such that 4 mini-CT specimens can be fabricated out of a half broken Charpy specimen [6, 7]. The additional advantage of the mini-Charpy is that specimen re-orientation is also possible. However, the geometry does not fully satisfy the ASTM requirements with respect to the various ratios of the specimen dimensions. In addition miniaturization induces a loss of constraint effect [7, 8] as was already assessed by 3D finite element simulations.


[1] E. Lucon and M. Scibetta, "Fracture toughness measurements in the transition region using miniature PCCv and CRB specimens", SCK.CEN report R-3400 (2000)
[2] E. Lucon and M. Scibetta, "Fracture toughness measurements in the transition region using sub-size pre-cracked Charpy and cylindrical bar specimens", SCK.CEN report BLG-863 (2001)
[3] E. Lucon, M. Scibetta, R. Chaouadi and E. van Walle, "Fracture toughness measurements in the transition region using sub-size pre-cracked Charpy and cylindrical bar specimens, small specimen test techniques: 4th volume, ASTM STP 1418, M.A. Sokolov, J.D. Landes, and G.E. Lucas, Eds., ASTM International (2002) 3-17
[4] J.L. Puzzolante and M. Scibetta, "Machining and fracture toughness testing of miniature compact tension specimens in hot cell", Hot laboratories and Remote Handling, HOTLAB-2003, September 22-24, Saclay (France)
[5] M. Scibetta, E. Lucon, R. Chaouadi, E. van Walle and R. Gérard, "Use of broken Charpy V-notch specimens from a surveillance program for fracture toughness determination", Journal of ASTM International 3 (2006)
[6] M. Scibetta, E. Lucon and E. van Walle, "Optimal use of broken Charpy specimens from surveillance programs for the application of the master curve approach", International Journal of fracture 116 (2002) 231-244
[7] M. Scibetta, "Constraint assessment in miniature C(T) specimens using 3D finite element simulations", SCK.CEN Report BLG-923 (2002)
[8] R. Chaouadi et al., "On the use of miniaturized CT specimens for fracture toughness characterization of RPV materials", Proceedings of the ASME 2016 Pressure Vessel and Piping conference (2016), Vancouver


At SCK.CEN, an extensive database of fracture toughness results of both reference as neutron irradiated material exists; tested with a large variety of specimen geometries (PCCv, CT, SENB, …) and sizes (1T-CT, 1/2T-CT, 1/4T-CT, …). The results in this database will be investigated and rationalized and further on used to obtain data on size effects, geometry and loss of constraints. A systematic analysis on specimens with a range of ligament (b) and thickness (B) values will be able to decouple size effects related to constraint loss (mediated by b and B) and statistical effects (mainly by B). Procedures will be developed to transfer toughness data to different conditions of constraint and thickness.

One part of the PhD will be dedicated to experimental verifications, namely to investigate the overall validity of the not standardized mini-CT geometry. The experimental part will contain mechanical tests (fracture toughness), supported by detailed analysis of the fracture surfaces, crack front and plastic deformation. Those will be analyzed by microstructural tools and digital image correlations. The effect of side-grooving will be examined as well.

The second part of the PhD will deal with the finite element modeling (FEM) to understand and investigate the effect of loss of constraint, ….with a 3D finite element critical stress area model. The link between experimental and finite element modeling will be performed by using the DIC (digital image correlation) approach. The final aim is to have a standardization of the mini-CT geometry in ASTM.