Simulation of Slip-Oxidation Process by Mesh Adaptivity in a Cohesive Zone Framework.

Adaptive oxide thickness was developed in a cohesive element based multi-physics model including a slip-oxidation and diffusion model. The model simulates the intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWR). The oxide thickness was derived from the slip-oxidation and updated in every structural iteration to fully couple the fracture properties of the cohesive element. The cyclic physics of the slip oxidation model was replicated. In the model, the thickness of the oxide was taken into consideration as the physical length of the cohesive element. The cyclic process was modelled with oxide film growth, oxide rupture, and re-passivation. The model results agreed with experiments in the literature for changes in stress intensity factor, yield stress representing cold work, and environmental factors such as conductivity and corrosion potential.

Overcoming the drawbacks of plastic strain estimation based on KAM.

Plastic strain estimation using electron backscatter diffraction (EBSD) based on kernel average misorientation (KAM) is affected by random orientation measurement error, EBSD step length, choice of kernel and average grain size. These sensitivities complicate reproducibility of results between labs, but it is shown in this work how these drawbacks can be overcome. The modifications to KAM were verified against a similar misorientation metric based on grain orientation spread (GOS), which does not show sensitivity to these factors. Both metrics were used in parallel to estimate the plastic strain distribution in Alloy 690 heat affected zones from component mockups, and showed the same results where the grain size was correctly compensated for.

On the Analysis of Clustering in an Irradiated Low Alloy Reactor Pressure Vessel Steel Weld.

Radiation induced clustering affects the mechanical properties, that is the ductile to brittle transition temperature (DBTT), of reactor pressure vessel (RPV) steel of nuclear power plants. The combination of low Cu and high Ni used in some RPV welds is known to further enhance the DBTT shift during long time operation. In this study, RPV weld samples containing 0.04 at% Cu and 1.6 at% Ni were irradiated to 2.0 and 6.4×1023 n/m2 in the Halden test reactor. Atom probe tomography (APT) was applied to study clustering of Ni, Mn, Si, and Cu. As the clusters are in the nanometer-range, APT is a very suitable technique for this type of study. From APT analyses information about size distribution, number density, and composition of the clusters can be obtained. However, the quantification of these attributes is not trivial. The maximum separation method (MSM) has been used to characterize the clusters and a detailed study about the influence of the choice of MSM cluster parameters, primarily on the cluster number density, has been undertaken.