Hitoshi Kaguchi

Proposal of a new estimation method for the thermal ratchetting of a cylinder subjected to a moving temperature distribution

Abstract In the structural design of an FBR component, thermal ratchetting without primary stress must be prevented. In this paper, thermal ratchetting of a hollow cylinder subjected to an axial movement of temperature distribution is focused on as a typical ratchetting mechanism of an FBR component. The basic estimation equations for this type of ratchetting are improved by using a theoretical model considering the effects of axial bending stress. The propriety of the proposed model is verified by comparing the predicted stress and strain with numerical results by FEM. Lastly, a new design procedure based on the improved estimation equation is proposed.

Applications of probabilistic fracture mechanics to FBR components

Abstract A probabilistic fracture mechanics code which evaluates fracture probability of a plate model with an elliptical surface crack caused by creep-fatigue crack growth has been developed. The code named PCCF (Probabilistic Fracture Mechanics Code for Creep-Fatigue Crack Growth) uses simplified methods of C ∗ and J- integral for evaluation of creep-fatigue crack growth and a stratified sampling method for two input variables to improve the solution convergency. According to the test analyses focused on an applied stress level using PCCF code, leak probability is sensitive to a stress level and increases rapidly when an applied stress is close to a yield stress level.

Study on Metallography of Low Cycle Creep Fatigue Fracture of Type 316 Stainless Steels

The metallography of creep fatigue fracture of conventional type 316 (SUS316) and low carbon medium nitrogen type 316 (316MN) steels has been studied. The creep fatigue lives depend on the grainboundary precipitation during creep fatigue. Coarse carbides in SUS316 would cause grainboundary embrittlement, while very fine Laves phase in 316MN may have no influence. Since carbide precipitation by aging results in loss of matrix strength of SUS316, creep fatigue life increases. On the other hand, the grainboundary precipitation of 316MN is so small and stable that creep fatigue life does not change by aging. The decrease in remaining ductility by loading cycles depends on grainboundary embrittlement by precipitation and work hardening.

Study on Fracture Mechanism and a Life Estimation Method for Low Cycle Creep-Fatigue Fracture of Type 316 Stainless Steels

In order to improve the accuracy of creep-fatigue life estimation method, experimental investigations were conducted focusing to the ductility exhaustion rule. At first, it was found by the tensile test for type 316 stainless steels that the ductility decreased and fracture mode changed with the decrease of strain rate. The tensile test was also performed using the creep-fatigue interruption test specimen and it was found that there was a good correlation between the decrease of residual ductility and the creep damage. From these points of view, the authors proposed the improved life estimation method based on the ductility exhaustion concept and confirmed its effectiveness.

Evaluation of creep-fatigue design methods by structural failure tests under thermal loads

Abstract Creep-fatigue tests were conducted under cyclic thermal stresses using two types of simple structural models, the free surface model and ring cylinder model. All models were made of SUS304 stainless steel and some of the specimens had longitudinal welds. Failure lives were defined as the cycle at which small visible cracks were detected. Three kinds of life evaluations were made. Two of these were based on elastic analysis and one of these was based on inelastic analysis. The estimated lives were compared with the experimental results and the results can be summarized as follows. 1. (1) Life estimation based on inelastic analysis was adequate and the estimated lives agreed well with the experimental results. 2. (2) Life estimation by the Monju Design Guide based on elastic analysis gave conservative results. However, the accuracy of life estimation could be improved by using the elastic follow-up factor ( q value) obtained from inelastic analysis.

Stress Corrosion Cracking Incidents and Repair Technologies on PWR Dissimilar Weld Metal Joints in Japan

Several Japanese PWR power plants have experienced Primary Water Stress Corrosion Cracking (PWSCC) on dissimilar weld joints since 2004. J weld of 3 Reactor Vessel Head Penetration in Ohi unit 3 is one of the PWSCC incidents occurred in 2004 and has been studied by sampling and opening the fracture surface after its repair. Including Ohi unit 3 Reactor Vessel Head Penetration repair, Japanese PWR utilities and MHI have been developing the preventive maintenance and repair technologies applicable to alloy 600 welds and base metal, following PWSCC events on the Bugey-3 and V.C. Summer. This paper describes recent Japanese PWSCC incidents and repair technologies developed in Japan.Copyright