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Abstract: The small-punch (SP) test and the SP creep test were carried out by using a further miniaturized plate-type specimen (3mm diameter×0.25mm thick). Those tests were applied to the electron-beam welded joint of reduced-activation ferritic steel for evaluating the distribution of high-temperature strength in the joint. The experimental results revealed that the distribution of the maximum load measured by the SP test at 873K was very similar to that obtained from Vickers hardness, and the fusion zone was relatively devoid of high-temperature ductility. In addition, the ratio of the load of SP creep test to the stress of standard uniaxial creep test was calculated so that both the creep rupture curves were overlapped to convert the results of SP creep test into those of standard test. As a result, the ratio was determined to be 0.43 for the base metal and this load-stress conversion coefficient is in good agreement with that obtained from finite element analysis. [Copyright &y& Elsevier]

Abstract: Type IV creep damage has recently been a worldwide issue for high Cr ferritic steels. The small punch (SP) creep test has been successfully applied to evaluate this damage of low alloy ferritic steel by the author’s group. However, the heat affected zone (HAZ) of fusion reactor material welded by electron-beam (EB) welding is so thin that it is not easy to evaluate its mechanical properties by the conventional SP test. In this study, the SP test using a further miniaturized specimen was applied to the EB welded joint of reduced activation ferritic steel (RAFs), for evaluating high-temperature tensile properties of the HAZs. As the result, the σ y and σ B of the tempered HAZ at 873K were estimated to be as low as 275–300MPa and 325–340MPa, respectively. [Copyright &y& Elsevier]

• The probability density function of material strength is then a fundamental input for determining design criteria. • A Bayesian estimation method was adopted to predict the dependence of neutron irradiation damage on the tensile properties of F82H steel. • Good predictions were obtained with the lognormal model for 0.2% proof strength and tensile strength, both exponential normal and exponential Weibull models for total elongation, and the exponential Weibull model for uniform elongation. The deterministic approach widely adopted in the design of structural components relies on systematically defined design limits using empirically determined safety factors. However, this approach is not always appropriate because structures are subjected to a variety of loads in the practical environment, which may result in excessively conservative design limits. In recent years, a more rigorous probabilistic approach that incorporates material strength distributions has become an important solution. In the probabilistic approach, the probability density functions of material strength properties underpin the design criteria. The objective of this study is to identify the density distribution functions that best describe tensile properties of irradiated F82H to define a reference strength for DEMO design. Due to the limited number of existing data, this study specifically employs a Bayesian prediction method based on Monte Carlo simulations to determine a material reference value with statistical reliability and to investigate its effectiveness. For example, the dependence of tensile properties of 300 °C irradiated materials on irradiation damage and the range predicted by 95% Bayesian estimation was evaluated. As a statistical model for the dose dependence of statistical parameters, the normal distribution exhibited a better fit for 0.2% proof strength and tensile strength, whereas the distribution of total elongation data gave comparable reference values for both the normal and Weibull distribution models. Both models gave comparable criteria for the distribution of total elongation data. The Weibull model also gave better results for uniform elongation. The function best describing the model was a logarithmic law for both 0.2% proof strength and tensile strength, while a power law for both total and uniform elongation, which allowed for more comprehensive data prediction of irradiation data with statistical accuracy for DEMO reactor design. [ABSTRACT FROM AUTHOR]

• We summarized and analyzed the data of tensile, creep, and fatigue properties to develop the material strength standard of F82H for RCC-MRx. • The standard developed in this work can be applicable to the design of blanket module made of F82H conforming to RCC-MRx after qualification processes. • There still remain some values to be specified and it is necessary to keep the material strength standard updated performing further tests and analyses. Non-irradiated and irradiated material properties of a reduced activation ferritic/martensitic steel, F82H, have been extensively accumulated through international collaborative researches. F82H then demonstrates material properties applicable to the structural material of breeding blanket module. At present, material strength standard needs to be developed for the design activity of blanket module. Material strength standard generally gives average, minimum, and design values of mechanical property and their equations complying with the definition in construction code. In this work, we summarized and analyzed the experimental data of tensile, creep, and fatigue properties, and developed the material strength standard for RCC-MRx. Obtained values were then compared to those of Eurofer. Though some minor differences were observed in minimum and average values of tensile and creep properties, no significant differences were observed in their design values. As for fatigue property, F82H showed conservative design curves. [ABSTRACT FROM AUTHOR]