Mechanical properties of structural metallic alloys for nuclear applications deduced by small punch test

Abstract

Small Punch Test (SPT) techniques are becoming a popular tool for the characterization of the irradiation damage effects in nuclear materials thanks to a number of advantages as compared to conventional test methods. As of today, there are two standards available (ASTM and EN) and several methods are developed to extract the tensile properties from the SPT force-displacement relationship. Here, we carry a set of benchmark tests using SPT and conventional uniaxial tensile tests on a number of metallic materials commonly applied in nuclear facilities. The investigation includes reactor pressure vessel steel, high-Cr ferritic martensitic steel, copper-chromium-zirconium alloy, nickel based super alloy, austenitic stainless steel and titanium. The SPT sample geometry and setup is designed according to the requirements of the EN10371 norm. As a result, we have deduced the tensile properties using both techniques and thus have revealed the accuracy/reliability of the currently available standards for the determination of the yield stress and ultimate tensile strength by the SPT.The study has revealed that in an overwhelming number of tests, the yield stress extracted from the SPT (for both EN and ASTM standards) is systematically overestimated as compared to the value measured from the uniaxial tensile test. However, the prediction for the ferritic and austenitic steels is close to the uniaxial stress, for both standards. In the case of Inconel material, the yield stress is underestimated. The ultimate tensile strength extracted by either of the existing methods is in a good agreement with the value otherwise measured from the uniaxial tests for all the materials except the titanium. Based on the obtained results and discussion, a number of recommendations for the evaluation of yield and ultimate tensile stress from the small punch test is given.