Yield Strength Evaluation by Small-Punch Test

Because of the mechanical property degradation experienced by the nuclear power plant components, it is important to evaluate the evolution of the mechanical properties during service, such as the yield strength. A lack of materials available from nuclear power plants has led to the development of more and more small-sized specimen tests such as the small-punch test that has the advantage of using very small amounts of material with very simple working conditions (machining and test). In this study, we will present a new method for the yield strength estimation. This method is based on the elastic deformation energy method and is compared with the current methods which include the "two tangents" method and the offset method. This new method consists of the determination of the yield strength by measuring the energy beneath the load-displacement curve in the elastic deformation domain. The elastic deformation domain is defined by measuring the elastic reverse displacement during an unloading phase. Subsequently, the elastic displacement reverse is applied at the beginning of the load-displacement curve. Good agreement has been found between the elastic deformation energy and the square of the tensile yield strength. This method allows a better evaluation of the tensile yield strength and with a reduced scatter compared to the current conventional methods.