Abstract
Testing and estimation procedures for obtaining true stress-strain curves of stainless steels were discussed in order to calculate load carrying capacity of nuclear power plant components by elastic-plastic finite element analyses. Type 316 stainless steel specimens of various degrees of cold working were subjected to tensile tests with different test speeds. It was shown that faster test speed reduced elongation and ultimate strength of the specimens. The strain on the specimen surface measured by the digital image correlation (DIC) technique exhibited an inhomogeneous strain distribution even when the strain was less than the uniform elongation (necking strain). The strain was elevated locally at the center of the specimen and its magnitude was about 1.2 times the nominal strain measured by an extensometer. A testing method (IFD method) has been developed to obtain the true stress-strain curve including post-necking strain by using an hourglass type specimen. In this study, the IFD method was improved so that it was applicable to the round-bar smooth specimens used for the tensile tests. Then, the stress-strain curves were estimated from the 0.2% proof and ultimate strengths by the K-fit method, which has been proposed by the current author. It was shown that K-fit method could estimate the stress-strain curves including the post-necking strain. Finally, a tensile test was carried out using a plate specimen with round notches. Elastic-plastic finite element analyses using the stress-strain curves estimated by the improved IFD method and K-fit method could simulate the deformation and strain distribution. The load carrying capacity obtained by the finite element analyses were almost equivalent to that obtained by the tensile test. However, the yielding load obtained by the finite element analyses were slightly higher than that obtained by the test due to the strain rate dependency of the stress-strain curve.
