A technique for the determination of post-yield material properties from the small punch test

The aim of the present work was to determine post-yield material properties from small punch test results, i.e. from the force-displacement curve obtained in such a test. This determination was made by comparing the experimental curve with a large set of previously determined finite element (FE) curves for differing post-yield properties expressed in terms of Ramberg and Osgood parameters. A simple cost function was then used to find the closest FE curve and thus provide an estimate of the post-yield properties. This estimate was then updated using an optimization technique based on the Matlab ‘fminsearch’ function and an interface with the ABAQUS FE code, giving a reliable estimate of the post-yield material properties. The FE analysis and model were validated by comparison with other small punch tests and the FE curves were additionally used to determine von Mises stresses, equivalent plastic strains and displacements.

The method used to determine post-yield properties from small specimens has been demonstrated by determining the material properties of stainless steel. The technique is particularly relevant to those steels used in pressure vessels.