An improved analysis of small punch deformation for evaluating tensile properties

Small punch (SP) method is a promising technique for evaluating tensile properties using small volumes of test material, yet its applicability is bound by large errors in estimation of tensile yield strength (YS) using the yield force (FY) determined by the existing two tangent, offset or bilinear function fitting methods. In this study, a yield force (FY) based on the occurrence of yielding across the specimen thickness is identified through finite element analysis and a methodology is formulated for determination of FY from experimental data, supported with acoustic emission (AE) technique. The YS-FY correlation for various structural steels, Inconel and Aluminum exhibit excellent linearity and standard errors within ±7%. Based on the onset of plastic instability in SP deformation at an inflection point (Fs, us) of force-deflection curve, the specimen deflection us is shown to correlate with tensile uniform strain better than parameter um (deflection at peak load). The tensile properties of neutron irradiated SS 316 evaluated from SP tests using the methodologies and SP-tensile correlations formulated in this work, are found to be within 6-8% of the uniaxial tensile test results.