Use of database and small punch test to estimate true stress-plastic strain curve of steels

The small punch test (SPT) can be recognized as an alternative to uniaxial tensile testing. Many attempts have been made to extract tensile strength properties from SPT results, but few works on estimating true stress-plastic strain curves. This paper aims to propose an approach for deriving a true stress-plastic strain curve from the force-deflection curve of SPT. Engineering stresses at different plastic strains are extracted from a force-deflection curve using a database method. These engineering stress and plastic strain points are employed to determine the parameters of Ludwik hardening law, then a true stress-plastic strain curve before necking is generated using those parameters. To verify the accuracy in estimating true stress-plastic strain curves in this way, the procedure was applied to three hypothetical materials. It is found that true stress-plastic strain curves before necking are accurately extracted from SPT data. The proposed procedure was also used to process the force-deflection curves of 3Cr1MoV, 2.25Cr1Mo and 16MnR. The results show that the obtained stress and strain relation can predict the force responses of SPT specimens well. Using a database to evaluate true stress-plastic strain curves is effective and with the support of theory that could promote the application of SPT in characterizing material mechanical properties.