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.

小冲孔试验（SPT）可被视为单轴拉伸试验的替代方法。已经进行了许多尝试来从SPT结果中提取抗拉强度特性，但是在估算真实的应力-塑性应变曲线方面所做的工作很少。本文旨在提出一种从SPT力-挠度曲线推导真实应力-塑性应变曲线的方法。使用数据库方法从力-挠度曲线中提取出不同塑性应变下的工程应力。这些工程应力和塑性应变点用于确定Ludwik硬化定律的参数，然后使用这些参数在缩颈之前生成真实的应力-塑性应变曲线。为了验证以这种方式估算真实的应力-塑性应变曲线的准确性，该程序应用于三种假设的材料。发现从SPT数据中准确提取出颈缩之前​​的真实应力-塑性应变曲线。拟议的程序还用于处理3Cr1MoV，2.25Cr1Mo和16MnR的力-挠度曲线。结果表明，所获得的应力和应变关系可以很好地预测SPT试样的力响应。使用数据库评估真实的应力-塑性应变曲线是有效的，并且在理论的支持下可以促进应用SPT表征材料的机械性能。