Evaluation of the Small Punch Test: Repeatability and Sample Parameter Influence

Abstract The small punch test (SPT) is a fast method to evaluate alloys and compositional gradients across small length scales. However, its repeatability is commonly in question given size effects and sample preparation requirements. This study analyzes cold drawn commercial grade mild steels, correlating testing parameters to differences in microstructure and comparing them to the literature. The samples tested produced force–displacement curves that exhibited the expected five-stage deformation sequence. Low variance between tests proved sound sample preparation and testing techniques were used. Distinguished values of the curves were then used to develop an empirical relationship to known yield and ultimate tensile strength of the material and comparatively assessed with values from the literature. This relationship can now be applied to determine properties of SPT’s completed with similar steels. Results were analyzed further through a correlation matrix, showing a high relation between transition force and energy values of the test. Fractographic and microstructural analyses revealed ductile fracture mechanisms consistent with the steel’s properties. A heterogeneous spatial distribution of the strain field across a short length scale was observed, which emphasizes the critical requirement of metallographically homogenous structured samples for reliable data reproducibility.