Developments in the estimation of tensile strength by small punch testing

The Small Punch (SP) test is a relatively simple test well suited for material ranking and material property estimation in situations where standard testing is not possible or considered too material consuming. The material tensile properties, e.g. the ultimate tensile strength (Rm) and proof strength (Rp02) are usually linearly correlated to the force-deflection behaviour of a SP test. However, if the test samples and test set-up dimensions are not according to standardized dimensions or the material ductility does not allow the SP sample to deform to the pre-defined displacements used in these correlations, the standard formulations can naturally not be used. Also, in cases where no supporting Rm data is available the applied correlation factors cannot be verified. In this paper a formulation is proposed that enables the estimation of Rm without supporting uniaxial tensile strength data for a range of materials, both for the soon to be standardized flat samples as well as for curved (tube section) samples. The proposed equations are based on the classical and recent SP and Small Punch Creep (SPC) formulations. It is claimed that the both equivalent stress in small punch creep and tensile strength can be robustly estimated with the same type of equations at least for ductile and semi-ductile ferritic/martensitic and austenitic steels. It is also shown that the same equations can be applied on non-standard test samples and test set-ups. The tensile strength of semi-ductile materials such as 46% cold worked 15-15Ti cladding steel tubes are successfully estimated by correcting the correlations for the curvature of the samples. The usability of the SP testing and assessment method for estimating tensile strength of engineering steels in general and for nuclear claddings in specific has been verified.