The sensitivity ranking of ductile material mechanical properties, geometrical factors, friction coefficients and damage parameters for small punch test

Abstract

Small punch test offers unique capabilities in extracting material properties from a very small volume of material. This is an attractive prospect for measuring the properties of hazardous materials such as those in the nuclear industry. Although standards are being developed for formalising small punch test, the uncertainty associated with its results due to issues with misalignment, sample geometry deviation, friction coefficients and damage evolution have not been fully understood. In this article, the effects of mechanical properties, damage parameters, friction coefficients, pre-tightening condition and geometry uncertainty on the small punch test response of ductile materials are evaluated by finite element analyses. A comprehensive sensitivity study has been carried out on the variation of the reaction force induced by above factors and their influences have been quantified and ranked at various stages of small punch testing. It was observed that the material mechanical properties and geometrical dimension deviations have significant effects on all stages of small punch test. However, damage parameters and friction coefficients mainly play roles at the maximum load point. The uncertainty in values measured for yield stress and ultimate tensile strength from small punch test of a sample with ±5% deviation in thickness from standard value was calculated to be of the same order of magnitude of the respective material properties. A nominalization method for considering the specimen thickness deviation is provided which can help to eliminate the effect of specimen thickness deviation in the measurements carried out by small punch test.