Evaluation of Uncertainty in Determining Average Grain Size by ASTM E112 Standard

Abstract

In this paper, the ASTM grain size number of aluminium alloy specimen was determined respectively by Abrams Three-Circle Procedure and Planimetric Procedure of ASTM E112-13 Standard, and the uncertainty of the result was evaluated. The results are as follows: 1) Using the Abrams Three-Circle Procedure determines G, G=4.13, U=0.26, k=2; Using the Planimetric Procedure determines G, G=3.94, U=0.15, k=2. 2) It is suggested that the ASTM E112 standard should provide that the errors of counting grain boundary intersection count or number of grains should be less than or equal to 2, and the ruler that determines the diameter of test circle or scale length should be with the scale that is less than or equal to 0.10 mm. On this condition, the uncertainties caused by them in determining G can be negligible. 3) The main sources of uncertainty for the determination of G by Abrams Three-Circle Procedure and Planimetric Procedure are repetitive measurement, which depends on the uniformity of grain size of specimen. 4) The %RA limit of ASTM E112 for determining G should be redefined according to the measurement uncertainty in order to be up to the precision requirement (±0.25).