On the Possibility of Adding a Repeatability Requirement for the Indirect Verification of Charpy Machines in ASTM E23.

Abstract

Since 1989, the National Institute of Standards and Technology (NIST) Charpy Machine Verification Program in Boulder, Colorado, has been indirectly verifying Charpy machines around the world according to ASTM E23, Standard Test Methods for Notched Bar Impact Testing of Metallic Materials, and ISO 148-2, Metallic Materials-Charpy Pendulum Impact Test-Part 2: Verification of Testing Machines. Most of the indirect verifications results have been logged in a database, which at the end of May 2024 included 77,105 records, each one corresponding to 4-5 absorbed energy values at one of three energy levels (low, high, and super-high). Based on the analysis of this database, the acceptability criteria of ASTM E23, exclusively based on bias, have been compared with those of ISO 148-2, which also include repeatability. The objective of this study is to support the proposal of revising ASTM E23 by introducing repeatability requirements in addition to the existing bias criteria. Four proposals have been considered and assessed, leading to the selection of a set of repeatability limits (larger of 4 J and 15 % of certified absorbed energy) that only moderately increases the severity of the standard but, most importantly, prevents deeming machines acceptable that satisfy ASTM E23 bias but fail ISO 148-2 repeatability (approximately one sixth of all the machines verified by the NIST since 1990).