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Dimensional Inspection of Charpy Indirect Verification Specimens By Means of a Digital Optical Comparator



Enrico Lucon, Raymond L. Santoyo, Allen Eckhardt


The Charpy reference specimens produced by NIST for the indirect verification of Charpy machines in accordance with ASTM E23 and ISO 148-1 must satisfy strict dimensional requirements, with tolerances that are in most cases tighter than those prescribed by the standards. In the past, Charpy specimens to be certified were dimensionally inspected by means of an optical comparator (shadowgraph), which has been replaced in 2019 by a digital optical comparator manufactured by Keyence, which provides enhanced measurement accuracy. This report provides step-by-step operating instructions for the dimensional inspection of Charpy certified reference specimens using the digital measurement system, as well as details about its annual recertification, and the NIST dimensional criteria for lot acceptance. Measurements conducted at NIST on five Charpy specimens using the digital comparator were found in excellent agreement with data provided by participants in an ASTM Interlaboratory Study (ILS 1151), demonstrating the accuracy and reliability of the Charpy measurement system currently used at NIST.
NIST Interagency/Internal Report (NISTIR) - 8507
Report Number


ASTM E23, Charpy reference specimens, digital optical comparator, dimensional requirements, indirect verification, Interlaboratory Study (ILS), ISO 148-1.


Lucon, E. , Santoyo, R. and Eckhardt, A. (2024), Dimensional Inspection of Charpy Indirect Verification Specimens By Means of a Digital Optical Comparator, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 19, 2024)
Created February 26, 2024