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The Army Materials and Mechanics Research Center, AMMRC, (formerly Watertown Arsenal Laboratories) has managed a program for many years on the certification of Charpy impact machines. During this period, approximately 200 machines have been evaluated annually.
This paper is a compilation of the findings of these certification tests. What is evident is that each model machine possesses its own characteristic weaknesses which, unless controlled, can easily result in erroneously high test values. It is estimated that approximately half of the machines in use today are producing values well in excess of the limits set in Army specifications; that is, plus or minus 5 percent or 1.0 ft∙lb, whichever is the greater. Since most discrepancies either slow down the pendulum or result in absorptional losses, the value recorded includes energy not expended in fracturing the specimen, thus creating a false sense of security for the investigator or design engineer.
impact tests, dynamic tests, calibrating, evaluation, tests
Mechanical engineer, chief, Army Materials and Mechanics Research Center, Watertown, Mass.