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Dynamic Calibration of Instrumented Charpy Strikers

Charpy impact test
Credit: Geoffrey Wheeler

The Charpy impact test is an experimental test used worldwide for characterizing the notch toughness of metals, and thereby their suitability for applications ranging from ship hulls and railroad tracks to nuclear reactor pressure vessels. A standard Charpy test measures the energy absorbed in fracturing a specimen impacted by a swinging hammer. The Charpy Machine Verification Program at NIST supplies thousands of customers worldwide with Charpy steel specimens that have been certified on the NIST reference Charpy machines.

In an instrumented  Charpy test, strain gauges attached to the striker provide an indication of the force applied to the specimen during impact. The force-time record offers additional information about the tested material’s properties in comparison to a standard Charpy test. Charpy impacts on metal specimens have duration typically ranging from 0.1 ms to 5 ms, with force pulse amplitudes typically exceeding 25 kN for steel specimens.

This activity seeks to provide SI-traceable force/time data from instrumented Charpy tests on the NIST machines by direct dynamic calibration. In this work, we have redesigned instrumented Charpy strikers for reduced force uncertainty, have performed dynamic calibration of Charpy strikers, and have estimated uncertainty of Charpy instrumented force measurements.

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Created January 16, 2020