Charpy Impact Testing of Metals: Problems and Mechanisms of Ensuring Measurement Traceability

Charpy impact testing of metals, along with static tensile testing, forms the basis for assessing their structural strength and reliability across various industries. Currently, the traceability of measurements performed during impact strength testing using pendulum impact testers is ensured mainly by the results of their verification. Existing verification procedures do not take into account the critical significance of one of the main subsystems of the impact tester – the impact and specimen fracture subsystem. As a result, an impact tester deemed suitable based on verification results actually shows overestimated absorbed energy measurement results due to parasitic energy losses.

An analysis of Russian and international standards on impact strength testing, as well as publications by domestic and foreign authors, has made it possible to identify factors leading to overestimated absorbed energy measurement results obtained with classical pendulum impact testers. The conducted interlaboratory comparison tests, on the one hand, confirmed this finding and, on the other hand, substantiated the impracticality of establishing measurement traceability based on the classical impact testing method.

It is proposed to use a reference pendulum impact machine of the highest accuracy, supporting the instrumented test method, as the basis for ensuring measurement traceability to the existing State Primary Standard of the unit of force GET 32–2011. The presence of a force measuring transducer in its composition allows it to be considered a working standard for further transferring the unit of force to reference measures (specimens), and from them, respectively, to instrumented and classical impact testers. It is also proposed to include the reference impact tester directly into the composition of the improved State Primary Standard of the unit of force GET 32–2011 or the State Primary Standard of the unit of impact acceleration GET 57–84.

To eliminate the problem associated with overestimated absorbed energy measurement results, it is necessary to develop and approve the type of force and absorbed energy measures and reference materials. Furthermore, for the widespread implementation of the considered approach, in addition to the State Verification Schedule, it is necessary to develop a unified verification procedure and extend it to all pendulum impact testers operated in Russia.

The measures described above will actually ensure the uniformity of measurements in impact strength testing performed using both classical and instrumented impact testers.

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