Certification of NIST Room Temperature Low-Energy and High-Energy Charpy Verification Specimens
Enrico Lucon, Christopher N. McCowan, Raymond L. Santoyo
The feasibility of certifying Charpy reference specimens for testing at room temperature (21 °C ± 1 °C) instead of −40 °C was demonstrated at NIST by performing 130 room-temperature tests from five low-energy and four high-energy lots of steel on the three master Charpy machines located in Boulder, CO. The statistical analyses performed show that in most cases the variability of results (i.e., the experimental scatter) is reduced when testing at room temperature. For eight out of the nine lots considered, both the coefficient of variation and the sample size were lower at 21 °C than at −40 °C. The results of this study will allow NIST to satisfy requests for room-temperature Charpy verification specimens that have been received from customers for several years: testing at 21 °C removes from the verification process the operator's skill in transferring the specimen in a timely fashion from the cooling bath to the impact position, and puts the focus back on the machine performance. For NIST, it also reduces the time and cost for certifying new verification lots. For one of the low-energy lots tested with a C-shaped hammer, we experienced two specimens jamming, which yielded unusually high values of absorbed energy. For both specimens, the signs of jamming were clearly visible. Jamming is slightly more likely to occur at 21 °C than at −40 °C, since at room temperature low-energy samples tend to remain in the test area after impact rather than exiting in the opposite direction of the pendulum swing. In the evaluation of a verification set, any jammed specimen should anyway be removed from the analyses.
Journal of Research of the National Institute of Standards and Technology
, McCowan, C.
and Santoyo, R.
Certification of NIST Room Temperature Low-Energy and High-Energy Charpy Verification Specimens, Journal of Research of the National Institute of Standards and Technology, [online], https://doi.org/10.6028/jres.120.020
(Accessed February 23, 2024)