Overview of NIST Activities on Subsize and Miniaturized Charpy Specimens: Correlations With Full Size Specimens and Verification Specimens for Small Scale Pendulum Machines

Abstract

NIST in Boulder, CO investigated the correlations between impact test results obtained from standard, fullsize Charpy Vnotch (CVN) specimens and specimens with reduced thickness (subsize Charpy Vnotch specimens (SCVN)) or reduced or scaled cross section dimensions (miniaturized Charpy Vnotch specimens (MCVN)). A database of instrumented impact test results was generated from four line pipe steels: two quenched alloy steels, a tempered alloy steel, and a 18 Ni maraging steel. Correlations between specimen types were established and compared with the previously published relationships, considering absorbed energy (KV), ductiletobrittle transition temperature (DBTT), and upper shelf energy (USE). Acceptable correlations were found for the different parameters, even though the uncertainty of predictions appears exacerbated by the expected significant experimental scatter. Furthermore, we report on the development of MCVN specimens for the indirect verification of smallscale pendulum machines (with potential energies between 15 J and 50 J), which cannot be verified with fullsize verification specimens. Smallscale pendulum machines can now be verified at room temperature with certified reference specimens of KLST type (3 mm أ— 4 mm أ— 27 mm), supplied by NIST at three certified KV levels (low energy (LL), 1.59 J; high energy (HH), 5.64 J; and superhigh (SH) energy, 10.05 J). These specimens can also be used to verify the performance of instrumented Charpy strikers through certified maximum force values. Certified reference values for both KV and maximum force were established by means of an interlaboratory comparison (RoundRobin), which involved nine qualified and experienced international laboratories.