Indentation-Energy-to-Fracture (IEF) Parameter for Characterization of DBTT in Carbon Steels Using Nondestructive Automated Ball Indentation (ABI®) Technique

This paper introduces the Indentation-Energy-to-Fracture (IEF) parameter — one of Haggag's most significant methodological advances. The IEF parameter enables extraction of the ductile-to-brittle transition temperature (DBTT) directly from ABI® load-displacement curves without requiring separate Charpy impact specimens.

The ductile-to-brittle transition temperature is the single most important parameter in nuclear reactor pressure vessel integrity assessment. As neutron irradiation accumulates over decades of operation, the DBTT of RPV steels shifts upward, reducing the margin against brittle fracture. Conventional DBTT determination requires a suite of Charpy V-notch impact specimens tested across a range of temperatures — destructive testing that consumes irreplaceable surveillance material.

Haggag's IEF approach computes the total energy absorbed during the ABI® indentation process at each test temperature. By plotting IEF values against temperature, a transition curve analogous to the Charpy transition curve is obtained. The IEF-derived DBTT was shown to correlate with the Charpy DBTT for carbon steels.

This methodological advance enabled ABI® to replace or supplement Charpy surveillance testing for nuclear reactor vessels — potentially extending the useful life of limited surveillance capsule material and enabling assessment of components where Charpy specimens cannot be fabricated.