Use of forces from instrumented Charpy V-notch testing to determine crack-arrest toughness

The objective of this investigation is an estimation of the crack-arrest toughness, particularly of irradiated materials, from voltage versus time output of an instrumented tup during a test on a Charpy V-notch (CVN) specimen. This voltage versus time trace (which can be converted to force versus displacement) displays events during fracture of the specimen. Various stages of the fracture process can be identified on the trace, including an arrest point indicating arrest of brittle fracture. The force at arrest, F₃, versus test temperature, T, relationship is examined to explore possible relationships to other experimental measures of crack-arrest toughness such as the drop-weight nil-ductility temperature (NDT), or crack-arrest toughness, K_a. For a wide range of weld and plate materials, the temperature at which F_a = 2.45 kN correlates with NDT with a standard deviation, σ, of about 11 K. Excluding the so-called 'low upper-shelf energy' (USE) welds from the analysis resulted in F_a = 4.12 kN and σ = 6.6 K. The estimates of the correlation of the temperature for F_a = 7.4 kN with the temperature at 100-MPa·√m level for a mean American Society of Mechanical Engineers (ASME) type K_Ia curve through crack-arrest toughness values show that prediction of conservative values of K_a are possible.