Volume 4, Issue 10 (November 2007)
Use of KLST-Type Miniature Charpy Specimens for Measuring Dynamic Fracture Toughness under Impact Loading Rates
The knowledge of dynamic mechanical properties is useful in all cases where the strain rate sensitivity of metallic materials is an issue, and whenever the actual loading conditions for a structure (either in normal operation or under accidental circumstances) are different from static. Furthermore, in some investigations, increasing the loading rate in a mechanical test is used to simulate other embrittling mechanisms such as thermal aging or neutron exposure. Precracked Charpy-type (PCVN) specimens, tested under impact loading rates using an instrumented pendulum, have been used for more than 30 years to measure dynamic fracture toughness; the experimental procedure and the analysis methodology are fairly well established, despite the lack of an ASTM or ISO official test standard. This paper addresses the applicability of fatigue precracked miniature Charpy specimens of KLST type (PKLST-B = 3 mm, W = 4 mm and L = 27 mm) for impact toughness measurements in the ductile-to-brittle transition regime and in fully ductile (upper shelf) conditions. In the transition region, tests have been analyzed using the Master Curve approach; the multiple-specimen (low-blow) method has been applied in the upper shelf regime. A well-known and fully characterized reactor pressure vessel steel of the A533B Cl.1 type (JRQ) has been used; the results obtained have been compared with data previously obtained from standard-size precracked Charpy specimens. It has been found that under impact loading conditions PKLST specimens suffer significant loss of constraint when compared to conventional precracked Charpy V-notch samples, in both transition and upper shelf conditions.