Kc. Koppenhoefer et Rh. Dodds, CONSTRAINT EFFECTS ON FRACTURE-TOUGHNESS OF IMPACT-LOADED, PRECRACKEDCHARPY SPECIMENS, Nuclear Engineering and Design, 162(2-3), 1996, pp. 145-158
Impact-loaded, precracked Charpy specimens often play a crucial role i
n irradiation surveillance programs for nuclear power plants. However,
the small specimen size B = W = 10 mm limits the maximum value of cle
avage fracture toughness J(c) that can be measured under elastic-plast
ic conditions without loss of crack tip constraint. In this investigat
ion, plane strain impact analyses provide detailed resolution of crack
tip fields for impact-loaded specimens. Crack tip stress fields are c
haracterized in terms of J-Q trajectories and the toughness-scaling mo
del which is applicable for a cleavage fracture mechanism. Results of
the analyses suggest deformation limits at fracture in the form of b >
MJ(c)/sigma(0), where M approaches 25-30 for a strongly rate-sensitiv
e material at impact velocities of 3-6 m s(-1). Based on direct compar
ison of the static and dynamic J values computed using a domain integr
al formulation, a new proposal emerges for the transition time, the ti
me after impact at which interial effects diminish sufficiently for si
mple evaluation of J using the plastic eta factor approach.