T. Pardoen et F. Delannay, A method for the metallographical measurement of the CTOD at cracking initiation and the role of reverse plasticity on unloading, ENG FRACT M, 65(4), 2000, pp. 455-466
A method is proposed for accurately estimating the Crack Tip Opening Displa
cement (CTOD) at physical cracking initiation in ductile materials. The met
hod requires a few precracked specimens to be loaded in such a way as to ex
hibit various crack extensions. The total opening of the blunted precrack,
delta(1), the opening of the tearing crack, delta(2), and the ductile teari
ng extension are measured for each specimens. The unloaded CTOD at cracking
initiation is equal to the difference of delta(1) - delta(2) extrapolated
for zero crack extension. Results obtained in two different applications, o
ne on plane strain specimens of copper and the other on TRIP assisted multi
phase steel plates, illustrate the potential of the method. A model based o
n fracture mechanics arguments is proposed in order to account for the reve
rse plasticity during unloading. This model is compared to results obtained
using more exact large strain finite element computations. 2000 Elsevier S
cience Ltd. All rights reserved.