Methodologies to evaluate fracture toughness in lamellar grey cast iron

Fracture mechanics properties in lamellar grey cast iron were traditionally evaluated from parameters calculated at maximum load values from load vs. crack mouth opening displacement records. The evaluation was carried out in this way as a consequence of the difficulty in measuring stable crack growth. The chemical tinting technique presented in this paper permits stable crack growth in lamellar grey cast iron to be measured, and then, the determination of R-Curves by a multiple specimens technique. A good agreement between the measured compliances and the theoretical ones was also observed. This demonstrates that the unloading compliance method can be used in stable crack growth measurements to determine J-R Curves. In fact, the R-Curves obtained by both methods, unloading compliance and multiple specimens, are consistent. A technological toughness value corresponding to Deltaa = 0.5mm, J.(5) was proposed because the R-Curves set apart from the blunting line at a very early stage. Maximum load values (K-Pmax, J(max) and K-Jmax) were also determined.