1992 Volume 78 Issue 6 Pages 926-933
Elastic-plastic fracture toughness JIC has been determined by the R-curve method and an ultrasonic single specimen method over the range below room temperature. Samples with high nodularity and with three kinds of graphite nodule spacings were taken from a thick walled cylindrical casting. Fracture toughness specimens used were compact tension (CT) specimens with 25mm in thickness.
Ductile-brittle transition occurred at a low temperature region. In the ductile fracture region, JIC increased with increasing graphite nodule spacing and with decreasing temperature. Estimated plain strain fracture toughness divided by yield stress was constant over the ductile fracture region. This parameter, therefore, can be used as a material constant representing the resistance to ductile fracture in the material used.
For the behavior of JIC in regard to graphite nodule spacing and temperature, a model of the onset of crack propagation is proposed using void growth and coalescence with the precrack tip.