DAMAGE EFFECT ON THE FRACTURE-TOUGHNESS OF NODULAR CAST-IRON .1. DAMAGE CHARACTERIZATION AND PLASTIC-FLOW STRESS MODELING

After chemical, morphological, and mechanical characterization of duct ile cast iron, the damage mechanisms were studied by tensile tests ins ide the scanning electron microscope (SEM). The evolutions of Young's modulus and of Poisson's ratio were measured in uniaxial tensile tests . Compression tests were used to measure the pressure sensitivity coef ficient of the flow stress; The damage is produced by early initiation of cavities at the pole cap of graphite nodules by debonding of the i nterface, followed by the growth of cavities. The mechanical behavior was modeled in the elastic region by calculating the Hashin-Shtrickman bounds. This provided the elastic constants for the graphite nodules; The plastic behavior was modeled by considering that the graphite nod ules were replaced by voids. The critical interfacial stress for debon ding was determined by analytical as well as by finite-element calcula tions. The growth rate of cavities was deduced from the evolution of t he Poisson's ratio and was compared with predictions from Grurson's po tential. The stress-strain behavior could be modeled either by extensi on of the Mori-Tanaka analysis in the plastic range or by finite-eleme nt computations. This allowed a fair prediction of the observed behavi or.