Issue 30

V. Di Cocco et alii, Frattura ed Integrità Strutturale, 30 (2014) 462-468; DOI: 10.3221/IGF-ESIS.30.56 462 Focussed on: Fracture and Structural Integrity related Issues Stress triaxiality influence on damaging micromechanisms in a pearlitic ductile cast iron Vittorio Di Cocco, Francesco Iacoviello, Alessandra Rossi Università di Cassino e del Lazio Meridionale, DICeM, via G. Di Biasio 43, 03043, Cassino (FR), Italy v.dicocco@unicas.it , iacoviello@unicas.it, alessandra.rossi@unicas.it Mauro Cavallini Università di Roma “La Sapienza”, DICMA, via Eudossiana 18, Roma, Italy mauro.cavallini@uniroma1.it A BSTRACT . In the last decades, damaging micromechanisms in ductile cast irons (DCIs) have been widely investigated, considering both the matrix microstructure and the loading conditions influence. Considering the graphite nodules, they were initially considered as voids embedded and growing in a ductile metal matrix (especially considering ferritic ductile cast irons). Recent experimental results allowed to identify a more complex role played by the graphite nodules, depending on the matrix microstructure. In this work, damaging micromechanisms in a pearlitic DCI were investigated by means of tensile tests performed on notched specimen, mainly focusing the role played by graphite elements and considering the stress triaxiality influence. K EYWORDS . Ductile Cast Irons (DCIs); Damaging micromechanisms; Microstructure influence; Stress triaxiality. I NTRODUCTION CIs damage micromechanisms analysis was often focused on voids nucleation and growth due to the matrix- graphite nodules debonding [1-5] and numerous studies provided analytical laws to describe a single void growth, depending on the void geometries and matrix behaviour. According to this approach, DCI damage evolution was summarized considering the following stages: - Separating between nodular graphite and matrix under low stress (matrix-nodule debonding). - Plastic deformation in matrix around nodular graphite. - Initiation of microcracks in deformed matrix between nodular graphite. - Linkage of graphites by microcracks and formation of larger microcracks. - Linkage of main crack and selected microcracks to form macrocracks. According to this scheme, graphite nodules are considered as voids embedded in a metal matrix. This approach allows to perform useful simulations of the DCIs mechanical behaviour often described according to Tvergaard Needleman modified Gurson’s model [6-8], but it is based on a non-completely correct analysis damaging micromechanisms: only D