Damage Analysis of a Ferritic SiMo Ductile Cast Iron Submitted to Tension and Compression Loadings in Temperature

Abstract

Tensile and compression tests were carried out on a ductile cast iron for temperatures up to 1073 K. The damage caused inside and around graphite nodules was evaluated as a function of the local equivalent plastic strain by using microstructural quantifications. The mechanical properties are strongly dependent on a temperature above 773 K. Concerning tensile behavior, an evolutional law issued from the Gurson model representing the void growth as a function of the deformation and temperature was successfully employed. It is demonstrated that the strain state and the temperature have a strong influence on the void growth function. In the case of compression tests, the temperature has a weak influence on the nodule deformation for temperatures lower than 773 K, and the mechanical behavior is driven by the viscoplastic properties of the ferrite. For higher temperatures, the mechanical properties in compression are progressively modified, since graphite nodules tend to remain spherical, and ferrite grains are severely deformed. A synthesis of the damage mechanisms is proposed in the studied range of temperature and plastic strain. It appears that the graphite nodule aspect ratio can be used OPEN ACCESSMetals 2015, 5 2352 as an indicator of the deformation under compression loading for temperatures ranging from room temperature to 673 K.

Microscopic approach to micromechanism of damage in spheroidal cast iron

“…As it was observed on the final crack surface, in the ferritic cast iron (SNi9), which was the most ductile, the G/M debonding at graphite/ferrite interface was localized mainly in the spheroid pole area (Figure 2), similar to the results of observations reported previously in Bonora and Ruggiero (), Di Cocco et al (), Di Cocco et al (), Dong and Prioul (), and Hervas et al ().…”

“…Observed morphological effects at the G/M interface, and inside graphite nodule on the fracture surface of tensile specimens allowed giving some preliminary assumptions concerning mechanism of the damage process, as a confirmation of the previously reported works (Andriollo et al, ; Andriollo et al, ; Bonora & Ruggiero, ; Cooper et al, ; Di Cocco et al, ; Dong & Prioul, ; Fukumasu et al, ; Hervas et al, ; Iacoviello et al, ; Iacoviello & Di Cocco, ; Zhang et al, ). In this stage of the examinations, a direct identification of the damage course in the G/M microregions was very difficult because of the observed diversity of morphological forms revealed on the fractured surfaces.…”

“…The decohesion at the G/M interface during static tensile tests were examined based on the SEM observations. Results of these examinations reported previously in Bonora and Ruggiero (), Dai, He, Zheng, and Mao (), Di Cocco et al (), Di Cocco et al (), Hervas et al (), Iacoviello, Cocco, Rossi, and Cavallini (), and Iacoviello, Di Bartolomeo, Di Cocco, and Piacente, (), allowed recognizing different damage effects at the G/M interface. However, in these works details of individual microstructure constituents directly involved in material's damage, were not revealed.…”

“…In the recently developed micromechanical models of cast iron damage, the effects of the anisotropy of the interatomic bonds in the graphite crystal lattice (Andriollo & Hattel, ; Pina, Kouznetsova, & Geers, ), and those related to complexity of the graphite spheroid's internal structure (Bonora & Ruggiero, ; Di Cocco, Iacoviello, & Cavallini, ; Iacoviello & Di Cocco, ) were introduced beside of these coming from mechanical properties of graphite (Andriollo, Thorborg, Tiedje, & Hattel, ; Bonora & Ruggiero, ; Hervas, Thuault, & Hug, ). However, a direct impact of each of these factors on local decohesion effects has not been identified unequivocally until now.…”

“…However, in these works details of individual microstructure constituents directly involved in material's damage, were not revealed. More detailed observations of the decohesion effects inside graphite nodule and at the G/M interface were limited by microscopic magnification used for such tests, that were usually in the range of 500–1,500× to 5,000×, for example, Hervas et al ().…”