Browsing by Subject "constitutive equations"

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Access status: Open Access ,
Comparison among different constitutive equations on investigating tensile plastic behavior and microstructure in austempered ductile iron
(AGH University of Science and Technology Press, 2018) Angella, Giuliano; Zanardi, Franco
The capabilities of different constitutive equations of approximating the tensile flow curves and correlating plastic behavior with the microstructure were investigated in austempered ductile iron ADI 1050. In a previous paper, the microstructure evolution of ADI 1050 during austempering was investigated through quenching the ADI 1050 after 14 increasing austempering times to room temperature. The 14 samples were tensile tested and two classes of constitutive equations were examined in the present paper. The Hollomon-type constitutive equations approximated all of the tensile flow curves of ADI 1050 very well but failed in correlating the plastic behavior with microstructure evolution. Voce-type constitutive equations approximated the tensile flow curves only at high stresses very well but could correlate the plastic behavior with the microstructure evolution of ADI 1050 during austempering excellently. The reason of this success was rationalized in terms of the physical basis of Voce-type equations, while Hollomon-type equations are empirical.
Access status: Open Access ,
The correlation between solidification rates, microstructure integrity and tensile plastic behaviour in 4.2 wt.% silicon strengthened ductile iron
(AGH University of Science and Technology Press, 2022) Angella, Giuliano; Taloni, Marcello; Donnini, Riccardo; Zanardi, Franco
High Silicon Strengthened Ductile Iron (HSiSDI) with 4.2 wt.% of silicon was produced in Y-blocks with different thicknesses to investigate the effects of the solidification rate on microstructure integrity and tensile mechanical properties. With decreasing solidification rates, the graphite degeneracy with the appearance of chunky graphite became more significant at the highest silicon contents, so chemical ordering and graphite degeneracy seemed to be qualitative explanations of tensile property degradation. However, a deeper analysis of the relationship between solidification rate, microstructure and tensile properties was realized through an innovative approach based on the Matrix Assessment Diagram (MAD), where the parameters of Voce equation resulting from best-fitting the experimental tensile flow curves of a significant number of HSiSDI samples, were plotted. For 3.5 wt.% silicon content, the MAD analysis indicated that the microstructure was sound for any solidification rate, while for 4.5 wt.% the microstructure was sound only for the fastest solidification rates. For 4.2 wt.% silicon content the MAD analysis pointed out that the tensile plastic behaviour and the microstructure integrity was in between the 3.5 and 4.5 wt.% silicon contents, representing a composition threshold where the reliable microstructures were only found with the fastest solidification rates, while considerable variability was found for the slowest ones. Support to the MAD analysis results was given from microstructure observations.