numero26

A. De Santis et alii, Frattura ed Integrità Strutturale, 26 (2013) 12-21 ; DOI: 10.3221/IGF-ESIS.26.02 20 - the Euler number is -41 (i.e. in one object minus 42 holes); - the solidity is 0.94; - the convex area is 163194; - the orientation (i.e. the angle, ranging from -90 to 90 degrees, between the major axis of the ellipse that has the same second moment of the nodule and the horizontal axis) is -88.9. All these information are in general available for each nodule in an image, allowing statistical considerations that may be useful to characterize the specimens. For example it may be useful to investigate the presence of objects with the same orientation, or if there are nodules particularly deformed (high eccentricity) or with ragged edges (low solidity). These characteristics are strictly related to the mechanical properties of the material, and the statistical analysis may help in the determination of residual life. Figure 13 : 2-levels segmentation of a graphite nodule (high magnification, 1000x) [V8]. C ONCLUSIONS uctile irons mechanical properties and damaging micromechanisms are strongly influenced by the matrix microstructure and by the graphite nodules morphology: a correct evaluation of graphite elements morphology is always the main goal in cast irons microstructural analyses. Graphite elements metallographic analysis standard is based on a visual qualitative approach, that does not seem to be sufficient to completely characterize the graphite elements morphology parameters (mainly, but not only, shape, dimension, distribution). In this work, the image segmentation by the active contours method is optimized in order to be applied on cast iron: this approach allows a quantitative analysis of the graphite elements, ranging from flakes to nodular ones. After the application of active contours method, it is possible to define many morphological parameters, both considering low magnification images (and focusing parameters like elements density and distribution) and high magnification images, allowing to quantitatively analyze every single graphite element. R EFERENCES [1] Iacoviello, F., Di Cocco, V., Piacente, V., Di Bartolomeo, O., Damage micromechanisms in ferritic-pearlitic ductile cast irons, Mater. Science and Engng. A, 478 (2008) 181-186. [2] Di Cocco, V., Iacoviello, F., Cavallini, M., Damaging micromechanisms characterization of a ferritic ductile cast iron, Engineering Fracture Mechanics, 77 (2010) 2016-2023. [3] Iacoviello, F., Di Cocco, V., Cavallini, M., Ductile cast irons: microstructure influence on fatigue crack propagation resistance, Frattura ed Integrità Strutturale, 13 (2010) 3-16. [4] Cavallini, M., Di Cocco, V., Iacoviello, F., Iacoviello, D., in: G. Ferro, F. Iacoviello, L. Susmel (Eds), XXI Convegno Nazionale del Gruppo Italiano Frattura (IGF), Cassino, Italy, (2011) 415-414. [5] Di Cocco, V., Iacoviello, F., Rossi, A., Cavallini, M., Natali, S., in: F. Iacoviello, G. Risitano, L. Susmel (Eds), Acta Fracturae, Gruppo Italiano Frattura (IGF), Rome, Italy, (2013) 1-8. [6] Di Cocco, V., Iacoviello, F., Rossi, A., Cavallini, M., Natali, S., Graphite nodules and fatigue crack propagation micromechanisms in a ferritic ductile cast iron, Fatigue Fract Engng Mater Struct (FFEMS), 36(9), (2013) 893-902. D