1,720,967 research outputs found
Resistenza alla propagazione delle cricche di fatica nelle ghise austemperate
No full textE' stata studiata la propagazione per fatica di cricche su ghise sottoposte a trattamenti di austempering
Fatigue crack propagation damaging micromechanisms in ductile cast irons
No full textDuctile iron discovery in 1948 gave a new lease on life to the cast iron family. In fact, these cast irons are characterized both by a high castability and by high toughness values, combining cast irons and steel good properties. Ductile cast irons are also characterized by high fatigue crack propagation resistance, although this property is still not widely investigated. In the present work, three different ferritic-pearlitic ductile cast irons, characterized by different ferrite/pearlite volume fractions, and an austempered ductile cast iron were considered. Their fatigue crack propagation resistance was investigated in air by means of fatigue crack propagation tests according to ASTM E647 standard, considering three different stress ratios (R = Kmin/Kmax = 0.1; 0.5; 0.75). Crack paths were investigated by means of a crack path profile analysis performed with an optical microscope. Crack surfaces were extensively analysed by means of a scanning electron microscope both considering a traditional procedure and performing a quantitative analysis of 3D reconstructed surfaces, mainly focusing graphite nodules debonding. © 2007 Elsevier Ltd. All rights reserved
Fatigue Damaging Micromechanisms in Ductile Cast Irons
No full textDuctile iron discovery in 1948 gave a new lease on life to the cast iron family. In fact these cast irons are characterised both by a high castability and by high toughness values, combining cast irons and steel good properties. Ductile cast irons are also characterised by high fatigue crack propagation resistance, although this property is still not widely investigated. In the present work we considered three different ferritic-pearlitic ductile cast irons, characterised by different ferrite/pearlite volume fractions, and an austempered ductile cast iron. Their fatigue crack propagation resistance was investigated in air by means of fatigue crack propagation tests according to ASTM E647 standard, considering three different stress ratios (R = Kmin/Kmax = 0.1; 0.5; 0.75). Crack surfaces were extensively analysed by means of a scanning electron microscope both considering a traditional procedure and performing a quantitative analysis of 3D reconstructed surfaces, mainly focusing graphite nodules debonding mechanisms and considering the microstructure influence
Meccanismi di danneggiamento nelle ghise sferoidali ferrito-perlitiche
No full textI meccanismi di danneggiamento nelle ghise sferoidali sono influenzati dalla matrice della microstruttura e dalla presenza degli elementi di grafite. In questo lavoro sono stati investigati i meccanismi di danneggiamento in quattro ghise sferoidali ferrito-perlitiche sottoposte a sollecitazione
di trazione mediante analisi delle superfici laterali dei provini al microscopio elettronico a scansione effettuate durante lo svolgimento della prova medesima (prove di trazione in situ). L’analisi di immagine quantitativa dell’evoluzione del danneggiamento ha permesso di quantificare l’evoluzione del processo, evidenziando l’importanza della microstruttura e l’importanza del ruolo svolto dagli elementi di grafite. L’importanza del distacco degli elementi di grafite dalla matrice metallica (debonding), spesso indicato come il principale o l’unico meccanismo di danneggiamento che coinvolge gli elementi di grafite, è confermata solo parzialmente
Microstructure features identification in ferritic-paerlitic ductile irons
No full textDuctile irons offer a wide range of mechanical properties at a lower cost than the older malleable iron. These properties mainly depend on the shape characteristics of the metal matrix microstructure and on the graphite elements morphology; these geometrical features are currently evaluated by the experts visual inspection. This work provides an automatic procedure for a reliable standard estimation of the material microstructure morphology based on a novel image segmentation technique. The procedure has been successfully tested on specimens of different kinds of ductile irons of a typical production
Procedure alternative per l'analisi quantitativa di immagini applicate alle ghise sferoidali
No full textDuctile cast irons are characterized by a wide range of mechanical properties that depend on graphite
elements morphology and microstructure properties. Both chemical composition and manufacturing
conditions control matrix microstructure, and ferritic, pearlitic, ferritic-pearlitic, martensitic, bainitic,
austenitic and austempered ductile irons can be obtained. Considering crack propagation resistance of ductile
cast irons, their peculiar behaviour is due to the graphite elements shape, that is approximately spheroidal.
Due to their morphology, graphite elements can act as crack arresters: as a consequence ductile cast irons are
characterized by high ductility and toughness values and can be used for loading conditions that could be
considered as critical for other cast irons types (e.g. fatigue loading conditions).
Up to some years ago, microstructure analysis was mainly performed by means of semi-quantitative
procedures applied to metallographically prepared specimens, with the characteristics evaluation that was
mainly based on the operator expertise. Only recently there has been an increasing interest in numerical
procedures of image analysis for quantitative evaluation of materials. In this work the problem of the
estimation of the morphological parameters of elements such as graphite nodules, domains of chemical etching
and metallic matrix has been taken up by a variational approach of image segmentation by active contours.
Considering ductile irons, images obtained by means of a light optical microscope (LOM) on
metallographically prepared specimens show both graphite elements (spheroids, nodules, lamaellas etc.) and
microstructure elements (ferrite grains, pearlite lamaellas, etc.) and some artefacts due the preparing
procedure that should be distinguished by more interesting elements. An automatic identification procedure
is here proposed to distinguish the nodules from the metallic matrix and to evaluate the nodules shape
parameters of interest and the composition of the metallic matrix (ferrite/pearlite volume fraction)
Quantitative shape evaluation of graphite particles in ductile iron
No full textDuctile irons' mechanical properties are strongly influenced by the microstructure of metal matrix, presence of impurities and presence of graphite particles. These particles are characterized by their morphological characteristics (e.g. shape, dimension, etc.): the more the shape of the graphite particles is near to a sphere (nodule), the better the mechanical properties (e.g. toughness and crack propagation resistance) are. The standard that is commonly used to characterize the morphology of graphite particles is only semi-quantitative. In this work, an image processing computer procedure is proposed for the characterization of the shape of graphite nodules. Pictures of the metallographic sections acquired by means of a light optical microscope are processed in order to obtain a simpler image representation where the nodules are black objects over a white background (image binarization). On this binary picture each nodule can be easily examined to estimate all the shape parameters of interest, lime area, eccentricity, solidity, etc. Suitable statistics of the shape parameters are adopted to classify the real data of ductile iron specimens. © 2007 Elsevier B.V. All rights reserved
Optimal binarization of images by neural networks for morphological analysis of ductile cast iron
No full textThis work aims to characterize different objects on a scene by means of some of their morphological properties. The leading application consists in the analysis of ductile cast iron specimen pictures, in order to provide a quantitative evaluation of the graphite nodules shape; to this aim the material specimen pictures are binarized. Such a binarization process can be formulated as an optimal segmentation problem. The search for the optimal solution is solved efficiently by training a neural network on a suitable set of binary templates. A robust procedure is obtained, amenable for parallel or hardware implementation, so that real-time applications can be effectively dealt with. The method was developed as the core of an expert system aimed at the unsupervised analysis of ductile cast iron mechanical properties that are influenced by the microstructure and the peculiar morphology of graphite elements
Impiego delle reti neurali nell’identificazione degli elementi di grafite nelle ghise sferoidali
No full textDiscrete Image Model and Segmentation for Microstructure Features Identification in Ductile Irons
No full textDuctile irons offer a wide range of mechanical properties at a lower cost than the older malleable iron. This work provides an automatic procedure for a reliable estimation of standard parameters of the material microstructure morphology
- …
