Classification of ductile cast iron specimens: A machine learning approach

In this paper an automatic procedure based on a machine learning approach is proposed to classify ductile cast iron specimens according to the American Society for Testing and Materials guidelines. The mechanical properties of a specimen are strongly influenced by the peculiar morphology of their graphite elements and useful characteristics, the features, are extracted from the specimens’ images; these characteristics examine the shape, the distribution and the size of the graphite particle in the specimen, the nodularity and the nodule count. The principal components analysis are used to provide a more efficient representation of these data. Support vector machines are trained to obtain a classification of the data by yielding sequential binary classification steps. Numerical analysis is performed on a significant number of images providing robust results, also in presence of dust, scratches and measurement noise

Damaging micromechanisms in an as cast ferritic and a ferritized ductile cast iron

Mechanical behavior and damaging micromechanisms in Ductile Cast Irons (DCIs) are strongly effected by matrix microstructure (e.g., phases volume fraction, grains size and grain distribution) and graphite nodules morphology peculiarities (e.g., nodularity level, nodule size, nodule count, etc.). The influence of the graphite nodules depends on both the matrix microstructure and the loading conditions (e.g., quasi-static, dynamic or cyclic loadings). According to the most recent results, these graphite nodules show a mechanical properties gradient inside the graphite nodules, with the graphite elements – matrix debonding as only one of the possible damaging micromechanisms. In this work, two different ferritic DCIs were investigated (a ferritic matrix obtained from as-cast condition and a ferritized matrix) focusing on the damaging micromechanisms in graphite nodules due to tensile stress. Specimens lateral surfaces were observed using a Scanning Electron Microscope (SEM) during the tests following a step by step procedure.Fil: D' Agostino, Laura. Università di Cassino e del Lazio Meridionale; ItaliaFil: Di Cocco, Vittorio. Università di Cassino e del Lazio Meridionale; ItaliaFil: Fernandino, Diego Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Lacoviello, Francesco. Università di Cassino e del Lazio Meridionale; Itali

Interlaminar shear strength study on CFRP/Al hybrid laminates with different properties

FML (Fibre Metal Laminate) is a hybrid material that presents outstanding structural properties, such as resistance to cyclic and dynamic loads, together with low specific weight. This material consists of metal sheets alternating to composite material layers. In the present work, the ILSS (Interlaminar Shear Strength) was evaluated for different types of carbon fibre/aluminium FML, produced varying the layer thickness and the bonding solution of layers. In fact, FMLs consisting of one or two metal sheets (a parameter strictly connected to the layer thickness, as the metal/composite volume fraction was kept at constant value) and bonded with structural adhesive or prepreg resin were considered for this study. The ILSS was determined according to the three-point bending method with short beam specimens. The experimental tests evidenced an effect of the adhesion methodology on the ILSS value, while the layer thickness did not influence the interlaminar strength. The mechanical behaviour after the maximum load point was investigated too, evaluating the trend of the shear stress as a function of the loading nose displacement

analysis of the intergranular corrosion susceptibility in stainless steel by means of potentiostatic reactivation tests

Abstract: Intergranular corrosion cracking in stainless steels is a selective corrosion attack due to a local (grain boundary) Cr depletion. An undesired Cr carbides (Cr 23 C 6 ) precipitation after heat treatment in the sensitization temperature range (usually between 550 and 850°C, depending on the steel chemical composition) is obtained with a kinetics that is mainly influenced by the C content. In this work, the sensitization susceptibility of four sensitized stainless steels was investigated by means of potentiostatic reactivations tests. In addition, chronoamperometric tests and scanning electron microscope (SEM) observations of the specimens surfaces were performed in order to analyze the evolution of the corrosion morphologies

Fatigue microstructural evolution in pseudo elastic NiTi alloy

Abstract Shape memory property characterizes the behavior of many Ti based alloys (SMAs). This property is due to a metallurgical phenomenon, which allows to change the lattice structure without boundaries changing as a reversible transition. Equiatomic NiTi alloys are among the most industrially used SMAs: they are characterized by two different mechanical behaviors in terms of shape recovering: • a shape memory effect (SME). This is obtained when the recovery of the initial shape takes place only after heating over a critical temperature, with a consequent crystallographic structure transition; • a pseudoelastic effect (PE). This is obtained when the critical temperature is lower than environmental temperature. In this case, the recovery of the initial shape takes place only after unloading. In recent years, research relating to materials of shape memory has gone in the direction of application in many fields of engineering such as aerospace or mechanical systems. In this work the evolution of microstructural lattice has been studied taking in to account the effect of low cycles fatigue loads

duplex stainless steels 475 c embrittlement influence of the chemical composition on the fatigue crack propagation

Abstract: Duplex stainless steels (DSSs) are prone to age hardening and embrittle over a wide temperature range depending on their chemical composition. This is mainly due to precipitation phenomena that may occur inside ferrite grains and at ferrite-austenite grain boundaries. The aim of this work is the analysis of chemical composition influence on fatigue crack propagation resistance of "475°C embrittled" duplex stainless steels. Fatigue crack propagation resistance of 21 Cr 1 Ni, 22 Cr 5 Ni and 25 Cr 7 Ni duplex stainless steels was investigated considering both as received and 475°C embrittled conditions (1000h). Microstructural analyses were performed using a transmission electron microscope (TEM). Concentrations of the main elements, but carbon, were evaluated using a standardless analysis program

Pearlitic Ductile Cast Iron: mechanical properties gradient analysis in graphite elements

Abstract Ductile Cast Irons (DCIs) are able to combine a good versatility and high performances with a low cost, especially if compared to steels with analogous performances. For these reasons, although these grades have been relatively recently developed, DCIs applications are more frequent. Analyzing the damaging micromechanisms in static, quasi-static or cyclic conditions, the analysis of the role played by the graphite elements is not univocal. Sometimes, they are considered as voids embedded in a more or less ductile matrix, sometimes they are considered as a soft but homogeneous material. In this work, the role played by the graphite nodules in pearlitic grains is reviewed and their mechanical properties are investigated by means of nanohardness tests

Ductile cast irons: microstructure influence on fatigue crack propagation resistance

Microstructure influence on fatigue crack propagation resistance in five different ductile cast irons(DCI) was investigated. Four ferrite/pearlite volume fractions were considered, performing fatigue crackpropagation tests according to ASTM E647 standard (R equals to 0.1, 0.5 and 0.75, respectively). Results werecompared with an austempered DCI. Damaging micromechanisms were investigated according to the followingprocedures:- “traditional” Scanning Electron Microscope (SEM) fracture surfaces analysis;- SEM fracture surface analysis with 3D quantitative analysis;- SEM longitudinal crack profile analysis- Light Optical Microscope (LOM) transversal crack profile analysis

A simple model to calculate the microstructure evolution in a NiTi SMA

Shape memory alloys (SMAs) are a wide class of materials characterized by the property to recover the initial shape. This property is due to ability of alloys to change the microstructure from a “parent” microstructure (usually called “Austenite”) to a “product” microstructure (usually called “Martensite”). Considering the tensile resistance, SMAs stress strain curves are characterized by a sort of plateau were the transformations from Austenite to Martensite (in loading condition) and from Martensite to Austenite (in unloading condition) take place. In this work a simple model to predict the microstructure modification has been proposed and verified with an equiatomic NiTi alloy characterized by a pseudo-elastic behavior

Influence of structural characteristics on the interlaminar shear strength of CFRP/Al fibre metal laminates

Abstract High mechanical characteristics, such as impact and fatigue resistance, coupled with low weight can be obtained combining metal sheets and composite laminates; in this way a new hybrid material is obtained: the FML (Fibre Metal Laminate). In the present paper, an analysis of the influence of both composite/metal interface and layer thickness on ILSS (InterLaminar Shear Strength) of a carbon fibre composite and aluminium FML is presented. In particular, two different interfaces were studied: one obtained with a structural adhesive and the other with the prepreg resin; as concerns the layer thickness, both one and two aluminium sheets were considered in laminate stacking, maintaining constant the metal/composite volume ratio. The produced laminates were tested following the short beam three-point bending standard, in such a manner the ILSS properties can be highlighted. From the test carried out for this work it can be concluded that the most influencing factor was the presence of the structural adhesive, while the number of metal sheets was unaffecting