Classification Of Microstructures Research Articles

Characterization of Cast Iron Microstructure Through Fluctuation and Fractal Analyses of Ultrasonic Backscattered Signals Combined with Classification Techniques

This work aims at evaluating the performance of pattern recognition methods in the identification of different microstructures presented by cast iron, namely, lamellar, vermicular and nodular microstructures, through the statistical fluctuation and fractal analyses of backscattered ultrasonic signals. The signals were obtained with a broad band ultrasonic probe with a central frequency of 5 MHz. The statistical fluctuations of the ultrasonic signals were analyzed by means of Hurst (RSA) and detrended-fluctuation analyses (DFA), and the fractal analyses were carried out by applying the minimal cover and box-counting techniques to the signals. The curves obtained from the statistical fluctuations and fractal analyses, as functions of the time window, were processed by using four pattern classification techniques, namely, principal-component analysis (PCA), Karhunen-Loève transformation (KLT), neural networks and Gaussian classifier. The best results were obtained by Karhunen-Loève expansion and neural networks, where an approximately 100% success rate has been reached for the classification of the different microstructures as well as for the training and the testing sets of events. The results presented correspond to an average taken over 100 randomly chosen sets of events. These results indicate that, within the techniques used, the Karhunen-Loève transformation and neural network associated with the statistical fluctuation analyses (RSA and DFA) are the best tools for the recognition of the different cast iron microstructures. It is worthwhile pointing out that the microstructure classification was made by using backscattering signals acquired during pulse echo ultrasonic nondestructive testing only. Therefore, that approach is a promising method for material characterization.

Characterization of the evolution of recrystallization by fluctuation and fractal analyses of the magnetic hysteresis loop in a cold rolled non-oriented electric steel

Silicon steels with non-oriented grains are widely used in the fabrication of electrical motor nucleus where a low magnetic loss is an important point. The performance of these motors is affected by the level of recrystallization of these steels which can come from the steel plant in a semi-processed condition. In this condition, they have a partially deformed structure and are submitted to an adequate annealing heat treatment, after reaching the end shape, to get an appropriate magnetic property. In this study, samples of an electric steel, cold rolled 50% in thickness, were withdrawn during the industrial heat treatment at temperatures of 575, 580, 600, 620 and 730 °C with the objective of evaluating the evolution of recrystallization with temperature. Magnetic properties were measured at room temperature in a vibrating sample magnetometer and the changes in magnetic hysteresis loop with temperature have been identified by using two pattern classification techniques, principal-component analysis and Karhunen-Loève (KL) expansion, associated with statistical fluctuations and fractal analyses. The fluctuation and fractal analyses were used as preprocessing tools of the series which are built from each hysteresis loop, properly renormalized, whose values correspond to the amplitudes of the loop at given equally spaced values of the renormalized field interpolated between the experimental data. The samples have been classified in four sets corresponding to different temperatures, and to samples without annealing heat treatment and recrystallized ones. The classification of the different microstructures have been obtained by applying the two pattern classification techniques to the vectors obtained from the preprocessing, and in particular a 100% success rate has been reached by using KL expansion.

Classification of low-carbon pipe steel microstructures

The expediency of classifying the microstructure of low-carbon pipe steels is demonstrated. The main structures that should be considered in its development are investigated.

Unambiguous classification of complex microstructures by their three-dimensional parameters applied to graphite in cast iron

Three-dimensional (3D) quantitative analysis is indispensable for the unambiguous characterization and objective classification of complex microstructures. Focused ion beam (FIB) nanotomography provides complete information of the spatial arrangement, chemistry and orientation of different phases of real microstructures on scales especially important in materials science (10nm–100μm). Complex graphite particles were analyzed in three-dimensions. Whereas nodular, vermicular and temper graphite particles can be characterized individually, the whole network of flake graphite has to be considered due to the high spatial interconnection of particles. The characterization method was verified in comparison to established two-dimensional stereological methods. The influence of anisotropy and image resolution was discussed. Basic stereological characteristics (volume, surface area, integrals of mean and total curvature) as well as 3D connectivity (Euler number) and shape parameters objectively differentiate these graphite morphologies and contribute to the understanding of their growth mechanisms and the properties of the cast iron.

Quantification and Classification of Complex Microstructures by means of FIB/SEM-Nanotomography

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Classification and reconstruction of three-dimensional microstructures using support vector machines

Reconstruction of three-dimensional (3D) microstructures is posed and solved as a pattern recognition problem. A microstructure database is used within a support vector machines framework for predicting 3D reconstructions of microstructures using limited statistical information available from planar images. The 3D distributions of the grain size of the reconstructed polyhedral microstructures exhibit qualitative agreement with stereological predictions. Amenability of the approach for studying microstructure–property relationships is shown by comparing the computed properties of reconstructed microstructures with available experimental results. Combination of classification methodology and principal component analysis for effective reduced-order representation of 3D microstructures is demonstrated. The pattern recognition technique discussed uses two-dimensional microstructure signatures to generate in nearly real-time 3D realizations, thus accelerating prediction of material properties and contributing to the development of materials-by-design.

Classification and quantification of microstructures in steels

The International Institute of Welding (IIW) microstructure classification scheme for ferrous weld metals has been investigated as a basis for the quantification of complex microstructures in steels. The aim has been to cover the full range of microstructures observed in plain carbon and low alloy steel products, as well as ferritic weld metals and parent plate heat affected zones. The mechanisms of formation of the principal structures and the characteristic ferrite morphologies produced in the reconstructive and displacive transformation regimes of ferrous materials have been briefly reviewed. The classification and terminology used for intragranular as well as austenite grain boundary microstructural constituents have been considered, and also the way in which transformation products are orientated in space. Problems encountered in relating microstructural constituents to principal structures have been discussed in detail and solutions proposed. The microstructure classification and terminology used in the IIW scheme have been built upon and new terminology incorporated into a table providing descriptions of the principal structures and sub-category components. A new classification scheme has been defined in the form of flow charts with guidelines for identifying the principal structures. Evaluation exercises have been carried out with the new scheme. These have shown that a reasonable degree of consistency may be obtained between operators in identifying primary ferrite, pearlite, martensite and the transformation products constituting ferrite sideplate and acicular ferrite structures, notably Widmanstätten ferrite and bainite. A means is thus provided of obtaining database information for developing microstructure–property relationships, or generating data for calibrating physical models, which have the principal structures as their output.

Micromorphological analyses of microfabrics and microstructures indicative of deformation processes in glacial sediments

Abstract Various forms of sediment deformation can be detected within glacial sediments at the microscopic scale. Analyses of these forms leads to a preliminary classification of microfabrics and microstructures of brittle, ductile and polyphase modes of deformation in glacial sediments. With the development of a taxonomy of different microfabrics and microstructures these processes, once differentiated, permit insights into glacial sediments to a scale and level of detail hitherto unknown. Examples are presented that illustrate some of these different forms of deformation often within a single glacial sediment sample. This research suggests many of the past ideas with regard to details of glacial depositional processes, especially in terms of diamicton deposition and subsequent classifications, need to be re-evaluated.

Microstructure formation phenomena in phase inversion membranes

Most structural studies of polymeric phase inversion membranes have focused on macrovoid formation, while the rich microstructure (size scale < 5 μm) has received little independent attention. We present a classification and qualitative description of possible microstructures on the basis of phase diagram, kinetic, and connectivity considerations. Special attention is given to the microstructural features resulting from a two-stage phase separation. Subsequently, our considerations are extended to the microstructure of the skin and that of the macrofinger boundaries. Finally, the features of actual phase inversion microstructures are described and interpreted.

Microstructure and flow stress of polycrystals and single crystals

The relation between polycrystal deformation and single crystal deformation has been studied in this work. A pure aluminium polycrystal having an average grain size of 300 μm has been strained in tension at room temperature. The flow stress has been determined at four different strains (0.05, 0.14, 0.22 and 0.34) and deformation microstructures have been characterized qualitatively and quantitatively by transmission electron microscopy. Improved experimental techniques have allowed large foil areas to be characterized and in total 89 grains have been examined. At the four strains examined a classification of the deformation microstructures into three different types has shown a correlation between the grain orientation and the type of deformation microstructure which develops during straining. The dislocation density has been calculated at each strain and by assuming that the shear stress is proportional to the square root of the dislocation density the shear stress–strain relationship has been derived for each of the three groups of grains showing different deformation microstructures. The stress–strain curves show a strain hardening behaviour which depends on the orientation of the grain. The behaviour of the grains embedded in the polycrystal is compared with the behaviour of single crystals and the stress–strain curve of the polycrystal is estimated with good accuracy from single crystal data, which are weighted based on a quantitative texture analysis of the polycrystal.

Engineering-geological classification of clay microstructures: Sokolov, V N Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P753–760. Publ Rotterdam: A A Balkema, 1990

Engineering-geological classification of clay microstructures: Sokolov, V N Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P753–760. Publ Rotterdam: A A Balkema, 1990

Classification of microstructures of loess in China and their collapsibility : Gao Guorui Scientia Sinica, V24, N7, July 1981, P962–974

Classification of microstructures of loess in China and their collapsibility : Gao Guorui Scientia Sinica, V24, N7, July 1981, P962–974

The classification of microstructures of clay soils

SUMMARYThis paper presents the results of experimental studies on the microstructure of clay soils, using scanning electron microscopy. Approximately 300 samples of clay soils of various ages, origin and degree of lithification have been analysed. Five main types of microstructure have been identified in clay soils of sedimentary origin, i.e. honeycomb, skeletal, matrix, turbulent and laminar. Among clay soils of sedimentary origin and hydrothermal origin three types of microstructure were distinguished; domain, pseudoglobular and globular.In natural environments, microstructures of mixed features have been found, i.e. honeycomb‐matrix, honeycomb‐skeletal, turbulent‐matrix, etc.The detailed description presented of the different microstructural types comprising morphology and quantitative calculations, shows a close relationship with mineral composition, origin and degree of lithification.In addition physical and mechanical properties as well as the resistance and deformation indices of clay soils have been found to be related to microstructural features.