Volume 8, Issue 2
May 1986, pages 91-263
pp 91-91 May 1986
pp 93-106 May 1986
Over the past 20 years computer modelling of fuel performance has developed into a well-established procedure, which has been valuable in the understanding and the improvement of fuel rod behaviour. The range of computer models presently applied to cylindrical ceramic fuels is reviewed. A critical appraisal is made of the numerical techniques used for mechanical and thermal analysis. The necessity for benchmark calculations is emphasized and various approaches for model validation are discussed. A number of special topics are chosen for deeper discussion. These include: improved description of cladding deformation and the estimation of failure; the analysis of stress concentrations in the cladding; fission gas analysis; and chemical modelling. Finally some speculation is made on the future of fuel rod modelling.
pp 107-121 May 1986
The thermodynamic route of establishing phase diagrams is a relatively recent activity, considering that till about the fifties most phase diagrams were determined by the measurement of certain physical property or quantitative microscopy using light optics or x-ray diffraction. The thermodynamic formalism used by Kaufman and Bernstein is explained and illustrated with examples of the development of hypothetical binary phase diagrams. The calculation of ternary phase diagrams can begin with the binary phase diagram data as a first approximation. However, to calculate a reasonably accurate ternary phase diagram a certain amount of ternary solution data is necessary. Various empirical equations have been proposed in the literature to express ternary thermodynamic data.
Calculation of simple ternary isothermal sections is illustrated with the examples of Mo-V-W and Cd-Sn-Pb systems. The numerical techniques which involve the differentiation of thermodynamic parameters with respect to composition get more involved with the number of components becoming 3 or more. A simpler approach has been applied recently to find the minimum position on the Gibbs free energy surface.
pp 123-132 May 1986
Computers have been used for design of rolling mills since 1960s. Easy access to high speed digital computers has facilitated use of more accurate rolling theories for design work and comprehensive computer simulations have been developed for all types of mills. These simulations include optimization of roll pass sequence, calculation of roll force, torque and temperature and detailed time studies for productivity calculations. These aspects of mill simulation are examined with specific examples.
In the design of rolling mills equipment, computer-aided design has been widely used. The available software, which covers both steady state and dynamic analysis of items such as mill stands, drive systems, manipulators, cooling beds, roll cooling, and automatic gauge control systems, is reviewed with special reference to the nature of analysis and range of applications.
Computer drafting is being increasingly used by rolling mills designers for both interactive and non-interactive applications. The integration of computer graphics with the design software holds promise for improving the productivity and creativity of designers and is an active area of development in rolling mills design organizations. A specific application where such integration has been achieved is discussed.
pp 133-146 May 1986
Defects introduced in pressure vessel components during fabrication processes act as potential sources for damage accumulation and subsequent catastrophic failure. Cracks nucleate at these stress risers and propagate aided by fatigue type of loading, corrosion and creep. Analysis of crack growth under conditions of ‘time-dependent fatigue’ is very important for the life prediction of pressure vessel components. In this paper the interaction of creep-hot corrosion and low cycle fatigue is analyzed based on the energy expended for the nucleation of damage at the advancing crack front. The total damage accumulation is divided into that due to (i) fatigue, (ii) corrosion and (iii) creep for modelling purpose. The analysis yields a relation in terms ofJ-integral which is applicable to both crack propagation and final failure. A corrosion-creep parameter (Fi) has been introduced at the crack propagation stage and raw data from different sources have been analyzed for different types of loading and compared with the theoretical predictions. The total energy in tension which includes the tension going time, appears to be a good parameter for the prediction of time-dependent fatigue life.
pp 147-153 May 1986
The development of mathematical models of furnaces is briefly reviewed. The basic processes taking place in furnaces and the problems associated with their mathematical formulation and the necessary assumptions are discussed. The difficulty of determining the process parameters, and the methods of their estimation are included. Applications of mathematical models for the study of cooling of ingots, heating of steel, cowper stoves and for the study of erosion of refractories are also discussed.
pp 155-167 May 1986
In this paper, we describe the computer simulation technique and its application to the study of radiation damage. Details of two important methods: the static and the dynamic methods have been discussed. Applications to the study of point defect formation and stability, their clusters, diffusion, dislocations and dislocation-point defect interaction are discussed drawing from our own work wherever possible. A short mention is made of the importance of the interatomic potential. Examples for the case of magnesium and other hcp metals, bcc iron and fcc Ni are cited and numbers for various quantities like formation energy, dipole tensor, interaction energy etc are quoted.
pp 169-182 May 1986
This paper explains the different types of specimens which are of a deterministic or stochastic nature. Especially for stochastic specimens it is pointed out that, before any measurement is done, the problem has to be analyzed as to why we measure. As a size per se does not exist it is shown that particles must be analyzed by size and shape. For this, two methods are indicated, while it is stressed that in materials science the Delfiner approach for description of particle sizes is the most practicable.
Based on Delfiner’s concept of size the classification of particles according to their size, shape and orientation is explained. For measuring use of the image transformationserosion, ouverture is proposed. In addition, a new transformation called “Template matching” is explained. This new transformation avoids the disadvantages of erosion and ouverture in case of concave particles. Besides, template matching, in contrast to erosion or ouverture, is able to give true values of area and circumference. The concept of classification is explained by simple examples.
pp 183-191 May 1986
A mathematical model has been developed for computing the geometrical dimensions of square-diamond square pass sequence for a continuous billet mill. The model is based on derivation of shape and size factor from the geometry of the pass taking into account pass filling, pass rounding etc. Using these factors and a basic equation of spread for flat rolling, a governing equation incorporating angle of diamond and reduction in consecutive passes has been formulated. Newton’s substitution method has been used to solve the equation. With known reduction between consecutive passes, geometrical dimension of square and diamond passes are computed. A model has been used to calculate pass design of a finishing train of a continuous billet mill producing 60 mm square billet from 120 mm square bloom. The elongation values have been optimized by varying the apex angle of diamond. A close agreement between computed and actual values shows the validity of the model.
pp 193-198 May 1986
Internal structure of materials uniquely decides their properties. The structure is a complicated function of composition and thermal and/or mechanical treatment. Inter-relation is so complex that a highly generalized correlation is very difficult. Steel is a very good example to illustrate this complexity. Advent of mini- and microcomputers have now paved way for handling such multiparametric problems in a more rational way, with greater ease and increased confidence. This paper is an attempt to develop a computer software which will assist the user in three different ways: (a) to determine the treatments that will generate a desired structure, when compositions are known; (b) to determine composition limits within which desired structure will result having defined the treatments, and (c) to predict structures that can be generated when composition and treatments are limited. This program has immense utility of (i) best use of available inventory, (ii) reduction of standards, varieties and inventory and (iii) most importantly to decide the best purchase based on treatment limitations in the shop. A large data bank is being built to support the program.
pp 199-207 May 1986
The densification process during pressure sintering has been analyzed using finite element analysis. This analysis uses an iterative solution algorithm. With this the densification process in complex geometries with complex boundary conditions can be analyzed and this technique is particularly suited for tackling material nonlinearity. Evolution of dense structures with gradual closure of pores is described for two typical geometries.
pp 209-216 May 1986
A model for serrated yielding based on the negative resistance characteristics of materials is discussed. An analog computer based on this model is described. The simulated curves show oscillations which are regular and uniform in amplitude. To simulate more realistic tensile test curves, a refined model which includes the effects of fluctuations in dislocation density and velocity is described. Some simulated curves using this refined model are presented. These results are close to observed tensile test curves.
pp 217-224 May 1986
Drop formation at conical tips which is of relevance to metallurgists is investigated based on the principle of minimization of free energy using the variational approach. The dimensionless governing equations for drop profiles are computer solved using the fourth order Runge-Kutta method. For different cone angles, the theoretical plots ofXT andZT vs their ratio, are statistically analyzed, whereXT andZT are the dimensionlessx andz coordinates of the drop profile at a plane at the conical tip, perpendicular to the axis of symmetry. Based on the mathematical description of these curves, an absolute method has been proposed for the determination of surface tension of liquids, which is shown to be preferable in comparison with the earlier pendent-drop profile methods.
pp 225-229 May 1986
A single board auxiliarycamac crate controller for a Z80-A based personal computer ZX-spectrum to drive thecamac crate housing multipleadc, tdc, dac and 16 I/O ports has been developed. Thecamac crate controller used in this system is of A2 type which supports multiple auxiliary crate controllers. Acamac exerciser/training software for the use ofcamac commands in process control as well as data acquisition has been developed.
pp 231-237 May 1986
This paper describes a Z-80 microprocessor-based image analyzer developed for global parameter evaluation of images over a 256 × 256 pixel frame. It consists of a microscope,ccd scanner, 6-bit videoadc, Z-80 computer and an image display monitor. Facilities are provided for feature erosion/dilation and halo correction. The paper also presents the details of another more powerful user microprogrammable HP1000 minicomputer-based image analysis system under development. This system consists of an optical microscope/epidiascope coupled to a chalnicon scanner. Here the 512 × 512 pixel image is acquired with 8-bit resolution. It provides for shading correction, auto-delineation, image processing and image analysis functions for evaluation of various basic and derived parameters.
Both the systems are software intensive and are realised according to requirements of quantitative metallography. They can also be used for analysis of images obtained in the fields of biology, medicine, geological survey, photography and space.
pp 239-246 May 1986
Image analysis systems have been used in metallurgy for over two decades and play a vital role in quality assessment for the steel industry. One major application is the characterization of steel by counting and measuring the non-metallic inclusion content. Visual steel assessment, relying on the comparison with idealized ‘charts’ of varying inclusion content, for example as defined byastm andsep, is the most common manual method employed.
However, this has proved to be most difficult to automate due to the degree of subjectivity associated with the manual methods. This has previously restricted the acceptance of image analysis systems for routine quality control. The increased software power of the more modern instruments has enabled the installation of systems which satisfactorily mimic the skilled observer in a reproducible manner. These work with an economically attractive throughput and produce results in the accepted standard format.
A limitation of these systems is that they grade a field on the basis of the majority inclusion type present. This can lead to significant but lesser inclusions being ignored altogether and presenting a false picture of the sample. This paper describes a new method which separately identifies individual inclusions in a field. The grade number of a field can then be determined for each inclusion type. This is known as the mixed field method. This paper describes this method and its implementation on the Cambridge Instruments’quantimet 920 image analysis system.
pp 247-251 May 1986
An atomistic computer model based on a rigid boundary method has been developed to estimate the interaction energy between a single edge dislocation and an impurity carbon interstitial in nickel. The simulation was carried out using the static relaxation technique on a total of 600 atoms, using an appropriate host-host pair potential. The impurity-host potential has been chosen to be a cubic function in this calculation. In the absence of the dislocation the dipole tensor for the octahedral site is seen to be spherical. Two impurity positions, one above and one below the slip plane were investigated. The carbon-dislocation interaction energies obtained were 1·4 eV and 0·7 eV respectively for the two impurity positions. The dipole tensor for the impurity in the presence of the dislocation was found to be non-diagonal.
pp 253-263 May 1986
This paper gives a brief description of the sub-models of important phenomena treated in computer codeprofess and presents some results ofprofess calculations for the fuel elements of D-Com blind problem.
Volume 42 | Issue 6
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