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Sintering Deformation Following sub-projects are undergoing: 1. Finite element analysis of sintering deformation using master sintering curve instead of a full constitutive law 2. Predicting maximum heating rate for sintering ceramic components 3. Predicting microstructural evolution and macroscopic deformation of bio- glass forms taking into account of glass crystallisation. 4. Multi-scale modelling of sintering Their details are as following 1. Finite element analysis of sintering deformation using master sintering curve instead of a full constitutive law Collaborators: Dr Julie Yeomans, University of Surrey; Dr Philippe Blanchart, Ecole Nationale Supérieure de Céramique Industrielle, France PhD Student: Mr. Sasan Kiani Project description: Various forms of constitutive laws have been developed for the finite element analysis of sintering. Some of these were developed based on micromechanical models and the others based on empirical fittings with experimental data. The mechanism-based constitutive laws differ from each other widely; it is difficult to know which one to use. On the other hand, obtaining fitting functions in an empirical constitutive law is very time consuming. In this project we have developed a finite element scheme which does not require a full constitutive law but only the densification data (density as function of time) in order to predict sintering deformation. The densification data can be derived from the master sintering curve of the powder material. Different sintering mechanisms and nonlinearity pose no difficulty to the method. The densification based finite element analysis (DFEA) follows the shape evolution of a sintering component from a given initial shape and density distribution. Fig. 1. A comparison between our finite element prediction and experimental measurement of sintering deformation. 2. Predicting the optimised heating rate for sintering ceramic components Postdoctoral Research Fellow: Dr Ruoyu Huang Project description: Ceramics manufactures have to rely on trial and error to determine the optimised heating rate in their sintering cycle. We are developing a software package to integrate the heat transfer analysis, sintering deformation analysis and failure analysis to predict the optimised heating rate for sintering sophisticated ceramic components. 3. Predicting microstructural evolution and macroscopic deformation of bio-glass forms during sintering taking into account of glass crystallisation. Collaborator: Dr Aldo Boccaccini, Imperial College Postdoctoral Research Fellow: Dr Ruoyu Huang Project description: Bio-glass forms have been sintered to make bioactive scaffolds for tissue engineering at Imperial. The sintering process is controlled by viscous deformation of the glass but complicated by crystallisation which may occur simultaneously. In this project we are developing a multi-scale modelling technique to predict the microstructural evolution and the macroscopic deformation of the glass form in order to optimise the processing parameters for different applications. 4. Multiscale modelling of sintering Co-investigators: Professor Alan Cocks (University of Oxford) Professor Saiful Islam (University of Bath) Dr Julie Yeomans (University of Surrey) Postdoctoral Research Fellow: Dr Ruoyu Huang PhD Student: Mr Lifeng Ding Project description: Sintering is a process in which powder compacts are fired and consolidated into strong solid. Almost all ceramic products and an increasing number of metal, polymer and glass products are made by sintering. Accurately predicting the shrinkage and microstructure of sintered products is very useful to manufactures. However modelling sintering is one of the most challenging problems in material modelling. Sintering deformation is fundamentally linked to microstructural evolution and depends on very subtle changes in microstructure and chemistry, sometimes at the atomic level. Consequently, the ability of prediction by the current generation of sintering models is poor. On the other hand, this challenge provides us with an ideal platform for integrating modelling techniques at the atomistic, particle and continuum levels. Bringing together multi-scale elements to create an integrated sintering model is the theme of this project. For the first time, the integrated model is able to take chemical impurity, doping, particle/pore size distribution, agglomeration and anisotropy into consideration. The compaction-sintering interface will take compaction history into consideration. Together these will form the next generation of sintering models with much improved ability of prediction. The mathematical techniques developed will also have a widespread and long-term influence on the materials engineering community.
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