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Process Controls and Materials Design to Improve Reliability of Ceramics

Associate Professor Kouichi Yasuda

Department of Metallurgy and Ceramics Science

Graduate School, Tokyo Institute of Technology

    Wide scattering in fracture strength is one of the most important problems in both fabrication and application of engineering ceramics. To find better solutions, we must increase our knowledge in process controls and/or materials design from the viewpoint of fundamental science. In this seminar, the presenter introduces you two recent topics in fundamental studies of engineering ceramics. One is “Densification mechanism of Cyclic CIP”, and other is “Theory of dissipation energy during fracture of fiber-reinforced composites”.

    About 20 years ago, my boss, Prof. Matsuo developed “Cyclic CIP” based on an idea of superimposing cyclically varying pressure onto a static hydraulic pressure during powder compaction. Recently, the presenter conducted a model experiment with spray-dried granule, and estimated the bulk density, pore size distribution and surface morphology of Cyclic CIP compacts. The densification mechanism is discussed with these experimental results, and also theoretically interpreted by using a multiple shell model. This is one of examples for process controls to improve the reliability.

    Fiber reinforcement is substantially only one solution to improve fracture resistance of ceramics, and therefore many efforts have been done for process development of the composites. The most important property of the fiber-reinforced composites must be the total dissipation energy during the fracture (viz. work-of-fracture), however, we have not paid much attention to a theoretical basis to predict the total dissipation energy of the composites. In this presentation a theoretical estimation is carried out for the work-of-fracture of fiber-reinforced composites based on the theory reported by the presenter. The theory is composed of three parts; energetics of interfacial debonding and fiber pullout processes in the composites; derivation of the combined probability density function of fracture stress and fracture location of the composites; formulation of the expected values of frictional dissipation energies caused by interfacial debonding and fiber pullout. This is one of examples for materials design to improve the reliability.

Personal history of the presenter

1983.3 graduated at Department of Inorganic Materials, Faculty of Engineering, Tokyo Institute of Technology

1985.3 graduated at Department of Materials Science, Graduate School, Tokyo Institute of Technology

1985.4 Researcher, in Materials Laboratory, Nissan Motor Company

1986.4 Research Associate, Department of Inorganic Materials, Tokyo Institute of Technology

1997.3 Associate Professor, Department of Inorganic Materials, Tokyo Institute of Technology

  1995.10~1996.3  Visiting Professor, Department of Physics, Washington State University (Pullman, Washington state, USA) for fractoemission research

Major Research Field: fracture mechanics, fracture statistics, micromechanics, atomistic theory of fracture etc.