1995 Fiscal Year Final Research Report Summary
Micromechanics-Based Approach to the Design of Ceramic/Metal Functionally Graded Materials.
| Project/Area Number |
06452318
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Composite materials/Physical properties
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
WAKASHIMA Kenji Professor, Precision and Intelligence Laboratory, Tokyo Institute of Technology, 精密工学研究所, 教授 (70016799)
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| Co-Investigator(Kenkyū-buntansha) |
TSUKAMOTO Hideaki Research Associate, Precision and Intelligence Laboratory, Tokyo Institute of Te, 精密工学研究所, 助手 (30227376)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Functionally Graded Materials / Heat-Shielding Structure / Composite Materials / Micromechanics / Thermal Stress / Elastoplastic Analysis / Thermal Conductivity Measurement / Failure Criterion |
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| Research Abstract |
This investigation is concerned with a computational mechanics-based architecture of ceramic-to-metal graded multilayr constructions, called "functionally graded materials (FGM) ", their prime application target being directed toward the improvement of conventional thermal barrier coatings in hot structural components. The most important feature of these multilayr constructions is a tailorability of heat-shielding and thermal stress-mitigating functions through compositional and microstructural control of individual composite layrs in between the outermost fully ceramic and fully metallic ones. The tailoring as such involves heat conduction and stress analyzes under various prescribed conditions of thermomechanical loading and, because of the dual-scale heterogeneity inherent to the FGM structure, these analyzes require both "macromechanical" and "micromechanical" approaches.
The computational procedure developed in the present work features an inelastic analysis that permits yielding a
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nd plastic flow of the metal phase. This is formulated via a straightforward extension of the classical laminated plate theory, wherein a micromechanical model of constrained plasticity is incorporated to derive the lamina constitutive equation in the elastoplastic regime. A systematic computational study has been carried out to demonstrate how the distributions of thermal stresses change by changing the gradations in composition and microstructure.
Some related experiments have also been done on the zirconia-nickel system using discshaped samples fabricated by hot pressing composition-graded multilayr green compacts of powder mixtures. These include (i) the measurement of steady state through-the thickness temperature distributions by means of thermography for "in situ" determination of the thermal conductivities of individual layrs, (ii) "disc-bending" tests of compositionally uniform samples corresponding to individual layrs in order to determine their failure strengths under equi-biaxial loading conditions, and(iii) repeated thermal loading tests of graded multilayr samples under quasi-unidirectional conditions of heat flow.
A general conclusion drawn from this investigation is that the FGM concept is quite attractive indeed and the present computational mechanics-based approach can produce many useful guidelines to the FGM architecture. Less
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