THERMAL AND THERMO-ELASTIC-PLASTIC RESPONSE OF CERAMIC-METAL FUNCTIONALLY GRADED MATERIALS—THERMAL SHOCK PROBLEM

The thermal and thermo-elastic-plastic response of newly developed ceramic-metal functionally graded materials under a thermal shock load is studied. The materials are heated at the ceramic surface with a sudden high-intensity heat flux input, and cooled at the metal surface with a flowing liquid nitrogen. Emphasis is placed on two aspects: (1) the influence of the graded composition of the materials on the temperature and stress response; and (2) the optimum design of the graded composition from a unified viewpoint of the heat insulation property and stress relaxation property. Moreover, a comparison between the thermoelastic stress and the thermo-elastic-plastic stress is also made to indicate the plasticity effect.

INSTANTANEOUS THERMAL EXPANSION BEHAVIOR OF HETEROGENEOUS MATERIALS WITH A WORK-HARDENING ELASTOPLASTIC MATRIX AND ELASTIC SPHEROIDAL INHOMOGENEITIES

The instantaneous thermal expansion behavior of-two-phase heterogeneous materials subjected to a uniform temperature change is explored in the present study. The matrix phase is assumed to be a work-hardening ductile metal and the dispersive phase is assumed to consist of either aligned or randomly-oriented, elastic,, spheroidal inhomogeneities. The plastic flow and decreasing stiffness of the matrix during Eshelby's transformation strain of the equivalent inclusions are accounted for by using the deformation theory of plasticity. The explicit results of the instantaneous overall thermal expansion coefficients and the critical inelastic temperature changes are presented for aligned disc- and fiber-inclusions. For the spherical and randomly-oriented spheroidal inclusion, the present study demonstrates that when the yielding of the composites is governed by the average matrix stress, the overall response is always elastic in spite of the temperature change.

Densification of the Tungsten Heavy Alloys at 1473 K and Fabrication of W-Mo System FGM with Density Gradient

The tungsten heavy alloys with Hi-Al and Fe-Al additives were sintered by hot-press method at 1473 K for 1 h. It was found that the relative density of the W-Fe alloy could be increased evidently by addition of Al. However, the relative density of W-Ni-Al alloy with low content of Al was conversely decreased considerably compared with that of W-Ni alloy. The causes have been studied. The sintering experiments of Mo alloy and W-Mo alloys with 3 wt pet Fe-1.5 wt pet Al additives were also carried out under the same sintering condition of low temperature. Finally, W-Mo system FGM with density gradient was successfully fabricated. Its density changed gradually from 17.0x10(3) kg/m(3) to 9.5x10(3) kg/m(3) within the middle 1.1 mm thickness range.

THERMO-ELASTIC-PLASTIC RESPONSE AND OPTIMUM DESIGN OF CERAMIC-METAL FGMS-CYCLIC THERML LOADING PROBLEM

The materials are made with a graded composition and microstructure in the thickness direction from the ceramic side to the metal side. The cyclic thermal loading and high temperasure gradient environment are simulated by heating the ceramic surface with a cyclic hear flux input and cooling the metal surface with a flowing liquid niterogen. The thermal and themo-elastic-plastic response of the materials is calculated using the isotropic hardening model and kinetic hardening model. Emphasis is placed on the response analysis under the different graded compositional distributions. Through the response analysis, the optimum design process of the graded composition under the dynamic case is established, which is bused on a unified viewpoint of the heat insulation property, thermal stress relaxation property and stress history feature.