Toshiaki Mizutani

RESIDUAL STRAIN ENERGY IN COMPOSITES CONTAINING PARTICLES

Selsings formula for radial tension at the particle-matrix interface is extended into a general formula which includes the effects of the amount of dispersed particles. A relationship is derived between individual volumes of strained unit cells in the crystal lattices of the particles and of the surrounding matrix. These relationships are used to predict the effect of the particles (2H−TiB 2 , 2H−ZrB 2 , and t−WB) on their unit cells and on the unit cell of the surrounding 6H–SiC matrix. The precision of these predictions was 7.1% or better. Hence, in principle, it is possible to investigate the distributions of residual bulk stress/strain. Estimates of characterizing values of the three composite systems are attempted on the rough basis of the elastic constants of the SiC matrix, confirming the physical validity of this approach as a first approximation. Further, the residual bulk strain energies of the particles and the matrix are discussed in connection with the elastic term involved in the fracture energy of such composites.

Residual strain in SiC composites containing particulate MeB2

The lattice constants of dispersed particles (2H-TiB2, 2H-ZrB2, 2H-VB2 and 2H-NbB2) and the surrounding 6H-SiC matrix of the surfaces of sintered composite blocks and the corresponding pulverized powders, respectively, were evaluated by X-ray diffraction analyses. An X-ray diffraction technique applied to polished surfaces of composite blocks was found to be a useful method for analyzing such composites. The deformations of the unit cell volumes for 6H-SiC (shrinkage) and 2H-MeB2 (expansion) were respectively intensified and reduced in accordance with the increase of dispersed MeB2 particles. Both detected deformations were relaxed by a pulverizing procedure. The origin of both deformations was not any residual surface strain but the residual bulk strains which originate from a thermal expansion mismatch between the dispersed particles and the surrounding matrix. Moreover, Selsings formulas for the residual bulk strains need to be improved to more generalized formulas.