MULTIAXIAL INTERNAL VARIABLE MODELING OF THE CREEP DEFORMATION AND FRACTURE OF AN ADVANCED SILICON NITRIDE

摘要

A three dimensional model for high temperaturedeformation and failure of an advanced silicon nitride, NT-154,is presented. The model uses a nonsymmetric flow surface toaccount for different creep behavior in tension and compression.Flow surface to account for different creep behavior in tensionand compression. An isotropic strain hardening variable is usedto describe the continuous drop in creep rates with deformation.The failure criteria uses a second order symmetric tensor as aninternal damage variable to describe the anisotropy of cavityformation under creep conditions. A one dimensional version ofthe model is compared with experimental creep tests at variousstresses and temperatures. The model captures the deformationand failure well to within the scatter in experimental data.