CAVITATIONAL STRAIN CONTRIBUTION TO TENSILE CREEP IN VITREOUS BONDED CERAMICS

Analysis of the role of cavitation during uniaxial creep deformation i n vitreous bonded ceramics reveals that the cavity volume contributes only to the strain in the direction parallel to the tensile stress reg ardless of the shape and orientation of cavities. Creep asymmetry resu lts from the fact that cavitation preferentially contributes to axial tensile strain while the strain observed under the same conditions in compression is produced only by volume-conserving mechanisms, The cont ribution of cavitational strain in the axial tensile strain is equal t o the volume fraction of cavities and proportional to the difference b etween tensile and compressive strains in the axial direction. The den sity change method and a newly proposed method based on the difference in the axial strains were used for separating the cavitational from t he true tensile strain in self-reinforced silicon nitride, Both method s consistently revealed more than 90% contribution of cavitation to th e total tensile strain, Cavitation is concluded to be the dominant mec hanism of tensile creep deformation in vitreous bended ceramics becaus e the reported volume fractions of cavities during their deformation a re usually in the range of 70-90% of tensile strain.