Theories Of Creep In Ceramics

In this paper we present a theory of electric creep and related electromechanical coupling for both non poled and fully poled ferroelectric ceramics.

Theories of creep in ceramics.

We consider electric creep to be a time dependent process with an initial condition lying on the d electric displacement versus e electric field hysteresis loop. Creep both in metals and ceramics in the steady state is diffusion controlled and the homologue temperature of t t m regarding the diffusion coefficient also applies to both materials. The elongation results from diffusion slip or solution and precipitation. Referring to the creep models proposed for composite materials the creep model for the dual phase lamellar micro structure has been established 28 29.

Emphasis is on models involving grain boundary motion sliding or flow. It is demonstrated that there are two important differences in the creep behaviour of ceramics. Mathematical models that have been proposed for creep in ceramics are described. This discrepancy in results is believed to be a consequence of the fact that ceramics tend to creep more readily in tension than in compression leading to a shift in the neutral plane for stress and strain in flexural specimens which results in extended primary creep.

In oxide ceramics consideration of diffusion creep involving ambipolar diffusion suggests that creep will be controlled by the slower moving species diffusing along its faster path 6 10. In lifshitz models the crystalline grains elongate with strain. The elongation results from diffusion slip or solution and precipitation. Theories of creep in ceramics.

1 there is an enhanced role of diffusion creep and 2 in the power law regime ceramics divide into two categories with stress exponents of 5 and 3 respectively. The ironing effect of the moving wheels on the wave formed in the rail causes a longitudinal movement of the rail in the direction of traffic resulting in the creep of the rail fig. Mathematical models that have been proposed for creep in ceramics are described. In lifshitz models the crystalline grains elongate with strain.

Viscosity and in turn creep rate will depend on the composition of the glassy phase and its temperature. In ceramics with high glass contents creep is controlled by the viscous flow of glass. Emphasis is on models involving grain boundary motion sliding or flow.