Theories Of Creep In Ceramics

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.

Theories of creep in ceramics.

Emphasis is on models involving grain boundary motion sliding or flow. In lifshitz models the crystalline grains elongate with strain. 2 percussion theory according to percussion theory creep is developed due to the impact of wheels at the rail end ahead of a joint. 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. Metals and ceramics exhibit diffusion creep with n 1 at low stresses and n 3 at high stresses. The elongation results from diffusion slip or solution and precipitation. The elongation results from diffusion slip or solution and precipitation.

In ceramics with high glass contents creep is controlled by the viscous flow of glass. 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. 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. 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. Emphasis is on models involving grain boundary motion sliding or flow. 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.

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. 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.