Theories Of Creep In Ceramics

In lifshitz models the crystalline grains elongate with strain.

Theories of creep in ceramics. It is demonstrated that there are two important differences in the creep behaviour of ceramics. 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 this paper we present a theory of electric creep and related electromechanical coupling for both non poled and fully poled ferroelectric ceramics.

Emphasis is on models involving grain boundary motion sliding or flow. 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. Mathematical models that have been proposed for creep in ceramics are described.

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. 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. Viscosity and in turn creep rate will depend on the composition of the glassy phase and its temperature. For the case of lamellae parallel to the stress axis ϕ 0 redistribution of stress must occur in the duplex structure because the creep resistance of the matrix tial is different from that of the reinforcement ti 3 al.

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. Referring to the creep models proposed for composite materials the creep model for the dual phase lamellar micro structure has been established 28 29. In lifshitz models the crystalline grains elongate with strain. 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.

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. 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.