STRESS-RELAXATION IN THE INTERFACE BETWEEN CREEP PARTICLE AND ELASTICMATRIX-STRENGTHENING MECHANISM

The effect of a power law creep particle on interface behavior between the particle and elastic matrix is investigated by stress analysis. U sing the results obtained through the stress analysis, the forces due to interaction of an applied stress and stress concentration with an e dge dislocation are determined. The direct interaction between the edg e-dislocation and-the creeping particle is studied under fully relaxed stress conditions. Through the investigation the following results ar e derived. Stress relaxation in the interface can be caused by power l aw creep along or by diffusion, or a combination of both mechanisms. T he degree of stress relaxation caused by diffusion;can be defined in t erms of the relaxation time for both boundary diffusion and volume dif fusion. The amount of stress relaxation caused by the power law creep particle is characterized by the quantity alpha(2) which is a function of Gamma(0) = 2(1/root 3)(1+m) x (sigma(infinity)/2 mu)(m) (sigma(0)/ sigma(infinity)t(m)), where m is strain rate hardening exponent, sigma (infinity) is applied stress, mu is the shear modulus, sigma(0) is the material constant of the power law-creep particle, and t is elapsed t ime. The value alpha(2) = 1.0 corresponds to the fully relaxed conditi on and alpha(2) = -0.6 corresponds to the initial state. The time to r each a fully relaxed condition is very sensitive to the strain rate ex ponent, with the smaller m values leading to longer times. The stress state of complete relaxation in the elastic matrix is equivalent to th e solution of a void in an elastic matrix superposed on the solution o f positive surface traction on the void. This result is identical to t hat obtained by Srolovitz et al. [Acta. Metall. 32, 1979 (1984)]. When the stress is completely relaxed in the particle, all stress componen ts (sigma(r), sigma(theta) and sigma(r theta)) are relaxed, while in t he matrix relaxations, are observed only for sigma(r) and sigma(r thet a). The critical resolved Shear stress and critical stress to climb th e dislocation in the neighborhood of the particle exceed the Orowan st ress. Also, the particle attracts the dislocation. Therefore the stren gthening of a power law creep particle in an elastic matrix is caused by the Orowan mechanism and by attraction of the dislocation. Copyrigh t (C) 1996 Published by Elsevier Science Ltd