MODELING AND NUMERICAL COMPUTATION OF TRANSIENT INTERNAL DAMPING DUE TO THERMAL-EXPANSION MISMATCH BETWEEN MATRIX AND PARTICLES IN METAL-MATRIX COMPOSITES

A new model of the transient internal damping (ID) associated with the emission and movements of dislocations around particles in metal matr ix composites (MMCs) is developed. These movements on which the propos ed model is based are mainly induced during thermal cycles by the inte rnal stress field around particles, which results from the thermal exp ansion mismatch between particles and matrix. First, from this thermal ly induced internal stress field, calculated by the Eshelby method, an d the critical shear stress opposing the motion of dislocations in the ir glide plane in the matrix, the number and positions of punched-out dislocations are determined as a function of temperature. Second, the actual positions due to the superposition on the thermal stress field of the alternating shear stress associated with the pendulum oscillati ons are calculated by a perturbation method. Then the internal damping is derived from the contribution of the dislocation movements to the inelastic strain over a period of oscillation. The role of the experim ental parameters is investigated. This simulated ID is compared with e xperimental results obtained in the case of aluminium-based MMCs. A go od agreement between simulated and experimental IDs is found.