WAVE-PROPAGATION IN STRESSED COMPOSITES

The performance of high-temperature composites can be significantly af fected by the presence of residual stresses. These stresses arise due to the mismatch of thermal expansion coefficients between matrix and f ibers during cooling from fabrication temperature to room temperature. This effect is especially pronounced in metal matrix and intermetalli c composites. It can lead to plastic deformation, matrix cracking and fiber/matrix interface debonding. Elastic wave propagation in homogene ously stressed media has been frequently addressed in the literature. However, the effect of nonhomogeneous stress distribution has not been investigated. This is especially important since the average residual stresses are zero in equilibrium and thus their distribution is inher ently nonhomogeneous. In this paper, the feasibility of using ultrason ic techniques for residual stress assessment in composites is addresse d. A theoretical method is presented for determining the velocities of ultrasonic waves propagating through a composite material with a nonh omogeneous distribution of residual stresses. It is based on the gener alized self-consistent multiple scattering model. Calculated results f or longitudinal and shear ultrasonic wave velocities propagating perpe ndicular to the fiber direction in SCS-6/Ti composite with and without residual stresses are presented. They show that velocity changes due to the presence of stresses are on the order of 1%. (C) 1998 Acoustica l Society of America. [S0001-4966(98)05609-4].