Towards virtual testing of textile composites: calibration of thermoelastic tow properties

We present a methodology for calibrating the thermoelastic properties of constituent tows in a woven C/SiC composite using a combination of experimental measurements and finite element simulations of strain distributions that arise upon heating. Because of the nonuniform distribution of the matrix phase and the presence of matrix microcracks, tow properties cannot be reliably predicted a priori using micromechanical models alone; instead, some can only be inferred from coupled experimental/numerical studies of the kind presented here. A small number of iterations of finite element simulations is required to achieve satisfactory agreement in all thermal strain components. The number of iterations is minimized by first performing simulations using model-based estimates of the effective tow properties, followed by judicious adjustments to select property values. Comparisons between measurements and simulations are performed on the basis of strains averaged over a characteristic area dictated by tow dimensions. The study reveals that, although each segment of a particular tow genus is nominally equivalent to all others, the strains within each population exhibit considerable variation. This is attributable to variations in both tow geometry and connectivity between adjacent tows. The virtual tests predict strain variations of comparable magnitude.