Thermal expansion coefficient of fiber composites

The thermal expansion coefficients of fiber composites are studied. A method of measuring the thermal expansion coefficient by piezoelectric photoacoustic technique was proposed. An intensity-modulated Ar+ laser beam was used as the incident light. The beam was focused on a spot with the diameter of about 1 μm diameter spot and illuminated the sample surface. Using the technique, piezoelectric photoacoustic signals as functions of different frequencies were experimentally measured. The thermal expansion coefficients can be obtained by fitting the experimental data. On the other hand, the thermal expansion coefficients of one-way composite C/C and C/Al in the transverse direction and the longitudinal direction were measured. The measured results are proved to be reliable by comparing with the results obtained by use of other calculation methods and experiment methods. Thermal expansion coefficients in arbitrary directions of C/C and C/Al were given. The defects of the theoretical calculation method, which is complicated and by which the thermal expansion coefficient in arbitrary direction can not be measured, are overcome.