Measurement of fiber reinforced composite engineering constants with laser ultrasonic

In this paper, a noncontact laser ultrasonic method is proposed to determine the engineering constants of fiber reinforced composite. The method is based on the measurements of the transverse wave velocities as well as the longitudinal wave velocities. In the experiment, the unidirectional carbon fiber reinforced bismaleimide resin matrix composite is measured and the sample is equivalent to a transversely isotropic material. Two longitudinal wave propagation velocities and three transverse wave propagation velocities in two specific directions are measured, respectively. On this basis, all five independent elastic constants can be obtained according to the Christoffel equation. In the finite element analysis, the model of laser induced ultrasonic in the composites is established. The pulsed laser is equivalent to the surface load and the relationship between the physical parameters of the laser and the load is established by the correction coefficient. The numerical results match well with experimental measurements, which show that the method presented in this paper can achieve an accurate measurement of the elastic constants of fiber reinforced composite.