Equivalent tensile elastic modulus measurement of cross-ply composite plates using S1 mode of Lamb wave

This paper proposes a simple and effective Lamb wave-based measurement method for the elastic moduli of cross-ply composite plates with large thickness, considered equivalent to a single-layer orthotropic plate with nine independent elastic constants. Due to the low-frequency signals required for measuring large thickness plates and the large wavelength of the low-frequency signals, the size of composite plates is highly required. Therefore, it is considered to use the first order symmetric (S1) mode wave to increase the signal frequency and reduce the wavelength. The effects of elastic constants on the phase velocities of the S1 mode are investigated. The phase velocity of the S1 mode depends only on the equivalent tensile elastic modulus and in-plane Poisson’s ratio in the low-dispersive frequency-thickness product regime. Moreover, the in-plane Poisson’s ratio of cross-ply laminates changes sufficiently small to neglect its effect on the phase velocities of the S1 mode. Therefore, the tensile elastic moduli of the cross-ply laminated plates can be estimated using the S1 mode, and the mapping relations between the phase velocities of S1 mode and the elastic moduli are established. The proposed approach has been numerically and experimentally tested on cross-ply glass fiber reinforced laminates with large thickness, and validated by theoretical values and conventional tensile tests.