Ultrasonic measurement of elastic constants in fiber-reinforced polymer composites under influence of absorbed moisture

This paper presents an attempt to quantify hygral aging in fiber-reinforced polymer composites by the elastic constants C11 and C33. Quantitative ultrasonic measurements of the elastic constants for three different unidirectional as well as three different cross-ply specimens were compared. The specimens were manufactured with different moisture resistant surfaces and immersed in water for 24 h. By calculating the elastic constants, it was taken into account that hygral aging was accompanied by absorption of moisture in the polymer matrix. Moisture changed the laminate dimensions significantly, and typically moisture expansion coefficients are reported. Moreover, as the ultrasonic pulse form changed in the anisotropic materials, different broadband methods were used to calculate the elastic constants.