Evaluation of structural joints in composites with modal parameters

The paper examines if modal parameters can be used in non-destructive test (NDT) methods for the control of the structural integrity of joints in large glass fiber reinforced polyester structures. Therefore, an attempt is made to look for a correlation between modal parameters and the accumulated damage of the joints of a stiffened plate structure that is subjected to several underwater explosions with successively higher shock loadings, until debonding of rib and panel is obtained. Attention is paid to the method used for the determination of the modal parameters. The evolution of the modal parameters in relation to the accumulated damage is discussed, after which it is concluded that modal frequency measurements are more appropriate as parameters in NDT of large structures than modal damping measurements.