Abstract: A new detection method using the power function of modal curvature differences as damage index was proposed to accurately identify the location and extent of composite material damage. Based on the APDL language of ANSYS， the Shell181 element was used to establish the simply supported laminate model， and the intra-laminar fiber failure model was constructed according to the Camanho damage criterion. The natural frequency of the laminate and the modal displacement of mesh nodes were obtained by modal analysis. The Gaussian curvature of the surface was obtained by the difference method， and the change of the Gaussian curvature difference before and after damage with the damage location and extent was studied. The square of the Gaussian curvature difference was used to increase the gap between the peak value and that of the other regions， which was defined as the modal displacement unevenness coefficient to detect the intra-laminar damage location and extent. The results show that the modal displacement unevenness coefficient improves the accuracy of the damage location detection， and it increases with the rise of the damage extent. The research conclusions provide guidance for improving the non-destructive testing methods for the intra-laminar damage of composite laminates.

Key words: composite material; intra-laminar damage; modal analysis; Gaussian curvature; unevenness coefficient