Damage detection of a woven fabric composite laminate using a modal strain energy method

Abstract

This paper presents the detection of surface cracks in a woven fabric composite laminate using a modal strain energy method. A carbon fabric F3T-282/epoxy (DICY) is used to fabricate a plain woven laminate. In the first place, the unknown material properties are computed by utilizing an inverse method through finite element analysis and experimental modal analysis. Three equivalent models, i.e. cross-ply [ 0 / 90 ] n s , orthotropic and representative cell, are established to simulate the woven laminate. Tensile tests are also performed to measure the mechanical properties for comparison. A surface crack is created to represent nominal damage which is comparatively small and does not significantly affect the global stiffness of the woven laminate. Experimental modal analysis is conducted on the woven laminate to obtain the modal displacements before and after damage. The modal displacements are used to compute the modal strain energies through the three equivalent models. A damage index is defined by employing the fractional modal strain energy of the woven laminate before and after damage, and then used to identify the location of the surface crack. Limited by grid points in measurement, a differential quadrature method is utilized to compute the partial differential terms in strain energy formula. Consequently, the damage indices obtained from global and local measurements successfully locate the surface crack in woven laminate. Only a few measured mode shapes are required in this method, which has a relatively low cost and flexibility in measurement, nondestructive evaluation, and feasibility of real-time detection in woven laminates.