Effects of Cutouts on the Dynamic Response of Curved Rectangular Composite Panels

Numerical results obtained by the finite-element method were compared with experimental results obtained by holographic interferometry to quantify the effects of cutout size and orientation on the first five natural frequencies and mode shapes of a curved Gr-Ep panel. The clamped-clamped panels had a quasi-isotropic layup [0, - 45, 45, 90]s and measured 12 in. (30.48 cm) high with a 12-in. (30.48-cm) chord. Cutouts having dimensions of 2 x 2 in. (5.08 x 5.08 cm), 2x4 in. (5.08 x 10.16 cm) and 4 x 4 in. (10.16 X 10.16 cm) were centrally located in the panels. The effects of the orientation of the 2x4 in. (5.08 x 10.16 cm) cutout were studied. When the finite-element results were compared with the time-averaged holograms, the two techniques showed close correlation of both the natural frequencies and mode shapes. Increasing the cutout size resulted in the expected reduction in natural frequency. An unexpected mode switch was observed to occur in the first two modes as more material was removed from the panel. It was found that the 0-deg cutout orientation had a significant effect on the panel stiffness, whereas the other cutout orientations did not significantly effect the stiffness. Nomenclature El == Young's modulus in longitudinal fiber direction E2 = Young's modulus in the transverse fiber direction Gn = shear modulus Keq - equivalent spring stiffness m - mass t = panel thickness *>12, *>2i = Poisson's ratios p = mass density QJ = frequency