Effect of Curvature on the Impact Damage Characteristics and Residual Strength of Composite Plates
The results of a study of the response and failure characteristics of thin, cylindrically cusrved, composite plates subjected to low-speed impact damage are presented. The results indicate that the plate radius and the plate thickness are important structural parameters that influence the nonlinear response of a plate for a given amount of impact energy. Analytical and experimental contact-force results are compared for several plates and the results correlate well. The impact-energy levels required to cause damage initiation and barely visible impact damage are a function of the plate radius for a given plate thickness. The impact-energy levels required to initiate impact damage for plates with a certain range of radii are greater than plates with other radii. The contact-force results corresponding to these impact-energy levels follow a similar trend. Residual strength results for plates with barely visible impact damage suggest that the compression-after-impact residual strength is also a function of plate radiu. The residual strength of impact-damaged flat plates appears to be lower than the residual strength of the corresponding cylindrically curved plates.
Experimental investigation of the impact response of cylindrically curved laminated composite panels
An experimental investigation was carried out on three different geometries for specimens which are cylindrically curved: 8 ply panels, with two radii of curvature, 0.381 m and 1.524 m; and 16 ply panels, with a radius of cuvature of 0.381 m. The panels were impacted by a mass dropped from a selection of heights. The impact force and panel center deflection were recorded with time. Each panel was C-scanned to determine the amount of damage present after impact, if any. Experimental results revealed that the geometry of a laminated composite structure strongly influences its impact response. It was shown that stiffer structures produce higher impact forces, smaller center deflections, and shorter contact duration times. The relative stiffness of each panel was explained by considering its load-deflection response. Xormalization of the force with respect to the critical dynamic load and the displacement with respect to the panel height is essential when con~paring the response of panels with different radii of curvature. A static nonlinear finite element model was developed and used for coniparison with tlie experimental impact data in an attempt to interpret the response behavior of these cylindrically curved panels.
On the non-linear free vibrations of curved orthotropic panels
Abstract This paper studies the non-linear free vibrations of simply supported curved orthotropic panels. The panels are modeled using the Donnell-Mushtari-Vlasov shell relationships. A combination of the Galerkin procedure and the Lindstedt-Poincare perturbation technique is used to construct an approximate solution to the resulting non-linear equations of motion. Algebraic manipulations show that the panel exhibits a non-linear response only when both the involved axial and circumferential modes are axisymmetric. Numerical studies of a Graphite/Epoxy panel show that its response is softening, i.e. the non-linear natural frequency decreases as the amplitude of motion increases. They also show that the lower modes are more non-linear than the higher, mainly flexural modes. The presented results also show that for the studied panels, the non-linear effects are the strongest for shallow, thin, and short panels.