Bending Analysis of Laminated Composite Sandwich Plates Reinforced with Carbon Nanotube Forests

In order to meet the ever-increasing demand for high-strength, lightweight aerospace structures, a new material is created via combination of three prior innovations: sandwich configurations, composites, and the addition of carbon nanotubes. A theoretical sandwich panel is created using facesheets of a novel woven microfibre composite reinforced by carbon nanotube forests, as created by Vinod P. Veedu, et. al., in “Multifunctional Composites Using Reinforced Laminae with Carbon-Nanotube Forests” (Nature Materials). This sandwich panel, and a similar panel without nanotube reinforcement, are weightoptimized and analytically subjected to a uniform load in order to compare the effect of adding nanotubes entirely parallel to the direction of the applied load. The analysis itself is carried out via the use of the higher-order finite element method developed for sandwich panels by S. Oskooei and J. S. Hansen in “Higher-Order Finite Element for Sandwich Plates” (AIAA Journal). The resulting x, y, and z direction displacements and compressive and tensile stresses are all significantly reduced for the nanotube-enhanced panel. Up to one-half the displacement and one-fifth the stress results from inclusion of the nanotube forest. Reduction in displacement and stress is found to be directly proportional to increase in applied load, as expected. Furthermore, the benefits of adding a nanotube forest to the woven composite are shown to be even greater in the sandwich configuration than in the composite configuration alone. Inclusion of the nanotube forest results in a 2.71-fold increase in allowable tensile stress and a 3.16-fold increase in allowable compressive stress, versus the 2.42-fold increase in the flexural strength for the facesheet panel alone (as measured by Veedu, et. al.). Finally, the use of a different epoxy with higher Poisson’s ratio is proposed for use in the composite facesheets. The effect of increased facesheet Poisson’s ratio on both displacement and stress is analyzed and shown to further reduce displacement in all directions and both compressive and tensile stresses in the panel. The greatest impact of higher Poisson’s ratio was found to occur in sandwich panels experiencing levels of lateral loading near panel failure. The proposed use of the woven composite reinforced by nanotube forests as a facesheet in sandwich panels, particularly with a higher facesheet Poisson’s ratio, is thus confirmed as a feasible and promising application warranting further study.