Keywords: optimal design, buckling, central hole, rectangular laminates.

Among the various aspects of the performance of structures made of composite materials, the mechanical behaviour of rectangular laminated plates has drawn much attention. In particular, consideration of the buckling phenomena in such plates is essential for the efficient and reliable design and for the safe use of the structural element.

There are numerous studies in the scientific press dealing with the behaviour and optimal design of laminated fiber reinforced plates subjected to buckling loads but most have ignored the effects of bending-stretching coupling. Some deal with plates with holes. For example, Akbulut and Sayman [1] used a first order shear deformation theory to determine the buckling loads of rectangular laminated plates under inplane loads for various hole sizes. In Ref [2], the buckling analysis of laminated composite circular plates having circular holes and subjected to a uniform radial load was investigated by using the finite element method. The effects of hole sizes, location of the hole, thickness of the laminates and the different boundary conditions were determined. An eight node isoparametric shell elements with twenty-four degrees of freedom was used during the investigation.

The present study uses the finite element method, based in Mindlin theory, to determine the optimal design of rectangular symmetrically laminated fiber-reinforced plates with circular central holes subject to in-plane loads. The design objective is to maximize the buckling load capacity of the plates, and the design variable is the ply angle. The effect of the plate size, hole size and boundary condition is investigated. It is shown that in many cases the holes typically increase the buckling load carrying capacity of the plate, and in a few cases, larger holes are more effective than smaller ones in strengthening a plate.

The numerical results are presented for plates made from a typical graphite/epoxy material, and four layers were chosen in order to emphasize the fact that bending-twisting coupling is accounted for. The effect of boundary conditions, load type, hole size and plate size was also investigated.

1

H. Akbulut, O. Sayman, "An investigation on buckling of laminated plates with central square hole", Journal of Reinforced Plastics and Composites, 20(13), 1112-1124, 2001. doi:10.1106/MN6W-FMDB-K7MJ-UQ08

2

A. Baltaci, M. Sarikanat, H. Yildiz, "Buckling analysis of laminated composite circular plates with holes", Journal of Reinforced Plastics and Composites, 25(7), 733-744, 2006. doi:10.1177/0731684406062065

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