Optimum design of stiffend composite plaates under impact loading

Abstract

Thin composite plates do not have sufficient strength and stiffness under trans verse loads and bending moments. One may increase thickness, but using stiffeners is a more effective way of improving their mechanical response. Stiffeners are sections joined to a plate to increase its stiffness against out-of-plane deformation. Composite parts are subjected not only to static loads but also impact loads. Their safe use under impact loading should be ensured during design process. Because composite materials are generally used in weight-critical applications, they should be optimally designed to achieve the most effective use of material. There are numerous studies on the op timization of stiffened laminates under static loads, but few researchers attempted to optimize stiffened laminates under impact loading. The objective of this study is to develop a methodology to find the optimum design of stiffened composite plates sub jected to low-velocity impact loads. The objective function to be minimized is taken to be the weight. A hat-stiffened composite plate is considered. The design variables are the dimensions of the stiffener. Three different constraints are imposed: Maximum deflection limit, delamination failure, and intralaminar failure. Thickness and fiber ori entations are kept constant; but optimum results are obtained for different thicknesses. An explicit finite element model is developed in LSDYNA to simulate the response of the plate under impact loading. A modified simulated annealing algorithm is used to find the globally optimal design. A code is developed in ANSYS Parametric Design Language to implement the search algorithm and carry out finite element analyses. At the end, the optimum stiffened plates are compared with unstiffened composite plates under impact loading and their performances are evaluated for different loading conditions including static transverse loading.