Minimum weight design of CNT/fiber reinforced laminates subject to a frequency constraint by optimal distribution of reinforcements across the thickness

Abstract

Present work involves minimization of the weight of a three-phase, glass and carbon nanotubes (CNT) reinforced angle-ply laminate, subject to a fundamental frequency constraint. Design variables include the optimal (nonuniform) distributions of the fibers and the CNTs across the laminate thickness, the stacking sequence, ply angles and ply thicknesses. In order to assess the effect of different design variables on weight minimization, a sequence of five different optimization problems is solved with an increasing number of design variables. The present approach has the advantage of comparing and assessing the effectiveness of different sets of design variables on the design efficiency and identifying the ones which are more effective in minimizing the weight. Design efficiency is defined as the ratio of the weight of the optimal laminate to the weight of a plate which is not reinforced, but subject to the same frequency constraint. It is observed that fiber and CNT reinforcements are used most effectively if placed close to or in the outer layers. It is also observed that CNT reinforcement affects the optimal values of the ply angles due to the fact that the directional properties of the fibers become less pronounced as the matrix is reinforced by CNTs.