Weight optimization for hybrid, multi-scale CNT/fibre reinforced composite laminates.
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In this study, an investigation on an optimal lightweight design of a 3-phase CNT/fibre reinforced nanocomposite plate was conducted, subject to a frequency constraint. The design variables for the optimization process are, fibre volume fraction, CNT weight fraction, fibre stacking angle, and layer thickness ratio. A literature study was carried out to set the foundation to the key concepts and methods used to carry out the optimization process. The effective material properties were obtained using a 2-step process which were formulated with Halpin-Tsai equations and fibre micromechanics. The solution for the natural vibration of composite laminates was carried out using the Ritz method and Classical Laminate Plate Theories (CLPT). For the design of the weight optimization of the composite plate, the Sequential Quadratic Programming (SQP) algorithm was adopted, using MATLAB, to carry out the non-linear optimization problems with the design constraints. A verification of the vibration and optimization methods was conducted using FEM and ANSYS. Five optimization problems were defined to assess the parameters which affect the weight optimization. The solution to the optimization problems reached an optimal fibre stacking angle of 45° for square laminates and increasing towards 90° for rectangular laminates with aspect ratios greater than 1, up to 2. The use of CNTs in the composite plate was highlighted where the addition of CNTs have improved the minimum weight design for higher non-dimensional frequencies from 1.75 up to 2.5. An optimum design efficiency was achieved, showing a 52.7% weight improvement of the 3-phase laminate with the design variables assigned. Efficient material utilization was implemented optimally, which allocated higher amounts of reinforcement materials, CNTs and fibre, in the exterior layers. The weight optimization using non-uniform layer thicknesses resulted in the exterior layers to have a higher thickness than the interior layers, which contributed to an efficient minimum weight design.