Optimum lay-up design of variable stiffness composite structures

Abstract

Advancements in automated fibre-placement (AFP) technology make it possible to take laminate tailoring further than just stacking sequence optimisation; they enable the designer to vary the fibre orientation angle spatially within each ply. Spatial variation of fibre orientation angles results in a variable stiffness (VS) laminate. The work presented in this thesis constitutes a possible second step of a two-step design process for VS composite structures. The first step is to optimise a VS composite structure in terms of lamination parameters (LP), in the second step the LP design is converted into a lay-up design. The objective of this work was to investigate the available methods and to develop new methods to obtain the optimal VS lay-up design for a given LP design of a VS composite laminate that satisfies prescribed manufacturing constraints. The work in this thesis was divided into three parts to fulfil this objective: conversion of LPs into a lay-up design, design of blended composite lay-ups, and design of fibre-steered composite lay-ups. The reasoning behind this division was that, after a design in terms of LPs is converted into a design in terms of fibre angles, there are two possible ways to arrive at a variable stiffness laminate design: laminate blending or fibre steering. In this thesis a flexible computational tool set is presented that was developed to be used to convert a variable stiffness composite design, given in terms of lamination parameters, into an optimal variable stiffness laminate or blended composite lay-up design.