High speed, high precision processing of dry pre-pregs for composite structures

Abstract

In this study, a computational code was developed that was used to optimise the fibre orientation angles, layer thicknesses, number of fibre layers and the weight in fibre reinforced composites. In addition, an interface was created between the computational code and the robotic apparatus that performed the fibre placement.

Fibre reinforced composites are extremely versatile materials and may be tailor designed to suit various applications. However, the design techniques commonly associated with composite structures make them inadequate for industries with high production rates. Conventional design techniques have the disadvantage of numerous tedious and laborious matrix calculations. Also, there is uncertainty with assigning values to the input parameters for the equations used in the design process. In addition, conventional design techniques result in constant stiffness structures, that is, structures with the same fibre layup throughout. These disadvantages result in increased manufacturing costs as more material and labour, than necessary, are used.

This study presents a solution in the form of computational codes developed in Matlab. The codes are used to perform all the necessary matrix calculations easily and swiftly. Further, the uncertainty experienced with the input parameters, in conventional design techniques, is removed. The code is used to optimise the fibre orientation angles and layer thicknesses in a composite structure, as well as the number of fibre layers and the weight. In addition, it is able to create variable stiffness structures, that is, structures where the fibre layup varies throughout. The use of the code in the design process would decrease the design costs, as the design time is reduced, and decrease the material costs, as only the required amount of material is used. The developed codes were validated using examples from texts, finite element modelling and experimental methods.

The development of the computational codes created a problem with regards to the fibre layup process. Any process that employed manual placement of the fibres became inadequate as they proved to be extremely labour intensive and would result in increased labour costs. Further, with manual placement of fibres, precise fibre orientation cannot be guaranteed. Therefore it was decided to use an automated system, such as Robotic Fibre Placement (RFP), to perform the fibre layup. Such a system was designed and built in-house in a previous study. In the current study, a Matlab code was developed as an interface between the developed computational code and the fibre placement system.

Other codes as well as graphical interfaces were developed in order to improve the interaction between the user and the codes.