Improving the Manufacturability of Aerospace Prepreg Composites for High-Rate Production

Abstract

Over the last few decades the aerospace industry has seen a rapid increase in the use of composite materials in structural applications. In order to meet composite demands in this high-volume low cost driven market, increased production rates have become essential. The solution to higher rates of production, accuracy and repeatability, is to move away from the common hand layup techniques and introduce automated manufacturing processes.

This thesis explores the automated manufacture of composite laminates and the associated challenge of part quality at increased production rates. The cost-efficient process of automated forming uses temperature and pressure to conform multi-layered laminates to single or doubly curved tool geometries. Common problems associated with this manufacturing technique are wrinkle defects, which arise due to the inability of individual plies within the laminate to effectively move in shear or slip deformation. These defects lead to significant reductions in laminate performance, inherently resulting in manufacturing cost and time inefficiencies. This must be avoided.

A laminate is formed into a C-section spar geometry using automated double diaphragm forming. The layup stacking sequence is designed according to a new compatibility index, predicting the ease of deformation within multi-layer arrangements. It is shown that the laminate stacking sequence, which previously has not been given much consideration in design for manufacture, has significant impact on the formability of laminates. Heavily defected quasi-isotropic laminates are redesigned according to the compatibility index, to then outline defect free laminate quality results. The developed compatibility index assessment provides a tool for industrial engineers to examine and develop stacking sequence designs for optimal formability, leading to higher production rates at increased laminate quality.

Aerospace laminate design has predominately been stagnant since its introduction in the 20th century, with regards to ply angle orientations of 0°, 90°, 45° and -45°. Venturing out into non-standard design space was considered overcomplicating the design process, due to the vast amount of possible non-standard angle combinations. A new method is developed, whereby an industrial laminate can effectively be replaced by a chosen range of non-standard fibre angles, while retaining identical stiffness performance. This novel approach establishes further possibilities for tailored laminate design and various design-for-manufacture driven solutions in the future.

Date of Award	24 Jun 2026
Original language	English
Awarding Institution	University of Bath
Supervisor	Richard Butler (Supervisor) & Andrew Rhead (Supervisor)