Studying Crystallinity Gradients in High Performance Composites Manufactured by Automatic Tape Placement

Academic Institution: University of Edinburgh

Academic Supervisor: Dr Dipa Roy

Industry Partner: Hexcel

PhD Student: Helena Perez Martin

Start Date: 1st July 2019

Abstract

The introduction of out-of-autoclave (OOA) processes and thermoplastics to the aerospace industry has made aerospace industry’s material and process options more complex.

Automated tape placement (ATP) is an OOA composite manufacturing process, which is becoming popular in recent years due to cost reduction potential. ATP uses computer-guided robotics to lay several layers of thermoplastic prepreg tapes onto a mould to create a part or a structure. The thermoplastic tape is heated, melted and laid down, so that the layer being applied under pressure from a roller permanently bonds to the previously laid layer. The interlaminar region of the final part does not have the optimum degree of crystallinity and evidence has emerged that laser-heating and associated rapid cooling cause a “heat-affected zone” of lower crystallinity, which could be expected through the thickness of the various over-placed thermoplastic tapes.

There is no scientific technique available which can detect the variation of crystallinity in the structure of the ATP consolidated laminates. Hence, OOA processing of thermoplastics still involves post-processing steps using an oven or an autoclave to ensure good quality laminates with uniform, desired crystallinity and the ATP process loses the benefit of time and cost. It is therefore very important to be able to measure the quality of the ATP produced laminates by detecting the variation of crystallinity across the laminate thickness. Differential scanning calorimetry and other conventional techniques measure the average crystallinity of the laminates, but cannot detect the variation across the thickness.

This PhD project will investigate and develop suitable non-destructive methodologies to measure the crystallinity level and gradient across the thickness of thermoplastic laminates manufactured by ATP. This will help in in-situ monitoring the quality of the laminates and will enhance the reliability of this manufacturing process for advanced thermoplastic composites.