Ply interface angles to promote automated forming of aerospace structures

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Abstract

The success of an automated vacuum forming process where flat prepreg laminates are formed into parts with complex curvature, is heavily influenced by the capacity of plies to deform during the forming procedure. Understanding the deformation behaviour in single and multi-layer prepreg arrangements gives insight into the likelihood of defect generation and the possible solutions which lead to defect free parts. The paper presents a theoretical model based on eigenvector and eigenvalue analysis to determine compatible modes of deformation within individual ply interfaces and complete stacking sequences. The model is validated using an experimental process where laminates are formed onto a doubly curved tool geometry using an industrial double diaphragm former. Stacking sequences with 90° interface angles outline the most formable solutions, whereas continuous 45° interfaces that spiral e.g. 45/0/-45/90 outline the most problematic forming conditions due to a locking behaviour. Optimising the interface angle within a stack for maximum compatibility is shown to completely remove defects at elevated temperature. Interface angles and stacking sequence are thus seen to be as significant as temperature and vacuum rate on the quality of formed parts.
Original languageEnglish
Title of host publicationProceedings of ICCM 2017
Publication statusPublished - 31 Aug 2017

Cite this

Ply interface angles to promote automated forming of aerospace structures. / Johnson, Kevin; Rhead, Andrew; Loukaides, Evripides; Butler, Richard.

Proceedings of ICCM 2017. 2017.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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AB - The success of an automated vacuum forming process where flat prepreg laminates are formed into parts with complex curvature, is heavily influenced by the capacity of plies to deform during the forming procedure. Understanding the deformation behaviour in single and multi-layer prepreg arrangements gives insight into the likelihood of defect generation and the possible solutions which lead to defect free parts. The paper presents a theoretical model based on eigenvector and eigenvalue analysis to determine compatible modes of deformation within individual ply interfaces and complete stacking sequences. The model is validated using an experimental process where laminates are formed onto a doubly curved tool geometry using an industrial double diaphragm former. Stacking sequences with 90° interface angles outline the most formable solutions, whereas continuous 45° interfaces that spiral e.g. 45/0/-45/90 outline the most problematic forming conditions due to a locking behaviour. Optimising the interface angle within a stack for maximum compatibility is shown to completely remove defects at elevated temperature. Interface angles and stacking sequence are thus seen to be as significant as temperature and vacuum rate on the quality of formed parts.

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