Understanding the influence of laminate stacking sequence on strain/stress concentrations in thin laminates at repair holes with large scarf angles

Damghani, Mahdi; Bakunowicz, Jerzy; Murphy, Adrian

Abstract

Scarf repair is widely used in the restoration of structural performance of damaged aircraft secondary structures. Such repairs result in reduced thickness sections which are significantly larger than those associated with typical fastener holes. Significant literature exists on the distribution of strain/stress concentration in fastener hole geometries, both straight sided and countersunk, but is lacking for the geometries associated with shallow scarf angles and thin laminates. Hence, herein three-dimensional finite element models are developed to understand the influence of stacking sequence and scarf angle on strain/stress concentrations. The results demonstrate and quantify for the first time that strain concentrations are not only dependant on the laminate membrane stiffness but also on laminate bending stiffness, due to the anisotropy created as a result of scarfing angle, hole geometry and laminate thickness. Scarfing is demonstrated, for typical repair geometry associated with foreign object damage (hole diameter 20 mm, scarf angles 3 deg to 7deg), to elevate strains by up to 2.5 times when compared to equivalent diameter straight-sided holes in laminates of thickness #1 mm.

• Journal Article Type: Article
• Acceptance Date: May 1, 2019
• Online Publication Date: Jun 18, 2019
• Publication Date: Dec 1, 2019
• Deposit Date: Jun 19, 2019
• Publicly Available Date: Jun 19, 2019
• Journal: Journal of Composite Materials
• Print ISSN: 0021-9983
• Electronic ISSN: 1530-793X
• Publisher: SAGE Publications
• Peer Reviewed: Peer Reviewed
• Volume: 53
• Issue: 28-30
• Pages: 4273-4284
• DOI: https://doi.org/10.1177/0021998319855772
• Keywords: scarf repair, scarf holes, scarf angle, stacking sequence, strain concentrations, stress concentrations, composite laminate
• Public URL: https://uwe-repository.worktribe.com/output/1492705
• Publisher URL: https://doi.org/10.1177/0021998319855772
• Additional Information: Additional Information : Copyright(c)2019 Reprinted by permission of SAGE publications.
• Contract Date: Jun 19, 2019