PSI - Issue 68

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Procedia Structural Integrity 68 (2025) 190–196 Procedia Structural Integrity 00 (2024) 000–000 Procedia Structural Integrity 00 (2024) 000–000

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European Conference on Fracture 2024 Comparative numerical analysis of gap and overlap e ff ect on mechanical properties of variable sti ff ness composites Gu¨l Demirer a, ∗ , Altan Kayran a a Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Tu¨rkiye Abstract Laminates incorporating curvilinear fibers are known as variable sti ff ness (VS) laminates due to their spatially varying sti ff ness, determined by the local orientations of the fibers in each ply. VS composites hold significant promise for enhancing structural performance across various industries, including aerospace and automotive engineering. However, the manufacturing process, par ticularly automated fiber placement (AFP), introduces defects such as gaps and overlaps, which can significantly impact mechanical properties and failure behavior. This study aims to compare two numerical methods for modeling these defects: the defect layer method and the pixelated FE method. A VS laminate with constant curvature fiber path is analysed. The distribution of gaps and overlaps is determined first, and their e ff ects on buckling load and in-plane sti ff ness are investigated using pixelated FE and defect layer methods. The capabilities and mesh dependency of methods are discussed. © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers. Keywords: variable sti ff ness composites; gaps; overlaps; AFP; buckling load; in-plane sti ff ness European Conference on Fracture 2024 Comparative numerical analysis of gap and overlap e ff ect on mechanical properties of variable sti ff ness composites Gu¨l Demirer a, ∗ , Altan Kayran a a Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Tu¨rkiye Abstract Laminates incorporating curvilinear fibers are known as variable sti ff ness (VS) laminates due to their spatially varying sti ff ness, determined by the local orientations of the fibers in each ply. VS composites hold significant promise for enhancing structural performance across various industries, including aerospace and automotive engineering. However, the manufacturing process, par ticularly automated fiber placement (AFP), introduces defects such as gaps and overlaps, which can significantly impact mechanical properties and failure behavior. This study aims to compare two numerical methods for modeling these defects: the defect layer method and the pixelated FE method. A VS laminate with constant curvature fiber path is analysed. The distribution of gaps and overlaps is determined first, and their e ff ects on buckling load and in-plane sti ff ness are investigated using pixelated FE and defect layer methods. The capabilities and mesh dependency of methods are discussed. © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers. Keywords: variable sti ff ness composites; gaps; overlaps; AFP; buckling load; in-plane sti ff ness © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Automated Fiber Placement (AFP) is an advanced manufacturing technology featured with its high production rate, precision and repeatability. A distinguishing feature of AFP is its fiber steering capability, which enables control over fiber orientation within a ply. This capability enlarges the design space, increases tailorability and allows to optimize the structural performance. By using steered fibers, one can modify the load distribution and improve the response of the structure under prescribed loading conditions. This great potential gives rise to a new research field focusing on variable sti ff ness (VS) laminates. The laminates incorporating curvilinear fibers are termed VS laminates because of their sti ff ness that varies spatially, determined by the local orientations of the fibers in each ply. Research in VS composites has shown significant improvements in buckling performance, progressive failure be havior, maximum fundamental frequency and aeroelastic design. For example, using a tow-steered design, Lopes et al. (2008) demonstrated cut-out insensitivity for buckling load while Liguori et al. (2019) achieved a 26% improvement Automated Fiber Placement (AFP) is an advanced manufacturing technology featured with its high production rate, precision and repeatability. A distinguishing feature of AFP is its fiber steering capability, which enables control over fiber orientation within a ply. This capability enlarges the design space, increases tailorability and allows to optimize the structural performance. By using steered fibers, one can modify the load distribution and improve the response of the structure under prescribed loading conditions. This great potential gives rise to a new research field focusing on variable sti ff ness (VS) laminates. The laminates incorporating curvilinear fibers are termed VS laminates because of their sti ff ness that varies spatially, determined by the local orientations of the fibers in each ply. Research in VS composites has shown significant improvements in buckling performance, progressive failure be havior, maximum fundamental frequency and aeroelastic design. For example, using a tow-steered design, Lopes et al. (2008) demonstrated cut-out insensitivity for buckling load while Liguori et al. (2019) achieved a 26% improvement 1. Introduction 1. Introduction

∗ Gu¨l Demirer. Tel.: + 90-312-210-4247 ; fax: + 90-312-210-4250. E-mail address: gdemirer@metu.edu.tr ∗ Gu¨l Demirer. Tel.: + 90-312-210-4247 ; fax: + 90-312-210-4250. E-mail address: gdemirer@metu.edu.tr

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 10.1016/j.prostr.2025.06.041 2210-7843 © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers. 2210-7843 © 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of ECF24 organizers.