A methodology to reproduce postbuckling in composite panels to study skin stringer separation

Doctoral thesis (2023)

Authors

Lucas Kootte Aerospace Structures & Computational Mechanics - Aerospace Engineering
Research Group
Aerospace Structures & Computational Mechanics (Aerospace Engineering) (TU Delft)
Copyright: © 2023 Lucas Kootte
DOI: https://doi.org/10.4233/uuid:cfccc1dc-df8a-4a49-8c1a-c2ebad7a1867
Postbuckling Fracture toughness Skin-stringer separation Building block approach Stiffened panels Thermoset composites Component testing
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Published Date

2023

Language

English

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Faculty

Aerospace Engineering

Department

Aerospace Structures & Materials

Research Group

Aerospace Structures & Computational Mechanics

Abstract

A building block pyramid is designed used to evaluate a composite aircraft structure, combining tests and analyses, using stiffened panels, single-stringer specimens and coupons. Failure in these structures can be caused by postbuckling-induced skin-stringer separation, which is complex, involving matrix cracks, fibre bridges, and delamination migrations. Standardized tests covering postbuckling-induced skin-stringer separation are lacking. First, a material characterization is performed on the coupon level. These properties are applied to a stiffened panel model to identify critical postbuckling regions. Then a single-stringer specimen is designed that combines the material complexities of the coupon level and the geometrical complexities of the panel by mimicking the postbuckling shape. Specifically a seven-point bending configuration to study bending-induced separation and a four-point twisting configuration for skin twisting-induced separation. The guidelines for modelling and testing can assist in standardising these test methods.
Using composite materials in aircraft structures can reduce weight compared to conventional metals. However, utilizing more of the material's load-carrying capabilities can further reduce weight.