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ISBN 9783843937603

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978-3-8439-3760-3, Reihe Ingenieurwissenschaften

Tobias Wehrkamp-Richter
Multiscale Analysis of the Mechanical Response of Triaxial Braided Composites (Band 49)

227 Seiten, Dissertation Technische Universität München (2018), Softcover, A5

Zusammenfassung / Abstract

New lightweight materials, such as carbon fibre reinforced plastics (CFRP) allow a significant reduction in structural weight. Specifically in high-volume production areas, such as the automotive industry, current manufacturing technologies face a twofold challenge: cost and cycle time. State-of-the-art composite braiding features a highly automated and reproducible process combined with an excellent rate of material deposition for mass-production at minimum waste, making it extremely economic. As a result of deficient design experience and sizing methods for braided composites, engineers rely on approaches developed for traditional unidirectional composites. However, such a methodology cannot be applied to highly non-linear problems, such as impact and crash, where the material exhibits a complex failure behaviour as a result of its inherent textile nature including out-of-plane waviness, interacting fibre bundles, and nesting of compacted plies. In this work, a high fidelity simulation framework for virtually predicting the non-linear mechanical response of triaxial braided composites is developed. In the first step, multiple braid architectures are investigated experimentally in order to understand the driving mechanisms of damage initiation and propagation. Subsequently, meso-scale finite element unit cell models with a realistic internal geometry are generated through an automated simulation work-flow by explicitly modelling the manufacturing process: after resolving initial interpenetration by means of a fictitious thermal step, a compaction simulation is performed to the desired target fibre volume fraction. For improved computational efficiency, special out-of-plane periodic boundary conditions allow an implicit consideration of the compaction of multiple braid plies in different nesting configurations. After validating the simulation framework against experimental data in terms of internal geometry, elastic properties, non-linear behaviour and damage morphology, the material response is predicted under variable uni-axial off-axis load cases. Finally, the effect of the textile topology on the ultimate strength of the material is investigated.