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Title: On delamination migration in composite laminates
Author: Pernice, Maria Francesca
ISNI:       0000 0004 6057 9560
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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Carbon fibre/epoxy composite laminates are well known to be susceptible to delamination. Delamination usually grows at interfaces between plies with dissimilar fibre orientation and may migrate from one interface to another, as in low-velocity impact damage or skin-stringer debonding. Much of the modelling work in the literature focuses on delamination contained within a single ply interface, using data from characterization tests in which delamination grows at interfaces between plies of the same fibre orientation, mainly because of a lack of understanding of the fundamental causes of delamination migration. However, to obtain representative results, delamination migration should be accounted for by finite element methods aimed at accurately simulating delamination growth. The objective of this work was to investigate and understand delamination migration at interfaces between plies with dissimilar fibre orientation in composite laminates. Initially, delamination migration was observed experimentally in a Double Cantilever Beam (DCB) specimen containing ±θ ply interfaces. Finite element analyses of the DCB specimen were then performed, to simulate delamination migration using a cohesive zone model-based approach. Comparison of experimental and numerical results highlighted the need for a more detailed experimental understanding of the fundamental driving forces for delamination migration, before methods to simulate delamination migration could be developed and validated. To this end, further experimental tests were conducted, using the Delamination Migration test method, recently developed at NASA Langley Research Center, which allows the isolation of a single migration event that can then be studied in detail. A novel delamination migration specimen was employed, to investigate delamination migration at a generic 0/θ° interface. Tests were performed in the laboratories of the Durability, Damage Tolerance and Reliability Branch at NASA Langley Research Center. Damage was characterised in detail using C-scan and X-ray Computed Tomography techniques. During the test, delamination initially propagated along a 0°/θ ply interface, by growing closer to one of the bounding plies, turning into it and subsequently arresting. Eventually, delamination migrated to a different 0/θ° ply interface. Linear elastic finite element analyses and the Virtual Crack Closure Technique were employed to interpret experimental results. Results suggested that delamination migration is governed by the shear stress sign and the strain energy release rate along the delamination front, which both vary across the specimen width at a 0/θ° ply interface. Results of this study represent a step forward in the understanding of the key mechanism of delamination propagation and migration at ply interfaces with dissimilar fibre orientation, and help in the understanding of complex damage patterns such as low-velocity impact. Understanding delamination migration can inform design of damage tolerant composite structures and provide guidelines and benchmark data to develop and validate modelling methods aimed at simulating and predicting delamination migration.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available