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Title: Size effects in notched quasi-isotropic carbon/epoxy laminates under tensile loads
Author: Xu , Xiaodong
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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In this thesis, experimental and numerical investigations into size effects in inplane scaled centre-notched, open-hole and Over-height Compact Tension (OCT) quasi-isotropic carbon/epoxy laminates under tensile loads are carried out. Interrupted tests and X-ray Computed Tomography scanning (CT) are carried out to study the damage at the crack tip. A Finite Element method using the explicit code LS-Dyna is also applied to study the detailed damage development at the crack tip. Cohesive interface elements are used to simulate splitting and delamination. A failure criterion based on Weibull statistics is used to account for fibre failure. Good correlation between the numerical and experimental results is achieved and the damage development can be simulated. The sharp centre-notched tensile tests are compared with the open-hole tests of the same notch length (hole diameter), material and stacking sequence. A similar strength reduction scaling trend is found for both configurations at small sizes, except with higher tensile strength for the centre-notched specimens than the open-hole specimens. However, there is a cross-over point when the sizes increase, with the centre-notched results approaching an asymptote based on Linear Elastic Fracture Mechanics (LEFM), and the open-hole results approaching an asymptote based on Wei bull theory. In in-plane scaled OCT tests, the scaling of the initial fracture follows LEFM indicating constant fracture toughness for initial fracture propagation. However, the OCT specimens are found to be not big enough to generate a selfsimilar damage zone during fracture propagation. A potential R -curve is also discussed. Quasi-isotropic OCT specimens of different stacking sequences are compared. Specifically, dispersed-ply laminates and blocked-ply laminates are compared. Specimens with surface 45 degree plies which have a double 0 degree ply on the midplane (effectively a double thickness ply) are compared with the ones with surface 90 degree plies which only have single 0 degree plies throughout.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available