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Lecture 3: Fibre architecture

Lecture 3: Fibre architecture. At the end of this lecture you will have an understanding of: Distribution of fibres Packing arrangements of fibres Orientation of fibres Length of fibres Defects. Lecture 3: Fibre architecture.

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Lecture 3: Fibre architecture

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  1. Lecture 3: Fibre architecture • At the end of this lecture you will have an understanding of: • Distribution of fibres • Packing arrangements of fibres • Orientation of fibres • Length of fibres • Defects

  2. Lecture 3: Fibre architecture • Composites properties are strongly dependant on the arrangement and the distribution of fibres: • Diameter and length • Volume fraction • Alignment • Packing arrangement (distribution)

  3. Lecture 3: Fibre architecture • Volume fraction and weight fraction: • Depending on the property we want to discuss, we need to consider either type of description • Volume fraction is used for most physical properties (strength …) • Weight fraction is used for properties such as density

  4. Lecture 3: Fibre architecture • Volume fraction and weight fraction: • Vf = (wf/ρf)/(wf/ρf+wm/ρm) • wf= vfρf/(vfρf+ vmρm) • With Vf , Vm, wf, wm, ρf, ρm, volume fraction, weight fraction, and density of fibre and matrix

  5. Lecture 3: Fibre architecture • Fibre packing arrangements: • In unidirectional lamina, fibres are aligned • Two ideal models Hexagonal and square packing 2R 2R 2r 2r h h

  6. Lecture 3: Fibre architecture • Fibre packing arrangements: 2R 2R 2r 2r h h h h

  7. Lecture 3: Fibre architecture • Fibre packing arrangements: • these ideal arrangement do not occur usually and there is usually clustering of fibres. • Properties are then affected because Vf is lower • For a resin to penetrate a dense pack of fibres is difficult which leads to defects (voids) and lower properties

  8. Lecture 3: Fibre architecture • Fibre packing arrangements:

  9. Lecture 3: Fibre architecture • Fibre packing arrangements: • Laminates: • Set of plies stacked together • Good properties within the plane of the plies • Plies can be arranged in a stack to make the properties isotrope

  10. Lecture 3: Fibre architecture • Fibre packing arrangements: • Laminates:

  11. Lecture 3: Fibre architecture • Fibre packing arrangements: • Laminates are described by their stacking sequence

  12. Lecture 3: Fibre architecture • Fibre packing arrangements: • Woven arrays of fibres:

  13. Lecture 3: Fibre architecture • Fibre packing arrangements: • Knitted arrays of fibres:

  14. Lecture 3: Fibre architecture • Fibre packing arrangements: • Braided arrays of fibres:

  15. Lecture 3: Fibre architecture • Orientation of fibres: • Occurs often during processing • Easier with short fibres • Dependant on strain, viscosity of matrix and fibre length

  16. Lecture 3: Fibre architecture • Short fibre arrangements: • Orientation is statistically measured by the texture of the composite (distribution of orientations)

  17. Lecture 3: Fibre architecture • Orientation of fibres:

  18. Lecture 3: Fibre architecture • Short fibre arrangements: • Length is also a distribution

  19. Lecture 3: Fibre architecture • Short fibre arrangements: • Length is also a distribution and often described by 2 averages: • Length number average: Ln=ΣNiLi/ΣNi • Length weight average: Lw=ΣWiLi/ΣWi

  20. Lecture 3: Fibre architecture • Voids: • Appear during manufacturing process, or • due to improper impregnation of the resin, or • appear during deformation of the composite • Measured either by direct observations, or by density measurements

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