Lecture 3: Fibre architecture
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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 12/01/2012 1
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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. - PowerPoint PPT Presentation
Transcript of Lecture 3: Fibre architecture
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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
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Composites properties are strongly dependant on the arrangement and the distribution of fibres:
o Diameter and length
o Volume fraction
o Alignment
o Packing arrangement (distribution)
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Volume fraction and weight fraction:
o 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
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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
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Fibre packing arrangements:
o In unidirectional lamina, fibres are aligned
o Two ideal models Hexagonal and square packing
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Fibre packing arrangements:
Lecture 3: Fibre architecture
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Fibre packing arrangements:
o these ideal arrangement do not occur usually and there is usually clustering of fibres.
o Properties are then affected because Vf is lower
o For a resin to penetrate a dense pack of fibres is difficult which leads to defects (voids) and lower properties
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Fibre packing arrangements:
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Fibre packing arrangements:
o 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
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Fibre packing arrangements:
o Laminates:
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Fibre packing arrangements:
o Laminates are described by their stacking sequence
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Fibre packing arrangements:
o Woven arrays of fibres:
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Fibre packing arrangements:
o Knitted arrays of fibres:
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Fibre packing arrangements:
o Braided arrays of fibres:
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Orientation of fibres:
o Occurs often during processing
o Easier with short fibres
o Dependant on strain, viscosity of matrix and fibre length
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Short fibre arrangements:
o Orientation is statistically measured by the texture of the composite (distribution of orientations)
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Orientation of fibres:
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Short fibre arrangements:
o Length is also a distribution
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Short fibre arrangements:
o Length is also a distribution and often described by 2 averages:
• Length number average: Ln=ΣNiLi/ ΣNi
• Length weight average: Lw=ΣWiLi/ ΣWi
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Voids:
o Appear during manufacturing process, or
o due to improper impregnation of the resin, or
o appear during deformation of the composite
o Measured either by direct observations, or by density measurements
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