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 12012012 1 Composites properties are strongly dependant on the arrangement and the distribution of fibres ID: 282794
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Lecture 3: Fibre architecture
At the end of this lecture you will have an understanding of:Distribution of fibresPacking arrangements of fibresOrientation of fibresLength of fibresDefects
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1Slide2
Composites properties are strongly dependant on the arrangement and the distribution of fibres:
Diameter and lengthVolume fraction Alignment Packing arrangement (distribution)
Lecture 3: Fibre architecture
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Volume fraction and weight fraction:
Depending on the property we want to discuss, we need to consider either type of descriptionVolume fraction is used for most physical properties (strength …)Weight fraction is used for properties such as densityLecture 3: Fibre architecture
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Volume fraction and weight fraction:
Vf = (wf/ρf)/(wf/ρf+ wm/ρm)wf =
vfρf
/(
v
f
ρ
f
+
v
m
ρ
m)With Vf , Vm, wf, wm, ρf, ρm, volume fraction, weight fraction, and density of fibre and matrix
Lecture 3: Fibre architecture
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Fibre packing arrangements:
In unidirectional lamina, fibres are aligned Two ideal models Hexagonal and square packingLecture 3: Fibre architecture
2R
2r
h
2R
2r
h
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Fibre packing arrangements:
Lecture 3: Fibre architecture
2R
2r
h
2R
2r
h
h
h
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Fibre packing arrangements:
these ideal arrangement do not occur usually and there is usually clustering of fibres.Properties are then affected because Vf is lowerFor a resin to penetrate a dense pack of fibres is difficult which leads to defects (voids) and lower propertiesLecture 3: Fibre architecture
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Fibre packing arrangements:
Lecture 3: Fibre architecture12/01/20128Slide9
Fibre packing arrangements:
Laminates:Set of plies stacked togetherGood properties within the plane of the pliesPlies can be arranged in a stack to make the properties isotrope
Lecture 3: Fibre architecture
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Fibre packing arrangements:
Laminates:Lecture 3: Fibre architecture
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Fibre packing arrangements:
Laminates are described by their stacking sequenceLecture 3: Fibre architecture
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Fibre packing arrangements:
Woven arrays of fibres:Lecture 3: Fibre architecture
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Fibre packing arrangements:
Knitted arrays of fibres:Lecture 3: Fibre architecture
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Fibre packing arrangements:
Braided arrays of fibres:Lecture 3: Fibre architecture
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Orientation of fibres:
Occurs often during processing Easier with short fibresDependant on strain, viscosity of matrix and fibre lengthLecture 3: Fibre architecture
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Short fibre arrangements:
Orientation is statistically measured by the texture of the composite (distribution of orientations)Lecture 3: Fibre architecture12/01/201216Slide17
Orientation of fibres:
Lecture 3: Fibre architecture12/01/201217Slide18
Short fibre arrangements:
Length is also a distributionLecture 3: Fibre architecture12/01/201218Slide19
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
Lecture 3: Fibre architecture
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Voids:
Appear during manufacturing process, or due to improper impregnation of the resin, orappear during deformation of the compositeMeasured either by direct observations, or by density measurements
Lecture 3: Fibre architecture
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