Upload
duante
View
46
Download
0
Tags:
Embed Size (px)
DESCRIPTION
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
Citation preview
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
12/01/2012
2
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)
Lecture 3: Fibre architecture
12/01/2012
3
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
Lecture 3: Fibre architecture
12/01/2012
4
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
Lecture 3: Fibre architecture
12/01/2012
5
Fibre packing arrangements:
o In unidirectional lamina, fibres are aligned
o Two ideal models Hexagonal and square packing
Lecture 3: Fibre architecture
2R
2r
h
2R
2r
h
12/01/2012
6
Fibre packing arrangements:
Lecture 3: Fibre architecture
2R
2r
h
2R
2r
h
𝑉𝑓=( 𝜋2√3 )( 𝑟𝑅 )
2
𝑉𝑓=( 𝜋4 )( 𝑟𝑅 )2
h h
12/01/2012
7
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
Lecture 3: Fibre architecture
12/01/2012
8
Fibre packing arrangements:
Lecture 3: Fibre architecture
12/01/2012
9
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
Lecture 3: Fibre architecture
12/01/2012
10
Fibre packing arrangements:
o Laminates:
Lecture 3: Fibre architecture
12/01/2012
11
Fibre packing arrangements:
o Laminates are described by their stacking sequence
Lecture 3: Fibre architecture
12/01/2012
12
Fibre packing arrangements:
o Woven arrays of fibres:
Lecture 3: Fibre architecture
12/01/2012
13
Fibre packing arrangements:
o Knitted arrays of fibres:
Lecture 3: Fibre architecture
12/01/2012
14
Fibre packing arrangements:
o Braided arrays of fibres:
Lecture 3: Fibre architecture
12/01/2012
15
Orientation of fibres:
o Occurs often during processing
o Easier with short fibres
o Dependant on strain, viscosity of matrix and fibre length
Lecture 3: Fibre architecture
12/01/2012
16
Short fibre arrangements:
o Orientation is statistically measured by the texture of the composite (distribution of orientations)
Lecture 3: Fibre architecture
12/01/2012
17
Orientation of fibres:
Lecture 3: Fibre architecture
12/01/2012
18
Short fibre arrangements:
o Length is also a distribution
Lecture 3: Fibre architecture
12/01/2012
19
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
Lecture 3: Fibre architecture
12/01/2012
20
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
Lecture 3: Fibre architecture
12/01/2012