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 12/01/20121

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 12/01/20122

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 12/01/20123

Volume fraction and weight fraction: V f = (w f /ρ f )/(w f /ρ f + w m /ρ m ) w f = v f ρ f /(v f ρ f + v m ρ m ) With V f, V m, w f, w m, ρ f, ρ m, volume fraction, weight fraction, and density of fibre and matrix Lecture 3: Fibre architecture 12/01/20124

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 12/01/20125

Fibre packing arrangements: Lecture 3: Fibre architecture 2R 2r h 2R 2r h 12/01/20126

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 12/01/20127

Fibre packing arrangements: Lecture 3: Fibre architecture 12/01/20128

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 12/01/20129

Fibre packing arrangements: o Laminates: Lecture 3: Fibre architecture 12/01/201210

Fibre packing arrangements: o Laminates are described by their stacking sequence Lecture 3: Fibre architecture 12/01/201211

Fibre packing arrangements: o Woven arrays of fibres: Lecture 3: Fibre architecture 12/01/201212

Fibre packing arrangements: o Knitted arrays of fibres: Lecture 3: Fibre architecture 12/01/201213

Fibre packing arrangements: o Braided arrays of fibres: Lecture 3: Fibre architecture 12/01/201214

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 12/01/201215

Short fibre arrangements: o Orientation is statistically measured by the texture of the composite (distribution of orientations) Lecture 3: Fibre architecture 12/01/201216

Orientation of fibres: Lecture 3: Fibre architecture 12/01/201217

Short fibre arrangements: o Length is also a distribution Lecture 3: Fibre architecture 12/01/201218

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 12/01/201219

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 12/01/201220