Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 619
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Full Record for Micrograph 619

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Micrograph no
619
Brief description
Tensile failure surface of a carbon fibre composite
Keywords
alignment, carbon, carbon fibres Link to MATTER Glossary entry for carbon fibres, CFC, composite material Link to MATTER Glossary entry for composite material, epoxy Link to MATTER Glossary entry for epoxy, fibre Link to MATTER Glossary entry for fibre, fracture Link to MATTER Glossary entry for fracture, neutral axis Link to MATTER Glossary entry for neutral axis, polymer composite, pull-out Link to MATTER Glossary entry for pull-out, reinforcement Link to MATTER Glossary entry for reinforcement
Categories
Composite, Fracture, Polymer, Polymer composite
System
CCcomposite
Composition
Carbon fibre, epoxy resin matrix
Standard codes
Reaction
Carbon fibres are produced by oxidising polyacrylonitrile in air at 230 deg C whilst applying tension, and then carbonising the product in nitrogen at 1000 deg C
Processing
A crude carbon fibre composite was made by laying out 40 tows of fibre, painting them with epoxy resin, compressing them in a mould, and curing them for five hours at 100-190 degrees C
Applications
Carbon fibre composites are used as a structural material in the aerospace and automotive industries, as well as in certain high-performance sporting equipment. They present exceptional stiffness and can be structurally optimised for particular load-bearing applications.
Sample preparation
The bar has been bent to failure in a three-point bending rig.
Technique
Scanning electron microscopy (SEM)
Length bar
100 μm
Further information
This is from the region of the fracture surface which was in tension. The fibres show clean, brittle fracture surfaces (with no fibrillation or distortion and little distortion of the matrix) and have broken at varying lengths and hence some stick out while others have left holes in the matrix. This is indicative of fibre pull-out having occurred after an initial failure of the matrix, followed by failure of the fibres themselves. This is a toughening mechanism in fibre reinforced composites. It is also involved in composite crack stopping properties; each fibre has briefly slowed the progress of the crack by opening it up along the weak fibre-matrix interface and hence blunting the crack tip. The crack therefore advances relatively slowly, with much lateral meandering.
Contributor
J A Curran
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
03/10/02
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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