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

DoITPoMS Micrograph Library Full Record for Micrograph 621

Full Record for Micrograph 621

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Micrograph no
Brief description
Kevlar fibre composite shear surface
alignment, 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, fibrillation Link to MATTER Glossary entry for fibrillation, fracture Link to MATTER Glossary entry for fracture, hackle region Link to MATTER Glossary entry for hackle region, Kevlar Link to MATTER Glossary entry for Kevlar, liquid crystalline polymer (LCP), lyotropic, polymer Link to MATTER Glossary entry for polymer, polymer composite, reinforcement Link to MATTER Glossary entry for reinforcement, shear Link to MATTER Glossary entry for shear
Composite, Fracture, Polymer, Polymer composite
Kevlar composite
Kevlar fibre, epoxy resin matrix
Standard codes
Kevlar is a lyotropic liquid crystal polymer. This means that it can be readily processed in solution (in this case, sulphuric acid). It is annealed under tension to increase its elastic modulus
A crude Kevlar 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
Kevlar 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.
Scanning electron microscopy (SEM)
Length bar
100 μm
Further information
This is an image of the shear surface in a failed composite beam. 'Hackles' of matrix are clearly visible where shear has occurred within the matrix and it is also clear that shear has occurred across the fibre/matrix interface. The fibres are for the most part totally unscathed, though some mis-aligned fibres have become caught between the shear surfaces and 'fibrillated' by rolling and bending actions. It may be that this failure mechanism has been partly inhibited by poor fibre alignment since some off-axis fibres will reinforce the matrix in shear. It will have been promoted, however, by the extensive longitudinal voids.
J A Curran
Department of Materials Science and Metallurgy, University of Cambridge
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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