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

DoITPoMS Micrograph Library Full Record for Micrograph 620

Full Record for Micrograph 620

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Micrograph no
Brief description
Kevlar fibre composite fracture 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
600 μm
Further information
Because a relatively short beam was used, significant shear stresses existed in the beam, and failure has occurred principally by shear. In this mode, the specimen splits longitudinally along planes parallel to its neutral axis, due to shear failure within the matrix and at the weak interface between fibres and matrix. Matrix porosity (and particularly the long longitudinal voids present in this specimen), the poor wetting of fibres by the resin, and poor fibre distribution will all promote failure by shear. However, 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
J A Curran
Department of Materials Science and Metallurgy, University of Cambridge
Licence for re-use
Attribution-NonCommercial-ShareAlike 4.0 International
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