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

DoITPoMS Micrograph Library Full Record for Micrograph 571

Full Record for Micrograph 571

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Micrograph no
571
Brief description
Strain-induced birefringence in a polycarbonate bar
Keywords
bending, birefringence Link to MATTER Glossary entry for birefringence, polycarbonate (PC), polymer Link to MATTER Glossary entry for polymer, stress Link to MATTER Glossary entry for stress
Categories
Polymer
System
Polycarbonate (PC)
Composition
Not specified
Standard codes
Reaction
Processing
Applications
Polycarbonate is a clear and relatively tough plastic used to make shatterproof windows, lenses and even helmets. It is also used to make compact discs.
Sample preparation
A four-point bending rig is used to apply stress.
Technique
Cross-polarised light microscopy
Length bar
14 mm
Further information
The colours in the image are the result of birefringence and relate to the strain-induced alignment of the polycarbonate molecules. Because the specimen is below the glass transition temperature of PC (145 deg C), the material will relax when the stress is removed and there will be no residual alignment. The colours reveal the pattern of stress concentration around the points of contact with the rig, with a neutral axis along the centre and opposite values of birefringence on either side.
Contributor
J A Curran
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
03/10/02
Licence for re-use
Attribution-NonCommercial-ShareAlike 4.0 International
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