Full Record for Micrograph 591

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Micrograph no

591

Brief description

Crazing near a fracture surface in polycarbonate

Keywords

craze

, fibril

, fracture $Link to MATTER Glossary entry for fracture$ , polycarbonate (PC), polymer

Categories

Fracture, 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

To induce crazing in polycarbonate, acetone is used. This results in the otherwise tough material becoming very brittle

Technique

Scanning electron microscopy (SEM)

Length bar

80 μm

Further information

The fracture surface shows fibrils of oriented polymer which are the remnants of crazes. Crazes are both a precursor to cracking and a toughening mechanism in stressed polymers. They only form when a certain critical tensile stress has been attained and form perpendicular to the largest tensile principal stress. They are very fine crack-like projections from the fracture surface but are bridged by even finer material, giving approximately 50% voids. It is these fibrils which interfere with light in an otherwise transparent polymer to make the crazing visible as a whitening of the strained material. The surface ridging, parallel to the principal stress, is a consequence of strain-induced crystallisation during the cold drawing of the polycarbonate.

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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