Micrograph 587 and full record

Micrograph no

587

Brief description

Parabolic beach marks on a polystyrene fracture surface

Keywords

beach marks

, fracture $Link to MATTER Glossary entry for fracture$ , polymer

Categories

System

Composition

Standard codes

Reaction

Processing

Applications

Polystyrene is hard and inexpensive and its use is very widespread. CD cases and clear plastic cups are common examples. Domestic appliance casings are also typically made from PS

Sample preparation

The surface has been sputter-coated with gold, to give a conducting surface

Technique

Scanning electron microscopy (SEM)

Length bar

80 μm

Further information

The fracture surfaces are generally very sharp and angular, indicating fast, brittle fracture with little ductile tearing. Parabolic 'beach marks', can be seen where the fracture has grown at a speed comparable to the speed of sound in the material. This results in periodic, momentary arrests in the crack propagation and periodic ridges in the fracture surface as it advances. These indicate the direction in which the fracture has occurred. Inside the beach marks is a disc-shaped flat region where the initial fracture was progressing significantly faster than the speed of sound. There is also evidence of the fracture surface branching onto different planes as it progresses.

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