Photoelastic Stress Pattern in Transparent Plastic Mouldings

by Robert Anderson

Description of Image: To the naked eye these injection moulded plastic components are colourless and transparent. Here, when viewed between crossed polarizing filters, a multi-coloured interference pattern is revealed. This pattern is due to the stress trapped in the moulding when it solidified rapidly. These transparent mouldings (components of a protective case), were placed between polarizing filters whose axes of polarization were at right angles (i.e. polariscope). They were photographed using a macro lens on a 35mm SLR camera.