Photoelastic stress analysis test

This photoelastic stress analysis is a technique for the nondestructive determination of stress and strain components at any point in a stressed product by viewing a transparent plastic product. If not transparent, a plastic coating is used such as certain epoxy, polycarbonate, or acrylic plastics. This test method measures residual strains using an automated electro-optical system. 

In basic mechanical testing, the mechanical characteristics that can be tested include expansion, penetration, extension, flexure, and compressive compliance. Photoelastic-stress analysis allows the stress distribution to be visually displayed, and strain gauging allows the stress distribution to be approximated. Residual stress, also known as molded-in stress, can be measured by a variety of techniques (1). 

Photoelastic stress analysis helps a processor determine why a part broke and how to prevent similar failures in the future. Parts ranging in size from structural composites to tiny thermoplastic heart valves can all be tested easily. The test method is also a valuable tool for predicting where prototype parts may fail, such as in poorly designed features... 

Photoelastic analysis, one of several related testing techniques, is easy to use and usually a more economical and positive method than computer analysis. From the information it provides, the test can lead to better-designed, lower-cost products. Traditionally used to test the integrity of metal parts, photoelastic analysis is now being used to physically test thermoplastics as well as thermosets. For transparent plastics, the analysis can be made directly on the plastic. For nontransparent plastics, a transparent coating is used. Actual parts and representative models can be tested by a simple procedure. The former may be stressed under actual use conditions, whereas models are tested under simulated conditions. 

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