DoITPoMS

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History

Photoelasticity was developed at the turn of the twentieth century. The early work of E Coker and L Filon at the University of London enabled photoelasticity to be developed rapidly into a viable technique for qualitative stress analysis. It found widespread use in many industrial applications, as in two dimensions it exceeded all other techniques in reliability, scope and practicability. No other method had the same visual appeal or covered so much of the stress pattern.

The development of digital polariscopes using LEDs and laser diodes enables continuous online monitoring of structures and dynamic photoelasticity. Developments in image processing allow the stress information to be extracted automatically from the stress pattern. The development of rapid prototyping using stereolithography allows the generation of accurate three-dimensional models from a liquid polymer, without the use of the traditional moulding method.

The advent of superior computer processing power has revolutionised stress analysis. Finite element modelling (FEM) has become the dominant technique, overshadowing many traditional techniques for stress analysis. Despite FEM advances, photoelasticity, one of the oldest methods for experimental stress analysis, has been revived through recent developments and new applications.

When using FEM, it is crucial to assess the accuracy of the numerical model, and ultimately this can only be achieved by experimental verification. For example, a threaded joint experiences non-uniform contact, which is difficult to incorporate accurately into a computer model. Idealised models therefore tend to underestimate the actual maximum stress concentration at the root of the thread. Photoelasticity therefore remains a major tool in modern stress analysis.


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