Full-field pulsed magnetophotoelasticity – a description of the instrument

Abstract

This paper describes a novel instrument used for the analysis of full-field through-thickness stress distributions using the theory of magnetophotoelasticity (MPE) developed by Aben [1] and developed by Clarke et al. [2, 3]. MPE is an experimental stress analysis technique that involves the application of a magnetic field parallel to an electromagnetic wave propagating through a birefringent model within a polariscope. The effect viewed through the polariscope is then a combination of the model's birefringence and the Faraday rotation created in the model by the magnetic field. Aben developed this technique especially for use in the measurement of stress profiles where the integrated photoelastic pattern alone yields little information. Clarke et al. developed MPE in order to study toughened glass. To date, the technique of MPE has been a single-point measurement, which is of limited utility in the investigation of three-dimensional stress in toughened glasses. The pulsed magnetopolariscope (PMP), described here, enables the full-field application of MPE. This paper contains a description of the novel apparatus and demonstrations used to validate the performance of a proof-of-concept PMP instrument. The paper also highlights improvements in the application of MPE, which are now possible with this new equipment. These improvements include the extension of MPE to larger areas of analysis, three-dimensional stress analysis, and the possibility of analysing a general unknown stress distribution.