Full-field pulsed magnetophotoelasticity – experimental implementation

Abstract

This paper contains a description of the experimental procedure employed when using a pulsed magnetopolariscope (PMP) and some initial full-field through-thickness measurements of the stress distribution present in samples containing three-dimensional stresses. The instrument uses the theory of magnetophotoelasticity (MPE), which is an experimental stress analysis technique that involves the application of a magnetic field to a birefringent model within a polariscope. MPE was developed for through-thickness stress measurement where the integrated through-thickness birefringent measurement disguises the actual stress distribution. The technique is used mainly in toughened glass, where the through-thickness distribution can reduce its overall strength and so its determination is important. To date, MPE has provided a single-point two-dimensional through-thickness measurement and the analysis time is prohibitive for the investigation of an area that may contain high localized stresses. The pulsed magnetopolariscope (PMP) has been designed to enable the application of full-field three-dimensional MPE, described in a companion paper. Using a proof-of-concept PMP, several experimental measurements were made; these were promising and demonstrate the potential of the new instrument. Further development of this technique presents several exciting possibilities, including a tool for the measurement of the distribution of the principal stress difference seen in a general three-dimensional model.