Towards uncertainty evaluation in photoelastic measurements

The absence of traceability has hindered the acceptance by certification authorities of stress/strain measurements made by optical methods. Standards to guarantee traceability and to enable the calibration of equipment are under development. They will make it possible to express the measurements made using these techniques alongside their corresponding uncertainties. The present article reviews the errors that arise in reflection photoelasticity and decribes the procedure to evaluate the uncertainty in photoelastic stress measurements. Two internationally accepted uncertainty evaluation methods are applied to the case of stress measurement at a point on the edge of a piece. It is shown that both methods give reliable results. Their application to the evaluation of uncertainties in photoelastic measurements will enable compliance with metrological requirements.