Metrological study for the optimal selection of the photoelastic model in transmission photoelasticity

In transmission photoelasticity, stresses and strains are not directly measured on the real piece, but on a photoelastic model. To improve accuracy, the photoelastic material type, size of the model, its thickness, and the applied load must be chosen properly. In this paper, the influence of selectable parameters in a photoelastic transmission analysis has been studied through the evaluation of measurement uncertainties. The experimental data and further study of a generic functional relationship, representative of a stress-separation technique, show that, for a given photoelastic material, the model of minimum uncertainty of measurement is the one whose ratio load/dimension is the maximum allowed by the data-acquisition technique used. The thickness affects only the amount of material used. Therefore, any size of the model can achieve maximum accuracy, provided that it is subjected to the greatest possible load within its elastic range.