ABSTRACT
This chapter examines the techniques available in providing an overall visualization of pressure distribution—explicitly or otherwise. One of the simplest ways to qualitatively visualize pressure, by dimensional changes, was by accessing indentations made in mud, clay, and other similar materials. However, such methods tend to measure the shape of the loading object instead of pressures. Under unloaded conditions, the presence of a large number of air gaps between the plastic and glass causes most of the light to undergo total internal reflection within the glass. A photoelastic material has the property of becoming birefringent when loaded. Birefringence in a material causes polarized light to be resolved into two orthogonal directions. Because the velocities of light propagation are different in each direction, the two components emerge out of phase from the photoelastic material. The relationship between pressure and intensity is nonlinear and pre-calibration is necessary. Since the calibration procedure requires a uniform pressure loading system, an air-pressure system is used.
