Jiangyu Li, University of Washington Linear Polarizer Jiangyu Li, University of Washington

Photoelastic Effect Polarizer Material Analyzer The photoelastic effect occurs when an object or material is strained and illuminated with a polarized light. The strain causes the polarized light to reorient itself as it passes through the material, causing it to interfere as it exits. The interference pattern, known as a fringe pattern, can then be viewed by an analyzer, which is a polarizer at 90o with the one polarizing the light. If the object is strained, a pattern appears. If not, then the light is not shifted in its orientation, and no signal will pass through the analyzer.

Jiangyu Li, University of Washington Stress-Optic Effect Jiangyu Li, University of Washington

Jiangyu Li, University of Washington Interference Jiangyu Li, University of Washington

Photoelasticity by Reflection Polarizer 1/4 Wave Plate Light Source Photoelastic Coating Test Part 1/4 Wave Plate Polarizer observer

Isoclinic vs. Isochromatic There are two methods of polarization used for photoelastic analysis. Polarizing the light linearly will allow the isoclinic fringe pattern to be seen. The Isoclinic fringe pattern is used to see the direction of the principal stresses at different angles, and is seen as a map of dark fringes overlaid on a colored map (when using white light.) The isoclinic fringes are load independent. Using a circularly polarized incident light, the isochromatic fringe pattern is seen. The isochromatic pattern is a colorful map in which different colors correspond to differing amounts of strain. The isochromatic fringe pattern can be used to determine the magnitude of the strain on an object, and is load dependent. Linear Polarization Circular Polarization

Figure 15.19 (p. 608) Photoelastic pattern of stresses in a spur gear tooth. (From T.J. Dolan and E.L. Broghammer, A Study of Stresses in Gear Tooth Fillets, Proc. 14th Eastern Photoelasticity Conf., PE December 1941.) Fundamentals of Machine Component Design, 4/E by Robert C. Juvinall and Kurt M. Marshek Copyright © 2006 by John Wiley & Sons, Inc. All rights reserved.

Increasing stress Zero Fringe orders 1 2 3

BEARING, CONTACT

GEOMETRIC DISCONTINUITY

Jiangyu Li, University of Washington Four Point Bending Jiangyu Li, University of Washington