Photoelasticity
Photoelasticity is a whole-field technique for measuring and visualizing stresses and strains in structures.The method utilizes a birefringent model of the actual structure to view the stress contours due to external loading or residual birefringence. When white light is used for illumination, a colourful fringe pattern reveals the stress/strain distribution in the part. Qualitative analysis such as strain concentration points, uniform stress regions etc. can be identified quite readily. For qunatitative information, a further analysis has to be performed. Upto quite recently this was done by transforming the colour patterns to a black and white picture by utilizing a monochromatic light source for illumination. Using monochromatic light enable better definition of fringes especially in areas with dense fringes as at stress concentration points. Details can be found in numerous books on this topic, with the Experimental Stress Analysis by J.W.Dally and W.F.Riley as a good starter.
Recent advances in Photoelasticity
Photoelasticity has staged a revival in the past few years with applications in Silicon Wafer Stress Analysis , Rapid Prototyping and Fiber Optic Sensor Development and Image Processing.
In addition new light sources such as laser diodes and LED's along with digital imaging technology have resulted in improvements to the basic polariscopes. Dynamic Photoelasticity and Colour Image Analysis now becomes simplified and available at low cost. Thus photoelasticity can be included back again in the curriculum with a fresher outlook.
Please contact masundi@ntu.edu.sgg for more info on these projects.