Photoelastic Effect Demonstration Device

Abstract

The purpose of this project was to design and build an affordable device to demonstrate to engineering students stress patterns in loaded samples of different geometries using the photoelastic effect. These devices use light and polarization filters to demonstrate the photoelastic effect in transparent materials and show their stress patterns. This project aims to improve upon existing designs of similar devices and create a functional device that professors can use to educate students with a visual real-life example. This paper focuses on the research done, design considerations, final decisions, and what was learned. Also, this paper discusses conceptual ideas for designs. First, research was done for the team to get a better understanding of similar devices. After this, research had to be done to better understand the fundamentals of optics relevant to this project. Then, once there was a better understanding of the problem and a better engineering background, some conceptual designs and one final design project for the device was designed. With our education we were able to design a device that meets the requirements and will function as intended. We were also able to provide more detailed information about what photoelasticity is and how polariscopes work. Also, we were able to simulate stresses on the device and ensure that the device will not fail under the intended amount of load. The team looked at each design and decided upon a final design to build for the final project. The team chose 10 unique geometries for the Lexan samples that will be tested in the polariscope, most of these geometries can be found in engineering textbooks used for talking about stresses. One design choice the team made for the project was to build a device that can fit on an overhead projector so the polariscope can be used in classrooms and projected onto a wall. The team had to cut a piece of square aluminum tubing that is about 5 inches long so the arm holding the head of the projector could be extended upward allowing for the projector to focus further from the base of the projector giving the team more room to build the rest of the project a little taller. The team built the polariscope so that it can be used as a linear or circular polariscope. The filters and mechanism used for applying tension are also easily adjustable up or down to allow for the sample to always be in focus.