Computer networking basics pdf book

Lab 2, photoelasticity

Introduction

Photoelasticity is used for observation of stress concentrations within a part. The light is projected onto the part and the reflection is viewed through a polariscope to view the fringe count on the surface. Under a constant tensile load, we neglect stress concentrations at the pinned ends and use a plastic plate of sufficient length to distribute the tensile load evenly before approaching the region that we were interested in finding the stress concentrations. Using the characteristic 8dimensions away from the applied tensile force ensures that our measurements can be as accurate as possible. Three points on the U-shaped specimen were studied where critical points of stress were expected to be (See Figure 1).

The purpose is this lab is to become more familiar with FEA and to find KT values using three different methods. The value is sought to be found by using good engineering judgement, results from FEA, and through hand calculations.

Governing equations include:

Methods

The material of the U-shaped specimen was polycarbonate. Our model was first measured, then dimensioned, and finally sketched in AutoCad. Placing our specimen in the tensioner within the polariscope, we applied load until we could see change within our specimen and took stress concentrations at the most critical point, which was around the radius of a fillet at point 3. We had to do this because our compensator dial for the fringe order was limited to a certain number and if load was excessively applied our model would not work. When the experiment proved to give usable results for point 3, point 1 and point 2 were tested (See Figure 1).

A polariscope consists of a plane light (Figure 2(a)), a linear polarization filter denoted “polarizer” (b), an optional λ/4-wave plate (c), the object to analyze (d), another optional λ/4-plate (e), another linear polarization filter denoted “analyzer” (f), and the observer or optical acquisition device (g). In a circular polariscope, both λ/4-plates are present, whereas they are missing in a plane polariscope. A wave plate causes a retardation, i.e., a lower speed of light, on the