Ae104a10_problemset_6_manuals

Ae104a10_problemset_6_manuals - AE 104a PHOTOELASTICITY LAB...

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Unformatted text preview: AE 104a PHOTOELASTICITY LAB PROCEDURES November 2010 Michael Mello Sharlotte Kramer Graduate Aerospace Laboratories California Institute of Technology Pasadena, CA 91125 Contents 1 INTRODUCTION: 3 2 PREREQUISITES: 3 3 OBJECTIVE: 5 4 LAB PROCEDURES (updated 11-24-10) 6 4.1 LAUNCHING THE IMAGE ACQUISITION SOFTWARE . . . . . . . . . . . . . . . 6 4.2 OPTO-MECHANICAL ALIGNMENT OF THE WEDGE SHAPED LINE LOAD TOOL 7 4.3 CONTROL OF IMAGE SATURATION . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.4 ESTABLISHMENT OF A PIXEL TO LENGTH CALIBRATION . . . . . . . . . . . . 9 4.5 ALIGNMENT OF THE SQUARE HOMALITE TEST SPECIMEN . . . . . . . . . . . 9 4.6 LOADING A HOMALITE-100 SPECIMEN AND ACQUIRING DARK FIELD FRINGE PATTERNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.7 LOADING A POLYCARBONATE SPECIMEN AND ACQUIRING DARK FIELD FRINGE PATTERNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.8 SHUT DOWN AND CLEAN UP PROCEDURE . . . . . . . . . . . . . . . . . . . . 14 5 FRINGE ANALYSIS: 14 6 QUESTIONS: 15 1 List of Figures 1 Mechanical loading arrangement used in the Photoelasticity lab . . . . . . . . . . 4 2 Schematic of Photoelasticity Lab Optical Setup and Loading Configuration . . . . . 5 3 Schematic of Polariscope (without beam expander or reducer): Angles refer to fast axis of optics; δ is the phase related to the stresses in the material by the Stress Optic Law, with λ as the wavelength, h as specimen thickness and A and B as the two photoelastic constants of the specimen; α is the direction of the principal stresses relative to Cartesian coordinates. . . . . . . . . . . . . . . . . . . . . . . . 6 4 Synthetic images of dark-field interferometry patterns at two loads, noting the zero fringe and δ = 2 π fringe, which is the next dark fringe, knowing that σ 1- σ 2 increases near the stress concentration: (a) low load, (b) medium load, (c) high load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5 Example phase information: converting cos- 1 [ cos ( δ )] and cos- 1 [- cos ( δ )] to the desired phase δ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2 1 INTRODUCTION: The photoelastic technique is applicable to a class of transparent materials which exhibit the stress induced birefringence (photoelastic) effect. When mechanically stressed, these materi- als exhibit changes in refractive index which are continuously aligned with the maximum and minimum principle stress directions in the medium. Two model materials which feature this opto- mechanical effect are Homalite-100 and Polycarbonate, both of which will be explored in this laboratory excersise. A small hydraulic press is used to exert a concentrated line load on the top surface of a transparent, test specimen by way of a sharp wedge shaped tool as shown in Fig. 1. An expanded, collimated, and circular polarized laser beam of wavelength λ...
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This note was uploaded on 01/05/2012 for the course AE 104a taught by Professor List during the Fall '09 term at Caltech.

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Ae104a10_problemset_6_manuals - AE 104a PHOTOELASTICITY LAB...

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