Date of Award

5-2018

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Mechanical and Aerospace Engineering

First Advisor

Ryan Berke

Abstract

Digital Image Correlation (DIC) is an experimental method used to produce full-field strain maps of specimens undergoing deformation. In this measurement, images of a specimen are taken before and after mechanical and thermal loading, then software is used to track deformation and compute strains. DIC has been recently adapted for high-temperature tests by using ultraviolet (UV) range cameras, lenses, and filters to produce the images.

Application of DIC to small length scales and at high temperatures can be performed with proper equipment. However, for these measurements, there is no commercially available high-magnification lens that will allow images to be taken in the UV range. A custom UV high-magnification lens was recently created by a senior design team at Utah State University, and this project evaluates the potential improvements to high-magnification, high-temperature DIC measurements it offers.

A series of tests was run on a stainless-steel ring specimen (inner diameter of 10 mm with a thickness of 1.2 mm). Two UV cameras and lenses were used to perform simultaneous measurements: one at lower magnification using a commercial lens with a 50 mm focal length, and one with the custom high-magnification UV lens. The low-magnification system captured the entire ring while the high-magnification system focused on a smaller region of interest, capturing just the thickness of the ring. A high-temperature test (900 °C) showed the ability of the custom lens to produce satisfactory images without oversaturation. A tension test was also performed and DIC was used to produce strain maps. In each test, images were taken outside the environmental chamber, necessitating the long working distance. Finally, translations were applied to the ring specimen and DIC software used images of the displacements to produce strain maps. In both the tension test and these rigid body motion tests, these DIC results highlight the advantages that the custom lens offers, in that significantly more data from the image is usable and relevant to a small region of interest. These tests show that the custom lens is suitable for use in high-magnification UV DIC measurements.

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