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iDEA: DREXEL LIBRARIES E-REPOSITORY AND ARCHIVES

iDEA: DREXEL LIBRARIES E-REPOSITORY AND ARCHIVES

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In-situ Grain Scale Strain Measurements using Digital Image Correlation

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Title
In-situ Grain Scale Strain Measurements using Digital Image Correlation
Author(s)
Saralaya, Raghavendra Nataraj
Advisor(s)
Kontsos, Antonios
Keywords
Mechanical engineering; Strains and stresses--Measurement; Digital image correlation
Date
2012-06
Publisher
Drexel University
Thesis
M.S., Mechanical Engineering -- Drexel University, 2012
Abstract
Materials used in engineering structures fatigue and ultimately fail due to the various applied loads they are subject to, a process which compromises structural performance and potentially poses threats to society. Commonly employed theoretical models capable of describing and predicting deformation and failure are typically validated by relevant experimental results obtained from laboratory testing. However, such models are also often based on simplifying assumptions including for example homogeneous composition and isotropic behavior, since available experimental information relates primarily to bulk behavior.Metals are crystalline in nature and their failure depends on several parameters that span a wide range of time and length scales. Therefore, significant efforts have been made over the past decades to investigate the mechanical behavior of polycrystalline metals by formulating important microstructure-properties relations. In this context, this thesis presents a framework to obtain reliable, non-destructive, non-contact, full field measurements of deformation and strain at the grain-scale of polycrystalline materials to assist the understanding of materials phenomena and contribute in the development of realistic mechanics models. To this aim, the method of Digital Image Correlation is used, adapted and expanded.Digital Image Correlation relies on images of the surface of tested specimens, components or structures and the identification of surface contrast patterns which are tracked as a function of deformation and are subsequently used to define displacements and strains. To quantify stains at the grain-scale, three different approaches based on Digital Image Correlation are described. The first involves the use of a commercial system adapted to make grain-scale measurements at the meso-scale (~4mm). A magnesium AZ31alloy was observed for this purpose and full field strain maps are reported. The second employs the same commercial system augmented with a long distance optical microscope to in-situ quantify strains at the tip of a propagating crack in a Compact Tension specimen of an Al2024 aluminum alloy subjected to Mode I loading and using a field of view of ~870 x 730 μm. Finally, the third approach uses an image series acquired from loading a stainless steel sample inside a scanning electron microscope equipped with a micro-tensile stage. Such information was post processed ex-situ and strains were obtained. The advantages and limitations of the proposed approaches are critically evaluated and future work is described to further enhance the reliability and repeatability of grain scale strain measurements using Digital Image Correlation.
URI
http://hdl.handle.net/1860/4125
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Theses, Dissertations, and Projects

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