Date of Award
Thesis - Restricted
Master of Science (MS)
Browning, Larry M.
Many standard techniques for measuring surface displacements in loaded structural elements exist. However, the optical measurement of full-field sub-surface displacement is much less common. It has been done in liquids using scattered-light speckle (SLS) metrology and internal strain measurements have been made in solid models using photoelastic methods. A few researchers have used SLS metrology to measure internal displacements in solids but no accurate results have been obtained so far. The present work has been performed to evaluate a new technique for measuring sub-surface displacements in structural elements. For the purpose of comparison, SLS metrology was used as an alternate method. Several models of the structural element (a simple beam) were constructed out of transparent material in which micro-particles ("scatterers") had been embedded. The micro-particles produced scattered light (speckles) from a selected interior plane of a sample when a thin sheet of laser light was allowed to pass through the sample. Specklegrams of this interior plane were made before and after the model was displaced slightly. The specklegrams were analyzed by using Young's fringes and then by digital correlation. Experiments were performed for linear translation and for two-dimensional bending. It has been observed that the seeding density of the micro-particles needs to be optimized. A very low seeding density does not produce an adequate number of bright speckles, which affects the accuracy of the measurements. However, when the samples were heavily seeded with micro-particles, light could not pass completely through the sample and did not produce a full-field specklegram of it. Between the two methods the digital correlation technique was found to be easier and more accurate.
Rahi, Mohammad Hanif, "Optical Measurement of Sub-Surface Displacement in Structural Elements Using Digital Correlation and Young's Fringe Technique" (1986). Master's Theses (1922-2009) Access restricted to Marquette Campus. 2292.