Digital speckle photography technique utilizing particle tracking algorithm for the measurement of strain.

摘要

Optical methodologies have been gaining in popularity over the past few years due to advancements in computer and digital technologies. Today there are a number of commercially available optical tools on the market that offer strain measuring and mapping capabilities. The recent developments are mostly for providing two-dimensional (2D) strain and three-dimensional (3D) deflection measurement capabilities. Most of today's optical techniques rely on the following three fundamental principles: the phenomenon interference of coherent light; the method of superposition of intensities using incoherent light; and the method of photogrammetry or videogrammetry.; In this thesis we present a new methodology for measuring 3D deformations or strain field in real time. It relies on stereoscopic camera calibrations, a 2D speckle tracking algorithm with each stereoscopic images, and a 3D track matching technique that converts 2D projection tracks from the two cameras back to 3D real tracks. This new methodology is based on the STV (Stereoscopic Tracking Velocimetry) technique that has been developed to measure and track 3D particle movements in fluid flow. The goal is to study the viability and feasibility of the underlying principles of STV for the purpose of applying them to solid mechanics, which has not been examined before. In the process, the methodology has been further refined. Here, this new technique is aptly called Stereoscopic Speckle-Tracking Photogrammetry (SSTP). SSTP like STV employs two orthogonally placed CCD cameras. Post processing software is then used to process the images and to obtain 3D deformations that in turn are converted into surface strains for an opaque object or 3D strain for a transparent object. The research also encompasses a thorough investigation refinement of the sensitivity of SSTP.; Based on the research here, SSTP is a viable new approach for measuring 3D deformations and strains for real world applications. It can be successfully utilized by using either an inscribed regular or stochastic pattern of dots, as well as the natural speckle pattern of the surface. At a minimum, this new methodology certainly warrants continual research for practical applications and can offer an alternative means to 3D deformations and strain measurement.