Yang, LianxiangFang, SiyuanBarber, GaryQu, HongweiGerini Romagnoli, Marco2026-07-172026-07-172026-01-01https://hdl.handle.net/10323/22156In sheet-metal forming, material elongation is commonly accompanied by rapid thinning, making thickness strain measurement important. While digital image correlation (DIC) is widely used for deformation measurement, a typical stereo DIC setup observes only one surface and thus cannot directly access thickness information. This work employs a white-light multi-camera DIC system that images both surfaces in a unified measurement frame, enabling direct measurement of thickness strain together with in-plane strains. We further improve thickness-strain measurement accuracy and demonstrate three applications: (1) direct R-value measurement without relying on volume-constancy assumptions; (2) identification of localized necking onset by analyzing the evolution of local cross-sectional area; and (3) tensile characterization of heat-affected zones (HAZ) in tailor-welded blanks (TWB), in which front- and back-surface strain fields are recorded and analyzed to reduce geometry-induced bending effects and to correct the HAZ stress–strain curve. Collectively, these applications demonstrate the advantages and practical utility of the multi-camera DIC system for characterizing sheet-metal properties. Beyond sheet-metal mechanics, this dissertation further develops laser-light speckle based optical methods for deformation and temperature measurement and for non-destructive testing (NDT). Controlled laser speckle is used as a high-contrast carrier for DIC, enabling robust deformation measurements under challenging conditions such as high temperature, small deformation, and biomaterials. In addition, laser speckle is employed as the background pattern for background-oriented schlieren (BOS), enabling quantitative temperature measurements that are directly compared with holographic interferometry. Furthermore, we investigate load- and temperature-induced decorrelation of laser speckle patterns as a potential new method for NDT, using correlation coefficient as indicators of local deformation. The basic theory, system configurations, results analysis and applications are shown in detail in this dissertation.