Full-field optical measurement of deformations and stresses on transparent brittle ceramics such as soda-lime glass is rather challenging due to the low toughness and high stiffness characteristics. Particularly, the surface topography and stress field evaluation from measured orthogonal surface slopes and stress gradients could be of considerable significance for visualizing and quantifying deformation of glass plates under dynamic impact loading. In this work, two full-field optical techniques, reflection Digital Gradient Sensing (or r-DGS) and a new DGS method, called transmission-reflection Digital Gradient Sensing (or tr-DGS) are employed to quantify surface slopes and stress gradients, respectively, as glass specimens are subjected dynamic impact loading using a modified Hopkinson pressure bar. These two methods can measure extremely small angular deflections of light rays caused by surface deformations and local stresses in specimens. The tr-DGS methodology is especially more sensitive than r-DGS. Using such optical methods, sub-micron surface deflections and the corresponding stress field, (σxx + σyy), can be quantified using a Higher-order Finite-difference-based Least-squares Integration (HFLI) scheme. When used in conjunction with ultrahigh-speed photography, microsecond or sub-microsecond temporal resolution is possible.
Digital gradient sensing Dynamic impact loading Transparent brittle ceramics Deflections and stresses Ultrahigh-speed photography
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Support for this research through Army Research Office grants W911NF-16-1-0093 and W911NF-15-1-0357 (DURIP) are gratefully acknowledged.
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