Dr. Andrew Gross

Digital Image Correlation (DIC) is a powerful optical method used to measure strain, deformation, and motion in materials by tracking surface features. Traditionally, randomness among the surface features has been a requirement for DIC. We investigated this assumption and found that well-designed periodic patterns with frequency content concentrated near the Nyquist limit reduce the experimental uncertainty and increase the spatial resolution of DIC. This concept is explored with a series of pattern optimization runs conducted with synthetic images to establish a link between the power spectrum of a pattern and DIC measurement uncertainty. Experimental demonstrations with a near Nyquist limit optimized pattern is conducted and compared to optimized traditional dot-based patterns. 

 

Architected materials can attain exceptional material properties by patterning matter to activate unique deformation modes or efficiently carry loads. Beam lattice architectures that exploit the pressure sensitive critical shear stress at which ceramic materials fail will be discussed. First, a new theoretical limit is established by considering when the shear--pressure relationship for stretching dominated lattices intersects the Mohr-Coulomb failure envelope of a ceramic parent material. Recognition of this new theoretical limit allows for a unique optimization of the lattice geometry. The optimization is conducted on Kelvin cell foams subjected to hydrostatic compression. The newly optimized designs mitigate the hazard from stress concentrations that are unavoidable in the nodal regions by collocating large confining pressure in these regions. At low densities, the newly optimized designs can reach strengths more than six times higher than the baseline designs. A related concept in fully-dense steel lattice reinforced cementitious materials will be discussed if time allows.