Browsing by Author "De Carlo, Francesco"
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- Development of A Micro-Scale Impact Tester for Characterizing Dynamic Properties of Biological Structural MaterialsRoth, Nicklas (Virginia Tech, 2023-06-28)This thesis presents the design and construction of a micro-scale, air powered, impact testing device for use in Virginia Tech's Biological and Bio-inspired Materials Laboratory. A brief overview of current projectile impact testers is presented along with motivation for the fabrication of a new testing system capable of firing a projectile with a maximum diameter of 0.5 mm at velocities ranging from 20 to 50 m/s. Initial design calculations and analysis were performed to optimize barrel length, projectile size, and air pressure for desired velocity ranges. Computer aided design was then utilized to create a digital model of the entire system before production began on the device. Within the scope of this project was the development of a large-scale projectile impact tester as a proof of concept of the system's design that would later be utilized by other researchers as well as the micro-scale tester which carried over the lessons learned and design improvements from the larger device. The culmination of the project was the testing of biological samples (sea urchin spine cross sections) to prove the viability of the device and highlight its research niche. Future use cases and design improvements of the small-scale impact tester were also investigated as part of this thesis work.
- Strategies for simultaneous strengthening and toughening via nanoscopic intracrystalline defects in a biogenic ceramicDeng, Zhifei; Chen, Hongshun; Yang, Tin; Jia, Zia; Weaver, James C.; Shevchenko, Pavel D.; De Carlo, Francesco; Mirzaeifar, Reza; Li, Ling (Springer Nature, 2020)While many organisms synthesize robust skeletal composites consisting of spatially discrete organic and mineral (ceramic) phases, the intrinsic mechanical properties of the mineral phases are poorly understood. Using the shell of the marine bivalve Atrina rigida as a model system, and through a combination of multiscale structural and mechanical characterization in conjunction with theoretical and computational modeling, we uncover the underlying mechanical roles of a ubiquitous structural motif in biogenic calcite, their nanoscopic intracrystalline defects. These nanoscopic defects not only suppress the soft yielding of pure calcite through the classical precipitation strengthening mechanism, but also enhance energy dissipation through controlled nano- and micro-fracture, where the defects’ size, geometry, orientation, and distribution facilitate and guide crack initialization and propagation. These nano- and micro-scale cracks are further confined by larger scale intercrystalline organic interfaces, enabling further improved damage tolerance.