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Browsing by Author "Deng, Zhifei"

Now showing 1 - 4 of 4
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    Bioinspired design of flexible armor based on chiton scales
    Connors, Matthew; Yang, Ting; Hosny, Ahmed; Deng, Zhifei; Yazdandoost, Fatemeh; Massaadi, Hajar; Eernisse, Douglas; Mirzaeifar, Reza; Dean, Mason N.; Weaver, James C.; Ortiz, Christine; Li, Ling (Springer Nature, 2019-12-10)
    Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities.
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    Biomineralized Composites: Material Design Strategies at Building-Block and Composite Levels
    Deng, Zhifei (Virginia Tech, 2023-01-12)
    Biomineral composites, consisting of intercrystalline organics and biogenic minerals, have evolved unique structural designs to fulfill mechanical and other biological functionalities. Aside from the intricate architectures at the composite level and 3D assemblies of the biomineral building blocks, the individual mineral blocks enclose intracrystalline structural features that contribute to the strengthening and toughening at the intrinsic material level. Therefore, the design strategies of biomineralized composites can be categorized into two structural levels, the individual building block level and the composite level, respectively. This dissertation aims at revealing the material design strategies at both levels for the bioinspired designs of advanced structural ceramics. At the building block level, there is a lack of comparative quantification of the mechanical properties between geological and biogenic minerals. Correspondingly, I first benchmark the mechanical property difference between biogenic and geological calcite through nanoindentation techniques. The selected biogenic calcite includes Atrina rigida prisms and Placuna placenta laths, corresponding to calcite {0001}, and {101 ̅8} planes. The natural cleavage plane {101 ̅4} of geological calcite was added to the comparative study. Under indentation load, geological calcite deforms plastically via twinning and slips under low loads, and shifts to cleavage fracture under high loads. In comparison, the P. placenta composites, composed of micro-sized single-crystal laths and extensive intercrystalline organic interfaces, exhibit better crack resistance. In contrast, the single-crystal A. rigida prisms show brittle fracture with no obvious plastic deformation. Secondly, how the internal microstructures and loading types affect the mechanical properties of individual building blocks is investigated. The prismatic building blocks are obtained from the bivalves A. rigida and Sinanodonta woodiana, where the former consists of single-crystal calcite and the latter consists of polycrystalline aragonite. The comparative investigation under different loading conditions is conducted through micro-bending and nanoindentation. The continuous mineral matrix in A. rigida prisms leads to comparable modulus under tensile and compressive loadings in the elastic regime, while the high-density intracrystalline nanoinclusions contribute to the conchoidal fracture behaviors (instead of brittle cleavage). In comparison, the interlocking grain boundaries in S. woodiana prisms correlate with easier tensile deformation (smaller tensile modulus) than compression, as well as the intergranular fracture morphologies. The third topic in the biomineral-level investigation focuses on how biomineral utilizes residual stress at the macroscopic scale. The selected model system is the spine from the sea urchin Heterocentrotus mamillatus, which has a bicontinuous porous structure and mesocrystalline texture. It is confirmed that the spine has a macroscopic stress field with residual tension in the central medulla and compression in the radiating layers. The multimodal characterizations on the spine conclude that the structural origins are not associated with the gradient distribution of the intracrystalline defects, including Mg substitution in the calcite matrix, intracrystalline organics, and amorphous calcium carbonates (ACC). It is hypothesized that the residual stress is generated due to the volume expansion during ACC crystallization at the compacted growth front. At the composite level, even though enhanced crack resistance is expected in biomineralized composites due to their hierarchical structures, the correlation between their 3D composite structures and damage/crack evolution is quite limited in the literature. I developed in-situ testing devices integrated with synchrotron-based X-ray tomography to capture the crack propagation in the materials, including the four-point bending and compression/indentation configurations. Two representative models are chosen to demonstrate the deformation of biomineralized composites under bending and compression, respectively, including the calcium carbonate-based gastropod shell (Melo diadema) and the hydroxyapatite-based fish teeth (Pogonias cromis). Also, the two composites are designed to achieve different functional requirements, i.e., enhanced fracture toughness vs. wear resistance. The comprehensive characterizations of these two composites revealed how biological structural composites are designed accordingly to their functional needs. For the crossed-lamellar M. diadema shell, directional dependence of the shell property was revealed, where the transversal direction (perpendicular to the growth line) represents both the stronger and tougher direction, but the longitudinal direction is more resistant to notches and defects. For the P. cromis teeth, the enhanced wear resistance of the near-surface enameloid originates from the intricate designs at the microscale, with c-axes of hydroxyapatite crystals and micro-sized enameloid rods coaligned with biting direction and F and Zn doping. In addition, the fracture morphologies of the fish teeth correlate with the microstructures; the enameloid exhibits corrugated fracture paths due to the interwoven fibrous building blocks, and the dentin exhibits clean planar fracture surfaces.
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    High strength and damage-tolerance in echinoderm stereom as a natural bicontinuous ceramic cellular solid
    Yang, Ting; Jia, Zian; Wu, Ziling; Chen, Hongshun; Deng, Zhifei; Chen, Liuni; Zhu, Yunhui; Li, Ling (Nature Research, 2022-10-14)
    Due to their low damage tolerance, engineering ceramic foams are often limited to non-structural usages. In this work, we report that stereom, a bioceramic cellular solid (relative density, 0.2–0.4) commonly found in the mineralized skeletal elements of echinoderms (e.g., sea urchin spines), achieves simultaneous high relative strength which approaches the Suquet bound and remarkable energy absorption capability (ca. 17.7 kJ kg⁻¹) through its unique bicontinuous open-cell foam-likemicrostructure. The high strength is due to the ultra-low stress concentrationswithin the stereom during loading, resulted from their defect-free cellular morphologies with near-constant surface mean curvatures and negative Gaussian curvatures. Furthermore, the combination of bending-induced microfracture of branches and subsequent local jamming of fractured fragments facilitated by small throat openings in stereom leads to the progressive formation and growth of damage bands with significant microscopic densification of fragments, and consequently, contributes to stereom’s exceptionally high damage tolerance.
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    Strategies for simultaneous strengthening and toughening via nanoscopic intracrystalline defects in a biogenic ceramic
    Deng, 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.