Browsing by Author "Chen, Hongshun"
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- High strength and damage-tolerance in echinoderm stereom as a natural bicontinuous ceramic cellular solidYang, 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.
- Multiscale Structures and Mechanics of Biomineralized Lattices in Hexactinellid sponges and EchinodermsChen, Hongshun (Virginia Tech, 2023-06-30)Biomineralized lattice materials with have high mineral contents (~ 99 wt%), usually "conceal" multiscale structural arrangements for unique mechanical or functional performance, such as the remarkable damage tolerance despite of the brittle nature of the constituents (e.g., biogenic silica and calcite). However, the quantitative explorations of the structure-mechanics relationships in multiscale of biomineralized lattices remain insufficient and hence hinder the leverage of the functional benefits to design architected cellular materials. In this dissertation, I selected two groups of marine animals (i.e., Hexactinellid sponges and Echinoderms) for systematic structural-mechanical study. Their biomineralized lattice skeletons exhibit three representative types of multiscale structures: 1) multiscale hierarchical structure: skeleton of Hexactinellid sponge such as Euplectella aspergillum; 2) multiscale functionally graded structure: spine of sea urchin Heterocentrotus mammillatus; and 3) dual-scale (atomic and microlattice scales) periodic structure: ossicle of starfish Protoreaster nodosus. This dissertation develops quantitatively the structural-mechanical/functional correlations in biomineralized cellular materials for bio-inspired material design. Four different species of Hexactinellid sponges have been studied with particular focus on the species E. aspergillum. As an example of the multiscale hierarchical biomineralized lattice, the extremely lightweight skeleton (~99% porosity) of E. aspergillum exhibits 1) amorphous nanoparticular biogenic silica; 2) micron-sized fibrous spicule with cylindrically laminated silica layers separated by organic interfaces; 3) spicule bundles where the individual spicules merged by secondary silica deposition; 4) a centimeter-sized Voronoi-like cellular dome known as sieve plate; and 5) a centimeter-sized cylindrically arranged rectangular lattice with double-diagonal reinforcement and external helical ridge. Here, we discovered a series of mechanical or functional properties or formation process of structures in different length scales: 1) for the biogenic silica in three different species of Hexactinellid sponge, consistent modulus and hardness of the biogenic silica throughout the cross section of the spicule are found via substantial correlation between the measured values and locations; 2) for the sieve plate, the Voronoi-like cellular dome constructed by porous branch with increased height achieves balance between improved mechanical stiffness and large pore opening for sponge's current pumping mechanism; 3) via microstructural study, the formation process of the sieve plate is proposed; and 4) for the cylindrical skeletal body, the double-diagonal configuration and the ridge structure are found to provide tendency to optimize torsional rigidity, and enhanced radial stiffening and improved permeability, respectively. The cellular structure in the spine of the H. mammillatus (i.e., stereom) made of ~99wt% of single-crystalline calcite shows a multiscale functionally graded structure. We developed and optimized a cellular network analysis workflow on the large-volume 3D lattice structure obtained from the synchrotron-based micro-Computed Tomography scan. The analysis provides quantitative descriptions of the branch, ring structure, and septum which reveals a functionally graded structure in multiscale from the center region to the edge region of the spine: 1) in microscale, the branch thickness and length increases, resulting in a significantly decreased porosity; and 2) in macroscale, the center region of the spine with galleried stereom of highly aligned branches transits to the edge region with laminar stereom of radially arranged septa and interconnecting branches. The multiscale structural variations lead to the mechanical variations the increased elastic modulus and mechanical isotropy from the center to the edge of the spine. This provides a biological pathway for designing the lightweight, strong, and tough beam with multiscale structural gradient. In previous work, we discovered that ossicle in starfish P. nodosus possesses a unique dual-scale periodic lattice structure, which means periodic single crystal calcite in nanoscale and diamond triply periodic minimal surface (diamond-TPMS) lattice in microscale. It has three unique structural features: 1) microlattice dislocations in ossicles similar to those found in crystals with diamond cubic lattice; 2) a diamond-TPMS microlattice with ca. 50% relative density; and 3) dual-scale crystallographic coalignment between c-axis of the single-crystalline constituent calcite and the [111] direction of the diamond-TPMS microlattice. Based on this work, this dissertation mainly reveals: 1) unique type and core structures of the dislocations in the ossicle for stiffness, strength, and toughness; 2) the 3D property compensation of dual-scale crystallographic coalignment for improved mechanical isotropy; and 3) mechanical benefits (improved mechanical isotropy and effective fragment jamming) and morphological benefits (minimal surface and highest surface area to volume ratio) for 50% relative density.
- 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.