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Cuttlefish, a unique group of marine mollusks, produces an internal biomineralized shell, known as cuttlebone, which is an ultra-lightweight cellular structure (porosity, ∼93 vol%) used as the animal’s hard buoyancy tank. Although cuttlebone is primarily composed of a brittle mineral, aragonite, the structure is highly damage tolerant and can withstand water pressure of about 20 atmospheres (atm) for the species Sepia officinalis. Currently, our knowledge on the structural origins for cuttlebone’s remarkable mechanical performance is limited. Combining quantitative three-dimensional (3D) structural characterization, four-dimensional (4D) mechanical analysis, digital image correlation, and parametric simulations, here we reveal that the characteristic chambered “wall–septa” microstructure of cuttlebone, drastically distinct from other natural or engineering cellular solids, allows for simultaneous high specific stiffness (8.4 MN·m/kg) and energy absorption (4.4 kJ/kg) upon loading. We demonstrate that the vertical walls in the chambered cuttlebone microstructure have evolved an optimal waviness gradient, which leads to compression-dominant deformation and asymmetric wall fracture, accomplishing both high stiffness and high energy absorption. Moreover, the distribution of walls is found to reduce stress concentrationswithin the horizontal septa, facilitating a larger chamber crushing stress and a more significant densification. The design strategies revealed here can provide important lessons for the development of low-density, stiff, and damage-tolerant cellular ceramics.

Biomineralized composites, which are usually composed of microscopic mineral building blocks organized in 3D intercrystalline organic matrices, have evolved unique structural designs to fulfill mechanical and other biological functionalities. While it has been well recognized that the intricate architectural designs of biomineralized composites contribute to their remarkable mechanical performance, the structural features within and corresponding mechanical properties of individual mineral building blocks are often less appreciated in the context of bio‐inspired structural composites. The mineral building blocks in biomineralized composites exhibit a variety of salient intracrystalline structural features, such as, organic inclusions, inorganic impurities (or trace elements), crystalline features (e.g., amorphous phases, single crystals, splitting crystals, polycrystals, and nanograins), residual stress/strain, and twinning, which significantly modify the mechanical properties of biogenic minerals. In this review, recent progress in elucidating the intracrystalline structural features of three most common biomineral systems (calcite, aragonite, and hydroxyapatite) and their corresponding mechanical significance are discussed. Future research directions and corresponding challenges are proposed and discussed, such as the advanced structural characterizations and formation mechanisms of intracrystalline structures in biominerals, amorphous biominerals, and bio‐inspired synthesis. The mineral building blocks in biomineralized composites exhibit salient intracrystalline structural features, such as organic inclusions, trace elements, varying crystalline features, residual stress/strain, and twinning, which significantly modifies the mechanical properties of biogenic minerals. This review discusses recent progress in elucidating the intracrystalline structural features of three common biomineral systems (calcite, aragonite, and hydroxyapatite) and their corresponding mechanical significance.

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-like microstructure. The high strength is due to the ultra-low stress concentrations within 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. Engineering ceramic foams are often limited for non-structural usages due to their brittleness. Here the authors elucidate the structural design strategies of echinoderm stereo as a biological ceramic cellular solid for achieving simultaneous high strength and damage tolerance.

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. Biominerals are nanocomposites that often incorporate nanoscopic defects such as organic inclusions within the mineral matrix. Here, the authors report on an experimental and computational study into the effects of intracrystalline defects on the intrinsic mechanical behaviour of biominerals.

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. Biology has often served as the inspiration for the design of body armor; one common limitation is the flexibility of the resultant armor. Here, the authors examine the armour of chiton and use the observed design principles to 3D print flexible armor.

The ability to lubricate and resist wear at temperatures above 600 °C in an oxidative environment remains a significant challenge for metals due to their high-temperature softening, oxidation, and rapid degradation of traditional solid lubricants. Herein, we demonstrate that high-temperature lubricity can be achieved with coefficients of friction (COF) as low as 0.10-0.32 at 600-900 °C by tailoring surface oxidation in additively-manufactured Inconel superalloy. By integrating high-temperature tribological testing, advanced materials characterization, and computations, we show that the formation of spinel-based oxide layers on superalloy promotes sustained self-lubrication due to their lower shear strength and more negative formation and cohesive energy compared to other surface oxides. A reversible phase transformation between the cubic and tetragonal/monoclinic spinel was driven by stress and temperature during high temperature wear. To span Ni- and Cr-based ternary oxide compositional spaces for which little high-temperature COF data exist, we develop a computational design method to predict the lubricity of oxides, incorporating thermodynamics and density functional theory computations. Our finding demonstrates that spinel oxide can exhibit low COF values at temperatures much higher than conventional solid lubricants with 2D layered or Magnéli structures, suggesting a promising design strategy for self-lubricating high-temperature alloys. The authors develop an approach for enhancing the wear resistance and lubricity of metals at elevated temperatures of in oxidative environments, where traditional solid lubricants fail. By engineering surface oxidation in additively manufactured Inconel, they achieve low friction coefficients, between 0.10 and 0.32 at 600-900 °C, through the formation of a spinel-based oxide layer.

Large earthquakes not only directly damage buildings but also trigger debris flows, which cause secondary damage to buildings, forming a more destructive earthquake-debris flow disaster chain. A quantitative assessment of building vulnerability is essential for damage assessment after a disaster and for pre-disaster prevention. Using mechanical analysis based on pushover, a physical vulnerability assessment model of buildings in the earthquake-debris flow disaster chain is proposed to assess the vulnerability of buildings in Beichuan County, China. Based on the specific sequence of events in the earthquake-debris flow disaster chain, the seismic vulnerability of buildings is 79%, the flow impact and burial vulnerabilities of damaged buildings to debris flow are 92% and 28% respectively, and the holistic vulnerability of buildings under the disaster chain is 57%. By comparing different vulnerability assessment methods, we observed that the physical vulnerability of buildings under the disaster chain process is not equal to the statistical summation of the vulnerabilities to independent hazards, which implies that the structural properties and vulnerability of buildings have changed during the disaster chain process. Our results provide an integrated explanation of building vulnerability, which is essential for understanding building vulnerability in earthquake-debris flow disaster chain and building vulnerability under other disaster chains.

Debris flow risk is growing with the current increases in landscape exploitation and extreme precipitation events associated with global warming. Insurance is an efficient approach to cope with disasters. Based on the quantitative assessment, the debris flow hazard was obtained by a dynamic run-out model (FLO-2D), and the pure risk premiums of debris flow disaster were rating in a high-risk region (Anzhou) in Sichuan, China. Simulation results indicated that disastrous debris flows would reoccur every 5 years on average under the contemporary climatic and geological conditions of the study area. The mountain region experienced a wider area affected by debris flows than plains and hills; however, its area affected by low debris flow depth (d < 0.1 m) accounts for a larger proportion (56.69% and 22.60%, respectively). The probability of sub-basins with basin slopes of 5°–10° experiencing serious debris flows was pretty close to the probability of sub-basins with slopes of 25°–35°, which are considered to be susceptible to trigger debris flows. Furthermore, for relatively flat sub-basins (slopes < 25°), the part closer to source was more susceptible to higher flow depth. Risk assessment results showed that the significant spatial difference between the distribution of debris flow risk and hazard largely linked to the distribution of at-risk element (buildings). The pure risk premium of Anzhou was rated as 0.69–25.48‰ depending on the proportion of at-risk buildings to insured buildings, which highlights the need to encourage or require more low-risk and secure buildings to participate in insurance schemes to share the debris flow risk of the entire region.

Although time-averaged shear wave velocity to the depth of 30 m (Vs30) is an important indicator of earthquake site effects, it is difficult to obtain. Several proxies have been used either individually or in combination to infer Vs30 values during seismic hazard estimation under limited observational conditions. Sichuan Province is an area highly prone to earthquakes. Complex geological structures and lack of drilling sites mean that it is particularly important to establish a suitable approach for the estimation of Vs30 values for site classification. This study compared the application of three proxy-based approaches—geology-based, topographic slope-based, and terrain-based—to the estimation of Vs30 values in Sichuan Province. The results revealed that the residual between the measured logVs30 values and the estimations derived from the terrain-based approach was smallest, indicating best predictability. Stability analysis of the three approaches also showed that the terrain-based approach performed best. However, its performance in the plain area was poor, that is, the Vs30 values were mostly underestimated. This might indicate that the old strata, hard rock, and alluvial deposits formed by Quaternary glacier sediments were not identified appropriately in the plain area, highlighting the need for localized corrections.

The rapid urbanization of China generated not only dozens of megacities but also a great number of surrounding small and medium-sized cities. The utter lack of seismic risk assessments for small and medium-sized cities is emerging as a potential threat. A seismic risk evaluation of a medium-sized city, Jiangyou, is presented with the modified vulnerability index method (VIM), based on the investigation of 6369 buildings for a scenario corresponding to the destructive historical earthquake of May 12, 2008 (MW 7.9). The population-time-land (PTL) model is used to estimate the human deaths (MD) and resettlement population (MR). The direct economic loss from physical damage to buildings is calculated. The results show that the modified VIM not only can indicate that the distributions of building seismic vulnerability and direct economic loss are closely related with city plans, but reflect the seismic performance characteristics of buildings and the huge differences in seismic consequences under different time scenarios. Evaluating seismic risk in small and medium-sized cities will support accurate and comprehensive seismic risk mitigation strategies setting in similar rapid urbanization areas under earthquake threats.