Spider silks show unique combinations of strength, toughness, extensibility, and energy absorption. To date, it has been difficult to obtain spider silk-like mechanical properties using non-protein ...approaches. Here, we report on an artificial spider silk produced by the water-evaporation-induced self-assembly of hydrogel fibre made from polyacrylic acid and silica nanoparticles. The artificial spider silk consists of hierarchical core-sheath structured hydrogel fibres, which are reinforced by ion doping and twist insertion. The fibre exhibits a tensile strength of 895 MPa and a stretchability of 44.3%, achieving mechanical properties comparable to spider silk. The material also presents a high toughness of 370 MJ m
and a damping capacity of 95%. The hydrogel fibre shows only ~1/9 of the impact force of cotton yarn with negligible rebound when used for impact reduction applications. This work opens an avenue towards the fabrication of artificial spider silk with applications in kinetic energy buffering and shock-absorbing.
A bio-inspired concept of non-uniform curved grid-stiffened composite structures with embedded stiffeners (embedded NCGCs) is proposed in the paper. Shallow curved stiffeners are embedded in the ...laminate skin to form an integrated structure to improve the skin–stiffener deformation compatibility. A method named streamline stiffener path optimization (SSPO) based on multiscale modeling is proposed for curved stiffener layout design of embedded NCGCs. Firstly, the homogenization-based global/local analysis is used to calculate structural responses on a global unstiffened model with the equivalent material properties obtained from local representative cell configurations (RCCs). Secondly, the discrete distribution of 2D curved stiffener paths is transformed into a continuous distribution of the streamline function values (SFVs) on a 3D level set surface. The stiffener path description using the streamline function is similar as the level set method with specific constraints. Projections of points with the same integral SFVs will form one stiffener path. Thirdly, optimal curved stiffener layout is achieved using shape design of local parallelogram representative cell configurations with analytical sensitivities calculated using the affine mapping from the square master domain to the parallelogram RCCs. Fourthly, stiffener spacing and angle constraints are added for manufacturing considerations and local buckling resistance, and optimization design is implemented to maximize the buckling load within a given weight. Finally, numerical examples of a square laminated panel under uniaxial and biaxial compressions validate the effectiveness of the proposed SSPO method and indicate the significant improvement of the buckling loads by steering the stiffener paths.
•Bio-inspired shallow stiffeners embedded inside the laminate skin is proposed.•Curved stiffener layout optimization is solved based on multiscale modeling.•Curved stiffener paths are interpreted using the streamline functions.•Parallelogram representative cell configurations provide analytical sensitivities.
Focusing on planar isotropic petal-shaped auxetics, an isogeometric design framework is presented to achieve tunable effective properties. Specifically, the design framework includes (i) a ...NURBS-based parametric modelling scheme that characterizes petal-shaped auxetics with a small number of design variables; (ii) a systematic consideration of petal form, component widths and base material properties; (iii) a semi-analytical sensitivity analysis method based on material derivatives; and (iv) constraints for effective stiffness and target Poisson ratio. Three cases are considered: Case A with the same component width, Case B with different component widths, and Case C for composite designs with multiple base materials. For each case, a design limit curve is obtained for the effective Poisson ratio over a range of effective stiffness constraints, to give a quick overview on the properties attainable for each design setting. The optimization framework is next demonstrated for designing composite petal-shaped auxetics with target effective properties.
An important feature that drives the auxetic behaviour of the star-shaped auxetic structures is the hinge-functional connection at the vertex connections. This feature poses a great challenge for ...manufacturing and may lead to significant stress concentrations. To overcome these problems, we introduced smoothed petal-shaped auxetic structures, where the hinges are replaced by smoothed connections. To accommodate the curved features of the petal-shaped auxetics, a parametrisation modelling scheme using multiple NURBS patches is proposed. Next, an integrated shape design frame work using isogeometric analysis is adopted to improve the structural performance. To ensure a minimum thickness for each member, a geometry sizing constraint is imposed via piece-wise bounding polynomials. This geometry sizing constraint, in the context of isogeometric shape optimization, is particularly interesting due to the non-interpolatory nature of NURBS basis. The effective Poisson ratio is used directly as the objective function, and an adjoint sensitivity analysis is carried out. The optimized designs – smoothed petal auxetic structures – are shown to achieve low negative Poisson’s ratios, while the difficulties of manufacturing the hinges are avoided. For the case with six petals, an in-plane isotropy is achieved.
Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially ...at the time of collision with India, not 10–20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the rest of Eurasia. Thus, the north‐south dimensions of the Tibetan Plateau were set mainly by differences in lithospheric strength, with strong lithosphere beneath India and the Tarim and Qaidam basins steadily encroaching on one another as the region between them, the present‐day Tibetan Plateau, deformed, and its north‐south dimension became narrower. Second, abundant evidence calls for acceleration of deformation, including the formation of new faults, in northeastern Tibet since ~15 Ma and a less precisely dated change in orientation of crustal shortening since ~20 Ma. This reorientation of crustal shortening and roughly concurrent outward growth of high terrain, which swings from NNE‐SSW in northern Tibet to more NE‐SW and even ENE‐WSW in the easternmost part of northeastern Tibet, are likely to be, in part, a consequence of crustal thickening within the high Tibetan Plateau reaching a limit, and the locus of continued shortening then migrating to the northeastern and eastern flanks. These changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation.
Key Points
The north‐south limits of Tibet were set by lateral variations in strength
Roughly 15 million years ago, deformation of NE Tibet accelerated
Since 20–15 million years ago, the orientation of shortening rotated eastward
Auxetic materials with the counter-intuitive effect of negative Poisson’s ratio (NPR) have potentials for diverse applications. Typical shape optimization designs of auxetic structures involve ...complicated sensitivity analysis and a time-consuming iterative process, which is not beneficial for designing functionally-graded structures where the auxetics at different locations need to be inversely designed. To improve the efficiency of the inverse design and simplify the sensitivity analysis, we propose a deep-learning-based inverse shape design approach for tetra-chiral auxetics. First, a non-uniform rational basis spline (NURBS)-based parameterization of tetra-chiral structures is developed to create design samples and computational homogenization based on isogeometric analysis is used in these samples to generate a database consisting of mechanical properties and geometric parameters. Then, the database is utilized to train deep neural networks (DNN) to generate a surrogate model that represents the effective mechanical properties as a function of geometric parameters. Finally, the surrogate model is directly used in the inverse design framework where sensitivity analysis can be calculated analytically. Numerical examples with verifications are presented to demonstrate the efficiency and accuracy of the proposed design methodology.
This paper focuses on a systematic isogeometric design approach for the optimal petal form and size characterization of tetra-petals auxetics, considering both plane stress and plane strain ...conditions. The underlying deformation mechanism of a tetra-petals auxetic is analyzed numerically with respect to several key parameters. Design optimizations are performed systematically to give bounding graphs for the minimum Poisson's ratio achievable with different stiffness constraints. Tunable design studies with targeted effective Poisson's ratio, shear modulus and stiffness are demonstrated. Potential application for functionally graded lattice structures is presented. Numerical and experimental verifications are provided to verify the designs. The out-of-plane buckling phenomenon in tension for thin auxetics with re-entrant features is illustrated experimentally to draw caution to results obtained using plane stress formulations for designing such structures.
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•NURBS parameterization of novel curved tetra-petals auxetics•Isogeometric analysis enhanced numerical homogenization framework.•A systematical study of designing tetra-petals auxetics with tunable properties•Bounding graph of achievable effective Poisson's ratio under different stiffness constraints•Experimental verifications for tunable design studies
Hydrogen peroxide (H
O
) is a major reactive oxygen species in unicellular and multicellular organisms, and is produced extracellularly in response to external stresses and internal cues
. H
O
enters ...cells through aquaporin membrane proteins and covalently modifies cytoplasmic proteins to regulate signalling and cellular processes. However, whether sensors for H
O
also exist on the cell surface remains unknown. In plant cells, H
O
triggers an influx of Ca
ions, which is thought to be involved in H
O
sensing and signalling. Here, by using forward genetic screens based on Ca
imaging, we isolated hydrogen-peroxide-induced Ca
increases (hpca) mutants in Arabidopsis, and identified HPCA1 as a leucine-rich-repeat receptor kinase belonging to a previously uncharacterized subfamily that features two extra pairs of cysteine residues in the extracellular domain. HPCA1 is localized to the plasma membrane and is activated by H
O
via covalent modification of extracellular cysteine residues, which leads to autophosphorylation of HPCA1. HPCA1 mediates H
O
-induced activation of Ca
channels in guard cells and is required for stomatal closure. Our findings help to identify how the perception of extracellular H
O
is integrated with responses to various external stresses and internal cues in plants, and have implications for the design of crops with enhanced fitness.
•An efficient DNN-based design framework for functionally graded lattices is established.•Functionally graded lattices are designed using the framework, fabricated using addictive manufacturing, and ...evaluated using experimental tests.•The effectiveness of the design framework is demonstrated with the performances of the functionally graded lattices.•This work is inspirable to promote advanced structures/materials with tailored properties.
Auxetic materials with counterintuitive negative Poisson’s ratio have been of significant interest due to potential applications across diverse engineering fields. Functionally grading such auxetics further enables customization of the structural response and harnesses the potential for multi-functional applications. However, a critical challenge in designing functionally graded lattices is to efficiently determine the spatial variation of the functional gradient and the corresponding geometric designs to achieve the desired response. In this paper, a highly efficient deep learning-based inverse design framework for functionally graded tetra-petal auxetics with spatially tailored properties is presented. This framework significantly improves the efficiency of tailoring functionally graded auxetics where many unit cells need to be tailor-designed. The graded tetra-petal auxetics obtained from the inverse design framework are additively manufactured and subjected to impact tests. The results show superior impact performance compared with uniform designs, demonstrating the effectiveness of the proposed inverse design framework, which can be inspirable to promote advanced structures/materials with enhanced impact resistance.
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