Nature utilizes the available resources to construct lightweight, strong and tough materials under constrained environmental conditions. The impact surface of the fast-striking dactyl club from the ...mantis shrimp is an example of one such composite material; the shrimp has evolved the capability to localize damage and avoid catastrophic failure from high-speed collisions during its feeding activities. Here we report that the dactyl club of mantis shrimps contains an impact-resistant coating composed of densely packed (about 88 per cent by volume) ~65-nm bicontinuous nanoparticles of hydroxyapatite integrated within an organic matrix. These mesocrystalline hydroxyapatite nanoparticles are assembled from small, highly aligned nanocrystals. Under impacts of high strain rates (around 10
s
), particles rotate and translate, whereas the nanocrystalline networks fracture at low-angle grain boundaries, form dislocations and undergo amorphization. The interpenetrating organic network provides additional toughening, as well as substantial damping, with a loss coefficient of around 0.02. An unusual combination of stiffness and damping is therefore achieved, outperforming many engineered materials.
Magnesium is a light metal, with a density two-thirds that of aluminium, is abundant on Earth and is biocompatible; it thus has the potential to improve energy efficiency and system performance in ...aerospace, automobile, defence, mobile electronics and biomedical applications. However, conventional synthesis and processing methods (alloying and thermomechanical processing) have reached certain limits in further improving the properties of magnesium and other metals. Ceramic particles have been introduced into metal matrices to improve the strength of the metals, but unfortunately, ceramic microparticles severely degrade the plasticity and machinability of metals, and nanoparticles, although they have the potential to improve strength while maintaining or even improving the plasticity of metals, are difficult to disperse uniformly in metal matrices. Here we show that a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium can be achieved through a nanoparticle self-stabilization mechanism in molten metal. An enhancement of strength, stiffness, plasticity and high-temperature stability is simultaneously achieved, delivering a higher specific yield strength and higher specific modulus than almost all structural metals.
Miniature cantilevers are associated with amplification in strain gradient and dislocation recovery. These contrasting phenomena interplay to impart strengthening via the injection of geometrically ...necessary dislocations because of strain gradients and softening due to the surface proximity effect. In this work, creep studies on Al cantilevers of thicknesses ranging from 0.070 to 7 mm demonstrate this interplay. The 2D strain field and dislocation substructure were examined to understand the steady-state creep response in miniaturized cantilevers. The average creep response of the cantilever strengthens with decreasing cantilever thickness; however, regimes of hardening, softening, and bulk-like behavior were observed while traveling along the length of the cantilever. Consistently, refinement in the steady-state dislocation substructure was observed in the regions of large strain gradients. The locations in a miniaturized cantilever with insignificant strain gradients registered surface proximity effect-induced enhanced creep rates. An analytical model has been developed to describe the strain gradient-surface proximity interplay.
Graphical abstract
Low fiber-direction compressive strength of high-modulus (HM) carbon fiber-reinforced polymers (CFRPs) has been their major weakness prohibiting implementation of such materials in aircraft primary ...structures despite improving mechanical stiffness at a lower weight. A new HM CFRP achieving fiber-direction compressive strength of intermediate-modulus (IM) CFRPs but with more than 30% higher axial modulus has been recently developed. This work looks into fiber-matrix interface shear strength as a potential mechanism driving the compression strength improvement of the new material system. In-situ scanning electron microscopy (SEM) based single fiber push-out experiments addressing standing challenges associated with manufacturing high-quality samples as well as distinguishing same-diameter HM and IM carbon fibers in the hybrid composite system are used to measure fiber-matrix interface shear strength. The experiments show a 29% lower average value of the fiber-matrix interface shear strength for the HM carbon fibers compared to the IM carbon fibers in the new material system. Such a significant reduction corresponds to a 22% lower fiber-direction compressive strength of the HM CFRP without the integrated IM fibers. The results support the idea of integrating off-the-shelf IM carbon fibers with a stronger fiber-matrix interface and a higher shear modulus into HM CFRPs to improve their compressive strength.
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•The interface behavior of single fibers in HM CFRPs has been investigated•In-situ SEM based fiber push-out testing assessed the interface shear strength.•High-quality microstructural samples are machined using femtosecond laser.•HM carbon fiber-matrix interface is weaker compared to IM carbon fiber-matrix interface.•Weak fiber-matrix interface of HM CFRPs corresponds to their low compressive strength.
Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have ...recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30-50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus-low density and high modulus-high damping material structures.
In this paper, we clarify some aspects of LCD codes in the literature. We first prove that non-free LCD codes do not exist over finite commutative Frobenius local rings. We then obtain a necessary ...and sufficient condition for the existence of LCD codes over a finite commutative Frobenius ring. We later show that a free constacyclic code over a finite chain ring is an LCD code if and only if it is reversible, and also provide a necessary and sufficient condition for a constacyclic code to be reversible. We illustrate the minimum Lee distance of LCD codes over some finite commutative chain rings with examples. We found some new optimal cyclic codes over
Z
4
of different lengths which are LCD codes using computer algebra system MAGMA.
Among the large number of promising two-dimensional (2D) atomic layer crystals, true metallic layers are rare. Using combined theoretical and experimental approaches, we report on the stability and ...successful exfoliation of atomically thin "gallenene" sheets on a silicon substrate, which has two distinct atomic arrangements along crystallographic twin directions of the parent α-gallium. With a weak interface between solid and molten phases of gallium, a solid-melt interface exfoliation technique is developed to extract these layers. Phonon dispersion calculations show that gallenene can be stabilized with bulk gallium lattice parameters. The electronic band structure of gallenene shows a combination of partially filled Dirac cone and the nonlinear dispersive band near the Fermi level, suggesting that gallenene should behave as a metallic layer. Furthermore, it is observed that the strong interaction of gallenene with other 2D semiconductors induces semiconducting to metallic phase transitions in the latter, paving the way for using gallenene as promising metallic contacts in 2D devices.
3D scaffolds of graphene, possessing ultra‐low density, macroporous microstructure, and high yield strength and stiffness can be developed by a novel plasma welding process. The bonding between ...adjacent graphene sheets is investigated by molecular dynamics simulations. The high degree of biocompatibility along with high porosity and good mechanical properties makes graphene an ideal material for use as body implants.
Self-Dual Cyclic Codes Over M2(ℤ4) Bhowmick, Sanjit; Pal, Joydeb; Bandi, Ramakrishna ...
Discussiones Mathematicae. General Algebra and Applications,
10/2022, Letnik:
42, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In this paper, we study the structure of cyclic codes over
(ℤ
) (the matrix ring of matrices of order 2 over ℤ
), which is perhaps the first time that the ring is considered as a code alphabet. This ...ring is isomorphic to ℤ
+
, where
is a root of the irreducible polynomial
+
+ 1 ∈ ℤ
and
. In our work, we first discuss the structure of the ring
(ℤ
) and then focus on the structure of cyclic codes and self-dual cyclic codes over
(ℤ
). Thereafter, we obtain the generators of the cyclic codes and their dual codes. A few non-trivial examples are given at the end of the paper.
High entropy alloys (HEAs) have attracted widespread interest due to their unique properties at many different length-scales. Here, we report the fabrication of nanocrystalline (NC) Al0.1CoCrFeNi ...high entropy alloy and subsequent small-scale plastic deformation behavior via nano-pillar compression tests. Exceptional strength was realized for the NC HEA compared to pure Ni of similar grain sizes. Grain boundary mediated deformation mechanisms led to high strain rate sensitivity of flow stress in the nanocrystalline HEA.
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