Metal

Failure of flight feathers under uniaxial compression

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Flight feathers are light weight engineering structures. They have a central shaft divided in two parts: the calamus and the rachis. The rachis is a thinly walled conical shell filled with foam, while the calamus is a hollow tube-like structure. Due to the fact that bending loads are produced during birds' flight, the resistance to bending of feathers has been reported in different studies. However, the analysis of bent feathers has shown that compression could induce failure by buckling. Here, we have studied the compression of feathers in order to assess the failure mechanisms involved. Axial compression tests were carried out on the rachis and the calamus of dove and pelican feathers. The failure mechanisms and folding structures that resulted from the compression tests were observed from images obtained by scanning electron microscopy (SEM). The rachis and calamus fail due to structural instability. In the case of the calamus, this instability leads to a progressive folding process. In contrast, the rachis undergoes a typical Euler column-type buckling failure. The study of failed specimens showed that delamination buckling, cell collapse and cell densification are the primary failure mechanisms of the rachis structure. The role of the foam is also discussed with regard to the mechanical response of the samples and the energy dissipated during the compression tests. Critical stress values were calculated using delamination buckling models and were found to be in very good agreement with the experimental values measured. Failure analysis and mechanical testing have confirmed that flight feathers are complex thin walled structures with mechanical adaptations that allow them to fulfil their functions.

This article originally appeared in Materials Science and Engineering: C 78, 2017, Pages 923-931.

Sign up or log in to your free Materials Today account to download the full article.

Published

3 years ago

September 8, 2017

Republished by Plato

Sign up or log in to your free Materials Today account to download the full article.

Flight feathers are light weight engineering structures. They have a central shaft divided in two parts: the calamus and the rachis. The rachis is a thinly walled conical shell filled with foam, while the calamus is a hollow tube-like structure. Due to the fact that bending loads are produced during birds’ flight, the resistance to bending of feathers has been reported in different studies. However, the analysis of bent feathers has shown that compression could induce failure by buckling. Here, we have studied the compression of feathers in order to assess the failure mechanisms involved. Axial compression tests were carried out on the rachis and the calamus of dove and pelican feathers. The failure mechanisms and folding structures that resulted from the compression tests were observed from images obtained by scanning electron microscopy (SEM). The rachis and calamus fail due to structural instability. In the case of the calamus, this instability leads to a progressive folding process. In contrast, the rachis undergoes a typical Euler column-type buckling failure. The study of failed specimens showed that delamination buckling, cell collapse and cell densification are the primary failure mechanisms of the rachis structure. The role of the foam is also discussed with regard to the mechanical response of the samples and the energy dissipated during the compression tests. Critical stress values were calculated using delamination buckling models and were found to be in very good agreement with the experimental values measured. Failure analysis and mechanical testing have confirmed that flight feathers are complex thin walled structures with mechanical adaptations that allow them to fulfil their functions.

This article originally appeared in Materials Science and Engineering: C 78, 2017, Pages 923-931.

Sign up or log in to your free Materials Today account to download the full article.

Source: https://www.materialstoday.com/biomaterials/features/failure-of-flight-feathers-under-uniaxial/

Metal

Microalloyed medium-entropy alloy (MEA) composite nanolattices with ultrahigh toughness and cyclability

Abstract: Three-dimensional nanolattices have recently emerged as an effective strategy to achieve high strength at low densities, by harnessing the combination of rationally designed topologies and nanoscale size effects [1], [2], [3], [4], [5]. However, most metallic and ceramic nanolattices show an ineludible deterioration of mechanical properties upon repeated loading due to localized brittle fracture. Here, by development and deposition of CoCrNiTi0.1 microalloyed medium-entropy alloy (MEA) with extra low stacking fault energy, we fabricated ultratough MEA-coated nanolattices that can exhibit unprecedented surface wrinkling under compression. Particularly, nanolattices with alloy film thickness?∼?30?nm can repeatedly withstand strains exceeding 50% with negligible strut fracture, while the elastic polymer core promotes recoverability and structural integrity. Furthermore, owing to the high strength of the metallic film, our MEA composite nanolattices exhibited high energy absorption (up to 60?MJ?m−3) and specific strength (up to 0.1?MPa?kg−1?m3), offering a plethora of robust micro/nano-mechanical and functional applications.

Published

1 day ago

February 28, 2021

Republished by Plato

Source: https://www.materialstoday.com/amorphous/articles/s1369702120303576/

Metal

Ultrahigh coulombic efficiency electrolyte enables Li||SPAN batteries with superior cycling performance

Abstract: Raising the coulombic efficiency of lithium metal anode cycling is the deciding step in realizing long-life rechargeable lithium batteries. Here, we designed a highly concentrated salt/ether electrolyte diluted in a fluorinated ether: 1.8?M LiFSI in DEE/BTFE (diethyl ether/bis(2,2,2-trifluoroethyl)ether), which realized an average coulombic efficiency of 99.37% at 0.5?mA?cm−2 and 1 mAh cm−2 for more than 900 cycles. This electrolyte also maintained a record coulombic efficiency of 98.7% at 10?mA?cm−2, indicative of its ability to provide fast-charging with high cathode loadings. Morphological studies reveal dense, dendrite free Li depositions after prolonged cycling, while surface analyses confirmed the formation of a robust LiF-rich SEI layer on the cycled Li surface. Moreover, we discovered that this ether-based electrolyte is highly compatible with the low-cost, high-capacity SPAN (Sulfurized polyacrylonitrile) cathode, where the constructed Li||SPAN cell exhibited reversible cathode capacity of 579 mAh g−1 and no capacity decay after 1200 cycles. A cell where a high areal loading SPAN electrode (>3.5 mAh cm−2) is paired with only onefold excess Li was constructed and cycled at 1.75?mA?cm−2, maintaining a coulombic efficiency of 99.30% for the lithium metal. Computational simulations revealed that at saturation, the Li-FSI complex forms contact ion pairs, with a first solvation shell comprising DEE molecules, and a second solvation shell with a mix of DEE/BTFE. This study provides a path to enable high energy density Li||SPAN batteries with stable cycling.

Published

1 day ago

February 28, 2021

Republished by Plato

Source: https://www.materialstoday.com/amorphous/articles/s1369702120303382/

Metal

Modulation of physical properties of organic cocrystals by amino acid chirality

Abstract: Amino acid chirality plays an important role in conveying directionality and specificity to their supramolecular organization. However, the impact of enantiopure and racemic amino acids on the favorable packing and macroscopic properties of organic cocrystals with nonchiral coformers is poorly understood. Herein, we performed a systematic study of the effect of chirality on the macroscopic properties of acetylated alanine (AcA) single crystals and cocrystals with a nonchiral photo-sensitive bipyridine derivative (BPE). Cocrystallization with BPE produced a marked morphology transition that improved the supramolecular chirality, thermal stability and mechanical strength of AcA crystals. The distinct supramolecular packing modes were analyzed by X-ray crystallography. The highest rigidity was observed for BPE/dl-AcA, while BPE/d-AcA and BPE/l-AcA crystals exhibited higher efficiency of photo-induced emission for fluorescent imprinting, as well as significantly higher piezoelectricity. This work provides a striking illustration that subtle differences in amino acid stereochemistry translate into tunable macroscopic properties of organic cocrystals for future applications in rigid solids, fluorescent imprinting, and energy harvesting.