Nature's masterfully synthesized biological materials take on greater relevance when viewed through the perspective of evolutionary abundance. The fact that beetles (order Coleoptera) account for a ...quarter of all extant lifeforms on Earth, makes them prime exponents of evolutionary success. In fact, their forewings are acknowledged as key traits to their radiative-adaptive success, which makes the beetle elytra a model structure for next-generation bioinspired synthetic materials. In this work, the multiscale morphological and mechanical characteristics of a variety of beetle species from the Cetoniinae subfamily are investigated with the aim of unraveling the underlying principles behind Nature's adaptation of the elytral bauplan to differences in body weight spanning three orders of magnitude. Commensurate with the integral implications of size variation in organisms, a combined material, morphological, and mechanical characterization framework, across spatial scales, was pursued. The investigation revealed the simultaneous presence of size-invariant strategies (chemical compositions, layered-fibrous architectures, graded motifs) as well as size-dependent features (scaling of elytral layers and characteristic dimensions of building blocks), synergistically combined to achieve similar levels of biomechanical functionality (stiffness, energy absorption, strength, deformation and toughening mechanisms) in response to developmental and selection constraints. The integral approach here presented seeks to shed light on Nature's solution to the problem of size variation, which underpins the diversity of beetles and the living world.
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Bamboo is becoming increasingly popular as an engineering material and source of bio-inspiration for instance in architecture and for the manufacture of a variety of woven products. Besides the ...properties of bamboo products for construction purposes, the bending deformability of thin bamboo slivers is of interest, as it appears that extraordinary large deflection can be achieved. To unravel the underlying mechanisms that may contribute to the high deformability at the tissue and cell level, bending deflection tests and additional
experiments were performed to record the deflection of bamboo slivers in dependence of the tissue composition and the deformations of individual cells. For the latter, a simple bending deflection setup was used employing micro-CT measurements to analyze the deformation of individual parenchyma cells (PCs), fiber bundles and vessel elements at different stages of bending deformation of the bamboo slivers. The results showed that the degree of displacement and the characteristic fracture behavior strongly depend on the volume fractions of PCs and fibres determined by the position in the bamboo culm. For slivers with a sufficiently high fibre volume content, the very high bending deformability could be facilitated by the deformation of PCs, which are squeezed between the fibre bundles during increasing bending deflection.
Controlling the domain wall motion in the 2D ferromagnetic materials is significantly critical to the topological spin electronics, non‐volatile magnetic memories, and logic devices. The elevation of ...the domain wall velocity has become an urgent challenge. Herein, a current‐pulse‐driving strategy is unprecedentedly established to boost the domain wall velocity with an out‐of‐plane magnetic field and a rising temperature in the Fe3GeTe2 by using the in situ Lorentz Transmission Electron Microscopy. Elevation of domain wall velocity depends on the demagnetization energy increase and Zeeman energy reduction, which originates from the magnetic moments tilting by a non‐parallel to the magnetic field. By injecting ≈2000 times of alternative current pulses, a uniform instead of an unsynchronized domain wall velocity is achieved. The key mechanism lies in the decrease of the domain wall number, leading to a reduction in the expansion and compression of the domain areas. Optimized pulse parameters are applied with a critical duration of 60 ns and the density of ≈2 × 1010 A m−2, leading to an elevation of velocity from 0.0308 to 0.39 m s−1. The elevation in magnetic domain wall velocity can be useful for the application of 2D van der Waals ferromagnetic materials in future spintronic devices.
The strategies for elevation of uniform domain wall velocity driven by the current are investigated by utilizing the physical properties in the 2D ferromagnet Fe3GeTe2 thin flake. With the tiny out‐of‐plane magnetic field and rising temperature, the velocity is elevated by an order of magnitude to accomplish higher reading‐and‐writing speed racetrack memory devices.
Dynamic time tracking of free water during first 48h of hydration of Portland cement paste using Raman Spectroscopy.
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•In situ Raman Spectroscopy used to examine the hydration process ...of OPC volcanic ash.•The effect of volcanic ash particle size on the cement paste hydration behavior were examined.•Free water found to increase with increasing the particle size and concentration of volcanic ash.
Raman Spectroscopy was used to track the free water and the cementitious gel phases when Ordinary Portland Cement (OPC) and tricalcium silicate (C3S) were partially substituted by natural pozzolanic volcanic ash. Two different particle sizes of volcanic ash (VA), (namely 17 and 6μm) were each used to substitute 10%, 30% and 50% of OPC and C3S by weight. Particle size and concentration of VA significantly affected the hydration behavior of cement paste by influencing the water dynamics during the course of hydration. Increase in concentration of VA also led to an increase in “free water” during the course of hydration. Calcium silicate hydrate (C-S-H) phases along with calcium/magnesium based zeolites were detected as the concentration of volcanic ash increased in the mix. This work shows that Raman spectroscopy is a powerful tool to examine the hydration process when Portland cements are substituted by volcanic ashes of different sizes.
In recent experiments on the solidification of the binary eutectic alloy succinonitrile-(D)camphor carried out on board of the International Space Station (ISS), a transition from rod to lamellar ...patterns was observed for low growth velocities. The transition was interpreted in terms of a competition between a propagative instability of lamellae and a drift induced by a transverse temperature gradient. Phase-field simulations of a symmetric model alloy support this scenario: for a fixed transverse temperature gradient, the transition from rods to lamellae occurs for a critical composition at fixed velocity, and for a critical velocity at fixed composition. Since the alloy and control parameters used in experiments and simulations are different, our results strongly suggest that this morphological transition is generic for eutectic alloys.
Within the context of deep geological radioactive waste disposal, the French National Radioactive Waste Management Agency (Andra) is conducting a research program including in-situ experiments at the ...Meuse/Haute-Marne Underground Research Laboratory (MHM URL), which aims to demonstrate the feasibility of constructing and operating a High Level Waste (HLW) disposal facility in the Callovo-Oxfordian (COx) claystone formation and to improve it. ALC1604 experiment is an in-situ heating test reproducing a full-scale HLW disposal cell. Heating devices were placed in the last 15 m of a 25 m long steel cased micro-tunnel to mimic the heat emitted by the HLW packages. The present experiment allows to study the response of the cell and the surrounding rock under thermal loading. More specifically, this experiment studied the thermo-mechanical (TM) behavior of the steel sleeve, equipped with strain gauges, displacement sensors, temperature sensors, etc., and monitored the evolution of the annular space (the gap between the sleeve and the rock). It also studied the thermo-hydro-mechanical (THM) behavior of the near/far field rock through pore pressure and temperature measurements installed in peripheral boreholes. The TM response of the steel sleeve and the THM response of the surrounding rock are numerically reproduced and the chosen THM parameters are compared with previous small-scale in-situ experiments conducted at the MHM URL in order to improve the reliability of the material parameters of the COx. The lessons learned from this experiment has provided valuable feedback towards implementing new full-scale heating experiments consistent with a new benchmark concept.
Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that perform a number of functions including the long-term isolation and containment of waste from the human ...environment, and the attenuation of radionuclides released to the subsurface. The rock laboratory at Mont Terri (canton Jura, Switzerland) in the Opalinus Clay plays an important role in the development of such repositories. The experimental results gained in the last 20 years are used to study the possible evolution of a repository and investigate processes closely related to the safety functions of a repository hosted in a clay rock. At the same time, these experiments have increased our general knowledge of the complex behaviour of argillaceous formations in response to coupled hydrological, mechanical, thermal, chemical, and biological processes. After presenting the geological setting in and around the Mont Terri rock laboratory and an overview of the mineralogy and key properties of the Opalinus Clay, we give a brief overview of the key experiments that are described in more detail in the following research papers to this Special Issue of the Swiss Journal of Geosciences. These experiments aim to characterise the Opalinus Clay and estimate safety-relevant parameters, test procedures, and technologies for repository construction and waste emplacement. Other aspects covered are: bentonite buffer emplacement, high-pH concrete-clay interaction experiments, anaerobic steel corrosion with hydrogen formation, depletion of hydrogen by microbial activity, and finally, release of radionuclides into the bentonite buffer and the Opalinus Clay barrier. In the case of a spent fuel/high-level waste repository, the time considered in performance assessment for repository evolution is generally 1 million years, starting with a transient phase over the first 10,000 years and followed by an equilibrium phase. Experiments dealing with initial conditions, construction, and waste emplacement do not require the extrapolation of their results over such long timescales. However, experiments like radionuclide transport in the clay barrier have to rely on understanding long-term mechanistic processes together with estimating safety-relevant parameters. The research at Mont Terri carried out in the last 20 years provides valuable information on repository evolution and strong arguments for a sound safety case for a repository in argillaceous formations.
The coupled Thermo-Hydro-Mechanical (THM) behavior of the Callovo-Oxfordian claystone (COx) is of great importance for the design and safety calculations of the high-level radioactive waste disposal ...project in this potential host rock in France. The heat emitted by the waste causes a pore pressure increase within the surrounding rock essentially due to the differential thermal expansion of the pore water and the solid skeleton. The low permeability of the COx and its relative rigidity inhibits the discharge of the induced pressure build-up. Moreover, thermal loading may provoke thermo-mechanical stresses within the formation due to mechanical confinement by the rigidity of the surrounding host rock. An important research program has been conducted by the French National Radioactive Waste Management Agency (Andra) since 2003 in order to investigate the THM response of the COx under thermal loading, through laboratory tests, in-situ experiments, model development and numerical modeling. Within Task E of the DECOVALEX-2019 project, five research teams investigated upscaling THM modeling from a small-scale in-situ experiment (TED) to a full-scale in-situ experiment (ALC). The upscaling modeling started with a verification test to validate the numerical codes. Then, an interpretative modeling of the TED experiment was performed to calibrate the THM parameters of the COx. Finally, the calibrated THM parameters were used for a blind prediction of the ALC experiment. The modeling teams each adopted a thermo-poro-elastic approach which yielded satisfactory results. The blind prediction of the temperature field showed an overestimation of less than 2 °C which was considered acceptable. On the other hand, pore pressure was well predicted only in the direction parallel to the bedding whereas the slow dissipation of the pore pressure in the direction perpendicular to the bedding was not captured by any of the modeling teams – which remains an open question of the present study.
Solid-state phase transformations in the γ-loop of the binary Fe-P system were studied using differential scanning calorimetry (DSC) and high-temperature laser scanning confocal microscopy (HT-LSCM). ...In total, eight alloys with varying P content from 0.026 to 0.48 mass pct. P were investigated in the temperature range of 800 °C to 1450 °C. The first part of the present work deals with the critical evaluation of the approach to couple DSC experiments and HT-LSCM observations in order to characterize bcc/fcc phase equilibria in Fe-based γ-loops. The phase transformation temperatures of a selected alloy with 0.394%P were analyzed by DSC and HT-LSCM and compared with results of the well-established techniques of dilatometry and high-temperature X-ray diffraction (HT-XRD). Then, the overall phase boundaries of the γ-loop were reconstructed by HT-LSCM and DSC data and the phase diagram was compared with thermodynamic assessments from literature. Finally, the quantitative phase fractions of fcc and bcc at 0.394%P were analyzed by Rietveld refinement at temperatures of 1050 °C, 1100 °C and 1150 °C using in-situ HT-XRD. Although the phase boundaries of the γ-loop and phase transformation temperatures have been reproduced accurately by recently published thermodynamic optimizations, larger deviations between HT-XRD measurements and the calculations were identified for the phase fraction prediction. The present work clearly demonstrates that coupling DSC and HT-LSCM is a powerful tool to characterize γ-loops in steel for future research work.
•In-situ characterization of the γ-loop in the Fe-P binary system.•Coupling of DSC and HT-LSCM to reconstruct the phase boundaries.•Critical evaluation of DSC and HT-LSCM results with HT-XRD and dilatometry data.•Phase fraction analysis of fcc and bcc by in-situ HT-XRD.•Comparison of experimental data with thermodynamic assessments of the Fe-P system.
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