Nanostructured adhesive hairs on the feet of spiders are responsible for strong adhesion, enabling the animals to walk vertically and upside down. In article number 2002758, Clemens F. Schaber, ...Martin Müller, and co‐workers use scanning nanofocus X‐ray scattering under force control to elucidate the mechanism of alignment and consequently strong attachment of the nanostructures to a glass surface. The spider attachment system is a promising model for the development of powerful residue‐free dry adhesives.
The interplay between the diffusion-controlled dynamics of a solidification front and the trajectory of a grain boundary groove at the solid-liquid interface is studied by means of thin-sample ...directional solidification experiments of a transparent alloy, and by numerical simulations with the phase-field method in two dimensions. Here, we find that low-angle grain boundaries (subboundaries) with an anisotropic interfacial free energy grow tilted at an angle θt with respect to the temperature gradient axis. θt remains essentially equal to its value imposed at equilibrium as long as the solidification velocity V remains low. When V increases and approaches the cellular instability threshold, θt decreases, and eventually vanishes when a steady-state cellular morphology forms. The absence of mobility of the subboundary in the solid is key to this transition. These findings are in good agreement with a recent linear-stability analysis of the problem.
Electrocatalysis is at the heart of a broad range of physicochemical applications that play an important role in the present and future of a sustainable economy. Among the myriad of different ...electrocatalysts used in this field, nanomaterials are of ubiquitous importance. An increased surface area/volume ratio compared to bulk makes nanoscale catalysts the preferred choice to perform electrocatalytic reactions. Bragg coherent diffraction imaging (BCDI) was introduced in 2006 and since has been applied to obtain 3D images of crystalline nanomaterials. BCDI provides information about the displacement field, which is directly related to strain. Lattice strain in the catalysts impacts their electronic configuration and, consequently, their binding energy with reaction intermediates. Even though there have been significant improvements since its birth, the fact that the experiments can only be performed at synchrotron facilities and its relatively low resolution to date (∼10 nm spatial resolution) have prevented the popularization of this technique. Herein, we will briefly describe the fundamentals of the technique, including the electrocatalysis relevant information that we can extract from it. Subsequently, we review some of the computational experiments that complement the BCDI data for enhanced information extraction and improved understanding of the underlying nanoscale electrocatalytic processes. We next highlight success stories of BCDI applied to different electrochemical systems and in heterogeneous catalysis to show how the technique can contribute to future studies in electrocatalysis. Finally, we outline current challenges in spatiotemporal resolution limits of BCDI and provide our perspectives on recent developments in synchrotron facilities as well as the role of machine learning and artificial intelligence in addressing them.
•Fatigue curve of micro-single-crystal Cu is obtained by in situ SEM fatigue tests.•Cyclic hardening and softening appear in the early stage of fatigue.•Large strain induces cyclic softening and ...secondary hardening in saturation stage.•Small strain leads to only slight cyclic hardening in saturation stage.•Fatigue life of micro-single-crystal Cu is much shorter than that of bulk.
A series of quantitative in situ tension-compression fatigue experiments in SEM are performed to investigate the fatigue curve of microscale single-crystal copper specimens with a test part of 1 × 1 × 2 μm under various strain amplitudes. The variation of resolved shear stress on the primary slip plane (τB4) and the corresponding evolution of crystallographic slips in each cycle are analyzed and in situ observed, respectively. The variation of τB4 during fatigue shows that, (i) the variation of τB4 clearly includes the early stage, the saturation stage, and the final fracture of the specimen; (ii) apparent cyclic hardening and softening appear in the early stage of all specimens; (iii) τB4 shows a strain-dependent variation in the saturation stage. Continuous cyclic softening and secondary cyclic hardening occur in specimens with relatively higher strain, while only slight cyclic hardening emerges in the specimen with the minimum strain. Based on in situ SEM observations, the variation trend of τB4 is interpreted from the evolution of geometrical characteristics of slip traces. Finally, we obtain the fatigue curve of microscale single-crystal coppers. The fatigue life is apparently dependent on the strain amplitude, while insensitive to the frequency of cyclic loading. Moreover, the fatigue lives of microscale single-crystal Cu are much shorter than those of bulks, indicating a significant size effect. The difference in fatigue lives of microscale and bulk ones reduces from about 360 to only 7 times with the decrease of applied strain, revealing the strain-dependence of size effect of fatigue life for microscale single-crystal coppers.
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It is known, that under constrained tensile deformation the mechanical response and the failure behavior of rubber vulcanizates reveal unlikely features. Due to multiaxial stress concentrations, the ...formation of internal cracks can be initiated.
For the first time, fundamental investigations on unfilled styrene-butadiene-rubber pancake specimens were performed. Via in situ dilatometry and X-ray microtomography experiments, the damage process under constrained tensile deformation is studied and discussed. Although cavitation has been often discussed for filler reinforced rubber vulcanizates, the results of this study demonstrate how it occurs also in unfilled rubbers. In fact, the stronger the geometrical constraints are, the higher is the number of small cavities. However, the integral cavity volume is not affected. Moreover, micrographs of fracture surfaces indicate that cavitation is controlled by an omnidirectional growth of radial side-cracks. Finally, an energy-based approach to describe the cavitation onset criterion initiating the damaging process is presented to revise Gent's theory.
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•In situ experiments to explore the formation and growth of cavities.•Often suspected, cavitation is monitored in unfilled rubber vulcanizates.•The cavitation process is controlled by confinements – also under uniaxial tension.•Cavity growth is driven by omnidirectional propagation of side-cracks.
Metal foams are cellular materials, offering a strong structure-property relationship. Their global properties are strongly connected to the local micromechanical properties of the struts and to the ...microstructure of the foams. The mechanical properties of individual struts differ widely from the bulk matrix material as a result of differences in solidification conditions and the surface-to-volume ratio. A robust micromechanical understanding and knowledge of micromaterial parameters is essential to design components made of foams e.g. supported by numerical simulations. However, up to now, micromechanical charaterisation of individual struts is very challenging but an emerging field of research.
The present contribution deals with the microstructural and micromechanical characterisation of individual struts of open-cell aluminium foams and Ni/Al hybrid foams. The crystallographic texture is investigated by electron backscatter diffraction. Microtensile testing is performed on individual struts to determine real micromechanical material properties by ex-situ testing using a specially developed device and a digital image correlation method. Furthermore, in-situ microtensile tests using scanning electron microscopy are conducted for high-resolution investigation of the micromechanical deformation and damage mechanism occuring under loading of individual struts. The experimentally determined Young's modulus of the nickel coating is compared with theoretical calculations based on the grain orientation data.
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•Investigation of structure-property relationship of individual struts from Al foams and Ni/Al hybrid foams•In-situ and ex-situ microtensile testing of individual foam struts•Determination of micromaterial properties of individual struts•Experimental and theoretical evaluation of coating effect on the global composite properties
Soil aquifer treatment (SAT) is an emerging, nature-based, economically viable wastewater treatment solution. Currently, most SAT experiments are done at the laboratory scale, which cannot generate ...the same conditions as natural field sites and limits the understanding of treatment efficiency. The current study carried out in situ SAT experiments in the Musi River basin in India, where wastewater irrigation is a common practice. SAT efficiency was determined using an integrated approach, including electrical resistivity tomography (ERT) surveys, soil investigations (grain size, permeability, and moisture measurements), and biochemical characterization of raw and SAT treated wastewater. The ERT scans of SAT column show lower order electrical resistivity 10-30 Ω-m with enhanced chargeability >5–6 mV/V attributed to the vadose zone, characterized by clay-rich soil and sandy soil up to 5–6 m depth. The increase in sand percentage (>70%) below 140–160 cm depth corroborates with the high moisture content (23.5%). The vadose zone permeability (K) 1.58 m/day and discharge (Q) 38.19 m3/day is used to determine the pollutants reduction efficiency of SAT column. Hydrogeological and biogeochemical observations reveal that the improved dissolved oxygen from <1.0 to 5–6 mg/L in the vadose zone catalyzes the oxidation of organic matter resulting in the reduction of BOD and COD up to 92% and 97%, respectively, and denitrification reducing NO3−− (0.55 kg/day). In addition, the precipitation and adsorption by kaolinite clay prompted the reduction of PO42− (0.26 kg/day). Furthermore, the oxic-vadose zone could not support the growth of coliforms and faecal coliforms, and the reduction observed was up to 99.99% in the SAT production well. Overall, the results indicated a positive outcome with SAT efficiency and framed the SAT sitting criteria for different geological environments.
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•SAT is emerging as a nature-based and economically viable wastewater treatment solution.•We employed a novel approach by integrating hydro-geophysical scans for assessing the SAT system behavior.•Vadose zone permeability, discharge rate, and oxic state aid in quantifying SAT efficiency.•More than a 90% reduction rate is observed in BOD, COD, nitrates, phosphates, and microbes.•SAT sitting criteria and performance evaluation are suggested in field settings.
Dynamic strain ageing in iron due to various interstitial (carbon) and substitutional (nickel, silicon, chromium, aluminum) solute atoms has been studied by in situ straining in a transmission ...electron microscope. The effect of carbon in solid solution is characterized by two different carbon-dislocation interactions in the jerky flow and serrated flow temperature domains, and by a low mobility of screw dislocations controlled by a “high-temperature Peierls mechanism”. Substitutional atoms in solid solution can either move the domain of dynamic strain ageing to higher temperatures or not, depending on their chemical affinity for carbon. The results are interpreted by a shielding effect of mobile carbon atoms, inhibiting the interaction between dislocations and substitutional solute atoms.
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An increase in fluid pressure in faults can trigger seismicity and large aseismic motions. Understanding how fluid and faults interact is an essential goal for seismic hazard and reservoir ...monitoring, but this key relation remains unclear. We developed an in situ experiment of fluid injections at a 10 meter scale. Water was injected at high pressure in different geological structures inside a fault damaged zone, in limestone at 280 m depth in the Low Noise Underground Laboratory (France). Induced seismicity, as well as strains, pressure, and flow rate, was continuously monitored during the injections. Although nonreversible deformations related to fracture reactivations were observed for all injections, only a few tests generated seismicity. Events are characterized by a 0.5‐to‐4 kHz content and a small magnitude (approximately −3.5). They are located within 1.5 m accuracy between 1 and 12 m from the injections. Comparing strain measurements and seismicity shows that more than 96% of the deformation is aseismic. The seismic moment is also small compared to the one expected from the injected volume. Moreover, a dual seismic behavior is observed as (1) the spatiotemporal distribution of some cluster of events is clearly independent from the fluid diffusion (2) while a diffusion‐type pattern can be observed for some others clusters. The seismicity might therefore appear as an indirect effect to the fluid pressure, driven by aseismic motion and related stress perturbation transferred through failure.
Key Points
The paper presents a comprehensive in situ investigation of the seismogenic and hydromechanical behavior of a fractured zone
The experiments show that fluid injections mainly induce aseismic motions that drive a sparse seismicity far from the injection point
The experiments are used to assess the role of fluid pressure diffusion and stress perturbation through failure as driving mechanisms for seismicity
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