Digital Twin Assistant Active Design and Optimization of Steel Mega-Sub Controlled Structural System under Severe Earthquake Waves.

In order to support the best optimized design or strategy based on life-cycle data, the interrelation mechanisms between structure-form and structure-performance should be considered simultaneously and comprehensively besides of the material-property relationship. Here, the structure-property-performance relationship of a designed steel mega-sub controlled structural system (MSCSS) under the reported earthquake waves has been investigated through integrating the finite element simulations and the experimental validations. It can be found that the MSCSS configurations are capable of effectively optimizing the vibration responses with significantly decreased acceleration, which is also much better than the traditional megaframe structure with extra weight. Moreover, if the horizontal connections between the sub- and the megastructures are broken, the displacement of the megastructure will be smaller than that of the substructure. This is because only the vertical connections between the sub- and megastructures work, the larger displacements or the obvious response of the substructures should be caused by the extra weight of the damper on the top floor. It is worth mentioning that the formation of abrupt amplified ß of the top floors should be attributed to the sheath effect. Furthermore, the displacement of the substructure is one kind of energy dissipation. Its larger displacement will result in a greater amount of energy dissipation and better performance of the designed configuration. This work supports a digital twin assistant active design and optimization strategy to further improve the control effectiveness of the system and to enhance the mechanical performance of the optimized configuration of MSCSS.

Lattice distortion-enhanced superlubricity of (Mo, X)S2 (X = Al, Ti, Cr and V) with moiré superlattice.

Two-dimensional (2D) materials with the advantage of low interlayer shear strain are ultilized as lubricants in aerospace and precision manufacturing. Moiré superlattices (MSL), with attractive physical properties of electronic structures, interlayer hybridization and atomic forces, have been widely investigated in superlubricity, which is caused by elimination of interlayer lock-in by incommensurate atomic reconstruction. Although the foundations of superlubricity and the development of 2D lubricants via vanishing friction have been investigated, it is still important to comprehensively reveal the influence of MSL on the interlayer van der Waals (vdW) interactions of 2D lubricants. Here, the contributions of lattice distortions of solute-doped twisted bilayers (Mo, X)S2 (X = Al, Ti, V and Cr) to superlubricity are comprehensively investigated by high-throughput modelling and DFT-D2 calculations. It is revealed that the lattice distortion not only breaks the interlayer balance of repulsion and van der Waals interactions but also yields layer corrugation. These layer-corrugation-induced changes of the interlayer interactions and spacing distances are utilized to optimize lubricity, which matches with the experimental friction coefficients in the order of (Mo, Al)S2 > (Mo, Cr)S2 > MoS2 >(Mo, V)S2 >(Mo, Ti)S2. The evolutions of the band structures show an exponential relationship of the band edge width and layer deformations, paving a path to accelerate the development of advanced superlubricity materials via lattice distortions.

The Localized Corrosion and Stress Corrosion Cracking of a 6005A-T6 Extrusion Profile.

In the present work, the localized corrosion and stress corrosion cracking (SCC) behaviors of a commercial 6005A-T6 aluminum extrusion profile was studied comprehensively. The velocity of crack growth in self-stressed double-cantilever beam (DCB) specimens under constant displacement was estimated, which also provides insight into the local microstructure evolutions at the crack tips caused by the localized pitting corrosion, intergranular corrosion (IGC), and intergranular SCC. Characterizations of local corrosion along the cracking path for a period of exposure to 3.5% NaCl were revealed via optical microscope (OM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The typical features of the pits dominated by the distribution of precipitates included the peripheral dissolution of the Al matrix, channeling corrosion, intergranular attack, and large pits in the grains. The discontinuous cracking at the crack tips indicated the hydrogen-embrittlement-mediated mechanism. Moreover, the local regions enriched with Mg2Si and Mg5Si6 phases and with low-angle grain boundaries presented better SCC resistance than those of the matrix with high-angle grain boundaries, supporting a strategy to develop advanced Al-Mg-Si alloys via interfacial engineering.

Robust Superlubricity and Moiré Lattice's Size Dependence on Friction between Graphdiyne Layers.

Structural superlubricity is a fascinating physical phenomenon that plays a significant role in many scientific and technological fields. Here, we report the robust superlubricating state achieved on the interface of relatively rotated graphdiyne (GDY) bilayers; such an interface with ultralow friction is formed at nearly arbitrary rotation angles and sustained at temperatures up to 300 K. We also identified the reverse correlation between the friction coefficient and size of the Moiré lattice formed on the surface of the incommensurate stacked GDY bilayers, particularly in a small size range. Our investigations show that the ultralow friction and the reduction of the friction coefficient with the increase in size of the Moiré lattice are closely related to the interfacial energetics and charge density as well as the atomic arrangement. Our findings enable the development of a new solid lubricant with novel superlubricating properties, which facilitate precise modulation of the friction at the interface between two incommensurate contacting crystalline surfaces.

Effect of High Strain Rate on Adiabatic Shearing of α+ß Dual-Phase Ti Alloy.

In the present work, the localized features of adiabatic shear bands (ASBs) of our recently designed damage tolerance α+ß dual-phase Ti alloy are investigated by the integration of electron backscattering diffraction and experimental and theoretical Schmid factor analysis. At the strain rate of 1.8 × 104 s-1 induced by a split Hopkinson pressure bar, the shear stress reaches a maximum of 1951 MPa with the shear strain of 1.27. It is found that the α+ß dual-phase colony structures mediate the extensive plastic deformations along α/ß phase boundaries, contributing to the formations of ASBs, microvoids, and cracks, and resulting in stable and unstable softening behaviors. Moreover, the dynamic recrystallization yields the dispersion of a great amount of fine α grains along the shearing paths and in the ASBs, promoting the softening and shear localization. On the contrary, low-angle grain boundaries present good resistance to the formation of cracks and the thermal softening, while the non-basal slipping dramatically contributes to the strain hardening, supporting the promising approaches to fabricate the advanced damage tolerance dual-phase Ti alloy.

Pitting Corrosion of Natural Aged Al⁻Mg⁻Si Extrusion Profile.

With the quick development of the high-speed railway and the service of the China Railway High-speed (CRH) series for almost a decade, one of the greatest challenges is the management/maintenance of these trains in environmental conditions. It is critical to estimate pitting damage initiation and accumulation and set up a corresponding database in order to support the foundations for interactive corrosion risk management. In this work, the pitting corrosion of a nature-aged commercial 6005A-T6 aluminum extrusion profile for 200 days was studied comprehensively. The heterogeneous microstructures were conventionally identified by the in situ eddy current, suggesting which investigated regions to fabricate samples for. After constant immersion for 240 h in 3.5 wt % NaCl, the shapes and depths of the pits were captured and measured by optical microscope (OM) and three-dimensional optical profilometry (OP), providing detailed quantification of uniform pitting corrosion. The typical features of the pits dominated by the distribution of precipitates include the peripheral dissolution of the Al matrix, channeling corrosion, intergranular attack, and large pits in the grains. Due to the high density of continuous anodic and cathodic particles constituted by alloying elements in coarse grains, the number of pits in the coarse grains was the highest while the number in the fine grains was the lowest, indicating that fine grains have the best corrosion resistance. The experimental dataset of the pit depth integrated with its corresponding microstructure would set the benchmark for further modeling of the pit depth and the remaining ductility, in order to manage the damage tolerance of the materials.

Electrocarving during Electrodeposition Growth.

Shape- and size-controlled synthesis of micro/nanostructures is of fundamental importance in many applications of physics and chemistry. Wet chemical growth methods have achieved shape- and size-controlled synthesis of colloidal nanocrystals of various compositions. Compared with wet chemical methods, electrochemical deposition (ECD) yields micro/nanostructures affixed to a substrate, but the resulting structures are poorly controlled. Herein, the controllable electrochemical fabrication of well-defined silver-oxide clathrate micro/nanostructures is realized by intentionally manipulating the previously neglected electrocarving process during electrodeposition growth (MEDEG). Most importantly, the dominance of the electrocarving and the electrodeposition growth process can be immediately manipulated by varying the deposition voltage and/or the composition of the electrolyte. Unique delta-wing-, arrowhead-, and butterfly-like silver-oxide clathrate structures are created using the MEDEG method. MEDEG complements the capability of ECD for controllable synthesis of micro/nanostructures of various materials directly on a substrate. The study details the mechanisms that may enable MEDEG to become a competitive alternative to traditional wet chemical methods in the controllable synthesis of micro/nanostructures. This understanding of MEDEG should motivate applications in fields which demand well-defined micro/nanostructures affixed to a substrate.

Circumventing silver oxidation induced performance degradation of silver surface-enhanced Raman scattering substrates.

Surface-enhanced Raman scattering (SERS) has been recognized as a promising sensing technique in biomedical/biosensing applications and analytical chemistry. Silver (Ag) nanostructures have the strongest SERS enhancement, but suffer from severe enhancement degradation induced by oxidation. Here, we introduce electrochemical reduction of silver oxide to produce Ag SERS substrates on request to partially circumvent the SERS enhancement degradation problem of Ag SERS substrates. Silver oxide nanostructures were first prepared in pure silver citrate aqueous solutions with controllable morphologies depending on the electrodeposition parameters. The transition process from silver oxide to Ag was investigated by density functional theory calculations. Based on the understanding of the transition mechanism, heating treatment, applying reducing agent, and electrochemical reduction were adopted to transform silver oxide to Ag. Notably, no organic agents were introduced neither in the electrodeposition of silver oxide nor electrochemical transformation of silver oxide to Ag. The electrochemical reduction strategy could produce Ag SERS substrates with a 'clean' surface with outstanding SERS performance in a simple as well as cost and time effective manner. Ag SERS substrates can be used in biomedical/biosensing fields. The approach through electrochemical reduction of silver oxide to generate Ag SERS substrate may push forward practical application process of Ag SERS substrates.

Effect of Cold Rolling on the Phase Transformation Kinetics of an Al0.5CoCrFeNi High-Entropy Alloy.

The solid state phase transformation kinetics of as-cast and cold rolling deformed Al0.5CoCrFeNi high-entropy alloys have been investigated by the thermal expansion method. The phase transformed volume fractions are determined from the thermal expansion curve using the lever rule method, and the deformed sample exhibits a much higher transformation rate. Two kinetic parameters, activation energy (E) and kinetic exponent (n) are determined using Kissinger- Akahira-Sunose (KAS) and Johnson-Mehl-Avrami (JMA) method, respectively. Results show that a pre-deformed sample shows a much lower activation energy and higher kinetic exponent compared with the as-cast sample, which are interpreted based on the deformation induced defects that can promote the nucleation and growth process during phase transformation.

Bonding charge density from atomic perturbations.

Charge transfer among individual atoms is the key concept in modern electronic theory of chemical bonding. In this work, we present a first-principles approach to calculating the charge transfer. Based on the effects of perturbations of an individual atom or a group of atoms on the electron charge density, we determine unambiguously the amount of electron charge associated with a particular atom or a group of atoms. We computed the topological electron loss versus gain using ethylene, graphene, MgO, and SrTiO3 as examples. Our results verify the nature of chemical bonds in these materials at the atomic level.