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A tunnel accommodating a hard X-ray-free electron laser device, a highly vibration-sensitive physics instrumentation, is under construction in Shanghai Zhangjiang High-Tech Park within a typically soft depositing estuary ground. In order to study the influence of ground-borne vibration from surrounding traffic facilities, centrifuge model tests were carried out for the ground-tunnel system and various structural systems for passive vibration reduction inside the tunnel. Eight sets of centrifugal simulation experiments were conducted by changing the mass of different parts of the tunnel and by using vibration-damping rubber at the tunnel interlayer. The vertical vibration propagation decay law in the stratum and the effect of acceleration and vibration reduction measures at both the invert and crown of the tunnel are analysed, compared, and evaluated. The research results show that the energy of vertical vibration decreases gradually as the propagation distance increases; the high-frequency part (40–100 Hz) decays faster than the low-frequency part (0–40 Hz); and the change of the tunnel invert mass has different effects on the vibration at the invert and crown of the tunnel. In addition, laying rubber pads on the invert has no noticeable vibration reduction effect on the centre of the tunnel invert, while laying a rubber strip on the crown of the tunnel has a positive vibration reduction effect on the centre of the tunnel crown in the frequency range 58–100 Hz. Furthermore, the rubber pads in the interlayer have a good damping effect on the centre of the tunnel invert in the frequency band 20–37 Hz. The test results can be used as reference for similar projects. [ABSTRACT FROM AUTHOR]

This study, using Jinan as a case study, systematically investigates the characteristics and geological genesis of loess-like silty clay in the middle and lower reaches of the Yellow River. The primary distribution of loess-like silty clay is revealed through field surveys, laboratory experiments, and previous literature reviews. The chemical and physical properties of the loess-like silty clay were examined, in addition to investigations into its mineral composition, microstructural characteristics, and engineering mechanical properties, in order to enhance comprehension of its attributes and formation mechanisms. The research suggests that the distinctive soil environment in the area has been influenced by numerous instances of the Yellow River overflow and channel shifts over its history, as well as the impacts of climate change, geological factors, and human activities. The primary sources of material for the loess-like silty clay consist of loess, Hipparion Red Clay, and paleosol layers. The discussion also addresses the impact of regional climate on the formation of mineral components. The aforementioned findings hold significant implications for advancing the understanding of historical climatic and paleogeographic shifts, as well as for addressing engineering challenges associated with the distribution of loess-like silty clay. [ABSTRACT FROM AUTHOR]

A mechanochemical model is proposed to investigate the non-uniform oxidation of thermal barrier coatings (TBCs) that involves large inelastic deformation and nonlinear reaction kinetics. The large-deformation theory incorporates the higher-order term of geometric nonlinearity for a more precise description of the deformation and stress evolution in an oxide layer. The effect of stresses on the reaction kinetics is considered, which is expressed as the Eshelby stress tensor to account for the conformational volume change and deformation energy. A nonlinear reaction kinetics is adopted for a more accurate description of the nonequilibrium thermodynamic processes. The 2D simulations reveal a non-uniform oxide growth, three modes of oxide-metal interfacial morphology evolution, and tensile stress concentrations in the oxide scale. These simulation results agree with the experimental observations that cannot be described by the previous models. With the model, it is further demonstrated that a stable interfacial morphology and a significantly reduced tensile stress can be achieved by increasing the creep rate of the oxide and the flatness of the oxide-metal interface. This model thus provides an approach to extend the service time of TBCs. [ABSTRACT FROM AUTHOR]

Achieving excellent strength-ductility synergy is a long-lasting research theme for structural materials. However, attempts to enhance strength usually induce a loss of ductility, i.e., the strength-ductility trade-off. In the present study, the strength-ductility trade-off in duplex stainless steel (DSS) was overcome by developing a bimodal structure using friction stir processing (FSP). The ultimate tensile strength and elongation were improved by 140% and 109%, respectively, compared with those of the as-received materials. Plastic deformation and concurrent dynamic recrystallization (DRX) during FSP were responsible for the formation of bimodal structure. Incompatible deformation resulted in the accumulation of dislocations at the phase boundaries, which triggered interpenetrating nucleation between the austenite and ferrite phases during DRX, leading to a bimodal structure. The in situ mechanical responses of the bimodal structure during tensile deformation were investigated by crystal plasticity finite element modeling (CPFEM). The stress field distribution obtained from CPFEM revealed that the simultaneous enhancement of strength and ductility in a bimodal structure could be attributed to the formation of a unique dispersion-strengthened system with the austenite and ferrite phases. It is indicated that the present design of alternating fine austenite and coarse ferrite layers is a promising strategy for optimizing the mechanical properties of DSSs. [ABSTRACT FROM AUTHOR]

With the rapid development of urban underground space, the depth of working shaft has been gradually becoming deeper to accommodate the underground construction needs. The existing studies for earth pressure distribution of shafts are mainly focused on sandy soils within 30 m. There is a strong need to investigate the earth pressure distribution on deep shafts (more than 30 m) in complicated soil conditions using centrifuge modelling to fill the knowledge gap and provide experimental basis for design. In this paper, geotechnical centrifuge modelling was used to investigate the earth pressure distribution along deep circular shaft structures (with a depth of 100 m) in composite geological strata. Three centrifuge tests on model shafts in layered ground with different thickness of clay and sand were carried out, respectively. Drainage method was used in the experiment to simulate the unloading effect caused by excavation of soils inside the shaft model. The earth pressure distributions along the shaft lining before and after the excavation were investigated. The results were analysed and compared with other existing earth pressure theories. This research provides valuable insights for earth pressure distribution for design of circular deep shafts (e.g. 100 m) in composite geological strata. [ABSTRACT FROM AUTHOR]

To understand the influence of recrystallization on the low-cycle fatigue behavior of directionally solidified nickel-based DZ4 superalloy, crystal plasticity-based finite element (CPFE) analysis was carried out to study the cyclic plastic behaviors. Using the design of experiments (DOE) technique, a series of CPFE simulations were designed and performed for DZ4 superalloy with recrystallized grains to examine the cyclic plastic shear deformation at the carbide/matrix interface, at the recrystallized grain boundary/matrix, and in the matrix. Seven influence factors, i.e., applied strain, strain ratio, carbide modulus, dwell time, misorientation angle, carbide aspect ratio, and carbide size, were considered, and the effects of which were quantitatively evaluated by the maximum accumulated plastic shear strains via CPFE-based DOE analysis. The results showed that carbide and recrystallized grain boundary had competitively significant effects on fatigue crack initiation. Applied strain was the most influential parameter among all the studied parameters. [ABSTRACT FROM AUTHOR]

Randomness in construction material properties (e.g. Young's modulus) can be simulated by stationary random processes or random fields. To check the stationarity of commonly used techniques, three random process generation methods were considered: X n ( t ), Y n ( t ), and Z n ( t ). Methods X n ( t ) and Y n ( t ) are based on a truncation of the spectral representation method with the first n terms. X n ( t ) has random amplitudes while Y n ( t ) has random harmonics phases. Method Z n ( t ) is based on the Karhunen–Loève expansion with the first n terms as well. The effects of the truncation technique on the mean-square error, covariance function, and scale of fluctuation were examined in this study; these three methods were shown to have biased estimations of variance with finite n . Modified forms for those methods were proposed to ensure the truncated processes were still zero-mean, unit-variance, and had a controllable scale of fluctuation; in particular, the modified form of Karhunen–Loève expansion was shown to be stationary in variance. As a result, the modified forms for those three methods are advantageous in simulating statistically homogenous material properties. The effectiveness of the modified forms was demonstrated by a numerical example. [ABSTRACT FROM AUTHOR]

Li-O (Li-air) batteries are among the most promising energy storage technologies due to their high theoretical specific capacity and energy density. Key challenges with this technology include high overpotential losses associated with catalyzing the electrochemical reactions (i.e., oxygen reduction and evolution reactions) at the cathode of the battery. In this contribution, we report through the example of LaNiO that layered nickelate oxide materials with rod-shaped nanostructure exhibit promising electrochemical performance as cathode electrocatalysts for Li-O batteries. We demonstrate the ability to control the nanostructure of LaNiO electrocatalyst at the nanoscale level using a reverse-microemulsion synthesis approach. We show that Li-O batteries with cathodes containing rod-shaped LaNiO electrocatalyst exhibit lower charging potentials and higher reversible capacities when compared to batteries with carbon-only cathodes. Our studies indicate that the enhancement in the battery performance induced by the rod-shaped LaNiO electrocatalyst can be attributed to the fact that LaNiO nanorods (i) facilitate the formation of nanosized LiO particles during discharge, and (ii) promote the electrocatalytic activity toward the oxygen evolution reaction during charging. These findings open up avenues for the utilization of (i) reverse-microemulsion method for controlling the nanostructure of layered oxide materials, and (ii) nanorod-structured nickelate oxides as efficient cathode electrocatalysts for Li-O batteries. [ABSTRACT FROM AUTHOR]

We define the relative local topological pressure for any given factor map and open cover, and prove the relative local variational principle of this pressure. More precisely, for a given factor map π: ( X, T) → ( Y,S) between two topological dynamical systems, an open cover U of X, a continuous, real-valued function f on X and an S-invariant measure ν on Y, we show that the corresponding relative local pressure P( T, f, U, y) satisfies , where M( X, T) denotes the family of all T-invariant measures on X. Moreover, the supremum can be attained by a T-invariant measure. [ABSTRACT FROM AUTHOR]

Ground buildings constructed above metro station have increased very quickly due to the limited land resources in urban areas. In this paper, the seismic response of the Underground subway station-Surrounding soil mass-Ground adjacent buildings (USG) system subjected to various seismic loading is studied through numerical analysis. The numerical model is established in terms of the calculation domain, boundary condition, and contact property between soil and structure based on the real project. The reciprocal influence between subway station and ground adjacent building, and their effects on the dynamic characteristics of surrounding soil mass are also investigated. Through the numerical study, it is found that the impact of underground structure on the dynamic characteristics of the surrounding soil mass depends on its own dimension, and the presence of underground structure has certain impact on the seismic response of ground adjacent building. Due to the presence of underground structure and ground adjacent building, the vertical acceleration generated by the USG system cannot be ignored. The outcomes of this study can provide references for seismic design of structures in the USG system. [ABSTRACT FROM AUTHOR]