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Silicon oxide (SiOx) material is gradually developing as a promising alternative to silicon due to a better trade‐off in terms of volume expansion and theoretical capacity. However, the low conductivity and the instability of the electrode–electrolyte interface caused by the penetration of the fluorine anion (F−) severely affect the stability of the solid electrolyte interphase (SEI), ultimately leading to capacity loss and cycling instability. In this work, an "ionic fence" idea is proposed, which effectively inhibits the shuttle of F− and promotes the stability of the SEI. Based on this, a dense and orderly silicon‐based interconnected assembly covered by a TiN protective ionic fence is designed using melt‐assembly technique and nitridation strategy. After 1000 deep cycles, the capacity can be maintained at 431.7 mA h g−1, the average Coulombic efficiency can reach 99.69% throughout the cycling process, and even a steady state after 2000 cycles, showing excellent electrochemical stability. Finite element analysis reveals that the TiN fence, as a stress management layer, effectively constrains the volume expansion of materials and improves the mechanical structural stability of the particles in the fully lithiated state, thus ensuring long‐term cycling stability. Selective fence design for material interface has great universality and development potential in building stable electrode materials. [ABSTRACT FROM AUTHOR]

To develop a geological nuclear waste disposal facility from scratch, the hydro-mechanical properties of the host rock are fundamental for its initial construction, long-term system evolution, closure, and post-closure phases. In this paper, a transversely isotropic damage constitutive model was developed to describe the nonlinear behavior of clayey rock, based on the modified Drucker–Prager Cap model. Considering the self-sealing effect, a hydraulic conductivity evolution law of typical clayey rock was established based on in situ measurements. These theoretical models were further implemented in the finite element method software ABAQUS FEA (Finite Element Analysis) utilizing the subroutine USDFLD, which is a user subroutine to redefine field variables at a material point in ABAQUS. The hydro-mechanical response of an underground research laboratory during excavation and operation was reproduced by three-dimensional numerical simulation to validate the proposed models. The results highlighted that the developed theoretical model could efficiently reproduce the evolution of pore water pressure and deformation, compared to the in situ measurements in the excavation damaged/disturbed zone (EDZ) and hydraulic disturbed zone (HDZ) driven by tunnel excavation. Highlights: A damage constitutive model and a permeability evolution law are developed. Theoretical models are implemented in the software ABAQUS FEA. Hydro-mechanical responses of an underground research laboratory during excavation and operation are simulated. Comparison with the in-situ measurements highlights the theories' efficiency. [ABSTRACT FROM AUTHOR]

This study investigated the flexural behavior of ultra‐high‐performance concrete decks with an innovative joint of fiber continuity at the joint interface. An experimental program with 21 specimens was designed and tested. Four types of joints were studied, that is, lap‐spliced rebar, fiber continuity, combination of fiber continuity and lap‐spliced rebar, and combination of additional reinforcement and lap‐spliced rebar. Finite element models were built and benchmarked using the test results. The influence of reinforcement ratio and interfacial fiber content was investigated. Experimental and numerical results showed that a joint with a combination of fiber continuity and lap‐spliced rebar achieved similar flexural performance as cast‐in‐place decks. In addition, the design theory of the Swiss code (SIA 2052‐2016) was recommended with promising accuracy in estimating the flexural capacity of precast ultra‐high‐performance concrete decks, based on the tensile strength of joint interface with various fiber contents. [ABSTRACT FROM AUTHOR]

An understanding of the creep behavior of clayey rocks is considered fundamental for further development in the fields of nuclear waste underground disposal, underground mine design, strata control, and many other geological phenomena occurring in the earth's crust. In this research, we performed a series of long-term triaxial compressive tests on a typical clayey rock, which confirmed its high creep potential beyond the creep threshold. Further analysis of the creep mechanism of this clayey rock indicated that two effects—strengthening and damage—are accompanied by the creep process. Additionally, based on the overstress theory and Drucker–Prager cap model, we developed a novel constitutive model considering two creep reference surfaces—cohesion and consolidation. Meanwhile, laws to reflect the strength and damage effect during creep were established and applied to the above constitutive model. Finally, the above theoretical studies were implemented in the finite element method software ABAQUS FEA using the subroutines CREEP and USDFLD. Some theory parameters were verified through back analysis. A comparison between the experimental results and numerical simulations confirmed the superiority of the established theoretical model. Highlights: Clayey rock exhibits high creep potential beyond the creep threshold. Two effects—strengthening and damage—are accompanied by the creep process. A novel creep constitutive model was established. Strengthening and damage laws during creep were developed. Model numerical implementation and parameters determination. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to explore the numerical simulation of damage process and results of a new environmentally friendly material, recycled coarse aggregate self-compacting concrete (RCASCC). Random aggregate model of mesoscopic viewpoint was used for the experimental simulation of RCASCC. Results show that the specimens with 50% substitution rate exhibited the best performance among the specimens (i.e., with rates of 25%, 50%, 75%, and 100%). The stress-strain curves after dimensionless treatment were fitted using the uniaxial compressive principal equation of concrete with control parameters a = 0.9 and b = 11, and the fitting degree of the curve was relatively good. Meanwhile, the change process of internal cracking was shown intuitively. The crack expansion process became more obvious in the specimens and beams with a high substitution rate of RCA. The simulation results of the bending process of RCASCC beams analyzed by the concrete damaged plasticity (CDP) model and extended finite element (XFEM) were compared with the test results. Both simulation results validated the applicability of the CDP model and XFEM in the mechanical tests of RCASCC and can provide valuable reference for future research on the mechanical properties of recycled aggregate self-compacting concrete. [ABSTRACT FROM AUTHOR]

The stability of a fractured rock mass around a subsurface opening is critical to tunnel excavation. The traditional underground excavation analysis is based on a continuum description of randomly distributed discrete pre-existing fractures. In contrast to this, we have developed an improved hybrid finite element method (FEM) to investigate the stability of fractured rocks around an excavation by incorporating the outputs into the FEM codes. The proposed model consists of a discrete fracture network (DFN) model and cohesive zone model (CZM). The DFN model automatically generates a fracture network with a given fracture opening distribution and provides grid generation strategy to the FEM. The CZM captures material failure and intersection and surface contacts through the fracture element with different constitutive laws. As a case study, a DFN model was formulated for the underground excavation at Jinping Hydropower Station, in light of the input requirements of our model, and its deformation analysis was performed. The comparison analysis of rock deformation was made for excavation in both intact rock mass and fractured rock mass under the same boundary conditions. The numerical results show that two different modes of rock failure exist in these two rock masses and that intense deformation at the fractures intersected by the tunnel is responsible for fractured rock mass instability. The proposed approach was verified using data from field investigations. A larger displacement can be produced if the rock mass is weakened by a key block. A sensitivity analysis was carried out to investigate the effects of different model parameters on deformation variations. This study provides an insightful understanding of the deformation of fractured rock mass during tunnel excavation. [ABSTRACT FROM AUTHOR]

Abstract In-situ stress is one of the most important factors affecting the safety and stability of underground excavations. Past measurement results show that the magnitudes and directions of in- situ stresses vary substantially in different lithological formations. However, the relationship between stresses distribution and rock mechanical properties is still unclear. In this paper, the stress distribution in interbedded strong and weak layers was analytically studied based on linear elastic mechanics. Derived solutions were validated by comparison with Finite Element Method (FEM) results and field measurement results. Comparisons show that analytical results agree with the numerical results, and the maximum difference is less than 1%. The maximum difference between the analytical results and field measurements is 10.8%. Furthermore, the derived solution was used to evaluate the stress distribution in a geologically abnormal area in the Neelum-Jhelum (NJ) hydroplant project. Stress concentration state in strong layers changes as the strata change from sub-vertical to sub-horizontal, and the stress state in the sub-horizontal strata greatly favours rockburst according to the Turchaninov criterion. The change in stress concentration state might be the underlying reason for the severe rockburst in the abnormal structure area in the NJ project. [ABSTRACT FROM AUTHOR]

In situ stress is one of the most important parameters that affect rock mass stability during tunnel excavation. High in situ stress may induce a series of geohazards, such as rockburst in strong rock and squeezing in weak rock. This paper presents a case study of a tunnel excavated using a tunnel-boring machine across interbedded strong and weak rock layers under high in situ stress in Pakistan. To estimate the induced geohazards during tunnel excavation, in situ stress was measured and the stability of the tunnel was analyzed using the finite element method. In situ stress measured in the strong rock layers shows that the maximum compressive stress is very high, and its direction is almost perpendicular to the tunnel axis. Using a simple analytical method, stress distribution in weak layers was determined and the results show that the magnitude of the maximum compressive stress in the weak layers is much less than that in strong layers, and the direction is almost parallel with the tunnel axis. The FEM simulation reveals that the redistributed stress due to the tunnel excavation is more concentrated in strong layers and less concentrated in weak layers. Both the initial in situ stress distribution and the stress redistribution after tunnel excavation predict geohazard in strong layers rather than in weak layers. This point is consistent with the field records, which indicated that rockbursts were frequent in the strong rock layers and no squeezing occurred in the weak rock layers. [ABSTRACT FROM AUTHOR]

An efficient computational fluid dynamics (CFD) method for simulating the flow and convective heat transfer process of airflow in a tunnel is required to analyze the freezing and thawing of surrounding rock and to apply the results to the design of the insulation layer for a tunnel located in a cold region. Comparisons of experimental data and CFD results using a standard k − ε turbulence model, a wall function, a thermal function and an adaptive finite element method are presented. Comparison of the results indicated that the proposed model and simulation method are efficient at determining the solid-air interface heat coefficient in a thin and infinitely wide horizontal plate and the hydrodynamic and thermal fields in a 3-D cavity. After demonstrating that the necessary validations are satisfied, this paper presents an analysis of the characteristics of airflow and air-rock heat transfer in a cold-region tunnel. [ABSTRACT FROM AUTHOR]

Fatigue cracks were found on a series of end-coped crane runway girders after 14 years of service in a steel mill building in China. Two typical crane runway girders with different spans were studied in this paper. Finite element analyses were conducted to investigate the stress concentration at the coped ends. Analytical results showed the stress concentration effect was highly localized and the stress concentration factor decreased with increasing cope radius and decreasing total depth. The analytical results agreed well with the field measured data. Fatigue tests were conducted to determine the fatigue strength using eight 1/5-scaled end-coped girder specimens. Based on the analytical results and limited test data, the fatigue strength for a maximum principal stress range of 103 MPa at 2 million cycles may serve as a possible design guideline for end-coped crane runway girders using the conventional S-N curves. Procedures for design and evaluation of the fatigue life of end-coped crane runway girders are suggested. [ABSTRACT FROM AUTHOR]

• Elastic field for layered composite rock with excavated tunnels is predicted by a semi-analytical method. • The layer and tunnel are considered as inhomogeneities of different elastic moduli through employing the EIM. • A yield approximate index is used to evaluate safety of layered composite rock with excavated tunnels. • Effects of parameters of the layer and tunnel on the elastic field and plastic zones are discussed. Tunnels excavation in layered composite rock subjected to ground loads to make the best of underground space is an important engineering problem in more and more mega-cities. Such a three-dimensional case, layered composite rock with excavated tunnels, is usually simplified as a two-dimensional plane strain problem in mechanics. The present study reports a Semi-Analytical Method (SAM) to predict elastic field of an excavated layered composite rock with the assistance of the Equivalent Inclusion Method (EIM) that can handle elastic field of the layers and tunnels simultaneously. In the EIM, the layer and tunnel are considered as inhomogeneities of different elastic moduli from the base rock, and the inhomogeneities are further equivalent to inclusions of identical elastic modulus to the base rock but including eigenstrains. Effectiveness of the SAM is examined by the Finite Element Method (FEM) through comparing their results. Moreover, a yield approximate index (YAI) is introduced to evaluate safety of excavated layered composite rock and acoustic emission (AE) event is used to count the number of plastic yield elements. Finally influences of depth of and distance between the tunnels, thickness, elastic modulus, number of the layer, range of ground load on principal stress, YAI , plastic zones are discussed, which may have potentials to provide guidance for practical engineering applications of tunnel excavation. [ABSTRACT FROM AUTHOR]

• Based on semi-analytical method, a novel model for the elastoplastic impact-contact of materials with coatings is developed. • The validity and accuracy of the proposed model are demonstrated by a nano-impact experiment conducted on a 304 stainless steel with Cr coating. • The effects of the coatings and surface roughness of the plasticity of the material are studied. Plastic deformation resulting from high stress exceeding material yield limit widely exists in many mechanical components, especially for those subjected to impact load, which further compromises the accuracy and reliability of the affected parts. Coating technology is an effective way to provides protection for the substrate against the heavy impact load. A novel solution method for simulating the elastoplastic impact-contact of coated medium is presented in the current investigation. The second-order Newmark algorithm is introduced for impact dynamics iteration. The plastic yielding and plastic strain accumulation during impact process are determined by the von Mises yield criteria. The effectiveness of the proposed solution method is demonstrated numerically by the finite element method (FEM) via commercial software and experimentally by a nano-impact test. Impact-contact problems for a rigid spherical punch against a coated medium with either a rough or smooth surface are further studied to illustrate the elastoplastic mechanical response of materials under impact contact load. [ABSTRACT FROM AUTHOR]

Laser etching process of aluminum thin film on polyimide substrate was simulated by the finite element analysis software ANSYS to study the etching results. Theoretical etching profiles of aluminum thin film with different laser parameters were obtained from the simulation, which is in good agreement with experimental results observed by SEM, it shows that a best etching result can be obtained and it corresponded to a set of reasonable parameters. By optimizing such laser etching parameters as laser power and beam scanning velocity, etc., aluminum thin film could be etched ideally without damaging the polyimide substrate. Therefore, the simulation results can be taken as a guide for determination of practical laser etching parameters in order to obtain ideal etching patterns. [ABSTRACT FROM AUTHOR]