The mechanism of external pressure suppressing dendrites growth in Li metal batteries

Li metal is considered an ideal anode material for application in the next-generation secondary batteries.However,the commercial application of Li metal batteries has not yet been achieved due to the safety concern caused by Li dendrites growth.Despite the fact that many recent experimental studies found that external pressure suppresses the Li dendrites growth,the mechanism of the external pressure effect on Li dendrites remains poorly understood on the atomic scale.Herein,the large-scale molecular dynamics simulations of Li dendrites growth under different external pressure were performed with a machine learning potential,which has the quantum-mechanical accuracy.The simulation results reveal that the external pressure promotes the process of Li self-healing.With the increase of external pressure,the hole defects and Li dendrites would gradually fuse and disappear.This work provides a new perspective for understanding the mechanism for the impact of external pressure on Li dendrites.

Thermal instability and dynamic response analysis of a tensioned carbon nanotube under moving uniformly distributed external pressure

Single-walled carbon nanotubes(SWCNTs)are receiving immense research attention due to their tremendous thermal,electrical,structural and mechanical properties.In this paper,an exact solution of the dynamic response of SWCNT with a moving uniformly distributed load is presented.The SWCNT is modelled via the theories of Bernoulli-Euler-thermal elasticity mechanics and solved using Integral transforms.The developed closed-form solution in the present work is compared with existing results and excellent agreements are established.The parametric studies show that as the magnitude of the pressure distribution at the surface increases,the deflection associated with the single walled nanotube increases at any mode whilst a corresponding increase in temperature and foundation parameter have an attenuating effect on deflection.Moreover,an increase in the Winkler parameter,as well as a decrease in the SWCNT mass increases its frequency of vibration.Furthermore,an increase in the speed of the external agent decreases the total external pressure as a result of the removal of dead loads.The present work is envisaged to improve the application of SWCNT as nanodevices for structural,electrical and mechanical systems.

Buckling response of offshore pipelines under combined tension, bending, and external pressure

The buckle and collapse of offshore pipeline subjected to combined actions of tension, bending, and external pressure during deepwater installation has drawn a great deal of attention. Extended from the model initially proposed by Kyriakides and his co-workers, a 2D theoretical model which can successfully account for the case of simultaneous tension, bending, and external pressure is further developed. To confirm the accuracy of this theoretical method, numerical simulations are conducted using a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness of this theoretical method. The model is then used to study the effects of several important factors such as load path, material prop-erties, and diameter-to-thickness ratio, etc., on buckling behaviors of the pipes. Based upon parametric studies, a few significant conclusions are drawn, which aims to provide the design guidelines for deepwater pipeline with solid theoretical basis.

Distribution laws and effects analysis of casing external pressure taking elastic parameters matching into account

Distribution laws of casing external pressure,which are obtained by different scholars in different conditions,are not the same.Thus,a model to calculate the external pressure of casing is established with finite element method.In the model a contact is built between the outer wall of the casing and the inner wall of the cement sheath.The casing external pressure can be got through extracting contact force of results.The numerical results and analysis show that:The largest casing external pressure exists in the direction of minimum horizontal stress of formation rather than in the direction of the maximum horizontal stress.There exists such matching between the cement sheath elastic modulus and formation elastic modulus:When the elastic modulus of the cement sheath is small,reducing its value is conducive to reduce the casing external pressure and to prolong casing service life.When the elastic modulus of the cement sheath is large,increasing its value is conducive to reduce the casing external pressure and to prolong casing service life.The casing external pressure will become large with the increase of Poisson's ratio of cement sheath.With the increase of the degree of the formation stress unevenness,the maximum casing external pressure increases and the smallest external decreases.The increasing of the non-uniformity degree of formation stress makes the non-uniformity degree of casing external pressure and the risk of casing failure increase.The study can provide certain reference for drilling workers to take measures to prolong service life of casing.

An analytical investigation of the collapse of asymmetrically corroded pipes under external pressure

This paper presents an analytical investigation of elastic collapse of asymmetrically corroded rings under external pressure when both internal corrosion and external corrosion exist.Governing equations are derived for membrane inextensible and membrane extensible cases;a full continuity condition is rigorously derived by the Euler-Bernoulli beam assumption.Comparison with finite element analysis(FEA)shows good agreement for load-displacement curves but membrane extensibility should be included to accurately predict the initial deformation phase,although the discrepancy for both the inextensible and extensible models vanishes for larger deformation phases.By the perturbation technique,the initial load-displacement slope is calculated,and extensive parametric analysis shows complicated dependency of this slope on the misalignment parameter and the angular extent of corrosion.We also present an infallible semi-analytical perturbation solution for both homogeneous and inhomogeneous cases by the Lyapunov arbitrary small-parameter method and show that the resulting power series always converges;then a mathematical argument of analyticity has been presented to illustrate that the so-called homotopy analysis method in the literature converges when the convergence controlling parameter is lying in(-2,0).This paper serves to enhance the understanding of asymmetrically corroded rings and it is mainly relevant to offshore engineering.

Mechanical Performance of Bio-inspired Bidirectional Corrugated Sandwich Pressure Shell Under External Hydrostatic Pressure

This paper aims to enhance the compression capacity of underwater cylindrical shells by adopting the corrugated sandwich structure of cuttlebone.The cuttlebone suffers uniaxial external compression,while underwater cylindrical shells are in a biaxial compressive stress state.To suit the biaxial compressive stress state,a novel bidirectional corrugated sandwich structure is proposed to improve the bearing capacity of cylindrical shells.The static and buckling analysis for the sandwich shell and the unstiffened cylindrical shell with the same volume-weight ratio are studied by numerical simulation.It is indicated that the proposed sandwich shell can effectively reduce the ratio between circumferential and axial stress from 2 to 1.25 and improve the critical buckling load by about 1.63 times.Numerical simulation shows that optimizing and adjusting the structural parameters could significantly improve the advantage of the sandwich shell.Then,the hydrostatic pressure tests for shell models fabricated by 3D printing are carried out.According to the experimental results,the overall failure position of the sandwich shell is at the center part of the sandwich shell.It has been found the average critical load of the proposed sandwich shell models exceeds two times that of the unstiffened shell models.Hence,the proposed bio-inspired bidirectional corrugated sandwich structure can significantly enhance the pressure resistance capability of cylindrical shells.

Mechanical behavior analysis of high power commercial lithium-ion batteries

In application,lithium-ion cells undergo expansion during cycling.The mechanical behavior and the impact of external stress on lithium-ion battery are important in vehicle application.In this work,18 Ah high power commercial cell with Li Ni_(0.5)Co_(0.2)Mn_(0.3)O_(2)/graphite electrode were adopted.A commercial compress machine was applied to monitor the mechanical characteristics under different stage of charge(SOC),lifetime and initial external force.The dynamic and steady force was obtained and the results show that the dynamic force increases as the SOC increasing,obviously.During the lifetime with high power driving mode,different external force is shown to have a great impact on the long-term cell performance,with higher stresses result in higher capacity decay rates and faster impedance increases.A proper initial external force(900 N)provides lower impedance increasing.Postmortem analysis of the cells with2000 N initial force suggests a close correlation between electrochemistry and mechanics in which higher initial force leads to higher direct current internal resistance(DCIR)increase rate.In addition,for the cell with higher external force,deformation of the cathode and thicker solid electrolyte interface(SEI)film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.In addition,for the cell with higher external force,deformation of the cathode and thicker SEI film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.

Numerical Analysis of Three-Layer Deep Tunnel Composite Structure

To date,with the increasing attention of countries to urban drainage system,more and more regions around the world have begun to build water conveyance tunnels,sewage pressure deep tunnels and so on.However,the sufficient bearing capacity and corrosion resistance of the structure,which can ensure the actual service life and safety of the tunnel,remain to be further improved.Glass Fiber Reinforced Plastics(GFRP)pipe,with light weight,high strength and corrosion resistance,has the potential to be applied to the deep tunnel structure.This paper proposed a new composite structure of deep tunnel lined with GFRP pipe,which consisted of three layers of concrete segment,cement paste and GFRP pipe.A new pipe-soil spring element model was proposed for the pipesoil interaction with gaps.Based on the C3D8R solid model and the Combin39 spring model,the finite element numerical analysis of the internal pressure status and external pressure stability of the structure was carried out.Combined with the checking calculation of the theoretical formula,the reliability of the two finite element models was confirmed.A set of numerical analysis methods for the design and optimization of the three-layer structure was established.The results showed that from the internal GFRP pipe to the outer concrete pipe,the pressure decreased from 0.5 to 0.32 MPa,due to the internal pressure was mainly undertaken by the inner GFRP pipe.The allowable buckling pressure of GFRP pipe under the cover of 5 GPa high modulus cement paste was 2.66 MPa.The application of GFRP pipe not only improves the overall performance of the deep tunnel structure but also improves the construction quality and safety.The three-layer structure built in this work is safe and economical.

均布外压下球形封头屈曲特性研究

This study aims to experimentally and numerically examine the buckling performances of stainless steel spherical caps under uniform external pressure.Three laboratory-scale caps were fabricated,measured,and tested.The buckling behaviors of these caps were investigated through experiments and three numerical methods,namely,nonlinear Riks algorithm,nonlinear bifurcation,and linear elastic analysis.The buckling of equal-radius caps was numerically analyzed with different methods to identify their applicability under different wall thicknesses.The results obtained from the nonlinear Riks algorithm are in good agreement with the experimental results,which means the nonlinear Riks algorithm can accurately predict the buckling performances of spherical caps,including the magnitude of critical buckling loads and the deformation of post-buckling modes.The nonlinear bifurcation algorithm is only suitable for predicting the buckling loads of ultra-thin or large-span caps,and the linear buckling method is inappropriate for predicting the buckling of metal spherical caps.

用于深水石油/天然气加工的海底功能舱的屈曲特性

Due to the complexity of installations and connections of subsea production equipment and the massive structures involved in a challenging environment,the failure of subsea production equipment could induce enormous loss to the safety and reliability of structures in addition to the cost of the oilfield development.One of the challenges that the subsea production structures face,as it moves to ultra-deep water and polar underwater equipment,is to design subsea shell structures capable of withstanding high external pressures.Hence,a subsea function chamber(SFC)has been lately proposed as a viable solution,which has a high level of safety and reliability,and a technique for the subsea production system.This paper presents a general and efficient buckling and collapse analysis strategy.In this work,the SFC is composed of cylindrical and hemispherical shaped steel material.Initial imperfection-based nonlinear buckling analysis has been carried out to investigate the buckling and risks associated with different thicknesses of the structure.Linear and nonlinear static buckling analyses have been carried out using ABAQUS software.By introducing the nonlinear properties of materials,the nonlinear numerical model of SFC is established.The effects of the thickness of differentmodels and the number of stiffeners on the bucklingmodes are discussed.The wall thickness is calculated by the Donnell equation and Timoshenko’s classical method.It has been found that the classical solutions given by the Donnell and Timoshenko equations are more accurate for structures with larger lengths and diam.The thickness and number of stiffeners have a great influence on the ultimate buckling external pressure load of SFC structure.

受均匀外压作用的多个贯穿球壳屈曲研究

This study explored the buckling of multiple intersecting spherical shells.A three-segment spherical shell was designed using the theory of deformation coordination;the design was compared with that of a volume-equivalent cylindrical shell and ring-ribbed cylindrical shell.The numerical results indicated that the buckling capacity of the three-segment spherical shell was superior to those of the other two cylindrical shells.To validate our numerical approach,three laboratory-scale shell models were fabricated.Each model was accurately measured and slowly tested in a pressure chamber;thus,the tested shells were studied numerically.The experimental collapse modes agreed well with numerical results,and the collapse load of the three-segment pressure shell was considerably higher than that of the two cylindrical shells.

Structural Analysis of Timber Gridshell Covered by OSB Panels Considering the Effect of Wind

Timber gridshells have been increasingly gaining attention for combining structural efficiency with an attractive architectural design.The use of timber in this structural system gives freedom to the architectural configuration and implies light and efficient construction.This study presents a methodology for the structural analysis of a gridshell covered by OSB(oriented strand board)panels,taken as a case study,and evaluates the model using finite element analysis.The gridshell’s final geometry was obtained from simulations of the effect of permanent load on the mesh.The structural evaluation was numerically estimated via ANSYS software’s CFX platform,considering the effect of wind on the fluid-structure interaction,as well as the results of a static analysis of the structure,including ultimate and serviceability limit state verifications.To assess the influence of the OSB panels on the gridshell’s behavior,two values of elastic modulus are considered.The analysis of a timber gridshell,which covers a span of 14 m by 28 m,demonstrated that this lightweight structure can be considered rigid,and the increase in stiffness of the OSB panels,used as the structure’s coating,can represent an expressive strength and stiffness gain for this type of gridshell.

Buckle Propagation in Steel Pipes of Ultra-high Strength:Experiments,Theories and Numerical Simulations

In this paper,experimental,theoretical and numerical approaches were employed to scrutinize the buckle propagation events occurring in pipes subjected to external pressure.Two groups of samples with different radius-to-thickness ratios were fabricated using steel pipes of ultra-high strength and were subjected to compression of external pressure in a sealed pressure vessel specially designed and customized for the experiment.Experimental results were recorded through a data acquisition system.For facilitating the theoretical calculations,uniaxial tensile tests were performed on tensile pieces cut from the same pipes to obtain the material properties.It was found from the experimental results that once a buckle is initiated in a pipe,the external pressure dropped to a specific value called buckle propagation pressure and kept at this level until the whole pipe is flattened into a dog-bone shape.Based on the measured material properties and geometric parameters,theoretical solutions were computed using established ring models and shell model,and finite element predictions were also obtained from ABAQUS software.The efficiency and accuracy of the shell model and finite element model were expounded by comparing various theoretical solutions and numerical predictions with the experimental results.With the authenticated shell model and finite element model,a deep insight into the phenomenon of buckle propagation of pressurized long pipes was provided by performing a series of parametric study.