A chemo-mechanical model coupled with thermal effect on the hollow core–shell electrodes in lithium-ion batteries

Electrode is a key component to remain durability and safety of lithium-ion（Li-ion） batteries. Li-ion insertion/removal and thermal expansion mismatch may induce high stress in electrode during charging and discharging processes. In this paper, we present a continuum model based on COMSOL Multiphysics software, which involves thermal, chemical and mechanical behaviors of electrodes. The results show that,because of diffusion-induced stress and thermal mismatch, the electrode geometry plays an important role in diffusion kinetics of Li-ions. A higher local compressive stress results in a lower Li-ion concentration and thus a lower capacity when a particle is embedded another, which is in agreement with experimental observations.

Application of the homotopy analysis method to nonlinear characteristics of a piezoelectric semiconductor fiber

Based on the nonlinear constitutive equation,a piezoelectric semiconductor(PSC)fiber under axial loads and Ohmic contact boundary conditions is investigated.The analytical solutions of electromechanical fields are derived by the homotopy analysis method(HAM),indicating that the HAM is efficient for the nonlinear analysis of PSC fibers,along with a rapid rate of convergence.Furthermore,the nonlinear characteristics of electromechanical fields are discussed through numerical results.It is shown that the asymmetrical distribution of electromechanical fields is obvious under a symmetrical load,and the piezoelectric effect is weakened by an applied electric field.With the increase in the initial carrier concentration,the electric potential decreases,and owing to the screen-ing effect of electrons,the distribution of electromechanical fields tends to be symmetrical.

Preliminary study on the determination of the Weibull modulus of strength distribution in quasi-brittle materials

In this paper,how to determine the Weibull modulus of a fracture strength distribution is discussed with its physical implications for quasi-brittle materials.Based on the Markov chain assumption,it is shown that the lifetime(i.e.,the time taken for formation of a critical defect)in a quasi-brittle material can be described by a gamma probabilistic distribution function.Prior to macroscopic failure,the effective number of energy barriers to be overcome is determined by the slope of the energy barrier spectrum,which is equivalent to the Weibull modulus.Based on a fracture mechanics model,the fracture energy barrier spectral slope and Weibull modulus can be calculated theoretically.Furthermore,such a model can be extended to take into account the crack interactions and defect-induced degradation.The predicted Weibull modulus is good agreement with that derived from available experimental results.

Deformation and failure processes of kaolinite under tension:Insights from molecular dynamics simulations

As a primary constituent of soft rocks, kaolinite plays an important role in large deformations of underground structures, which usually leads to serious safety risks. This paper investigates the deformation and failure processes of kaolinite under tension using molecular dynamics simulations. Based on the atomistic scale of these deformation and failure processes and their stressstrain curves, Young's moduli and strengths in three crystal directions and the surface energy of the(001) plane were obtained,which were consistent with theoretical predictions. The number of broken bonds and their corresponding broken sequences were determined. The results of our study indicated that as more bonds break during tension, the initiation of crack led to a sharp decrease in stress. We also explored the influence of temperature on the mechanical properties of kaolinite, which indicated that as temperature increased, the tensile strength and Young's modulus decreased.

Prediction of Failure Modes during Deep Drawing of Metal Sheets with Nickel Coating

To optimize the process parameters, it is necessary to exactly predict failure modes during deep drawing of coated metal sheets, where two main failure forms are fracture and wrinkling. In this paper, finite element simulations based on continuous damage mechanics were used to study the failure behavior during a cylindrical deep drawing of metal sheets with nickel coating. It is shown that taking the effect of blank holder force into account, these two failure modes can be predicted. The simulation results are well consistent with that obtained from experiments.

Mathematical Analysis on the Uniqueness of Reverse Algorithm for Measuring Elastic-plastic Properties by Sharp Indentation

The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In this paper, mathematical analysis on a reverse algorithm from Dao model （Dao et al., Acta Mater., 2001, 49, 3899） was carried out, which thought that only when 20 ≤E＊/σ0.033≤ 26 and 0.3n≤ 0.5, the reverse algorithm would yield two solutions of n by dimensionless function Π2. It is shown that, however, there are also two solutions of n when 20≤E＊/σ0.033≤ 26 and 0≤n0.1. A unique n can be obtained by dimensionless function Π3 instead of Π2 in these two ranges. E and H can be uniquely determined by a full indentation curve, and σy can be determined if n is unique. Furthermore, sensitivity analysis on obtaining n from dimensionless function Π3 or Π2 has been made.

Determination of the Fracture Toughness of Glasses via Scratch Tests with a Vickers Indenter

Fracture toughness is an important index in safety evaluation for materials and structures.Its convenient and accurate characterization has attracted extensive attention.For small specimens,traditional testing methods of fracture toughness are not suitable due to limitations in sample size and shape.In this work,a new formula is proposed to determine the fracture toughness of glasses using scratch tests with a Vickers indenter based on dimensional analysis and finite element analysis.Fracture toughness of glasses could be calculated with elastic modulus,crack depth of scratched materials and normal force applied during the scratch tests.The effects of plastic deformation and interfacial friction between the Vickers indenter and scratched materials are considered,and the crack shape is consistent with experimental observations.The proposed formula is verified by comparing the fracture toughness of soda-lime and borosilicate glasses obtained from scratch tests with those obtained via indentation tests.This work provides an alternative method to determine the fracture toughness of glass materials.