International Journal of Computational Materials Science and Engineering

In this study, we adopt different material models to study the strength and stiffness of menisci of the knee joint using finite element method. The three-dimensional (3-D) knee joint finite element model is constructed based on the Magnetic Resonance (MR) images of a human knee joint, and the strength of menisci is analyzed under a specific vertical loading case. In this paper we categorize and implement three types of appropriate material properties, namely isotropic linearly elastic, transversely isotropic elastic and isotropic hyperelastic for menisci of the knee joint. Different strain energy models are also studied and compared under hyperelastic category. The comparative study demonstrates that the hyperelastic model with Ogden form is more appropriate in modeling menisci of the knee joint. By referring to the test data of different material properties from earlier studies by various researchers, we hope to provide a comparative study leading to appropriate menisci material models and properties for finite element analyses of knee joint structures.

Purpose- This paper describes finite element fatigue damage modeling.

Design/Methodology/Approach- Fatigue life prediction and damage progressive evaluation are analytically studied. We present a numerical implementation of the studied models into the home made finite element code MPEF. Numerical simulations are performed on composite and metallic material. We carried out a parametric study to investigate the influence of model's parameters on the damage accumulation and their sensitivity on its kinetics. Simulations are conducted for two different loading levels to characterize cumulative damage and to study loading sequence effect. A comparative study is performed to characterize the efficiency of the two models to describe the damage evolution for the two different materials.

Findings- Numerical examples are presented to illustrate its performance.

Originality/value- This paper intends to present a comparative study of the damage evolution for metallic and composite material under uniaxial loading. The effect of the loading sequence will be investigated.

Observations are reported on isotactic polypropylene in tensile relaxation tests and in loading–unloading tests followed by relaxation after retraction at temperatures ranging from room temperatures up to 100°C. A two-phase constitutive model is developed for the mechanical response of semicrystalline polymers where crystalline and amorphous phases are treated as viscoelastoplastic continua with different laws of plastic flow. Adjustable parameters in the stress–strain relations are found by fitting the observations. Ability of the model to describe characteristic features of the viscoelastic and viscoplastic behavior of polypropylene at various temperatures is confirmed by numerical simulation and comparison of its results with experimental data in additional tests.

Two dimensional multi-atom Archimedean-like phononic crystals (MAPCs) can be obtained by adding "atoms" at suitable positions in primitive cells of traditional simple lattices. Band structures of solid-solid and solid-air MAPCs are computed by the finite element method in conjunction with the Bloch theory. For the solid-solid system, our results show that the MAPCs can be suitably designed to split and shift band gaps of the corresponding traditional simple phononic crystal (i.e., with only one scatterer inside a primitive cell). For the solid-air system, the MAPCs have more and wider band gaps than the corresponding traditional simple phononic crystal. Numerical calculations for both solid-solid and solid-air MAPCs show that the band gap of traditional simple phononic crystal can be tuned by appropriately adding "atoms" into its primitive cell.

Theoretical approach was developed for description of clathrate hydrates stability area at low and modestly high temperatures on molecular level. The approach permits to account for interactions between guest molecules and dependence of unit cell structure upon guest's sort, temperature and pressure. Non-ideality of the gas phase was accounted using Van-der-Waals equation of state. Within this approach, methane hydrate calculations have been performed both for low temperature and low pressure region (in equilibrium with ice Ih) and for modestly high temperatures and pressures (in equilibrium with liquid pure water). Calculations show the notable dependence of hydrates thermodynamic properties upon the guest-guest interactions. For methane hydrates, the guest-guest interaction energy can reach 10% of the guest-host value. The results of calculations are in good agreement with available experimental data. This method is applicable for accurate prediction of clathrate hydrate stability in a wide range of P–T conditions.

Cluster Variation Method (CVM) is a powerful statistical mechanics means to investigate phase equilibria of an alloy. The advantageous feature of the CVM stems from the fact that wide range of atomic correlations which play an important role at the phase transition is efficiently incorporated into the free energy formula. Hence, configurational fluctuation can be systematically studied through the calculations of correlation functions in the real space and short range order diffuse intensity spectrum in the k-space. However, one of the deficiencies of the conventional CVM is the fact that local lattice distortion (local atomic displacement) is not correctly dealt with. In order to improve such shortcomings, Continuous Displacement Cluster Variation Method (CDCVM) has been developed. In the CDCVM, local lattice distortion is mapped onto the configurational freedom of a multi-component alloy on a rigid (uniformly deformable) lattice. With CDCVM, the applicability of CVM is enlarged and the calculations of diffuse intensity spectrum originating from local lattice distortion can be performed.

The objective of this work is to numerically study the individual and mixed mode fracture behavior of open-cell foams. Three-dimensional tetrakaidecahedron model is adopted and finite element method is employed in analysis. The overall elastic properties of open-cell foams are numerically obtained. Then, modes I, II, III and mixed mode I–II fracture behavior of open-cell foams are numerically predicted respectively, in which both solid/hollow and square/circular strut cross-sections are considered. It is seen that the relationship between the overall critical stress intensity factor and the relative density of foam obeys power law for individual crack problems. Effects of the shape and the topology of strut cross-section are discussed in detail. For mixed mode I–II crack problem, the relationship between K_I/K_IC and K_II/K_IIC is obtained and the effect of the shape of strut cross-section is discussed.

A simple first principle model was developed based on extended Hückel-type orbital calculation, Marcus electron transport theory and two-dimensional-electron-gas model for the treatment of charge transport in conjugated polymers. Though simple and easy to compute, the effect of the applied electric-field is factored in. Based on this, a complete one-dimensional device model with a single layer of conjugated polymer sandwiched between two electrodes was developed with poly(3-hexylthiophene) (P3HT) as a case study. Simulated J-V curves show that π-π charge transport is much more pronounced than intra-chain transport, hence agree with previous findings. Using the same framework, we also calculated the absorption spectra of P3HT by considering the electronic energy barrier for electronic transitions that would satisfy Franck–Condon principle. Absorption spectra closely harmonize to experimental UV-Vis result. The model also reveals intra-chain electronic transitions to be the dominant absorption mechanism. All parameters of the model are obtained from either ab-initio Density Functional Theory (DFT) or Molecular Dynamics (MD) calculations, so that this model is capable of predicting charge transport and light absorption properties of new conjugated polymers without introducing fit parameters.

The DC electrical transport in a quantum well (QW) with parabolic confinement potential (where m and ω_z are the effective mass of electron and the confinement frequency in z direction, respectively) subjected to a crossed DC electric field and magnetic field, is studied theoretically. The scattering by optical phonons is taken into account at high temperatures and strong magnetic fields. We obtained the expression for nonlinear current density (NCD) involving external (electric and magnetic) fields and characteristic parameters of QW. The dependence of NCD on the DC electric field is complicated. The analytical result is computationally evaluated and graphically plotted for a specific parabolic QW of GaAs/AlGaAs. The numerical results show the appearance of maximum peaks satisfying the condition of intersubband magnetophonon resonance (MPR) effect in the presence of a DC electric field. Especially, we show that the effect can be applied in experiment to determine some physical parameters by using magnetic field, such as the numbers of Landau levels for which electrons transfer, the effective mass, the charge of electrons or the confinement frequency characterized for PQW.

The creep behavior of a thick walled hollow circular cylinder, made of aluminum silicon carbide particulate composite material has been investigated in the present study and creep behavior in this case is assumed to follow Sherby's constitutive model. The stress and strain rate distributions of cylinder rotating about its own axis, have been obtained using von Mises and Tresca yield criteria. The effect of pressure on the stresses and strain rates in the cylinder has been investigated and it is observed that with the increase of the internal pressure in the cylinder the strain rate increases. The introduction of external pressure along with the internal pressure causes the strain rates to decrease. It is also observed that the values of effective stress and strain rate obtained using Tresca criterion are higher than those obtained using Mises criterion. Thus it is suggested to use Tresca criterion for the analysis while designing the cylinder.