In this paper, the mechanical behavior of a functionally graded nano-cylinder under a radial pressure is investigated. Strain gradient theory is used to include the small scale effects in this analysis. The variations in material properties along the thickness direction are included based on three different models. Due to slight variations in engineering materials, the Poisson’s ratio is assumed to be constant. The governing equation and its corresponding boundary conditions are obtained using Hamilton’s principle. Due to the complexity of the governed system of differential equations, numerical methods are employed to achieve a solution. The analysis is general and can be reduced to classical elasticity if the material length scale parameters are taken to be zero. The effect of material index n, variations in material properties and the applied internal and external pressures on the total and high-order stresses, are well examined. For the cases in which the applied external pressure at the inside (or outside) radius is zero, due to small effects in nano-cylinder, some components of the high-order radial stresses do not vanish at the boundaries. Based on the results, the material inhomogeneity index n, as well as the selected model through which the mechanical properties may vary along the thickness, have significant effects on the radial and circumferential stresses.

Vessel flexure can be triggered naturally by surgical operation, heart pulsation and body movement. It may affect the mechanical behavior of the stent and the existence of a stent may in turn cause vessel injury. In the present study, the finite element method is employed to study the interaction between stent and vessel during vessel flexure. Two- and four-link stents made of stainless steel 316L and magnesium alloy WE43 are considered. Results indicate that longitudinal deformation of the stent can be caused by vessel flexure, and the higher levels of stress exist in the link struts. The existence of the stent could induce significant stress concentration and straightened deformation on vessel wall in the course of vessel flexure. Stents with more links or made of harder materials show greater anti-deformation capability, thus inducing a more severe stress concentration and straightened deformation on the vessel wall. The bending direction also affects the mechanical performance of the vessel-stent system. The results obtained could provide useful information for better stent designs and clinical decisions.

Flexibility is a particularly important biomechanical property for intracranial vascular stents. To study the flexibility of stent, the following work was carried out by using the finite element method: Four mechanical models were adopted to simulate the bending deformation of stents, and comparative studies were conducted about the distinction between cantilever beam and simply supported beam, as well as the distinction between moment-loading method and displacement-loading method. A complete process as implanting a stent including compressing, expanding and bending was also simulated, for analyzing the effects of compressing and expanding deformation on stent flexibility. At the same time, the effects of the arrangement and the number of bridges on stent flexibility were researched. The results show that: 1. A same flexibility index was obtained from cantilever beam model and simply supported beam model; displacement-loading method is better than moment-loading for simulating the bending deformation of stents. 2. The flexibility of stent with compressing and expanding deformation is lower than that in the initial form. 3. Crossly arranging the neighboring bridges in axial direction, can effectively improve the stent flexibility and reduce the flexibility difference in various bending directions; the bridge number, has proportional non-linear correlation with the stent rigidity as well as the maximum moment required for bending the stent.

A multi-scale strategy is employed in the paper to investigate the thermo-mechanical properties of 2.5D angle-interlock woven shape memory polymer composites (SMPCs). In the study, the mesoscopic model of 2.5D woven SMPCs and microscopic model of yarns are firstly developed. After that, the themo-viscoelastic constitutive relationship of the yarn is described in the form of hereditary integral and the parameters of relaxation moduli are obtained from nonlinear fitting of Prony series based on the results of finite element method (FEM). Based on the multi-scale models and the constitutive relationship, the effects of warp and weft arranged densities on viscoelastic properties of 2.5D woven SMPCs are studied in detail. Finally, the shape memory behavior along the warp direction in small strain region is also analyzed. The research in the paper lays a foundation for design and application of woven SMPCs in engineering.

This study provides a solution for the bass extension of a microspeaker system in a mobile device that involves using a resonant combination of a front chamber and a rectangular, long, pipe-shaped port. The efficient resonant coupling of the microspeaker system to the acoustic load in this structure enables a microspeaker with modest cone displacement to achieve a high sound pressure level (SPL) and bass extension below the resonance of the microspeaker in free air, and the total dimensions of the structure are minimized. A combination of electro-mechanic-acoustic and finite element methods was applied to determine the SPL and bass extension levels for mobile devices. Simulation results show acceptable agreement with experimental results. A suitable extended-range microspeaker system was applied in a 10 inch tablet. The audio frequency response could be extended from 630 to 300 Hz with the greatest loudness. As much as possible add low bound frequency extension to make the article more clear. Finally, five cases of parameter settings for the front chamber volume, rear chamber volume, rectangular pipe-shaped port, cross-sectional area, and opening area were studied. The results can be applied for optimizing a suitable extended-range microspeaker system.

A modified bi-layer beam model is proposed to study the fracture-dominated scratch process of the brittle material with surface modification layer considering residual stress. The nonlinear analytical solution of the energy release rate is derived considering the graded distribution of the elastic modulus and residual stress. Finite element analysis is also conducted. Both analytical and numerical results show that the graded distribution of the material properties and residual stress plays an important role in the fracture process. Based on the inverse analysis, the proposed model could provide a convenient way to determine the energy release rate of materials possessing a surface modification layer.

An approach is presented for solving membrane vibration problems using an integrated scheme consisting of the Craig-Bampton (CB) reduction technique and a 2D dynamic infinite element modeling (DIEM) method. In the proposed CB-DIEM scheme, the substructure domain is partitioned into multiple layers of geometrically-similar infinite elements (IEs) which use only the data of the boundary nodes. A convergence criterion based on the first invariant of the DIEM mass matrix is used to determine the optimal parameters of the CB-DIEM scheme, namely the proportionality ratio and number of layers in the DIEM partitioning process and the number of retained frequency modes in the CB reduction method. Furthermore, in implementing the CB method, the inversion of the global stiffness matrix is calculated using only the stiffness matrix of the first element layer. Having reduced the DIEM model, a coupled DIE-FE algorithm is employed to model the dynamic problems of the full structure, which removes the respective methods disadvantages while keeping their advantages. The validity and performance of the proposed CB-DIEM method are investigated by means of three illustrative problems.

The present analysis has been developed to investigate the heat transfer phenomenon in peristaltic flow of Carreau fluid in a curved channel with rhythmic contraction and expansion of waves along the walls (similar to blood flow in tubes). Magnetic field is imposed in radial direction. The heat transfer aspect is further studied with viscous dissipation effect. The curved channel walls are influenced by flow and thermal partial slip. In addition the flow stream comprised porous medium. The system of relevant non-linear PDEs have been reduced to ODEs by utilizing the long wavelength approximation. The striking features of flow and temperature characteristics under the involved parameters are examined by plotting graphs. The generation of fluid temperature and velocity due to viscous dissipation and gravitational efforts are recorded respectively. Moreover indicated results signify activation of velocity, temperature and heat transfer rate with Darcy number.

This work analyzes the pressure driven flow of a power law fluid in a slit microchannel of asymmetric walls with electroviscous effects. The steady state Cauchy momentum and the Poisson-Boltzmann equation are solved for the velocity and the potential distribution inside the microchannel. The Debye-Huckel approximation as applicable for low zeta potentials is not made in the present work. The unknown streaming potential is solved by casting the governing equations as an optimization problem using COMSOL Multiphysics. This proposed method is very robust and can be used for a wide variety of cases. It is found that the asymmetry of the zeta potential at the two walls plays an important role on the streaming potential developed. There is a unique zeta potential ratio at which the streaming potential exhibits a maxima for both Debye-Huckel parameter and the power law index. Shear thinning fluids exhibit a stronger dependency of the streaming potential on asymmetry of the zeta potential than shear thickening fluids. For Newtonian fluids narrow slit microchannels develop larger streaming potentials compared to wider microchannels for a given asymmetry.

Full-scale simulations of a (Magnetorheological) MR damper are carried out for revealing its hysteretic behaviors associated with implementation of semi-active control using the routine of computational fluid dynamics. By virtue of the structural symmetry of the MR damper, a two-dimensional configuration for finite element simulation is built up. Herschel-Bulkley model is employed to represent the property of the MR fluid, of which the control parameters and their relevances to the input current are addressed. Typical cases involving sinusoidal and irregular displacements, steady and transient currents loaded upon the MR damper are investigated. Numerical investigations reveal that the damper force has a positive correlation with input current, excitation amplitude and excitation frequency. The full-scale simulation is proved to exhibit a sound accuracy through the validation of experimental data. It provides a logical manner revealing the true performance of MR dampers under desirable operating modes in practice, and can be readily integrated with the gain design of the associated semi-actively controlled structure. This progress bypasses the technical challenge inherent in the traditional tests with low-frequency cyclic loadings due to the limitation of experimental setup. Besides, comparative study between two-dimensional and three-dimensional configuration simulations of the MR damper shows that former has a better applicability, which can be carried out on a low-cost platform.

Free convective flow and heat transfer of nanofluid close to the inclined plate immersed in the porous medium under the effects of uniform magnetic field and solar radiation has been studied. Boundary-layer approach, Boussinesq approximation and two-phase nanofluid model have been used for a formulation of the governing equations taking into account convective-radiative heat exchange with an environment. The local similarity method has been adopted for the analysis of the considered phenomenon. The obtained equations have been solved numerically using MATLAB software. The effects of control characteristics on profiles of velocity, temperature and nanoparticles volume fraction as well as Nusselt number have been studied in detail.

This study aims at improving the performance of a centrifugal pump by using different angular diffusers on the downstream side of the centrifugal pump impeller. Numerical and experimental studies have been carried out on different vaned and non-vaned diffuser with three different wall divergence angle (α) of 0°, 5° and 10° to achieve that purpose. The data analyses show good agreement between the numerical and experimental results. They reveal profound effect of the divergence angle (α) of angular vaned diffuser on the head and overall efficiency of centrifugal pumps especially at high flow rates as they broaden operating region of the centrifugal pump. In fact it is found that the head and overall efficiency of impeller with vaned diffuser α = 10° enhance by 15.4 and 9 percent respectively compared to that of centrifugal pump with no vaned diffuser at high flow rates. Furthermore the head and overall efficiency of impeller with vaned diffuser α = 10° increase by 5.7 and 7 percent respectively in comparison with the impeller with vaned diffuser α = 0°.