The reflection of longitudinal micro-rotational wave at the viscoelastically supported boundary of micropolar half-space is studied in this paper. The viscoelastic boundary is described by spring-dashpot model with parallel or serial connection. Both the spring and the dashpot contribute to the displacements and micro-rotation and the boundary conditions include the force stress and couple stress components. From the boundary conditions, the amplitude ratios and phase shifts of reflection waves with respect to the incident wave are obtained. Further, the energy flux ratios of the reflection waves to the incident wave are estimated. In order to validate the numerical results, the energy flux conservation with consideration of the energy dissipation of dashpot is used. Based on the numerical results, the influences of elastic parameters and viscous parameters are studied, respectively. It is found that the elastic parameters and the viscous parameters have evident influences on the amplitude ratio, the phase shift and the energy partition. The causes resulting in these deviations are related with the instantaneous elasticity of spring and the time-delay effects of dashpot.

Existing studies reveal that the shape corners of hexagonal fiber affect the degree of constraint on the matrix material. However, none of these studies included the effect of orientation of hexagonal fibers. In this study, a computational micromechanics model of oriented hexagonal fibers in periodic unidirectional composite materials is established for the determination of effective orthotropic elastic properties of the composite. In the present numerical modeling, the representative unit composite cell including the matrix material and the single oriented hexagonal fiber or random oriented hexagonal fibers is solved by micro-scale finite element analysis with different stress loads and periodic displacement boundary conditions, which are applied along the cell boundary to meet the requirement of straight-line constraint during deformation of the cell. Subsequently, the effective elastic properties of the composite are evaluated for periodic regular packing and random packing using the homogenization approach for investigating the influence of unified orientation and random orientation of the hexagonal fibers on the overall elastic properties of the fiber-reinforced composites. The numerical results are verified by comparing with other available results.

Modal analysis is developed in this paper in order to study the dynamic characteristics of rotating segmented blades assembled with spar. Accordingly, a three dimensional finite element model was built using the three node triangular shell element DKT18, which has six degrees of freedom, to model the blade and the spar structures. This study covers the effect of rotation speed and geometrically nonlinear problems on the vibration characteristics of rotating blade with various pretwist angles. Likewise, the effect of the spar in the blade is taken into consideration. The equation of motion for the finite element model is derived by using Hamilton's principle, while the resulting nonlinear equilibrium equation is solved by applying the Newmark method combined with the Newton Raphson schema. Results show that the natural frequencies increase by taking account of the spar, they are also proportional to the angular rotation speed and influenced by geometric nonlinearity and pretwist angle.

In this study, wave propagation in beams is studied using different beam theories like Euler-Bernoulli, Timoshenko and Reddy beam theories. Dispersion curves obtained for these beam theories are compared with the exact plane elasticity solutions. It is obtained that, there are two branches for Reddy beam theory similar to the Timoshenko beam theory. However, one branch is obtained for Euler-Bernoulli beam theory. The effects of in-plane load on Timoshenko and Reddy beam theories are examined and dispersion curves of the Timoshenko and Reddy beams are compared with exact plane elasticity solution. In Timoshenko beam theory, qualitative difference between the two spectrums has been lost with in-plane loads for some wave numbers.

This work presents a new method to minimize artificial stiffness in linear tetrahedral element using virtual mesh refinement (VRM) method. The basic idea behind this work is to give additional degree of freedom by using internal mesh over the linear tetrahedral element. This local internal mesh and its corresponding equilibrium condition under particular boundary condition are invisible to users or virtual. Using specialized displacement test vectors, strain energy is obtained and used to calculate reduction factor for artificial stiffness. Numerical experiments are performed at the end to briefly qualitatively show performance of our proposed method.

Functionally graded material (FGM) has some particular characteristics due to the gradual variation of physical properties. The study on mechanical behavior of FGM is of great research value. In this work, a large scale FGM which filled with small glass spheres has been prepared by gravity assisted casting technique. The elastic material constants in static condition are measured. One optical experimental method, coherent gradient sensing (CGS), is introduced to study the mechanical behavior of FGM which has variation of material property in power-law. The governing equations of CGS which is used to represent the optics-mechanics relation of the singular field near the point of the outside force are derived based on the power-law asymptotic expansion. The experimental result shows this CGS method as a nondestructive methodology can be used to detect the damage in FGM with high accuracy.

The strain gradient elasticity theory including only three independent material length scale parameters has been proposed by Zhou et al. to explain the size effect phenomena in micro scales. In this paper, the general formulations of strain gradient elasticity theory in orthogonal curvilinear coordinates are derived, and then are specified for the cylindrical and spherical coordinates for the convenience of applications in cases where orthogonal curvilinear coordinates are suitable. Two basic problems, one is the twist of a cylindrical bar and the other is the radial deformation of a solid sphere, are analyzed under the cylindrical and spherical coordinates, respectively. The results reveal that only the material length scale parameter l2 enters the torsion problem, while completely disappears in the problem of radial deformation of a sphere. The size effect of radial deformation of a solid sphere is controlled by the material length scale parameters l1 and l2. In addition, for the incompressible solid sphere especially, only the material length scale parameter l1 enters this radial deformation problem by neglecting the strain gradient terms associated with hydrostatic strains. Predictably, the present paper offers an alternative avenue for measuring the three independent material length scale parameters from bar twisting and sphere expansion tests.

There has been wide-spread use of plane wave theory in muffler design in industry. However, This has led to an underestimation of acoustical performances at higher frequencies. To overcome the above drawback, the finite element and boundary element methods have been developed. Nevertheless, the time consumed in calculating the noise level is unacceptable. Moreover, considering the acoustical effect and necessity of space-constrained situation in industry, a compact design of reverse mufflers which may improve the acoustical efficiency is then proposed.

In this paper, a numerical assessment of rectangular mufflers hybridized with straight/reverse chambers using eigen function, four-pole matrix, and genetic algorithm under limited space is developed. Before the optimization is performed, an accuracy check of the mathematical models for the muffler will be carried out. Results reveal that the noise reduction will increase when the number of chambers increases. In addition, the acoustical performance of the mufflers is reversely proportional to the diameter of the inlet/outlet tubes. Also, the TL of the mufflers will be improved when using more number of target tones in the objective function. Consequently, a successful approach in searching optimal shaped rectangular straight/reverse mufflers using an eigen function and a genetic algorithm method within a constrained space has been demonstrated.

With the aid of the Green's function method and complex function method, the scattering problem of SH-wave by a circular inclusion near the two symmetrically permeable interfacial cracks in the piezoelectric bi-material half -space is considered to obtain the steady state response. Firstly, by means of the image method, the essential function of Green's function is constructed, which satisfies the stress free and electric insulation conditions on the horizontal boundaries in a right-angle space including a circular inclusion and bearing a harmonic out-plane line source force on the vertical boundary. Secondly, the bi-material media is divided into two parts along the vertical boundary. According to continuity condition, the first kind of Fredholm integral equations containing undetermined anti-plane forces are established by “the conjunction method” and “the crack-division technology”, then the integral equations are reduced to the algebraic equations including finite items by effective truncation. Finally, the dynamic stress concentration factor around the edge of circular inclusion and dynamic stress intensity factor at the crack tip are calculated, then the influences of the frequency of incident wave, the length of crack, the position of the crack, the position of circular inclusion, etc. on the dynamic stress concentration factor and dynamic stress intensity factor are discussed.

The study aims to estimate the stress-strain constitutive behavior of intermetallic compounds (IMCs) observed in a solder interconnect from experimental nanoindentation responses through a modified analysis procedure for improved solution robustness based on Cheng and Cheng's and Dao et al.'s models. On the basis of parametric finite element nanoindentation simulation and dimensional analysis together with the concept of representative strain, a set of universal dimensionless functions are established, by which a forward and reverse analysis algorithm are created to predict nanoindentation responses from given elastoplastic properties and vice versa, respectively. The proposed analysis procedure is validated through comparison with the experimental nanoindentation responses and limited literature data. The results show that the proposed analysis procedure is an effective means for plastic property characterization of micro/nanoscale IMCs. The representative strain is found to be 0.056, which differs from the Dao et al.'s and Giannakopoulos and Suresh's estimate. Besides, though generally brittle and hard in nature, the IMCs in a micro/nanoscale thickness show high plasticity, and comprise a yield strength surpassing most typical engineering metals.

Influence of variable viscosity the peristaltic flow of pseudoplastic fluid in a tapered channel is discussed. The effects of magnetohydrodynamics (MHD) are also studied. Asymmetric channel is considered. The relevant problem is first formulated and then non-dimensionalized. The nonlinear different system subject to lubrication approach is solved. Expressions for pressure gradient, pressure rise and velocity are constructed. Graphs reflecting the variations of sundry parameters on pressure rise and velocity are examined. Trapping and pumping phenomena are also studied.

A two-phase flow parametric study on an air induction nozzle with water and air as the working fluids is presented. Liquid was supplied at the pre-orifice with various inlet pressures ranging from 3 to 6 bar. The interaction between air and water at the molecular level at the orifice exit leads to formation of a strong shear layer that is intensified with the increase in inlet pressure. Thus, it is vital to regulate the ratio of the intake air to the supplied liquid so that the generated micro bubbles fit the design criteria. CFD analysis was conducted using the commercial software STAR CCM+ from Siemens and validated against experimental data to investigate the design parameters and their effect on the ALR. A volume of fluid (VOF) method of the RANS models was used to undertake the air-water interaction. Parameters such as the throat, air orifice, and air inlet diameter, along with the diffuser angle, were investigated. It was found that certain parameters such as the throat diameter have a more significant effect on the air/liquid entrainment ratio than other parameters.

In this study, the dynamic stability of double-walled carbon nanotubes (DWCNTs) conveying pulsating viscous fluid located on visco-Pasternak medium is investigated. The effects of small scale are considered using Eringen's non-local theory. The surrounding medium of DWCNT is anticipated as a visco-Pasternak foundation including the normal, shear, and damping forces. The van der Waals (vdWs) force is considered among the inner and outer layers of DWCNT. Three types of temperature changes, i.e. uniform, linear and sinusoidal temperature rise, through the thickness are studied. The equations of motion are obtained using higher order sinusoidal shear deformation shell theory (SSDT), in which the surface effects are included. Dynamical equations of DWCNT are extracted using the energy method and Hamilton's principle. Due to orthogonal conditions, the governing equations are solved based on Bolotin method. The effects of different parameters such as surface stress, non-local parameter, fluid velocity, Knudsen's number, fluid density, dimensions ratio and various temperature loadings on the dynamic stability regions of DWCNTs are discussed.