Couple Stress Research Articles

Entropy Generation Analysis in Magnetohydrodynamic Couple Stress Nanofluid Flow Through an Oblique Microchannel in a Permeable Medium with Thermal Radiation

The present work examines the flow and thermal energy process in conducting couple stress nanofluid flows through an oblique microchannel. The microchannel is embedded with permeable medium and thermal radiation is implemented. The microchannel boundaries retain the slip boundary conditions. The impact of buoyancy force and magnetic field are incorporated. The temperature dependent heat source effect was also taken into account. The momentum equation has been made by the permeability of the porous medium. The equations are modeled and non-dimensionalized using non-dimensional entities and further solved with the aid of the Runge-Kutta Fehlberg method and the shooting procedure. The detailed discussions about the importance of the effective parameters on entropy generation, the Bejan number have been observed through graphs. The findings of the examination depict that rise in radiation parameter augments the entropy generation and the Bejan number in the channel. The entropy generation and Bejan number diminishes with inflation of the permeability parameter.

稻田株间除草部件有限元模拟

Mechanical weeding in paddy fields is a green and environmentally friendly way to control weeds, which has the advantages of reducing the amount of pesticides and improving the physical structure of the soil. This paper briefly describes the composition and relevant parameters of the mechanical weeding environment in rice fields. Using Creo 5.0, HyperMesh 2017, and LS-PrePost and LS-DYNA software to jointly simulate the interaction process between inverted V-shaped inter-plant weeding component and the soil in the paddy field, the single-point ALE multi-material unit algorithm is used to couple the soil and water with multiple substances, and realize the material movement between the soil and the water layer. Using the penalty function method, a fluid-solid coupling finite element modelled on the interaction between inter-plant weeding components and soil-water was established. The dynamic behavior of the interactions shows that the coupling stress increases and then decreases periodically, and the teeth of the spring cross the soil with a "bending moon (fish scale)" scratch, which can effectively avoid rice seedlings and reduce the injury rate.

The Effect of Rotation on the Heat Transfer of a Couple Stress Fluid in A Nonuniform Inclined Asymmetrical Channel with Inclined MHD

The purpose of this research is to investigate the effects of rotation on heat transfer usinginclination magnetohydrodynamics for a couple-stress fluid in a non-uniform canal. When theReynolds number is low and the wavelength is long, math formulas are used to describe the streamfunction, as well as the gradient of pressure, temperature, pressure rise and axial velocity perwavelength, which have been calculated analytically. The many parameters in the current modelare assigned a definite set of values. It has been noticed that both the pressure rise and the pressuregradient decrease with the rise of the rotation and couple stress, while they increase with anincrease in viscosity and Hartmann number. The explanation of parameters is shown graphicallyby a series of figures using "MATHEMATICA".

Couple Stress Sodium Alginate-Based Casson Nanofluid Analysis through Fick’s and Fourier’s Laws with Inclined Microchannel

Casson nanofluid plays a vital role in food industries with sodium alginate nanoparticles. That is why many researchers used Casson nanofluid in their study. Due to this, the main objective of this study is to investigate the inclined microchannel flow of a Casson nanofluid based on sodium alginate (SA) under a few stresses. Because the plate at y = d is stationary and the plate at y = 0 is in motion, the fluid flows. Physically existent things utilize partial differential equations as a method of derivation. By using dimensionless variables, the underlying PDEs are dimensionless. Applying Fourier’s and Fick’s laws to the time-fractional model makes the classical model dimensionally stable by generalization. A generalized fractional model is solved using the Laplace and Fourier integral transformations. In addition, the parametric influence of other physical elements, such as the Casson parameter, coupling velocity, temperature, and stress parameters, is considered (Grashof, Schmidt, and Prandtl numbers). Concentration distributions are shown using graphs and discussed with accompanying text. We compute and describe the Sherwood number, rate of heat transfer, and skin friction. It is concluded that skin friction and Nusselt number can be enhanced by adding nanoparticle. Also, the fractional derivative makes the study more realistic by incorporating Fick’s and Fourier’s laws as compared to the classical one.

Coupling stress fields and vacancy diffusion in phase-field models of voids as pure vacancy phase

High vacancy concentrations in crystals may lead to formation and growth of voids, which is connected to swelling under irradiation and degradation of material properties. Recent experimental work suggests that vacancy condensation may also be involved in nucleation and evolution of porosity in early stages of ductile fracture. Mostly in the realm of irradiation effects, void formation and growth has been simulated with phase-field methods, where voids are treated as pure vacancy phases. Since vacancies induce an eigenstrain field, it is well-known that the evolution of vacancy concentrations is coupled to the elastic stress field. However, the few existing elastically coupled diffuse interface models of void growth seem to face a conceptual problem in the diffuse interface; in the center of which they predict the highest eigenstrains, which results in unrealistically high, fluctuating stresses. In the current work, we present a new model for coupling elastically driven vacancy diffusion with a diffuse interface model of void surfaces, which overcomes the named short-comings and closely reproduces the sharp interface solution. This is achieved by making the eigenstrain a function of the non-conserved order parameter used to distinguish the crystal and void phase. The model is verified for two-dimensional example problems by comparison to the analytical solution of the according sharp interface model. Eventually, the model is used to show the impact of elasto-diffusional coupling on void growth in mechanically loaded systems. We analyze the model with regard to the bi-stable energy landscape and discuss limitations and future prospects of the approach.

A study on the crack presence effect on dynamical behaviour of bi-directional compositionally imperfect material graded micro beams

This work uses the Quasi-3D (Q3D) shear and normal deformation beam concept in combination with the length scale capturing theory through the “Modified Couple Stress Theory” (MCST) and the novel computational approach namely, Differential Quadrature Finite Element Method (DQFEM) to investigate free vibratory conducts of an imperfect BD-FG microbeams with a crack. To obtain the relevant governing equations, the Lagrange's rule is utilized. “The differential quadrature” (DQ) and “Gauss-Lobatto quadrature” procedures for weighting coefficient matrices are used to easily construct the mass and stiffness matrices. The Gauss-Lobatto node scheme is used to determine the griding knots. In order to show the efficiency and exactness of the described numerical resolution method, the attained outcomes are authenticated with the similar results found in the literature. The effects of the crack position, crack depth, beam thickness by material length scale aspect, the volume fraction of material imperfection, edge supports state types, length through thickness factor, and the two-way material grading indexes on the nondimensional natural frequencies of 2D porous FG microbeams are inspected. This work will provide a numerical basis for the design of FG microstructures in the field of micromechanics. These findings can be used to construct porous FG microstructures in engineering.

Investigation of stepped microbeam vibration motions according to modified couple stress theory

Abstract In this study, linear and nonlinear vibration movements of simply supported stepped microbeams placed in a magnetic field have been analyzed using Modified Couple Stress Theory. By taking into account the step radius ratio, step-change position, and material size parameter, the equations of motion of the stepped-microbeam are obtained using the Hamilton principle. The resulting equations of motion are nondimensionalized to eliminate dependence on material type and geometric structure. The approximate solution of the dimensionless equations of motion is calculated using the method of multiple scales, one of the perturbation methods. The solution stages of the study are divided into two separate parts as linear and nonlinear problems. Firstly, the linear issue of the stepped microbeam is addressed. The natural frequencies of the system are derived by solving the linear problem. Linear and nonlinear effects of step radius ratio, step-change position, and microbeam coefficient are investigated and frequency-amplitude graphs are presented. The resonance state where forcing frequency is equal to natural frequency is examined and stability analysis has been made.

Thermomechanical Oriented Reliability Enhancement of Si MOSFET Panel-Level Packaging Fusing Ant Colony Optimization With Backpropagation Neural Network

Considerable advancements in power semiconductor devices have resulted in such devices being increasingly adopted in applications of energy generation, conversion, and transmission. Hence, we proposed a Fan-Out Panel-Level Packaging (FOPLP) design for 30V Si based Metal Oxide Semiconductor Field Effect Transistor (MOSFET). To achieve superior reliability of the packaging, we applied the Nondominated Sorting Genetic Algorithm with elitist strategy (NSGA-II) and Ant Colony Optimization–Backpropagation Neural Network (ACO–BPNN) to optimize the design of redistribution layer (RDL) in FOPLP. We first quantified the thermal resistance and thermo-mechanical coupling stress of the designed package under thermal cycling loading. Next, NSGA-II and ACO–BPNN were used to optimize the size of the RDL blind via. Finally, the effectiveness of the proposed reliability optimization methods was verified by performing thermal shock reliability ageing tests on the prepared devices.

Dynamic Characteristics of a Small-Size Beam Mounted on an Accelerating Structure

This study focuses on the nonlinear vibration of a small-size beam hosted in a high-speed moving structure. The equation of the beam’s motion is derived using the coordinate transformation. The small-size effect is introduced by applying the modified coupled stress theory. The equation of motion involves quadratic and cubic terms due to mid-plane stretching. Discretization of the equation of motion is achieved via the Galerkin method. The impact of several parameters on the non-linear response of the beam is investigated. Bifurcation diagrams are used to investigate the stability of the response, whereas softening/hardening characteristics of the frequency curves are used as an indication of nonlinearity. Results indicate that increasing the magnitude of the applied force tends to signify the nonlinear hardening behavior. In terms of the periodicity of the response, at a lower amplitude of the applied force, the response appears to be a one-period stable oscillation. Increasing the length scale parameter, the response moves from chaotic to period-doubling to the stable one-period response. The impact of the axial acceleration of the moving structure on the stability as well as on the nonlinearity of the response of the beam is also investigated.

Numerical Solution for Thermal Elastohydrodynamic Lubrication of Line Contact with Couple Stress Fluid as Lubricant

In this paper, the detail analysis of the influence of thermal and non-Newtonian aspects of lubricant (couple stress fluid) on EHL line contact as a function of slide-roll ratio is presented. The novel low complexity FAS(Full approximation scheme), of Multigrid scheme, with Jacobi dipole and Gauss Seidel relaxationis used for the solution of coupled equations viz.modified Reynolds equation, film thickness equation and energy equation satisfying appropriate boundary conditions. The analysis reveals the combined influence of non-Newtonian, thermal and slide-roll ratio (of bearing movingwith different speeds) on pressure, film thickness and pressure spike covering wide range of physical parameters of interest. Results show that pressure spike is strongly influenced by thermal, slide-roll ratio and non-Newtonian character of lubricant with negligible effect on overall pressure distribution. Also, minimum film thickness is slightly altered and it increases with increase in couple stress parameter. These findings confirm the importance of non-Newtonian and thermal effects in the study of EHL.

A Size-Dependent Finite Element Method for the 3D Free Vibration Analysis of Functionally Graded Graphene Platelets-Reinforced Composite Cylindrical Microshells Based on the Consistent Couple Stress Theory

Within a framework of the consistent couple stress theory (CCST), a size-dependent finite element method (FEM) is developed. The three-dimensional (3D) free vibration characteristics of simply-supported, functionally graded (FG) graphene platelets (GPLs)-reinforced composite (GPLRC) cylindrical microshells are analyzed. In the formulation, the microshells are artificially divided into numerous finite microlayers. Fourier functions and Hermitian C2 polynomials are used to interpolate the in-surface and out-of-surface variations in the displacement components induced in each microlayer. As a result, the second-order derivative continuity conditions for the displacement components at each nodal surface are satisfied. Five distribution patterns of GPLs varying in the thickness direction are considered, including uniform distribution (UD) and FG A-type, O-type, V-type, and X-type distributions. The accuracy and convergence of the CCST-based FEM are validated by comparing the solutions it produces with the exact and approximate 3D solutions for FG cylindrical macroshells reported in the literature, for which the material length scale parameter is set at zero. Numerical results show that by increasing the weight fraction of GPLs by 1%, the natural frequency of FG-GPLRC cylindrical microshells can be increased to more than twice that of the homogeneous cylindrical microshells. In addition, the effects of the material length scale parameter, the GPL distribution patterns, and the length-to-thickness ratio of GPLs on natural frequencies of the FG-GPLRC cylindrical microshells are significant.

Investigation on TiO2 photocathodic protection based on lattice distortion and stress engineering

Anatase TiO2 has always been a research hotspot of photocathodic protection materials because of its high photocatalytic activity. However, improving the utilization rate of TiO2 to visible light and reducing the recombination rate of photoinduced carriers need to be resolved urgently. Here, TiO2 nanofilms photocathodic protection regulation mechanism was explored by coupling size-dependent lattice distortion and stress engineering in combination with the first-principles calculation and experiment. The results indicated that the uniaxial compression stress can effectively reduce the band gap of TiO2, which is conducive to the photocathodic protection of TiO2. Moreover, the low compression stress (Com'-TiO2) can significantly improve the photocathodic protection performance of TiO2 was confirmed experimentally. These findings provide a new idea for the regulation of TiO2 nanofilm’s photocathodic protection performance.

Prediction of ring crack initiation in ceramics and glasses using a stress–energy fracture criterion

AbstractCrack initiation in brittle materials upon spherical indentation is associated with the tensile radial stresses during loading. However, location of crack onset often differs (offset) from the site of maximal stress. In addition, experiments reveal a strong dependency of crack initiation forces on geometrical parameters as well as the surface condition of the sample. In this work, a coupled stress–energy fracture criterion is introduced to describe the initiation of ring cracks in brittle materials, which takes into account the geometry of the contact and the inherent strength and fracture toughness of the material. Several experiments reported in literature are evaluated and compared. The criterion can explain the location offset of the ring crack upon loading, as observed in various ceramics and glasses. It also predicts the ring crack initiation force upon contact loading, provided that surface compressive stresses, introduced during grinding or polishing processes, are taken into account. Furthermore, the stress–energy criterion may be employed to estimate the surface residual stress of ceramic parts, based on simple contact damage experiments.

Couple stress ternary hybrid nanofluid flow in a contraction channel by means of drug delivery function

The rheological perception of blood circulation with the dispersion of metal or non-metal nanomaterials via a squeezing channel is gaining more attention because of implementations in the blood filtration system, nano-pharmacology, obstructed hemodynamics, nano-hemodynamics, care of hemodynamic diseases, and some other areas. Inspired by the innovative importance and study in such a domain a computational hemodynamically framework is developed to simulate the hemodynamic properties of blood steam under the composition of nanomaterials through a squeezing channel. CuO, TiO2, and Al2O3 nanoparticles are dissolved in the blood to generate a tri-hybrid nano-blood emulsion (CuO+TiO2+Al2O3/blood). The blood flow is commonly described using the couple stress, fluid model. The concept of nonlinear radiation is also utilized in the equation of heat for the viability of drug delivery. The effects of MHD and the heat source are also considered. According to the existing research, the interaction of TiO2 nanoparticles with any other metal nanoparticle can kill more cancer cells than TiO2 alone. The mathematical framework of a squeezing channel is formulated for motion and energy and then solved the model problem by using the HAM technique. The numerical outputs were presented in the form of graphs for a random interval of model factors included for thermal and velocity distributions additionally to this, Cf and Nu are also deliberated through charts. Furthermore, the percentage-wise enhancement in Nul and Nuu is also displayed. The thermal profile improves as the values of M,ϕ,Rd and λ>0 grow, but it declines as λ<0 increases. The conclusions of the current model could be pertinent to regulating blood circulation and drug delivery systems.

Numerical simulation the fracture of rock in the framework of plastic-bond-based SPH and its applications

In this paper, a two-dimensional numerical approach named plastic-bond-based smoothed particle hydrodynamics (PB-SPH) is proposed to simulate the fracture of rock with pre-existing flaws. Under the PB-SPH framework, interaction particles are interconnected through bonds. The Drucker–Prager criterion of a tensile zone cut-off coupled maximum tensile stress criterion is applied to judge shear failure and tensile failure. To verify the capability of the PB-SPH method in simulating rock fracture behavior, two-dimensional numerical simulations of a single flaw, two coplanar flaws, and multiple flaws of uniaxial compression are carried out. Compared with previous experimental and numerical results, the present numerical results show good agreements on crack initiation positions, crack morphology and crack patterns. The numerical simulation of the progressive failure process of rock slope with multiple flaws is carried out, which shows that the PB-SPH method can be well applied to rock mechanics engineering. The present results show that the PB-SPH method has a certain reference in the study of rock fracture mechanics and the application of rock mechanics engineering.

Peristaltic Transport of a Couple Stress Fluid through a Horizontal Tapered Asymmetric Channel

Abstract: The peristaltic transport of a Couple stress fluid in the horizontal tapered asymmetric channel is examined, concealed by long wavelength and low Reynolds number assumptions. The tapered asymmetric channel is produced due to the peristaltic motion on the walls of the non-uniform channel having alternative amplitudes and phases. Excellent velocity, pressure gradient, and stream function results have been determined. Numerical evaluation has also been found for investigating the pumping characteristics with various flow values of parameters. It has been shown that the peristaltic transport pumping decreases with an increase in non-uniform rheological parameters. Further, our conclusion is created to be very relevant to [19] when the absence of the tapered asymmetric nature of the channel and couple stress fluid parameter.

Boosting Cycling Stability of Polymer Sodium Battery by "Rigid-Flexible" Coupled Interfacial Stress Modulation.

The discontinuous interfacial contact of solid-state polymer metal batteries is due to the stress changes in the electrode structure during cycling, resulting in poor ion transport. Herein, a rigid-flexible coupled interface stress modulation strategy is developed to solve the above issues, which is to design a rigid cathode with enhanced solid-solution behavior to guide the uniform distribution of ions and electric field. Meanwhile, the polymer components are optimized to build an organic-inorganic blended flexible interfacial film to relieve the change of interfacial stress and ensure rapid ion transmission. The fabricated battery comprising a Co-modulated P2-type layered cathode (Na0.67Mn2/3Co1/3O2) and a high ion conductive polymer could deliver good cycling stability without distinct capacity fading (72.8 mAh g-1 over 350 cycles at 1 C), outperforming those without Co modulation or interfacial film construction. This work demonstrates a promising rigid-flexible coupled interfacial stress modulation strategy for polymer-metal batteries with excellent cycling stability.

Analysis and numerical simulation of fractal-fractional order non-linear couple stress nanofluid with cadmium telluride nanoparticles

It is generally considered that fractal-fractional order derivative operators are highly sophisticated mathematical tools that can be applied in a variety of physics and engineering situations to obtain real solutions. By using fractal-fractional derivatives, we can simultaneously investigate fractional order and fractal dimension. Due to extensive applications of fractal-fractional derivatives, in the present article fractal-fractional order model of non-linear Couple stress nanofluid has been analyzed. The homogenous mixture of base fluid and nanoparticles has been formed by the uniform dispersion of cadmium telluride nanoparticles in mineral transformer oil. Primarily, the classical mathematical model has been formulated via relative constitutive equations and then generalized by using fractal-fractional derivative operator. This model has been numerically solved using Crank-Nicolson technique. Using numerical solutions, various graphs are plotted to analyze how physical parameters alter Couple stress nanofluid rheology. As can be seen from the graphical study, couple stress slows down fluid velocity. Adding cadmium telluride nanoparticles to transformer oil increased its efficacy by 15.27%.

Inverse Design of Micro Phononic Beams Incorporating Size Effects via Tandem Neural Network

Phononic crystals of the smaller scale show a promising future in the field of vibration and sound reduction owing to their capability of accurate manipulation of elastic waves arising from size-dependent band gaps. However, manipulating band gaps is still a major challenge for existing design approaches. In order to obtain the microcomposites with desired band gaps, a data drive approach is proposed in this study. A tandem neural network is trained to establish the mapping relation between the flexural wave band gaps and the microphononic beams. The dynamic characteristics of wave motion are described using the modified coupled stress theory, and the transfer matrix method is employed to obtain the band gaps within the size effects. The results show that the proposed network enables feasible generated micro phononic beams and works better than the neural network that outputs design parameters without the help of the forward path. Moreover, even size effects are diminished with increasing unit cell length, the trained model can still generate phononic beams with anticipated band gaps. The present work can definitely pave the way to pursue new breakthroughs in micro phononic crystals and metamaterials research.

Effect of Electro-Thermo-Mechanical Coupling Stress on Top-Cooled E-Mode AlGaN/GaN HEMT

This work investigated the effects of single stress and electro-thermo-mechanical coupling stress on the electrical properties of top-cooled enhancement mode (E-mode) Aluminium Gallium Nitride/Gallium Nitride (AlGaN/GaN) high electron mobility transistor (HEMT) (GS66508T). Planar pressure, linear deformation, punctate deformation, environmental temperature, electro-thermal coupling, thermo-mechanical coupling, and electro-thermo-mechanical coupling stresses were applied to the device. It was found that different kinds of stress had different influence mechanisms on the device. Namely, excessive mechanical pressure/deformation stress caused serious, irrecoverable degradation of the device's leakage current, with the gate leakage current (Ig) increasing by ~107 times and the drain-to-source leakage current (Idss) increasing by ~106 times after mechanical punctate deformation of 0.5 mm. The device characteristics were not restored after the mechanical stress was removed. Compared with three mechanical stresses, environmental thermal stress had a greater influence on the device's transfer characteristic and on-resistance (Ron) but far less influence on Ig and Idss. As was expected, multiple stress coupled to the device promoted invalidation of the device. For more in-depth investigation, finite element simulation carried out with COMSOL was used to analyze the effect of electro-thermo-mechanical coupling stress on top-cooled E-mode AlGaN/GaN HEMT. The results of the experiments and simulation demonstrated that single and coupled stresses, especially mechanical stress coupled with other stresses, degraded the electrical properties or even caused irreversible damage to top-cooled E-mode AlGaN/GaN HEMT. Mechanical stress should be reduced as much as possible in the packaging design, transportation, storage, and application of top-cooled E-mode AlGaN/GaN HEMT.