Couple Stress Research Articles

Entropy minimization on magnetized Boussinesq couple stress fluid with non-uniform heat generation

This article aims to investigate the generation of entropy for the magnetized coupled stress fluid passed through a permeable stretching cylinder that creates the condition of convective heat transfer. Additionally, in the uneven heat source in the flow field, we also analyzed our research. The properties of heat transfer taking into account in the perspective of thermal radiation. The main nonlinear partial differential equations (NPDE) become ordinary nonlinear differential equations by adopting the corresponding dimensionless variables. The recognized repeated shooting technique combined with the fourth-order standard Runge-Kutta integration solution to evaluate the resulting nonlinear ODE numerically. The velocity, temperature profile, streamline, number of local entropy generations, Bejan number, local friction coefficient, and Nusselt number effects of the new flow parameters are explained by graphs and tables. The flow system’s physical properties and the correlation between the parameters were clarified by using statistical methods. The results show that the Bejan number is reduced due to the magnetic source. Generation of entropy promotes the growth of the magnetic field and the Brinkman number, but the coupling stress aspect shows a double effect. The coupled stress parameter reduces the number of Nusselt by a fraction of 4.46%, while in the attendance of a magnetic field, the radiant heat transfer rate increases at a rate of 2.65%. In the attendance of a magnetic field, skin friction reduces the coupling stress factor by a rate of 24.67%. Besides, the current outcomes have been verified by previously published studies and are very acceptable. For the stretched cylinder, which has a curvature parameter of γ = 1.0, and for the flat, stretched surface, γ = 0.0, the thickness of the momentum and the thermal boundary layer are greater.

Convective Flow of Hydromagnetic Couple Stress Fluid with Varying Heating through Vertical Channel

This article addresses the impact of magnetic field induction on the buoyancy-induced oscillatory flow of couple stress fluid with varying heating. Modelled equations for the incompressible fluid are coupled and nonlinear due to the inclusion of viscous heating and thermal effect on the fluid density. Approximate solutions are constructed and coded on a symbolic package to ease the computational complexity. Graphical representations of the symbolic solutions are presented with detailed explanations. Results of the present computation show that the effect of induced magnetic field on the oscillatory flow and heat transfer is significant and cannot be neglected.

Size effects on the band gap of flexural wave propagation in one-dimensional periodic micro-beams

The mechanical properties of micro-scale materials are different from their macroscopic counterparts. This study investigates the impact of the size effect on the band structure of a one-dimensional periodic microstructure. The equation of motion for the Euler–Bernoulli beam model considering the size effect is derived based on the modified coupled stress theory, and the transfer matrix method is employed to obtain the band structure considering the size effect. The results obtained with the modified couple stress theory are compared with those obtained using the classical theory. The size effect increases the flexural stiffness of the micro-beams, causing the band gap to move to a higher frequency. In addition, the effects of the material distribution and geometric period on the band gap are also investigated. It is found that the size effect, which has a significant effect on the band structure of the microstructure, cannot be neglected.

Examination of Couple Stress Hybrid Nanoparticles (CuO-Cu/Blood) as a Targeted Drug Carrier with Magnetic Effects Through Porous Sheet

Examination of Couple Stress Hybrid Nanoparticles (CuO-Cu/Blood) as a Targeted Drug Carrier with Magnetic Effects Through Porous Sheet

MHD Mixed Convection Flow of Couple Stress Fluid Over an Oscillatory Stretching Sheet with Thermophoresis and Thermal Diffusion Using the Overlapping Multi-domain Spectral Relaxation Approach

MHD Mixed Convection Flow of Couple Stress Fluid Over an Oscillatory Stretching Sheet with Thermophoresis and Thermal Diffusion Using the Overlapping Multi-domain Spectral Relaxation Approach

Transient thermoelastic response of a size‐dependent nanobeam under the fractional order thermoelasticity

AbstractWith the miniaturization of structures, such as MEMS/NEMS, the size‐dependent effect has become an issue and attracted much attention. The well‐known theories describing the size‐dependent effect mainly include the nonlocal elasticity theory, the strain gradient theory and the modified coupled stress theory. Based on these theories, a number of works have been conducted to explore the size‐dependent behaviors of structures or devices in micro/nano‐scale, among them, majorities are on elastic performances, while, minorities are on thermoelastic performances. It is inevitable for structures suffering changeable temperature, as a consequence, thermal‐induced stress and deformation occur in structures and they are worth being fully concerned. For thermoelastic behaviors limited to small scale problems, the classical Fourier's heat conduction law may fail, meanwhile, new models, for example, fractional order heat conduction model, have been developed to modify Fourier's law. In present paper, the transient thermoelastic response of a nanobeam subjected to a ramp heating is investigated by combining the nonlocal elasticity theory and the fractional order heat conduction model. The governing equations are formulated and then solved by Laplace transform and its numerical inversion. The non‐dimensional temperature, displacement, stress, and deflection in the nanobeam are obtained and illustrated graphically. In calculation, the effects of the ramp‐heating time parameter, the nonlocal parameter and the fractional order parameter on the considered physical quantities are examined and discussed in detail.

Mechanical Characteristics of Coal and Rock in Mining under Thermal-Hydraulic-Mechanical Coupling and Dynamic Disaster Control

In order to reduce the risk of coal and rock dynamic disasters in the coal mine production process, the coupling mechanics characteristics of coal and rock produced in the process of coal mining in the Dingji Coal Mine are taken as the research object, and the experimental study on the deformation characteristics and the variation rule of mechanical parameters of raw coal under multifield coupling (temperature, gas, and stress coupling) was carried out. The results show that the elastic modulus, peak strain, and peak stress of raw coal samples under the thermal-hydraulic-mechanical coupling have the same change law in the test temperature range and all of them show a linear decreasing law as the temperature increases. Under the same temperature gradient increasing condition, the elastic modulus, peak strain, and peak stress show a nongradient decreasing trend as the temperature increases. Both the deformation modulus and the lateral expansion coefficient show a linear increase as the temperature increases, while the deformation modulus and the lateral expansion coefficient show a nongradient increase trend as the temperature increases under the same temperature gradient increasing condition. Under the action of the thermal-hydraulic-mechanical coupling, unloading confining pressure obviously accelerated the yield process of the coal sample, and the confining capacity of confining pressure on transverse strain of the coal sample decreased. To prevent the occurrence of coal and gas outburst, it is necessary to take specific prevention measures according to the change law of triaxial compression mechanics of a raw coal specimen under the action of the thermal-hydraulic-mechanical coupling.

Finite element analysis on processing stress of polysilicon cut by diamond multi-wire saw

At present, diamond multi-wire sawing technology has been applied to the slicing of polysilicon wafers. The residual microcracks on the surface and subsurface of the silicon wafer due to material brittle removal are prone to expand and interfere under the sawing stress, which reduces the fracture strength of the silicon wafer and leads to breakage. However, the dynamic change and distribution of sawing stress is still difficult to measure by experiment. In this paper, the two ways of ductile and brittle material removal of abrasives at different azimuth angles on the saw wire surface were considered, the sawing force model of diamond wire sawing was established. Then based on the sawing force model, a finite element model of multi-wire sawing polysilicon was established. The distribution and coupling characteristics of sawing stress and the influence of process parameters and silicon wafer size characteristics on the stress value and distribution were studied. The research results show that the mechanical stress value during the sawing process is relatively small and accounts for a small proportion of the coupling stress, but it will affect the distribution of the coupling stress, and the thermal stress is dominant. The coupling stress increases with the increase of saw wire speed and feed speed. When the ratio of saw wire speed to feed speed is constant, the larger the value of saw wire speed and feed speed is, the larger the coupling stress is. The increase in the size and thickness of the silicon wafer will increase the coupling stress, while the change in the thickness of the silicon wafer has little effect on the value of the coupling stress. The research results of the paper provide a theoretical reference for understanding the changes and distribution of sawing stress, optimizing process parameters and improving the quality of sawing.

Free Vibration Analysis of Rotating Beams Based on the Modified Couple Stress Theory and Coupled Displacement Field

In this paper, transverse vibration analysis of rotating micro-beam is investigated based on the modified couple stress theory. The simply-supported micro-beam is modeled utilizing Euler-Bernoulli and Timoshenko beam theories. The system is rotating around a fixed axis perpendicular to the axial direction of the beam. For the first time, displacement filed is introduced as a coupled field to the translational field. In other words, the mentioned rotational displacement field is expressed as a proportional function of translational displacement field using first (axial), second (lateral), and third (angular or rotational) velocity factors. Utilizing Hamilton’s approach as a variational method, dynamic-vibration equations of motion of the proposed model are derived. Galerkin’s method is adopted to solve the equation corresponding to the Euler–Bernoulli and Timoshenko beams. For the case considering shear deformation effects, Navier method is chosen. For evaluation of current results and models, they are compared with those available at the benchmark. In this paper; effects of slenderness ratio, axial, lateral, and angular velocity factors, and rotations of the beam on the frequency are reported. Based on the results presented, mentioned factors should be counted in the analysis and design of such rotating micro-systems.

Impact of mechanical stiffening and softening on the spatial distribution of lithium ions in spherical electrode particle under galvanostatic charging

This article investigates the lithiation of low-expansion electrode particles with concentration-dependent properties. The conventional electrochemical coupled stress equations do not take into account concentration dependency, especially for particles with a low volume of expansion, as they are assumed to have no impact on the lithium-ion (Li-ion) migration. However, considerable changes are observed in the present study when this factor is included. The Li-ion concentration gradient is observed to decrease with stiffening and increase with softening in an electrode particle. The stresses at the center of the particle increase with stiffening and reduce with the softening. It is observed that the effect of concentration-dependent elastic modulus on the concentration gradient of lithium ions at the surface of the particle is more prominent at higher charging rates. The stresses in the electrode particle are observed to increase in proportion to an increase in the charging rate up to a critical limit beyond which its magnitude reduces.

Study on fracture occurrence characteristics and wellbore stability of limestone formation

The development of micro fractures in the KT-II formation in a block of China National Petroleum Corporation (CNPC) overseas caused the downhole collapse and touching resistance repeatedly occurs, which seriously hindered the normal drilling process. To solve these problems, the occurrence of fractures in the underground was sorted out based on the field data, and the physicochemical and mechanical properties of the downhole cores were analyzed under different downhole conditions via systematic experiments to determine the main factors affecting the formation collapse and instability. Based on the main control factors of wellbore collapse and experimental data, the wellbore-formation coupling stress field and wellbore stability evaluation and prediction method for unstable KT-II formation were established. Results show that the unstable KT-II strata are mainly fractured limestone strata having a “thousand-layer cake” shape. Clay or mudstone intercalations with strong hydration and expansion capacity can be observed between cracks. Deviation angle, azimuth and fracture tendency have obvious influence on wellbore stability of KT-II fractured limestone formation. The straight hole runs vertically through the fracture plane, and the borehole wall exhibits good stability. When the deviation angle becomes larger than 50°, the weak plane effect of fracture mechanics is prominent and the borehole wall will easily collapse along the crack. For the formation with horizontal fractures, the optimal wellbore stability can be observed when drilling is performed in the direction of the minimum horizontal principal stress. For limestone formation with a certain dip angle fracture, horizontal well is drilled in the direction opposite to the fracture tendency, i.e., the fracture tendency +180° direction, the equivalent density of the collapse pressure is the lowest. The seepage and pressure penetration effects between wellbore and formation lead to an increase in the equivalent density of caving pressure by 0.08–0.1 g/cm 3 . Improving the sealing characteristics of drilling fluid will improve the wellbore stability. The results of this study will provide guidance for achieving effective and safe drilling in fractured limestone formations. • The occurrence of fractures in the underground was sorted out based on the field data, and the main influencing factors of formation collapse and instability were determined through systematic experimental tests. • Based on the main control factors of wellbore collapse and experimental data, the wellbore-formation coupling stress field and wellbore stability evaluation and prediction method for unstable KT-II formation were established. • For limestone formation with a certain dip angle fracture, horizontal well is drilled in the direction opposite to the fracture tendency, the equivalent density of the collapse pressure is the lowest.

Coupled nonlinear stress and electric field numerical simulation for all-solid-state lithium-ion batteries

An accurate analysis of ion transportation in an all-solid-state battery is crucial to improve and estimate performance. For an all-solid-state battery using sulfide solid electrolytes, coupling the stress and electric field simulations is required because the battery is pressurized, this affects the void space, which then affects ion transportation. In this paper, we propose a new method to analyze the ionic conductivity in a pressurized all-solid-state battery by coupling nonlinear stress analysis and electric field analysis. The nonlinear stress analysis can estimate the stress distribution of solid electrolyte and it was found that nonlinear stress-strain characteristics that originate from the voids diminished with increased pressure. The numerical results based on a model-electrode were nearly identical to the experimental results. • Numerical simulation method with nonlinear FEM and FVM are proposed. • Nonlinear mechanical characteristics of SE are simulated with nonlinear FEM. • The numerical results are validated with EIS and X-ray CT measurements. • The numerical and experimental results are in good agreement.

Structure optimization of gasket based on orthogonal experiment and NSGA-II.

With the aim of enhancing both reliability and fatigue life of gasket, this study combines finite element analysis, orthogonal experimental design, dynamically-guided multi-objective optimization, and the non-dominated sorting genetic algorithm with elitist strategy to optimize the geometric parameters of the cylinder gasket. The finite element method was used to analyze the temperature field, thermal-mechanical coupling stress field, and deformation of cylinder gasket. The calculation results were experimentally validated by measured temperature data, and comparison results show that the maximum error between calculated value and experiment value is 7.1%, which is acceptable in engineering problems. Based on above results and orthogonal experiment design method, the effects of five factors, including diameter of combustion chamber circle, diameter of coolant flow hole, length of the insulation zone between third and fourth cylinders, thickness of gasket, and bolt preload, on three indexes: temperature, stress, and deformation of gasket, were examined in depth. Through the variance analysis of the results, three important factors were identified to proceed later calculation. The dynamically guided multi-objective optimization strategy and the non-dominated sorting genetic algorithm were effectively used and combined to determine the optimal geometric parameters of cylinder gasket. Furthermore, calculation results suggest that temperature, stress, and deformation of the optimized cylinder gasket have been improved by 27.88 K, 16.84 MPa, and 0.0542 mm, respectively when compared with the origin object, which shows the excellent performance of gasket optimization and effectiveness of the proposed optimization strategy.

Study on Tensile-Shear and Compressive-Shear Coupling Strength of Saturated Clay

Traditional soil strength research mainly focused on compressive shear or uniaxial tensile stress state, and rarely considered the tensile-shear coupling strength characteristics in soil. Based on the tensile-shear and compressive-shear coupling strength model established earlier, which consider the tensile-shear coupling strength comprehensively, relevant tests are carried out to verify the strength model. Different types of saturated clay are selected for the uniaxial tensile test, direct shear test and triaxial shear test. The strength model is verified based on experimental data and compared with the existing joint strength model, and the coupling strength model shows good applicability and accuracy. The result shows the strength model can accurately describe the nonlinear strength characteristics of soil under tensile-shear coupling stress.

Numerical Analysis of Couple Stress Nanofluid in Temperature Dependent Viscosity and Thermal Conductivity

This communication reports on an innovative study of two-dimensional couple stress fluid 3 with effect of viscosity and conductivity. We proposed a new model based on temperature dependent variable thermal conductivity on kinetic theory. Our model assumes that thermal conductivity is a decreasing function of temperature rather than an increasing function. The effect of the three key parameters, viscosity, thermal conductivity and couple stress parameter are analyzed. The coupled non-linear system is further validated numerically using the spectral quasilinearization method. The method is found to be accurate and convergent. Increasing the temperature dependent parameter for viscosity is shown to reduce the heat mass transfer rates at the surface. Increasing thermal conductivity and the couple stress parameter increased the heat mass transfer rates on the boundary surface

Design of Harmonic AFM Probe Subjected to van der Waals Force in the Modified Couple Stress Theory

The conventional design of harmonic AFM probe geometry is made in neglect of the effects of the size-dependency factor and the tip-sample interacting force. Obviously, the effect of these two factors on the natural frequencies of a probe is significant. In this study, the effects of the two factors on the integer-multiples relation among frequencies are investigated. In this study, the effects of the two factors on the integer-multiples relation among frequencies are investigated. It is discovered that, in general, the integer-multiples relations of the probe’s frequencies in the classical model does not be kept as the same as that in the system with the effect of the size-dependency factor under the same material and geometry properties of probe. In addition, when the probe is used to measure the sample, the deviation of the relations will happen. The smaller the tip-sample distance is, the larger the deviation of integer-multiples frequencies is. The analytical method is presented here such that during scanning a sample at some tip-sample distance, the material and geometry properties of the probe can be tuned to the integer-multiples relation of resonant frequencies. Moreover, five similarity conditions among the systems with and without the effects of size-dependency and the tip-sample interacting force are discovered. According to these conditions, the integer-multiples relation is kept in different systems.

A Review on the Size-Dependent Models of Micro-beam and Micro-plate Based on the Modified Couple Stress Theory

Micro scale experiments demonstrated that the material deformation behaviors of some metals and polymers deformed elasticity are size dependence, and the modified couple stress theory (MCST), which introduce an additional material length scale parameter, could capture the size dependences. The article reviews the available size-dependent models of micro-beam and micro-plate based on the MCST. For the representative micro-beams and micro-plates, the relevant mechanical models of micro-structures for static bending, vibration, buckling and pull-in instability, have been established based on the MCST, and the analytical and numerical solutions have been obtained. The results show that the size effects on the mechanical properties of the micro-structures are obvious and significant. Further possible researches on the size-dependent behaviors of the micro-structures are proposed.

Mechanical behavior of composite bistable shell structure and surrogate-based optimal design

A challenge in designing a bistable structure is the need to have low energy input for state change while maximizing the load-carrying capability. Here, we present an optimization framework for a bistable structure such that the maximum load-bearing ability can be achieved based on the investigation on mechanical performance and surrogate models. Firstly, an analytical expression of radius for the second state of the bistable structure is derived and verified by numerical simulation using a two-point loading method. Then, the transforming process of a bistable structure is analyzed by the force-displacement curve, and the transformed load is identified as an indicator measuring the load-bearing capacity. Secondly, the influence of changing parameters, including length, ply angle, thickness, and radius of the bistable shell structure on the transformed load is carried out systematically to choose optimal design variables. Thirdly, the optimal model is established, targeting the transformed load with the constraint of coupling stress in the second stable state. Model selection is conducted to determine the surrogate model that maps design variables into objective and constraint functions. And then, the improved genetic algorithm is developed to solve the optimal model, and optimal results are analyzed and discussed. Ultimately, we achieve an optimal bistable structure with the maximum load-bearing capacity while satisfying constraint, which is validated by numerical simulation. These computational and optimal strategies can provide design ideas for new structural optimization design.

Heat and Mass Transfer of a Peristaltic Electro-osmotic Flow of a Couple Stress Fluid through an Inclined Asymmetric Channel with Effects of Thermal Radiation and Chemical Reaction

The presented article addresses the electro-osmotic peristaltic flow of a couple stress fluid bounded in an inclined asymmetric micro-channel. The viscous dissipation, Joule heating and chemical reaction effects are employed simultaneously in the flow analysis. Heat and mass transfer have been studied under large wavelength and small Reynolds number. The resulting nonlinear systems are solved numerically. The influence of various dominant physical parameters is discussed for velocity, temperature distribution, concentration distribution and the pumping characteristics. Electro kinetic flow of fluids by micro-pumping through micro channels and micro peristaltic transport has accelerated considerable concern in accelerated medical technology and several areas of biomedical engineering. Deeper clarification of the fluid dynamics of such flow requires the continuous need for more delicate mathematical models and numerical simulations, in parallel with laboratory investigations.

Creep-Fatigue Experiment and Life Prediction Study of Piston 2A80 Aluminum Alloy.

In order to improve the reliability and service life of vehicle and diesel engine, the fatigue life prediction of the piston in a heavy diesel engine was studied by finite element analysis of piston, experiment data of aluminum alloy, fatigue life model based on energy dissipation criteria, and machine learning algorithm. First, the finite element method was used to calculate and analyze the temperature field, thermal stress field, and thermal–mechanical coupling stress field of the piston, and determine the area of heavy thermal and mechanical load that will affect the fatigue life of the piston. Second, based on the results of finite element calculation, the creep–fatigue experiment of 2A80 aluminum alloy was carried out, and the cyclic response characteristics of the material under different loading conditions were obtained. Third, the fatigue life prediction models based on energy dissipation criterion and twin support vector regression are proposed. Then, the accuracy of the two models was verified using experiment data. The results show that the model based on the twin support vector regression is more accurate for predicting the material properties of aluminum alloy. Based on the established life prediction model, the fatigue life of pistons under actual service conditions is predicted. The calculation results show that the minimum fatigue life of the piston under plain condition is 2113.60 h, and the fatigue life under 5000 m altitude condition is 1425.70 h.