Couple Stress Research Articles

Theoretical Analysis of Orifice Compensated Symmetric and Asymmetric Hydrostatic Non-Recessedjournal Bearings Under Couple Stress Lubricants

In this research a hole-entry hydrostatic journal bearings with couple stress and Newtonian lubricants have been examined analytically. The Newton Rapshon Method and Finite Element Method have been applied on Reynolds equation for couple stress and for the Newtonian lubricants to achieve the film pressure. The results of disparate factors of couple stress lubricants and the external load have been modeled. The outcome of the achieved results showed that the static and dynamic actions of bearings enhanced under a couple stress lubricants assessed the bearings performance with Newtonian lubricant.

Gear contact fatigue prediction under mixed elastohydrodynamic lubrication with ellipsoidal asperity rough surface: Experimental and numerical investigation

A three-dimensional(3D) line-contact mixed lubrication model and contact fatigue life prediction model for gears are established, considering the elastoplastic contact of ellipsoidal asperities and their interactions. The localized lubrication states across the actual 3D rough surfaces are visually depicted. The direct asperity contact pressures calculation exhibits greater accuracy and universality. The proposed mixed lubrication model can be applied accurately and efficiently to heavy-load conditions. The synergistic mechanisms of multi-scale surface integrity parameters, such as surface morphology-lubrication coupling, hardness gradient, and residual stress, on gear contact fatigue has been revealed. The results reveal that surface roughness significantly affects the competitive failure mechanism between surface-initiated micropitting and subsurface-initiated macropitting. The increase in surface compressive residual stress is more sensitive to the enhancement of near-surface and subsurface fatigue lives, compared to the increase of peak residual stress and the depth of peak residual stress. The proposed physics-based gear contact fatigue life prediction model has been validated through gear contact fatigue experiments under various operating conditions. The maximum deviation between the predicted and experimental fatigue lives is within 10%. This paper presents theoretical methodologies and data-driven support for optimizing the design and manufacturing processes of gears, specifically focusing on enhancing anti-fatigue properties.

Vibration Study of Functionally Graded Microcantilever Beams in Fluids Based on Modified Couple Stress Theory by Considering the Physical Neutral Plane

Theoretical studies on the vibration of microcantilever beams in fluids, which are commonly used in micro- and nanoelectromechanical systems (MEMS/NEMS). When microcantilever beams are subjected to photo-thermal excitation, they show that the material properties such as the dynamic response and the one-dimensional temperature field will show significant differences from the macroscopic properties when the size appearance of the microbeam decreases to the scale below a dozen micrometers. In this paper, by correcting the scale constants of the beams, the photothermal vibration model of the microbeam is established using the physical neutral plane theory. The one-dimensional heat transfer equations and scale-corrected temperature field of the microcantilever beam under laser excitation are derived, which are solved by Galerkin’s method, based on the theory of thermoelasticity, the hydrodynamic model of the beams vibrating in incompressible liquids proposed by Sader et al. and the theory of Euler–Bernoulli beams. The equations governing the vibration of micro-cantilever beams corrected for scale effects in different fluids when subjected to photothermal excitation are obtained. The results show that the temperature field, resonant frequency, and quality factor of the microbeam will have a significant upward drift when the size of the microbeam is close to the scale parameter, and the scale effect has a non-negligible influence on the macroscopic performance parameters; the upward drift is gradually weakening when the thickness to scale ratio gradually increases. Finally, the property of the beam is almost the same as that of the theory when the thickness of the beam is 10 times the scale constant. The correction of the theory by the scale effect is insignificant.

Vibration Analysis of Porous Cu-Si Microcantilever Beams in Fluids Based on Modified Couple Stress Theory.

The vibrations in functionally graded porous Cu-Si microcantilever beams are investigated based on physical neutral plane theory, modified coupled stress theory, and scale distribution theory (MCST&SDT). Porous microcantilever beams define four pore distributions. Considering the physical neutral plane theory, the material properties of the beams are computed through four different power-law distributions. The material properties of microcantilever beams are corrected by scale effects based on modified coupled stress theory. Considering the fluid driving force, the amplitude-frequency response spectra and resonant frequencies of the porous microcantilever beam in three different fluids are obtained based on the Euler-Bernoulli beam theory. The quality factors of porous microcantilever beams in three different fluids are derived by estimating the equation. The computational analysis shows that the presence of pores in microcantilever beams leads to a decrease in Young's modulus. Different pore distributions affect the material properties to different degrees. The gain effect of the scale effect is weakened, but the one-dimensional temperature field and amplitude-frequency response spectra show an increasing trend. The quality factor is decreased by porosity, and the degree of influence of porosity increases as the beam thickness increases. The gradient factor n has a greater effect on the resonant frequency. The effect of porosity on the resonant frequency is negatively correlated when the gradient factor is small (n<1) but positively correlated when the gradient factor is large (n>1).

Viscous dissipation effects on time-dependent MHD Casson nanofluid over stretching surface: A hybrid nanofluid study

The study of MHD Couple stress Casson flow of a hybrid nanofluid is paramount due to its potential applications in advanced engineering systems, particularly in enhancing thermal management and efficiency in various industrial processes. In this report, the time-dependent MHD Couple stress Casson flow of a hybrid nanofluid, considering the impact of viscous dissipation over a stretching surface is presented. The main objective of this work is to enhance the transformation heat ratio to meet the requirements of the engineering and manufacturing industries. After conducting a continuity check, the issue is analyzed by applying the principles of momentum and energy conservation. This modeling process generates nonlinear partial differential equations (PDEs), which are subsequently converted into nonlinear ordinary differential equations (ODEs) using similarity transformation and thermophysical characteristics. To solve these ODEs, the Approximate Analytical Method HAM is employed, which is specifically designed for nonlinear problems. Velocity decreases with increasing values and higher nanoparticle volume fraction further slows the velocity. Increasing the couple-stress parameter reduces velocity; increasing the Casson parameter slows the velocity profile. Increasing magnetic parameter enhances temperature profile; profile escalates with Eckert number magnitude. These findings contribute significantly to understanding the structure, interactions, and dynamics of such liquids, aligning with the focus on exploring the fundamental properties of simple, molecular, ionic, and complex liquids.

Nonlocal Couple Stress Vibration of Pasted Thermo Elastic Multilayered Cylinder with Hall Current and Multi Dual Phase Lags

Nonlocal Couple Stress Vibration of Pasted Thermo Elastic Multilayered Cylinder with Hall Current and Multi Dual Phase Lags

Predictive Association between Perceived Social Support and Infertility-Related Stress in Married Couples in Pakistan

Predictive Association between Perceived Social Support and Infertility-Related Stress in Married Couples in Pakistan

On the experimental determination and prediction of damage evolution in composites via cyclic testing

This study introduces a novel approach to obtaining and predicting damage evolution laws using quasi-static cyclic testing within the framework of continuum damage mechanics. To achieve this, a comprehensive set of characterization and parameter identification tests was performed. Carbon-epoxy specimens were manufactured using the filament-winding technique, and these laminates were tested using a universal testing machine. Digital image correlation was employed in all experiments to capture strain fields, and an alternative method utilizing the combined loading compression device is presented to obtain mechanical properties. Once the material was characterized, cyclic tests were conducted, including [Formula: see text], [Formula: see text], and [Formula: see text] tensile tests, and shear v-notch tests. These aim to determine damage evolution laws for both conditions, pure and coupled stress states. From these tests, values for damage onset and threshold were obtained and used to define four new parameters. These parameters permit the estimation of degradation relationships for any arbitrary orientation without requiring additional tests. This approach was tested as the proof-of-concept within the positive range of transverse tension and in-plane shear stress domain. The obtained results are promising, justifying its extension to other failure mechanisms. While acknowledging its limitations, this new approach holds potential for implementation in the analysis of progressive failure in fiber-reinforced composite materials, possibly in conjunction with established failure criteria and computational tools, mainly in the finite element method domain.

Coupling structural, chemical composition and stress fluctuations with relaxation dynamics in metallic glasses

Understanding the atomistic mechanisms of relaxation dynamics in metallic glasses remains a longstanding challenge. Here, using microsecond time scale molecular dynamics simulations, three main relaxation stages in metallic glasses are identified. At about 0.6Tg, chemical composition plays a dominant role in the relaxation, manifested by stress accumulation and only minimal variations in structure. As Tg approaches, the confluence of structural heterogeneity and chemical composition leads to the decoupling of relaxation mechanisms. At this temperature, the relaxation results in a structure with a lower energy state and a lower level of stress. In the supercooled liquid regime, an extensive increase in the number of closed-packed icosahedral clusters is responsible for accelerated structural relaxation while their packing frustration leads to the accumulation of intrinsic residual stresses in the glass. The atomistic origin of these dynamic relaxation modes is discussed in terms of structural, chemical composition and stress variations.

Impact of Couple Stresses on Slow Rotation of a Slip Sphere: Brinkman’s Medium

Impact of Couple Stresses on Slow Rotation of a Slip Sphere: Brinkman’s Medium

The Impact of Marangoni Convection on Carbon Nanotube Blood Base Hybrid Nanofluid with Thermal Radiation Viscous Dissipation and Couple Stress, Analytical Study

The Impact of Marangoni Convection on Carbon Nanotube Blood Base Hybrid Nanofluid with Thermal Radiation Viscous Dissipation and Couple Stress, Analytical Study

Band gap study of periodic piezoelectric micro-composite laminated plates by finite element method and its application in feedback control

Phononic crystals are materials or structures with periodic variations of elastic constants and density. Elastic waves in phononic crystals cannot propagate within a certain frequency range, called the band gap, due to the interference of their internal structure. This article investigates how fiber orientation affects the band gap properties of periodic micro-composite laminated plates. We examined the impact of five common composite laminate configurations on the system’s band gap and discovered that the antisymmetric configuration had superior high-frequency band gap performance. Based on this finding, we further explored how the antisymmetric angle influenced the system’s band gap. Since the study was conducted at a micro scale, micro structural effects were considered. Therefore, we used the modified coupled stress elastic dynamics and a four-node quadrilateral non-conforming element to discretize the micro composite laminated plate model, which had the nodal compatibility of high-order elasticity theory. Moreover, we employed feedback control to the proposed structure to dynamically adjust the band gap width according to different practical needs. This research supports the design of periodic micro-composite laminated plates and the piezoelectric feedback control system, which can control the vibration and wave propagation behaviors of micro structures using coupled piezoelectric sensors and actuators. The piezoelectric feedback control employed two control methods: direct proportional control and acceleration control. This article compared the single and multiple control methods of these two approaches to determine the optimal control strategy.

A Unified Technique for Stability Analysis of an Embedded FG Porous Nano/Microbeam via Modified Couple Stress Theory

A Unified Technique for Stability Analysis of an Embedded FG Porous Nano/Microbeam via Modified Couple Stress Theory

Impact of Shape Factor on a Couple Stress Flow of a Ternary Hybrid Nanofluid over an Inclined Flat Plate when Non-Uniform Heat Source and Thermal Radiation are Significant: A Darcy-Forchheimer Model

Abstract The study of fluid flow over an inclined flat plate finds applications in a diverse range of engineering fields including aerodynamics, energy production and automotive design. This study theoretically investigates the steady and radiative flow of a ternary hybrid nanofluid (Water + TiO2 + CoFe2O4 + MgO) with couple stress, using the Darcy-Forchheimer model. The flow occurs through a tilted flat plate and is subjected to irregular heat source parameter and entropy generation. The problem’s equations have been transformed into a collection of ordinary differential equations (ODEs), which has been skillfully resolved using the bvp4c solver. Graphs are utilized to elucidate outcomes for two instances of shape components, namely platelet and spherical. An escalation in the couple stress parameter (S) is demonstrated to be inversely related to the fluid velocity, resulting in a drop. Specifically, when 0.5 ≤ S ≤ 3, the friction factor exhibits a decline, with rates of 0.306201851 (for Platelet shape) and 0.304466755 (for Spherical shape). An intriguing observation reveals an augmentation in the generation of entropy as the volumetric fraction of TiO 2 rises. Upon investigation, it has been determined that when the Eckert number (Ecn) increases within the range of 0 ≤ Ecn ≤ 0.3, there is a significant reduction in the Nusselt number. Specifically, the decline is measured to be 0.328685192 for the platelet shape and 0.308939422 for the spherical shape. The utility of the Forchheimer number in regulating the fluid’s motion has been unveiled.

Nonlinear dynamics of contact interaction porous size-dependent Euler-Bernoulli beams resonators with clearance: Numerical analysis of the stability problem

In this study, a new mathematical model is developed to study the contact interactions of nano- and micro-electro-mechanical (NEMS/MEMS) beam resonators. The structural elements are considered as porous, size-dependent Euler-Bernoulli beams subjected to a variable transverse load. The beams resonators are located one above the other with minimal clearance. The analysis includes interactions between beams of both linear elastic and physically nonlinear materials, following the approach of Professor B. Ya. Kantor. Modified Coupled Stress Theory (MCST) is used to account for size-dependent effects. Hamilton's principle is applied to derive new size-dependent equations of motion together with the corresponding boundary and initial conditions. This study presents a new approach to the analysis of the chaotic dynamics of the contact interaction of porous, size-dependent Euler-Bernoulli beams. They are considered as systems with an "almost" infinite number of degrees of freedom. This innovative approach uses Principal Component Analysis (PCA) and Wavelet Analysis to filter out noise from signals. In addition, different beam interaction scenarios are classified including static Euler and Rayleigh instabilities as well as interactions between Koning-Taub and Richtmeyer-Meshkov instabilities. A significant discovery of this investigation is the chaotic behaviour of nonlinear vibrations during the contact interaction of these closely positioned beams. This demonstrates the complex dynamics involved in these high technology mechanical systems.

Improving the rheological behavior of magnetiz couple stress Buongiorno's nanofluid through resilient wavy channel with curvature effect: Nonlinear analysis

In biological systems, fluids with complex rheological behavior often encounter complex microenvironments. Couple stress fluids can be applied to model the flow of biological fluids in micro-vessels, capillaries, and other intricate structures. Couple stress fluids can be employed to model drug transport in microfluidic devices and capillaries, providing insights into the behavior of pharmaceuticals at small scales. Studying the couple stress fluids is crucial, particularly when considering the impact of particle viscosity in the existence of induced magnetic fields and nanoparticles that might enhance the characteristic motion. So, we studied the moderate and magnetic Reynold numbers and curvature effects of magnetized couple stress Buongiorno's nanofluid model through resilient wavy channel. The governing equations of this model are formed in non-dimensional form without any approximation, i.e., in the companionship of moderate Reynolds number and curvature effect, which aren't studied in this form. Using the Adomian decomposition approach, it is possible to obtain a solution of nonlinear system of partial differential equations analytically. The semi-analytical results are obtained and represented graphically for characteristic motion and bio-thermal properties for temperature and concentration, as well as magnetic features. Physically, by rising the magnetic Reynolds number, the magnetic permeability raises, so the ability of the couple stress fluid to form an internal magnetic field within itself with the impact of an applied magnetic field increases, which increases the magnetic force.

Impact of porous material and slip condition on the MHD flow of immiscible Couple stress-Newtonian fluids through an inclined channel: Head loss and pressure difference

Nowadays, non-Newtonian and Newtonian non-miscible fluid flow problems are much more effective in real-life physical problems. The understanding of flow behavior of magneto-hydrodynamic non-miscible fluids through a porous region playing an important role in the areas of biochemical sciences, crude oil extraction, transport issues and biomedicine. The aim of the present study is to know the impact of inclination angle of the channel, porous material used in the channel, slip boundary condition and applied magnetic field on the flow variables such as velocity profile, wall shear stress, pressure differences, head loss and volumetric flow rate of the two electrically conducting non-miscible couple stress and Newtonian fluids flowing through an inclined channel occupied with porous material of different porosity and permeability. An inclined channel is divided into two sub-regions of equal width through which the Newtonian and Couple stress fluids flow, respectively. Here, Brinkman’s model has been used to study the flow of immiscible fluid in their respective porous region. The equations that govern the flow of non-miscible fluids are solved using a well-defined analytical method and Mathematica 10.3 software. The present study concludes that the porous materials can be used to control the velocity of immiscible fluids in an inclined channel. It is also concluded from the present study that the use of slip condition promotes the values of velocity, volumetric flow rate, pressure differences and head loss. This work is validated with the previously published research work. Such models can be helpful in industries for filtering or refining immiscible oils.

Nonlinear Convection Flow of a Micropolar Nanofluid Past a Stretching Sphere with Convective Heat Transfer

An incompressible, steady combined nonlinear convective transport system on a micropolar nanofluid through a stretching sphere with convective heat transfer was investigated. The conservation equations corresponding to momentum, microrotation, thermal energy, and concentration particles have been formulated with suitable boundary constraints. By using the required non-dimensional variables, the conservation equations have been turned into a set of high-order standard differential equations. Then, an implicit finite difference method, also known as the Keller-Box Method (KBM), was used to numerically solve the flow problem. The obtained outcomes are displayed through graphs and tables to explain the impact of various governing variables over velocity, temperature, concentration, number of skin friction, wall coupled stress, Nusselt number, and Sherwood number. The findings demonstrate that increasing the convective heat parameter Bi enhances the factor of skin friction, local Nusselt number, Sherwood number, velocity field, and temperature profile while lowering the wall-coupled stress. It is observed that for high values of the material parameter β, the fluid velocity and the spin of the micro-elements both increase, which causes the dynamic viscosity and microrotation velocity to decrease. In addition, as the rates of magnetic constant Ma, thermophoresis Nt and Brownian movement Nb rise, the thermal distribution and its thickness of boundary layer increase. However, it decline along the enlarging quantities of nonlinear convection parameter λ, Prandtl number Pr, material parameter β, and solutal Grashof number Gm, which agrees to increase fluid density. When the range of thermophoresis Nt surges, it causes an increment in the nanoparticle species, but the opposite behavior have seen in the case of Brownian number Nb, and Lewis number Le. The comparison made with the related published paper achieves a significant agreement. The numerical result is generated through the implementation of the computational software MATLAB R2023a.

Vibration analysis of Timoshenko microbeams made of functionally graded materials on a Winkler-Pasternak elastic foundation

In this work, the free vibration analysis of Timoshenko microbeams made of the Functionally Graded Material (FGM) on the Winkler-Paternak elastic foundation based on the Modified Coupled Stress Theory (MCST) is investigated. Material characteristics of the beam vary throughout the thickness according to the power distribution and are estimated through Mori–Tanaka, Hashin-Shtrikman and Voigt homogenization techniques. The Timoshenko microbeam model considering the length scale parameter is applied. The free vibration differential equations of FGM microbeams are established based on the Finite Element Method (FEM) and Kosmatka’s shape functions. The influences of the size-effect, foundation, material, and geometry parameters on the vibration frequency are then analyzed. It is shown that the study can be applied to other FGMs as well as more complex beam structures.

Effects of physical parameters on shear wave in a porous piezoelectric model with imperfect interface

This study investigates the impact of interfacial imperfection on shear horizontal wave propagation in a microstructural coupled stress half-space beneath a porous piezoelectric layer adjacent to air. The validity of dispersion relations is shown by deriving special cases and comparing them with the classical dispersion relation of Love wave. Furthermore, a comparative analysis has been conducted to analyze the effect of various parameters on the phase velocity of shear wave by considering perfect and imperfect interfaces under electrically open and short conditions. The findings provide a theoretical framework for developing and designing underwater acoustic devices for sensing and nondestructive testing.