Effects Of Couple Stresses Research Articles

Study of MHD on porous flat and curved circular plate lubricated with couple stress fluid-a slip velocity model

The current study achieved to explore novel of curved circular and porous flat plate under the existence of MHD and slip velocity. The gap between the plates is filled with conducting non-Newtonian lubricant as a couple stress fluids. We considered the phenomena of Darcy law is account for porous medium and Stokes theory is used to incorporate to couple stress effects. The effect of MHD slip velocity and couple stress lubricant is studied. By taking into account the couple stresses due to the microstructure additives and the magnetic effects due to the magnetization of the magnetic fluid modified Reynolds equation is obtained. The Reynolds equation is solved we obtain the derivation of non-dimensional pressure distribution, load carrying capacity and squeeze film time. Employing the Simpsons 1/3rd rule for numerical analysis in Mathematica tool and Origin Software to illustrate the behavior of pressure profile, load carrying capacity and squeeze film time in effect of Harmann number, couple stress parameter, slip velocity and permeability parameter. The results indicate that the influence of couple stresses and magnetic effects on the bearing characteristics are significantly apparent. It is concluded that fluids with couple stresses are better than Newtonian fluids. The improvement of the bearing characteristics is enhanced if the magnetic effects and slip velocity are present. But reverse effect due to upsurge of permeability parameter.

Convective heat transfer in Brinkman–Darcy–Kelvin–Voigt fluid with couple stress and generalized Maxwell–Cattaneo law

This article investigates thermal convection in Kelvin–Voigt fluids saturating a Brinkman–Darcy-type porous medium. We examine the linear (stationary and oscillatory), nonlinear, and unconditional nonlinear stability of this fluid under the generalized Maxwell–Cattaneo law with couple stress effects. Using the normal mode technique, we calculate the critical Rayleigh number for the linear stability under stress-free boundary conditions for both stationary and oscillatory convection. Additionally, we employ the energy method to determine the critical Rayleigh number for nonlinear and unconditional nonlinear stabilities under the same boundary conditions. All critical values were determined numerically, and various graphs were plotted to illustrate the results. Our findings reveal that a higher couple stress parameter leads to increased critical Rayleigh numbers for stationary, oscillatory, and nonlinear stability, indicating greater fluid stability and reduced susceptibility to convection. Additionally, the Kelvin–Voigt parameter significantly affects oscillatory convection, though it remains crucial within the nonlinear stability framework. These findings provide a detailed understanding of the stability behavior in this complex fluid system.

Influence of thermal radiation, viscous dissipation, and joule heating on entropy generation and flow of a Maxwell hybrid nanofluid over an exponentially stretching sheet with couple stress effects

Using a numerical technique, this study explores the flow and thermal aspects of a Maxwell hybrid nanofluid across an exponentially stretched sheet. The analysis incorporates the effects of thermal radiation, viscous dissipation, Joule heating, and chemical reaction. We use the in-built MATLAB function bvp4c to successfully solve the governing equations after we convert them to ordinary differential equations. The key novelty of this work lies in employing the Maxwell hybrid nanofluid, a more complex fluid than traditional nanofluids or regular Maxwell fluids and conducting a multifaceted analysis that considers factors like couple stress, chemical reaction, and entropy generation optimization alongside flow and heat transfer. The findings demonstrate that the Maxwell parameter and the magnetic field parameter both reduce fluid velocity due to opposing forces and enhanced elasticity, respectively. The temperature profile exhibits a rise with increasing thermal radiation, volume fraction of nanoparticles, and Eckert number due to enhanced radiative absorption, improved heat transfer, and internal heat generation respectively. As the Brinkman number and volume percentage of copper nanoparticles increase, the entropy generation becomes more intense and the Bejan number decreases as a result of enhanced viscous dissipation and friction. Between the values of 0.1 and 0.7 for Maxwell parameter, the friction factor exhibits a decrement of 0.1077. The Nusselt number, signifying heat transfer efficiency, reduces with the Eckert number but increases with the radiation parameter and volume fraction of nanoparticles. Between the values of 0.1 and 0.7 for Eckert number, the friction factor exhibits a decrement of 0.1077. Lastly, a steeper concentration gradient causes the Sherwood number, which is an indication of the mass transmission rate, to rise with the Schmidt number. it is detected that the rate of heat transfer increases at a rate of 0.0721 when chemical reaction values lie between 0 and 1.8.

Study on the coupling effect and construction deformation control of large deep foundation pit groups involving iron considering the coupling effect of seepage stress

Due to factors such as groundwater seepage and soil stress coupling effect, significant deformation and instability problems often occur during the construction process of super large deep excavation groups involving iron, seriously affecting the safety and stability of the project. This article aims to explore the coupling effect of super large deep excavation groups involving railways during the construction process, and how to effectively control construction deformation. This article combines theoretical analysis and numerical simulation to study the coupled effects of seepage and stress during the construction process of super deep excavation groups involving iron. With the help of finite element software, a numerical model of a large and deep excavation group involving iron was established, and the deformation and stress distribution at different construction stages were simulated. The research results indicate that the coupling effect of groundwater seepage and soil stress has a significant impact on the deformation and stability of the super deep excavation group involving iron. Therefore, reasonable construction measures and deformation control methods should be taken during the construction process.

Coupling effects of stress, seepage and damage during reconstruction and excavation of abandoned deep water-rich roadways

A stress–seepage–damage coupling model considering the long-term creep of a deep rock mass was established to study the mechanism of evolution of stability of the surrounding rock during reconstruction and excavation of abandoned deep water-rich roadways in a mine. The research shows that the maximum compressive stress in a circular cavern is significantly lower than that in a horseshoe-shaped cavern. Stress is distributed more uniformly in the circular cavern, and appropriately enlarging the size of the reconstructed excavation site can improve the stability of the surrounding rock. As the creep duration for abandoned roadways increases from 1 to 9 years, the growth rates for vault settlement and horizontal clearance convergence remain constant and the roadway undergoes steady-state creep. With increasing burial depth of the abandoned roadway (200–400 m), a pressure arch is gradually formed in the roadway roof in the reconstruction and mining process. The surrounding rock forms a ‘self-bearing structure’ with arch mechanical characteristics and a load transfer mechanism to maintain its own stability, and the overall bearing capacity of the surrounding rock is greatly improved. However, once the burial depth exceeds 400 m, the effect of the pressure arch begins to diminish with further increases in burial depth. Furthermore, porewater pressure significantly weakens the surrounding rocks.

Irreversibility analysis of EMHD ternary nanofluid flow: Unveiling the combined effects of thermal radiation, chemical reactions and cross-diffusion

Comprehending the behaviour of ternary hybrid nanofluids with the influence of couple stress effects on a flat plate will provide vital insights for the development of more effective heat exchangers and cooling systems. In this investigation, we analyzed the impact of various factors, including couple stress and cross-diffusion parameters (Dufour and Soret), on a ternary hybrid nanofluid flow [Formula: see text] across a convectively heated flat plate. The analysis takes into account non-Fourier heat flux and irreversibility. The governing equations are converted into a set of ordinary differential equations using appropriate similarity transformations, and then the bvp4c solver is used to find solutions. Outcomes are provided for two instances, that is, nanofluid ([Formula: see text]) and ternary hybrid nanofluid [Formula: see text] The fluid velocity is found to be negatively correlated with the couple stress parameter rises ([Formula: see text]) which is one of the major findings in this study. Within the range of [Formula: see text] it is seen that the friction factor exhibits a gradual increase with a rate of 0.02878 (in the case of nanofluid flow) and 0.038083 (in the case of ternary hybrid nanofluid flow). Additionally, when the Dufour number is between 0 and 0.6, the Nusselt number exhibits a discernible decrease of 0.27678 (in the case of nanofluid flow) and 0.26428 (in the case of ternary hybrid nanofluid flow). Furthermore, at [Formula: see text] (the Sherwood number), the Sherwood number drops at a rate of 0.0786 (in the case of nanofluid flow) and 0.05592 (in the case of ternary hybrid nanofluid flow). It has been observed that an increase in the chemical reaction parameter [Formula: see text] lowers the fluid concentration. It is observed that the Sherwood number increases at a rate of 0.037654 (in the case of nanofluid flow) and 0.037661 (in the case of ternary hybrid nanofluid flow) when [Formula: see text].

Acceleration model considering multi‐stress coupling effect and reliability modeling method based on nonlinear Wiener process

AbstractEstablishing an accurate accelerated degradation model is paramount for ensuring precise reliability evaluation results. Unfortunately, current accelerated degradation tests often lack test groups for investigating multi‐stress coupled phenomena. Consequently, existing multi‐stress accelerated models fail to adequately consider the impact of stress coupling when data with stress coupling information is absent. This limitation leads to the development of inaccurate models, ultimately affecting the precision of reliability assessment. To address this challenge, this paper introduces a new modeling method for multi‐stress accelerated degradation models that takes into account stress coupling effects. The proposed modeling method aims to improve the accuracy of reliability assessment under multi‐stress conditions. In the proposed model, the main effect function of stress is determined based on existing single‐stress accelerated models. The coupling effect is first examined through the Multivariate Analysis of Variance (MANOVA), and then the functional form of the coupling effect function is determined from the given candidate functions through correlation analysis. Next, the coupling effect is incorporated into a Wiener process to establish a multi‐stress accelerated degradation model, and the two‐step estimation method combining Least Squares Method (LSM) and Differential Evolution Algorithm (DEA) is proposed. The accuracy and effectiveness of the coupling effect test method, model establishment, and parameter estimation method were validated using two Monte Carlo simulation experimental data sets. Finally, the superiority of the proposed model is demonstrated through examples, providing feasible ideas and technical support for the research on multi‐stress accelerated degradation modeling considering stress coupling.

Analytic investigation of stress coupling effects of spherically anisotropic functionally graded piezoelectric hollow spheres

Analytic investigation of stress coupling effects of spherically anisotropic functionally graded piezoelectric hollow spheres

Experimental Study and Creep-Fatigue Life Prediction of Turbine Blade Material DZ125 Considering the Nonholding Effect and Coupling Effect of Stress and High Temperature

Abstract In response to the problem of creep-fatigue interaction damage failure of aero-engine turbine blade material, based on the modified damage evolution model of Kachanov-Rabotnov and Chaboche, a creep-fatigue life prediction model for nickel-based superalloy DZ125 is constructed considering the nonholding effect and coupling effect of stress and high temperature with the nonlinear interaction and superposition of creep damage and fatigue damage according to the continuum damage mechanics theory. Simultaneously, the microfracture morphology of DZ125 was analyzed using a scanning electron microscope, revealing the micromechanism of creep-fatigue interaction. The research results manifest that the creep-fatigue life prediction model has a high life prediction ability within ±2.0 times the dispersion band of the prediction results. Concurrently, a large number of intertwined tearing edges, microcracks, and microvoids appear in the fracture morphology, and creep and fatigue interact with each other in the form of effective stress. The above research can provide theoretical support for predicting the lifespan of mechanical structures in a high-temperature environment.

Initiation mechanism of micro-defects in polycrystalline iron under high-temperature stress coupling effect

To investigate the failure mechanism of high-temperature fracture in polycrystalline iron, this study conducted in-situ observation experiments to study the dynamic damage evolution process of iron under tensile loading at high temperatures. Meanwhile, through molecular dynamics simulation, the micro-defect initiation mechanism of polycrystalline iron under the coupling effect of high temperature and stress was revealed at the microscopic scale. The results indicate that during the high-temperature deformation process of polycrystalline iron at 1400 K, grain boundary slip is the main deformation mechanism. When the grain boundary slip is obstructed, stress concentration can easily occur at the grain boundaries (especially the triple junctions), leading to crack initiation. Furthermore, molecular dynamics simulations have shown that in the initial stage of deformation, with increasing strain, both HCP phase transformation atoms and dislocation length exhibit a trend of initially increasing followed by decreasing, peaking at around 5 % strain. Afterward, the system undergoes dynamic recrystallization, with dislocation movement and grain boundary migration leading to dislocation elimination. When the strain reaches 12.3 %, microvoids initiate at the triple junctions and grow up in an O shape. At a strain level of 12.45 %, there is a sudden drop in system stress, indicating fracture initiation.

Stability and instability of thermosolutal convection in a Brinkman–Darcy–Kelvin–Voigt fluid with couple stress effect

In this article, the phenomenon of thermosolutal convection within a fluid characterized by the Brinkman–Darcy–Kelvin–Voigt (BDKV) model is delved into, while the impact of couple stresses on this process is considered. Both linear instability and nonlinear stability analyses are encompassed in our investigation. Several noteworthy observations have been made. When the fluid layer is heated from below and salt is introduced from above, it is found that the points at which stability and instability thresholds are reached coincide. This alignment is supported by the validity of the linear theory in predicting the initiation of convection under these conditions. However, the scenario changes when the layer is salted from the bottom while being heated. In this case, the stability thresholds remain constant, regardless of variations in the salt Rayleigh number. This discrepancy between the thresholds of linear instability and nonlinear stability is deemed significant. To gain a deeper understanding, numerical computations were conducted to identify and thoroughly discuss the thresholds of linear instability. These findings offer valuable insights into the behavior of the system under study. It is indicated by our results that parameters such as Brinkman, couple stresses, and Kelvin–Voigt contribute to stabilizing the system. Additionally, it was noted that the salt Rayleigh number has a stabilizing effect when the layer is salted from below, whereas it has a destabilizing effect when salt is introduced from above.

Isogeometric analysis of magneto-electro-elastic functionally graded Mindlin microplates

In this study, an accurate numerical method for the static and dynamic response analysis of magneto-electro-elastic functionally graded (MEEFG) microplates with complex geometries is proposed with the application of isogeometric analysis (IGA). Leveraging Hamilton's principle and the extended modified couple stress theory, the weak form of motion equations is derived. By performing convergence analysis, the accuracy of the proposed numerical method is verified. To show the applicability of the new method, the influences of the microstructure effect and gradient index on the static and dynamic behaviors of both the MEEFG square and elliptical microplates with various boundary conditions are discussed in detail. Results illustrate that the microstructure effect dominated by the couple stress effect has an obvious impact on both the mechanical and electromagnetic behavior of structures with microscopic scales which will cause hardening of microstructural stiffness, whereas the macrostructures are minimally affected by the couple stress effect. Besides, microstructures with lower stiffness exhibit a more pronounced microstructure effect and a greater degree of stiffness hardening. The proposed IGA method could serve as a basis for the design and optimization of microelectromechanical devices with complex shapes.

Analysis of size-dependent response of surface excited functionally graded layer with consideration of couple-stress effects

This paper focuses on a theoretical examination of the mechanical behavior of elastic layers made of functionally graded (FG) materials. It particularly highlights the impact of material microstructures by utilizing the couple stress theory to introduce FG characteristics of the coating material across the thickness direction, along with size effects. The study distinctively addresses both surface loading and contact problems, employing various indenter shapes and eccentric indentation forces. The Fourier transform is utilized to solve for displacements and stress fields resulting from surface tractions. The method for approximating the pressure distribution under the indenter is based on a collocation method with a simple discretization of the contact pressure. Brent's method is applied to determine the unknown contact region when using indenters with non-sharp edges. The results demonstrate that the shear modulus ratio and the intrinsic material length scale significantly influence the pressure intensity, highlighting a substantial dependence on the mechanical properties of materials under indentation force. The research also shows that the effect of the length scale and shear modulus ratio affects the limit eccentricity and tilt angle. The results highlight the necessity of considering both the size effect and material gradation when analyzing FG materials under mechanical stress.

Stability analysis of GO‐EG and GO‐blood base nanofluids by implementing of thermal radiation phenomena

AbstractThis work leaves to explore the stability of a 2‐D, time free, thermal boundary layer of graphene oxide ethylene glycol (GO‐EG,) where GO‐blood is taken as base nanofluids over a stretchable surface by executing a magnetic field (MHD), coupled stress effects, heat source/sink, and sun‐oriented radiations. This work is done due to the reason that nanofluids have a higher heat conductivity level rather than regular liquids. Nonlinear partial differential equations (N‐PDEs) are modeled utilizing the notable boundary layer equations. Dimensionless ordinary differential conditions (ODEs) are made from the created NPDEs by utilizing dimensional analysis and group theoretic approach. We examine the obtained ODEs through the notable homotopy analysis technique (HAM). The impacts of different parameters on temperature distribution and velocity profiles are shown graphically. However, some tables are constructed in support of the presented study to confirm the stability and convergence of the solutions. The main intentions in this work are to underline the enhancement of traditional heat transfer's thermal conductivity.

Three-dimensional analysis of thermoelastic damping in couple stress-based rectangular plates with nonlocal dual-phase-lag heat conduction

Since thermoelastic damping (TED) plays a decisive role in the functioning of micro/nanoresonators, accurate assessment of its magnitude in these tiny systems is imperative. Successfully simulating the thermomechanical behavior of various mechanical elements requires consideration of heat transfer in all three principal directions. Furthermore, there is no denying the impact of size on the mechanical and thermal domains. In light of these reasons, the current study strives to create a three-dimensional (3D) size-dependent TED model for rectangular micro/nanoplates via the use of the modified couple stress theory (MCST) and nonlocal dual-phase-lag (NDPL) heat transfer model concurrently for the first time. To accomplish this, by applying the Galerkin method to the 3D NDPL-based heat equation, the relation of temperature field is derived. Moreover, the coupled thermoelastic constitutive relations are extracted by including the couple stress effect. Lastly, by exploiting the obtained relations in the energy dissipation approach, an analytical TED formula in the form of infinite trigonometric series is attained. To appraise the rightness of derived formulation, the method of model reduction is applied. Moreover, an elaborate convergence analysis is implemented to realize the number of sufficient terms of the provided solution that result in well-grounded outcomes. A rigorous simulation study is also accomplished on the role of 3D heat conduction, scale parameters of MCST and NDPL model, boundary constraints, geometry and material in the variations of TED. Findings imply the definite impact of heat conduction dimension on TED value in rectangular plates with a large ratio of thickness to length and width.

Study on mechanical and degradation behavior of Zn–Mn-xMg alloys under coupling effects of stress and SBF

Zinc-based implants will be subjected to combination of physiological corrosive media and stress during service in vivo. In this study, the mechanical and degradation behavior of Zn–Mn-xMg alloys under coupling effects of stress and simulated body fluid (SBF) were investigated. As a result, the ultimate tensile strength of Zn–Mn-xMg alloys decreased and incline to brittle fracture under the condition of slow strain rate tensile test in SBF. In addition, at a slower strain rate (1 × 10−6 s−1), the stress corrosion cracking susceptibility value will increase with the rise of Mg content. The immersion test under different compressive stresses shows that the corrosion will be inhibited under high pressure stress (50 MPa) compared with the lower one (10 MPa). The residual compressive strength of Zn-0.8Mn-xMg alloys decreases after immersion. A dense oxide layer could be induced with the increase of compressive stress, and it would inhibit the corrosion of the Zn-0.8Mn-xMg matrixes. These results indicate that Zn-0.8Mn-xMg alloys are expected to be a promising biodegradable material for biomedical applications.

A STUDY OF THE COUPLE-STRESS ON MICRO POLAR ROTATING FLUID FLOW WITH THERMAL CONVECTION

The effect of couple-stress on micro-polar rotating fluid layer heated from below in the presence of uniform vertical magnetic field in a porous medium is studied. The dispersion relation has been analyzed, using normal mode and it is found that the medium permeability has destabilizing effect. The rotation, couple-stress parameter and micro-polar parameters have stabilizing effect. The sufficient condition for the non-existence of over stability has also been obtained.

Effect of Couple Stresses on Peristaltic Flow in a Doubly Connected Region

Effect of Couple Stresses on Peristaltic Flow in a Doubly Connected Region

Couple-stress effects in a thin film bonded to a half-space

This study investigates the contact mechanics of a thin film laying on an elastic substrate within the context of couple-stress elasticity. It aims to introduce the effects of material internal length scale, which has proven an effective way of modeling structures at micro- to nano-scales, allowing to capture their size-dependent behavior. Specifically, stress analysis for a thin film bonded to a couple-stress elastic half-space is considered under plane strain loading conditions by assuming that both shear stress and couple tractions are exchanged between the thin film and the substrate. The problem is converted to a singular integral equation, which is solved by expanding the shear stress tractions as a Chebyshev series. The results show that the introduction of couple tractions decreases the shear stress tractions and the axial load in the thin film. When the characteristic length is sufficiently small, but still finite, the results for classical elastic behavior are approached.

Large Deflection and Post-Buckling Analysis of Cantilever Nanorods Including Effects of Couple and Surface Stresses by Intrinsic Coordinate Finite Elements

This paper presents a novel approach to the analysis of large deflection and post-buckling behavior of cantilever nanorods under different load conditions. The proposed approach utilizes a variational method, incorporating the Gurtin–Murdoch surface elasticity theory and the consistent couple stress theory to account for size-dependency effects. By accounting for the strain energy contributions of the bulk material, surface layer, and load conditions, this approach expresses the behavior of the nanorods in terms of their intrinsic coordinates. A finite element method was used to solve this numerical problem, generating a system of non-linear equations that were iteratively solved using the Newton–Raphson method. The results obtained from the finite element method were confirmed by those from the shooting method. Also, it highlights the effectiveness of the variational model in predicting the large deflection and post-buckling behavior of cantilever nanorods while considering both surface stress and couple stress effects. Furthermore, the study investigated the influence of surface stress and couple stress on the response of the nanorods to point and uniform loads. The results showed that incorporating both effects enhanced the stiffness of the nanorods compared to scenarios in which these effects were neglected. In addition, the couple stress effect was found to have a greater influence on the stiffening of nanorods for the same value of unitless parameters compared to surface stress effects. These findings offer valuable insights into the large deflection and post-buckling behavior of cantilever nanorods and highlight the importance of surface stress and couple stress effects. The model proposed in this study has potential applications in advanced technological device designs by providing a comprehensive understanding of the mechanical response of nanorods, allowing for more accurate predictions and enhanced device performance.