Model For Chemomechanical Coupling Research Articles

A curvature-dependent chemo-mechanical coupling model for two-dimensional oxidation on the curved surface

Understanding the chemo-mechanical coupling effect during oxidation at elevated temperatures is of critical importance for revealing complicated oxidation mechanism and oxidation behavior, as well as proposing countermeasures for oxidation protection. There has been an intensive investigation of the chemo-mechanics in planar oxidation, while much less attention is paid to the issue of non-planar oxidation. In this work, we proposed a curvature-dependent chemo-mechanical coupling model to investigate the two-dimensional oxidation process on curved surfaces. The oxidation kinetics including the oxide thickness and oxide growth rate on the curved surfaces, as well as the stress distribution and evolution at the substrate-oxide interface, were demonstrated. Comparisons between the experimental observations and theoretical predictions validated the accuracy of the proposed model, and the phenomenon of inhibition of oxidation on both convex and concave surfaces was explained by the stress-curvature effect on the oxidation process. Furthermore, based on the proposed model, we proposed a parameter and established a phase diagram to characterize the interactions between the curvature effect and the oxide growth effect.

A chemo-mechanical coupling model of oxidation and interlayer cracking of copper nanowires

Copper nanowires have received extensive attention for their potential applications in optics, electricity and catalysis, while oxidation erosion has become the biggest obstacle to their widespread application. Here, we present a chemo-mechanical coupling model to investigate the interlayer cracking behaviors of nanowires during oxidation. In contrast to existing chemo-mechanical models, the present model emphasizes that the process of oxygen entry into copper nanowires is chemical reaction-mediated layer-by-layer replacement rather than vacancy-mediated diffusion, which means the oxygen ions in the outer layer would not cross over the oxygen atoms in the inner layer during their entry. These conclusions are validated by molecular dynamics simulations. We then discuss the effect of the chemical reaction-induced free energy on the stress state of the nanowire during the reaction. Finally, a self-developed finite difference procedure is used to solve the control equations and the fracture location is determined according to the energy release rate analysis. We find the fracture of nanowires is closely dependent on the size of nanowire, the reaction rate and the oxygen concentration. This work deepens our understanding of the mechanism of chemo-mechanical coupling and fracture behavior of metals due to oxidation, thus has implications in other areas involving chemo-mechanical coupling.

The effect of futile chemical cycles on chemical-to-mechanical energy conversion in interacting motor protein systems

We consider the non-equilibrium steady-state conversion of chemical to mechanical energy in motor protein systems with protein–protein interactions. Our approach combines a two-dimensional chemomechanical coupling model with a simple exclusion process. The chemomechanical model explicitly includes both chemical and mechanical degrees of freedom to describe not only coupled chemomechanical transitions but also uncoupled transitions, such as futile chemical cycles, that lead to energy loss. The simple exclusion process describes strong repulsive protein–protein interactions in the mechanical degree of freedom and these interactions have implications for the chemical degree of freedom via the chemomechanical coupling. Using the combined chemomechanical exclusion model, we determine the efficiency of energy conversion as a function of motor density and chemical driving force. We show that as motor density increases, mechanical motion is blocked, losses due to futile chemical cycles increase, and the efficiency of chemical-to-mechanical energy conversion is reduced.

Creep Effect on Chemo-Mechanical Coupling Oxidation of Thermal Barrier Coatings

In this paper, a chemo-mechanical coupling model considering the creep effect during high-temperature oxidation is developed based on the diffusion-reaction equation. A sinusoidal curve model is developed by the finite element method to simulate the thickness and stress distribution of thermally grown oxide (TGO). The thickness and stress distribution of the TGO in the thermal barrier coating was investigated by changing the coupling effect and creep effect conditions of the model. The results show that with the increase of the coupling coefficient, the thickness of TGO gradually becomes smaller. In the late stage of oxidation, this effect diminishes, and the compressive stress located in the BC/TGO layer groove keeps decreasing, while the tensile stress located in the TC layer groove is the opposite. As the creep rate increases, the maximum tensile/compressive stress in the Y-direction within the thermal insulation coating slowly decreases, and the oxidation rate of the oxide layer moderately decreases. This study is important to find the corresponding solutions and preventive measures for the failure of the thermal barrier coating.

Non-Euclidean geometry model for chemo-mechanical coupling in self-assembled polymers towards dynamic elasticity

Self-assembly plays a fundamental role to determine thermodynamic properties of polymer systems, e.g., resulting in the formation of dynamically cross-linked networks with varied elasticity. However, the working principle of chemo-mechanical coupling between the self-assembly and elasticity of polymers is complex and has not been well understood. In this study, a non-Euclidean geometry model incorporating thermodynamics of microphase separation is proposed to understand the chemo-mechanical coupling in self-assembled triblock polymers. The thermodynamic separation of microphases, which is resulted from the self-assembly of polymeric molecules, is formulated using a non-Euclidean geometry equation, of which the geometrical parameters are applied to characterize the topologies of self-assembled and cross-linked networks. The non-Euclidean geometry model is further employed to describe chemo-mechanical coupling between the self-assembled network and dynamic elasticity of the triblock polymers, based on the rubber elasticity theory. Effectiveness of the proposed model is verified using both finite-element analysis and experimental results reported in literature. This study provides a new geometrical approach to understand the mechanochemistry and thermodynamics of self-assembled block polymers.

Strain-modulated initial oxidation of Al(1-x)Nix alloy surface

Despite of extensive studies about surface oxidation of metals and alloys, the impact of external loadings on nanoscale initial oxidation remains relatively unclear. Here, we demonstrate that surface prestrains and dynamic loadings can effectively modulate the initial oxidation of Al(1-x)Nix alloys. We find that prestrains can not only suppress or promote outward and inward ionic diffusions, but change the oxygen Ehrlich-Schwöbel (ES) barrier across oxide islands. The former affects the oxidation kinetics while the latter leads to a oxide growth mode transtion, which comprehensively determines the evolution of oxide nanostructure. In addition, we propose a theoretical chemo-mechanical coupling model to predict the internal stress evolution and the stress relaxation in Al0.7Ni0.3 oxidation. Finally, the study of Al and Al0.7Ni0.3 oxidations under dynamic strains shows that alloying nickel in aluminum effectively enhances the oxidation resistance under cyclic loadings by intensifying the chemo-mechanical coupling effect. Findings in this work may shed the light on the modulation of surface oxidation through applying mechanical loadings, and is helpful to the materials design and protection.

Experimental and chemo-mechanical analysis of hot corrosion influence on creep properties of DD6 single crystal superalloy in molten NaCl salt

The creep tests of specimens coated with NaCl salt were carried out to investigate the influence of hot corrosion on the creep properties of DD6 under 980 °C and 275 MPa. Bared specimens were also studied to make comparison. Creep lives of the salt-coated specimens are much lower than those of the bared specimens. Metallographic analysis of the fracture surface shows that creep-rupture of the salt-coated specimens is caused by a main tearing ridge rather than the connection of dimples in the bared specimens. Directional diffusion of metallic elements, i.e. Cr, Ta, and W, happens in hot corrosion-creep test due to the chemical gradient. The location of Al-rich region in the salt-coated specimen is found along the path of crack propagation. The microstructure evolution of γ/γ′ is different between the salt-coated specimens and the bared specimens. A chemo-mechanical coupling model was used to assist the understanding of the failure mechanism of the salt-coated specimen. The simulation results prove that the anodic concentration is a basic factor for the appearance of the main tearing ridge and Al-rich region in the salt-coated specimen. These findings can be helpful to understand the mechanical properties of Nickel-based single crystal superalloys in marine environment.

Acceleration of DNA Replication of Klenow Fragment by Small Resisting ForceSupported by the National Natural Science Foundation of China (Grant Nos. 11674381, 21991133, 11774407, 11874415, 11874414, and 31770812), the Key Research Program on Frontier Science (Grant No. QYZDB-SSWSLH045), the National Key Research and Development Program of China (Grant No. 2016YFA0301500), the CAS Strategic Priority Research Program (Grant No. XDB37010100), and

DNA polymerases are an essential class of enzymes or molecular motors that catalyze processive DNA syntheses during DNA replications. A critical issue for DNA polymerases is their molecular mechanism of processive DNA replication. We have proposed a model for chemomechanical coupling of DNA polymerases before, based on which the predicted results have been provided about the dependence of DNA replication velocity upon the external force on Klenow fragment of DNA polymerase I. Here, we performed single molecule measurements of the replication velocity of Klenow fragment under the external force by using magnetic tweezers. The single molecule data verified quantitatively the previous theoretical predictions, which is critical to the chemomechanical coupling mechanism of DNA polymerases. A prominent characteristic for the Klenow fragment is that the replication velocity is independent of the assisting force whereas the velocity increases largely with the increase of the resisting force, attains the maximum velocity at about 3.8 pN and then decreases with the further increase of the resisting force.

Chemo-mechanical coupling model of off-shore concrete structures

Seawater represents a complex phenomenon due to the presence of multiple ions. Previous researches aimed to estimate the resistance losses due to sulphate and chloride attacks based on probabilistic approaches. Few studies have focused on the complex chemo-mechanical modeling by coupling all the ions present in seawater and in concrete. In this study, the model proposed is based on the coupling between two codes CemPP- for the microstructure generation of the cementitious material, the evolution of the hydration and chemical reactions - and Cast3M - for the mechanical calculations and damage modeling. Results highlight the importance of considering each effect of cement paste’s ion reacting with seawater and their role on the overall mechanical behaviour of the structure affected by the chemical phases present at equilibrium.

A common ATP-dependent stepping model for kinesin-5 and kinesin-1: Mechanism of bi-directionality of kinesin-5

Kinesin-5 and kinesin-1 proteins are two families of kinesin superfamily molecular motors that can move processively on microtubules powered by ATP hydrolysis. Kinesin-1 is a unidirectional motor. By contrast, some yeast kinesin-5 motors are bidirectional and the directionality can be switched by changing the experimental conditions. Here, on the basis of a common chemomechanical coupling model, the dynamics of kinesin-1 and in particular the dynamics of kinesin-5 is studied theoretically, explaining the available experimental data. For example, the experimental data about different movement directions under different experimental conditions for kinesin-5 are explained well. The origin of why kinesin-1 can only make unidirectional movement and kinesin-5 can make bidirectional movements is revealed. The origin of mutations or deletions of several structural elements affecting the directionality of kinesin-5 is revealed. Moreover, some predicted results for kinesin-5 are provided.

An Analytical Solution for Chemo-Mechanical Coupled Problem in Deformable Sphere with Mass Diffusion

In this paper, a thermodynamically consistent chemo-thermo-mechanical coupled constitutive relationship is developed based on the local energy conservation equation, the entropy inequality and mass conservation equation, and the constitutive relation for chemo-mechanical coupled problem was degraded when the temperature was kept constant. The governing equations of chemo-mechanical coupling model were established by combining the force balance equation with the Fick diffusion equation. Then we considered a case of a sphere with symmetrical boundary and initial conditions, and the diffusion conducted along the radial direction. Using the symmetry of the spherical structure, the chemo-mechanical coupled governing equation was simplified, and then analytically solved by the separation variable method. The analytical expressions of concentration and displacement were obtained, and the variations of stresses, concentration, displacement and chemical potential with time were deduced. The results showed that the deformation of the sphere and species diffusion was not independent, but interacts with each other. The chemical potential in the sphere could be affected by both of them.

A common chemomechanical coupling model for orphan and conventional kinesin molecular motors

Orphan and conventional kinesin dimers represent two families of the kinesin superfamily molecular motors. Conventional kinesin, having a 14-residue neck linker (NL) in each head, can step processively on microtubule (MT), with an ATP hydrolysis being coupled with a mechanical stepping under no load. Orphan kinesin phragmoplast-associated kinesin-related protein 2 (PAKRP2) dimer, despite having a NL of 32 residues in each head, can also step processively on MT and exhibits tight chemomechanical coupling under no load. However, the dynamic properties of the wild type PAKRP2 and the mutant one with each NL truncated to 14 residues are very different from those of the wild type conventional kinesin and the mutant one with each NL being replaced by the 32-residue NL from PAKRP2. Here, based on a common chemomechanical coupling model we study computationally the dynamics of the two families of the kinesin dimers, with the simulated results explaining quantitatively the available experimental data. The large differences in the dynamics between the two families of kinesin dimers arise mainly from different rate constants of NL docking and ATPase activity and different weak affinities of the head in ADP state for MT. The studies indicate that both the orphan kinesin PAKRP2 and conventional kinesin use the same mechanism for processive motility.

A chemo-mechanical coupling model for concrete lining subjected to external sulfate attack

Concrete is widely used for lining structure in underground facility and unfortunately it is often attacked by coupling effects of external sulfate and triaxial compressive stress transferred from surrounding soil or rock formations. In this text, a model is developed to depict the coupling effects of mechanical loading and external sulfate attack on concrete lining. The total strain is composed of elastic strain and plastic strain characterised by modified Drucker–Prager criterion, and the deterioration of mechanical properties is related to both mechanical damage and chemical damage. The former considers microcracks generation through micromechanical operations, and the latter is defined by the molar concentration of total sulfates in concrete. A simple diffusion equation is deduced from the sulfate ions diffusion-reaction process to depict the distribution of the total sulfates in both solution and solid phase. A relationship between chemical damage and sulfates concentration is established based on experimental results. The proposed model is then implemented into COMSOL multiphysics to analyse the long-term stability of concrete lining subjected to external sulfate attack in a tunnel. The numerical results show that the simulation results match the experimental data.

Chemo-mechanical coupling analysis of composites by second-order multiscale asymptotic expansion

A novel second-order multiscale asymptotic expansion is developed in this work to analyze chemo-mechanical properties of composites with periodic microstructure. The chemo-mechanical coupling model which considers mutual interaction between the displacement and concentration fields of composites is introduced at first. Then, the second-order multiscale formulas based on homogenization methods and multiscale asymptotic expansion for evaluating the chemo-mechanical coupling problems are proposed, including the microscale cell functions, homogenized coefficients and homogenized equations. Further, the related numerical algorithms on the basis of the proposed multiscale models are brought forward. Finally, by some representative examples, the efficiency and accuracy of the presented algorithms are verified. The numerical results clearly illustrate that the second-order multiscale methods proposed in this work are effective and valid to predict the chemo-mechanical coupling properties, and can capture the microscale behavior of the composites accurately.

A non-tight chemomechanical coupling model for force-dependence of movement dynamics of molecular motors.

Based on the available experimental evidence, we present a simple and general model to describe the movement dynamics of molecular motors that can move processively on their linear tracks by using the chemical energy derived from ATP hydrolysis. An important aspect of the model is the non-tight coupling between the ATP hydrolysis and mechanical stepping, in contrast to the prevailing models presented in the literature that assume the tight chemomechanical coupling. With kinesin as an example, based on the current model, we study in detail its movement dynamics under a backward load, reproducing well the diverse available single-molecule experimental data such as the forward to backward step ratio, velocity, dwell time, randomness, run length, etc., versus the load. Moreover, predicted results are provided on the force-dependence of the mean number of ATP molecules consumed per mechanical step. Additionally, the theoretical data for the dynamics of myosin-V obtained based on the model are also in good agreement with the available experimental data.

A chemomechanical coupling model for stress analysis of oxide scale growing between ceramic coating and substrate

The thermal growth of the oxide scale between the ceramic coating and substrate due to high-temperature oxidation is regarded as the dominating cause for the failure of the ceramic/substrate system, for example the thermal barrier coating. Based on the irreversible evolution equations, the growth strain in the oxide scale is formulated by considering the coupling effects of stress and chemical reaction during isothermal oxidation. A model which accounts for the growth strain, thermal expansion strain, and viscoplastic effect is developed for the stress analysis of the oxide scale. Numerical results reveal that there is a significant gradient in the oxide scale with the maximum compressive stress at the oxide/substrate interface and the minimum compressive stress at the ceramic/oxide interface, and the stress in the oxide scale is larger than those in the ceramic coat and bond coat. The effects of the growth strain, viscoplasticity, chemomechanical coupling, and chemical reaction on the stresses are numerically discussed.

A chemomechanical coupling model for oxidation and stress evolution in ZrB2–SiC

Abstract

A chemo-mechanical coupling model of deviated borehole stability in hard brittle shale

Abstract A chemo-mechanical coupling model of borehole stability in hard brittle shale considering structure characteristics and targeted hydration was established, the influencing factors of the distribution of collapse pressure were analyzed based on the model, and a field case analysis was conducted. Based on the physicochemical properties of hard brittle shale, a drilling fluid activity window was proposed for calculating collapse pressure by establishing the relationships of drilling fluid activity vs. swelling ratio of rock and rock activity vs. moisture content to determine critical swelling ratio of rock and reasonable moisture content. The results show that, when fixing the dip angle of weak plane, the collapse pressure appears a quarter symmetric distribution with the change in tendency, there is no azimuth angle who has a monotonic increasing or decreasing collapse pressure, and dangerous sections and safe sections exist alternately; compared with cohesion of weak plane, collapse pressure is more sensitive to internal friction angle. Field case shows that, accurate prediction of collapse pressure distribution can be obtained by the chemo-mechanical coupling model, in which borehole stability can be ensured and the density of drilling fluid can be decreased as long as the drilling fluid activity is controlled in the window.

Analytical solutions for a one-dimensional chemo-mechanical coupling problem

Chemo-mechanical coupling exists in a lot of intelligent materials including hydrogels, biological tissues and other soft materials. These materials are able to respond to external stimulus, such as temperature, chemical concentration, and pH value. In this paper, a one-dimensional theoretical model for chemo-mechanical coupling is proposed for analyzing the uniaxial stress/strain state of coupling materials. Based on the chemo-mechanical coupled governing equation, the displacement function and concentration function are derived and the stress and chemical potential are obtained. It is shown that the present chemo-mechanical theory can characterize the chemo-mechanical coupling behavior of intelligent materials.

Dynamics of strand passage catalyzed by topoisomerase II

DNA topoisomerase II is a homodimeric molecular machine that uses ATP hydrolysis to untangle DNA by passing one double-stranded DNA duplex (T-segment) through another double-stranded duplex (G-segment). However, despite extensive studies, the dynamics of ATP-dependent T-transport is still not very clear. Here, based on the proposal that transport of the T-segment through the transiently cleaved G-segment and the opened C-gate of the enzyme is via a free diffusion mechanism, the dynamics of T-transport are studied theoretically. Our results show that, to complete passage of the strand with nearly 100% efficiency, the C-gate is required to open by a width that is only slightly larger than the width of DNA duplex and for a time shorter than 100 micros in the presence of several k (B) T binding affinities of the T-segment for the B' domains. The results are implied by our understanding of the opening and closing dynamics of the C-gate. Moreover, the dependence of chemomechanical coupling efficiency on degrees of DNA supercoiling by gyrases can also be explained by using our results. On the basis of these theoretical results and previous experimental data, a modified two-gate model for chemomechanical coupling of the topoisomerase II enzyme is proposed.