Nano-scale Interfacial Friction Behavior between Two Kinds of Materials in MEMS Based on Molecular Dynamics Simulations

The aim of this article was to provide a systematic method to perform molecular dynamics simulotion or evaluation for nano-scale interfacial friction behavior between two kinds of materials in MEMS design. Friction is an important factor affecting the performance and reliability of MEMS. The model of the nano-scale interracial friction behavior between two kinds of materials was presented based on the Newton＇ s equations of motion. The Morse potential function was selected for the model. The improved Verlet algorithm was employed to resolve the model, the atom trajectories and the law of the interfacial friction behavior. Comparisons with experimental data in other paper confirm the validity of the model. Using the model it is possible to simulate or evaluate the importance of different factors for designing of the nano-scale interfacial friction behavior between two kinds of materials in MEMS.

Interfacial friction at action: Interactions, regulation, and applications

Friction is a fundamental force that impacts almost all interface-related applications.Over the past decade,there is a revival in our basic understanding and practical applications of the friction.In this review,we discuss the recent progress on solid–liquid interfacial friction from the perspective of interfaces.We first discuss the fundamentals and theoretical evolution of solid–liquid interfacial friction based on both bulk interactions and molecular interactions.Then,we summarize the interfacial friction regulation strategies manifested in both natural surfaces and artificial systems,focusing on how liquid,solid,gas,and hydrodynamic coupling actions mediate interfacial friction.Next,we discuss some practical applications that are inhibited or reinforced by interfacial friction.At last,we present the challenges to further understand and regulate interfacial friction.

PHYSICAL SIMULATION OF INTERFACIAL CONDITIONS IN HOT FORMING OF STEELS

In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of steels. Emphasis has been placed on the influence of the oxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. Theses include hot flat rolling of steel slabs and hot axi- symmetric forging of steel cylinders and rings.Temperature measurements and computations demon- strate that for similar conditions, similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis,physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot' sandwich' rolling and hot tensile tests with finite element modelling have been carried out to evaluate the hot ductility of the oxide scale.The results indicate that the defomation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface.Finaly, friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported.

Experimental Study on Performance of Multidirectional Geogrid and Its Application in Engineering of High Slope

By analyzing the grille mechanical property, tensile strength and creep tests, and the fi eld tests, we investigated the characteristics and the reinforcement principle of multidirectional geogrid, and obtained the effect factors of grid characteristics, load and time curve and the shear stress of grille and sand interface. The reinforcement effect of geogrid in combination of typical project cases was illustrated and the following conclusions were presented. Firstly, multidirectional geogrid has ability to resist structural deformation, node distortion or soil slippage under stress, and can effectively disperse load. Secondly, with the increase of tensile rate, grille intensity increases and the creep value also increases with the increase of load. Thirdly, the frictional resistance balance between horizontal thrust of damaged zone and reinforced soil in stable region can avoid slope failure due to excessive lateral deformation. Fourthly, the multidirectional geogrid is able to withstand the vertical, horizontal and diagonal forces by combing them well with three-dimensional orientation, realizing the purpose of preventing soil erosion and slope reinforcement, which has a wide range of application and development in engineering fi eld.

A new model for predicting the critical liquid-carrying velocity in inclined gas wells

Based on the assumption of gas-liquid stratified flow pattern in inclined gas wells,considering the influence of wettability and surface tension on the circumferential distribution of liquid film along the wellbore wall,the influence of the change of the gas-liquid interface configuration on the potential energy,kinetic energy and surface free energy of the two-phase system per unit length of the tube is investigated,and a new model for calculating the gas-liquid distribution at critical conditions is developed by using the principle of minimum energy.Considering the influence of the inclination angle,the calculation model of interfacial friction factor is established,and finally closed the governing equations.The interface shape is more vulnerable to wettability and surface tension at a low liquid holdup,resulting in a curved interface configuration.The interface is more curved when the smaller is the pipe diameter,or the smaller the liquid holdup,or the smaller the deviation angle,or the greater gas velocity,or the greater the gas density.The critical liquid-carrying velocity increases nonlinearly and then decreases with the increase of inclination angle.The inclination corresponding to the maximum critical liquid-carrying velocity increases with the increase of the diameter of the wellbore,and it is also affected by the fluid properties of the gas phase and liquid phase.The mean relative errors for critical liquid-carrying velocity and critical pressure gradient are 1.19%and 3.02%,respectively,and the misclassification rate is 2.38%in the field trial,implying the new model can provide a valid judgement on the liquid loading in inclined gas wells.

Solar-powered miniature robot for on-site oil spill treatment under magnetic steering

Walking on the water surface is an effective method for miniature robots to transport payloads with dramatically decreased interfacial drag. Current aquatic robots reported are generally actuated by a beam of focused light that can trigger asymmetrical deformation, enabling the directional movement through horizontal momentum transfer of photoinduced actuation force to the water. However, the operations are heavily dependent on manual manipulation of the focused light, making the long-term actuation and application of the aquatic robots in vast scenarios challenging. Herein, we developed a kind of water striderinspired robot that can autonomously manage the motion on the water surface under solar irradiation, with their direction steerable by a magnetic field. The motion of this bioinspired robot on the water surface was achieved by the use of a solar cell panel as a driving module to enable propulsive motion based on the conversion of light-electric-mechanical energies. The superhydrophobic design of its leg surfaces enables the aquatic robots with weight-bearing and drag-reducing abilities. With the assistance of magnetic navigation, the bioinspired robot can continuously and controllably locomote to the oily spill floating on the water body and collect them with high efficiency. For further demonstration, the treatment of oil spills in a campus pool with high efficiency has also been achieved. This on-site oil-spill treating strategy, taking advantage of a home-made bioinspired robot actuated by natural sunlight under magnetic steering, shows great potential applications in water-body remediation.