In this study, the reverse osmosis (RO) of a salt solution was investigated using a molecular dynamics method to explore the performance of a multilayer porous graphene membrane. The effects of the salt solution concentration, pressure, layer separation and pore offset on the RO performance of the membrane were investigated and the influences of the number of layers and the gradient structure were determined. The results show that as the salt solution concentration increases, the energy barrier of the water molecules passing through the bilayer porous graphene membranes changes slightly, indicating that the effect of the water flux on the membrane can be ignored. The salt rejection performance of the membrane improves with an increase in the concentration of the salt solution. When the pressure is increased, the energy barrier decreases, the water flux increases and the salt rejection decreases. When the layer separation of the bilayer porous graphene membrane is the same as the equilibrium spacing of the graphene membrane, the energy barrier is the lowest and the membrane water flux is the largest. The energy barrier of the bilayer porous graphene membrane increases with increasing layer separation, resulting in a decrease in the water flux of the membrane. The salt rejection increases with increasing layer separation. The water flux of the membrane decreases as the energy barrier increases with increasing pore offset and the salt rejection increases. The energy barrier effect is more pronounced for a larger number of graphene layers and the water flux of the membrane decreases because it is more difficult for the water molecules to pass through the porous graphene membrane. However, the salt rejection performance improves with the increase in the number of layers. The gradient pore structure enhances the energy barrier effect of the water molecules permeating through the membrane and the water flux of the membrane decreases. The salt rejection performance is improved by the gradient pore structure. The research results provide theoretical guidance for research on the RO performance of porous graphene membranes and the design of porous graphene membranes.

Using an atomic force microscope (AFM), the wear of monocrystalline silicon (covered by a native oxide layer) at high humidity was investigated. The experimental results indicated that tribochemistry played an important role in the wear of the silicon at different relative humidity levels (RH = 60%, 90%). Since the tribochemical reactions were facilitated at 60% RH, the wear of silicon was serious and the friction force was around 1.58 μN under the given conditions. However, the tribochemical reactions were restrained when the wear pair was conducted at high humidity. As a result, the wear of silicon was very slight and the friction force decreased to 0.85 μN at 90% RH. The slight wear of silicon at high humidity was characterized by etching tests. It was demonstrated that the silicon sample surface was partly damaged and the native oxide layer on silicon sample surface had not been totally removed during the wear process. These results may help us optimize the tribological design of dynamic microelectromechanical systems working in humid conditions.

Surface morphology impacts material performance and durability significantly. To gain a deeper understanding of the impact of laser shock peening (LSP) treatment on the surface morphology of materials and to explore more optimized LSP treatment strategies, this study presents an investigation into the surface morphology of 20CrMnTi steel following LSP treatment. Through the application of statistical analysis, the study examines the induced surface morphology variations resulting from both single-point repetitive LSP and multiple LSP treatments. Experimental results demonstrate significant alterations in surface roughness and peak height distribution after LSP treatments, accompanied by the presence of high amplitude compressive residual stress (CRS). Moreover, the depth of laser-induced indentations is found to be closely related to the number of impacts, and the incidence angle of the laser exhibits a discernible influence on the directional texture and periodicity of the impacted surfaces. This investigation also proposes a method for estimating surface morphology variations after LSP treatment by means of analysis of impact patterns, thereby offering the potential for enhancing the friction and wear performance of the impacted surfaces through the adjustment of the impact region position during multi-layer LSP treatment.

The dual-robotic ultrasonic nondestructive testing (NDT) system equipped with extension arm is an effective means to realize automatic ultrasonic testing of composite semi-enclosed workpieces. However, this cantilever structure amplifies the tiny vibrations of the inspection system, which seriously affects the coupling effect and the resolution of ultrasonic inspection. To solve the problem, this paper proposes a S-shaped acceleration and deceleration feature control algorithm to improve the motion stability and further to improve the inspection resolution of dual-robotic ultrasonic NDT system. Furthermore, the specific steps of S-shaped acceleration and deceleration features control algorithm in trajectory planning of the dual-robotic ultrasonic NDT system are described in detail. Comparative experiments of motion stability show that the acceleration in the x direction at the left and right ends of the detection area decreased significantly, from 0.15 to 0.08 m/s² and the ultrasonic image of the internal defects have a higher resolution and smoother edges. The improvement plays an important role in promoting the resolution at the left and right ends of the detection area.