Fracture Mechanism of Nanocomposite of Metal and Graphene with Defect Pores.

Molecular dynamics simulations were performed to investigate the fracture mechanism and mechanical response of Ni/Graphene nanocomposites under nanoindentation. The effects of size and location of defect pores were explored by examining the pore structure transition, microstructure transition, variation of HCP atomic fraction and dislocation density with indentation depth, load-displacement relationship, and stress distribution. It was found that when the long edges of the pore are located along the longer dimension, the pores are fractured by indentation forces from the short edges. The closer the pore is to the indent, the smaller loading force is required for the pores to reach its fracture limit. For the long edges located along the transverse direction, the maximum indentation depth increases with the distance of the pore away from the indenter. The density of HCP atoms and dislocations in the composite gradually increases with the indentation depth. To understand the physical mechanism of the fracture behavior, we also evaluated the stress distribution in graphene at the fracture point.

Confinement Dynamics of Nanodroplets between Two Surfaces: Effects of Wettability and Electric Field.

The electrowetting effect and related applications of tiny droplets have aroused widespread research interest. In this work, we report molecular dynamics simulations of confinement dynamics of nanodroplets under different droplet-surface interactions and surface distances under an external electric field. So far, the effect of the surface-droplet interactions on electric field-induced dynamics behaviors of droplets in confined spaces has not been extensively studied. Our results show that in the absence of electric field there is a critical value of surface wettability for the shape transition of droplets. Above this value, the droplet is divided into small droplets adhered on the bottom and top surfaces; below this value, the droplets are detached from the surfaces. When an external electric field is applied parallel to the surfaces, the droplet spreads on the surface along the direction of the electric field. It was found that the surface separation significantly influences the transition of the droplet shape. The steady morphology of the droplets under the electric field depends on the surface-droplet interaction and surface separation. We explore the underlying mechanism causing the morphological transition through analyzing the molecular interactions, the number of interracial molecules and the interaction force between the droplets and surfaces. These results provide basic insights into the molecular interactions of nanodroplets under different confined environments, and clues for applications of confined nanodroplets under the control of electric field.

Investigation of the Effect of Process Parameters on Bone Grinding Performance Based on On-Line Measurement of Temperature and Force Sensors.

This study investigates the effect of process parameters on neurosurgical bone grinding performance using a miniature surgical diamond wheel. Bone grinding is an important procedure in the expanded endonasal approach for removing the cranial bone and access to the skull base tumor via nasal corridor. Heat and force are generated during the grinding process, which may cause thermal and mechanical damage to the adjacent tissues. This study investigates the effect of grinding process parameters (including the depth of cut, feed rate, and spindle speed) on the bone grinding performance using temperature and force measurement sensors in order to optimize the grinding process. An orthogonal experimental design with a standard orthogonal array, L9 (33), is selected with each parameter in three levels. The experimental results have been statistically analyzed using the range and variance analysis methods in order to determine the importance order of the process parameters. The results indicate that the effect of the cutting depth on the grinding temperature and normal force is the largest, while the effect of the spindle speed on the tangential force is the largest. A high spindle speed would make the temperature rise to a certain extent; however, it significantly reduces the grinding force. At a certain spindle speed, a lower depth of cut and feed rate help to reduce the grinding temperature and force.