NANOINDENTATION SIMULATION OF PE/POSS UNDER DIFFERENT SHAPES OF INDENTERS

In this paper,the nanoindentation simulation on the two models of neat polyethylene（PE） and the polyethylene incorporated with 25wt% POSS（POSS-PE） is performed to reveal the reinforcing mechanism of the mechanical properties.The influence of the indenter shapes on nanoindentation is researched by using three different shapes of diamond indenters（cube-corner indenter,cylindrical indenter with spherical tip and cylindrical indenter with flat tip）.The molecular mechanics method is adopted to eliminate the temperature effects.Under different indenters,the load-displacement responses,hardnesses（indentation hardness and Martens hardness） and Young＇s moduli of PE and POSS-PE are obtained.Compared with PE,all the mechanical properties are improved dramatically.Then,we analyze the source of loading drop phenomena and the enhancement mechanism of POSS.Furthermore,the result shows that the different shapes of indenters cause a large impact on indentation hardness,but a little impact on Martens hardness.And Young＇s modulus of the flat indenter is much larger than that of cube-corner indenter and spherical indenter.

MULTISCALE SIMULATION OF INCIPIENT PLASTICITY AND DISLOCATION NUCLEATION ON NICKEL FILM DURING TILTED FLAT-ENDED NANOINDENTATION

Multiscale simulations of the tilted flat-ended nanoindentation with different tilted angles （from 5° ～ 30°） on the （-1 1 0） surface of nickel crystal were studied using the QC method. The model of the indentation is a flat-end indenter inclined by an angle ε driven into a half- plane vertically. Load-displacement responses, initiM stages of the plasticity deformations and dislocation emissions for nickel film at different inclined angles were obtained and analyzed as well. An energy criterion was successfully proposed to analyze the critical load for the first dislocation emission beneath the edge of the indenter. Simulation results agree well with analytical ones. An elastic model based on the contact theory and the Peierls-Nabarro dislocation model were combined to analyze when and where the dislocation will be emitted beneath the lower surface of an inclined indenter. Results indicate that the key parameter is the ratio of the contact half- width to the position of the slip plane. This parameter shows the range in which a dislocation will probably be emitted. This mechanism explains the simulation results well. This work is of value for understanding the mechanism of dislocation emissions of FCC crystals under tilted flat- ended nanoindentation while providing approaches to predicting when the first dislocation will be emitted and where subsequent dislocations will probably be emitted.

Visible-light-promoted oxidative decarboxylation of arylacetic acids in air:Metal-free synthesis of aldehydes and ketones at room temperature

A metal-free photocatalytic oxidative decarboxylation reaction at room temperature was developed for the synthesis of aromatic aldehydes and ketones from the corresponding arylacetic acids.The reaction was realized under blue-light irradiation by adding 1 mol%of 4 CzIPN as photocatalyst and air as oxidant.This reaction represents a novel decarboxylation of a sp^3-hybridized carboxylic acids without traditional heating,additional oxidants,and metal reagents under mild conditions.