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 ...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.展开更多
The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high pre...The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high precision. The optimal small cutter is determined based on the geometric information of the points where a cutter most probably collide with the machined surface. Several larger cutters are selected to machine the surface in order to find the interference-free area. The difference of machining time for this area between the optimal small cutter and the large cutters is calculated. The functional relationship between the machining time and the radius of a cutter is established, by which the optimal number of cutters is obtained. The combination of cutters, which possesses the minimum overall machining time, is selected as the optimal cutter sizes. A case study has demonstrated the validity of the proposed methodology and algorithms.展开更多
The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces.In the past,the influence of roughness has been investigated thoroughly.However,even ...The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces.In the past,the influence of roughness has been investigated thoroughly.However,even in the presence of perfectly smooth surfaces,geometry can come into play in form of the macroscopic shape of the contacting region.Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft,adhesive counterpart.When it is carefully pulled off,we find that in contrast to circular shapes,detachment occurs not instantaneously but detachment fronts start at pointed comers and travel inwards,until the final configuration is reached which for macroscopically isotropic shapes is almost circular.For elongated indenters,the final shape resembles the original one with rounded corners.We describe the influence of the shape of the stamp both experimentally and numerically.Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov.It is based on a local,mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion.The validation of the suggested method is made both by comparison with known analytical solutions and with experiments.The method is applied for simulating the detachment of flat-ended indenters with square,triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to 'brushes'.The method is extended for describing power-law gradient media.展开更多
基金supported by the Science and Technology Innovation Talents Special Fund of Harbin(No.2012RFQXG001)the National Natural Science Foundation of China(No.11102053)the China Scholarship Council(CSC)
文摘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.
基金Funded by the Doctorate Degree Program Foundation of the Ministry of Education (No. 2000061120)
文摘The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high precision. The optimal small cutter is determined based on the geometric information of the points where a cutter most probably collide with the machined surface. Several larger cutters are selected to machine the surface in order to find the interference-free area. The difference of machining time for this area between the optimal small cutter and the large cutters is calculated. The functional relationship between the machining time and the radius of a cutter is established, by which the optimal number of cutters is obtained. The combination of cutters, which possesses the minimum overall machining time, is selected as the optimal cutter sizes. A case study has demonstrated the validity of the proposed methodology and algorithms.
文摘The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces.In the past,the influence of roughness has been investigated thoroughly.However,even in the presence of perfectly smooth surfaces,geometry can come into play in form of the macroscopic shape of the contacting region.Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft,adhesive counterpart.When it is carefully pulled off,we find that in contrast to circular shapes,detachment occurs not instantaneously but detachment fronts start at pointed comers and travel inwards,until the final configuration is reached which for macroscopically isotropic shapes is almost circular.For elongated indenters,the final shape resembles the original one with rounded corners.We describe the influence of the shape of the stamp both experimentally and numerically.Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov.It is based on a local,mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion.The validation of the suggested method is made both by comparison with known analytical solutions and with experiments.The method is applied for simulating the detachment of flat-ended indenters with square,triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to 'brushes'.The method is extended for describing power-law gradient media.
