Generalized Aifantis strain gradient plasticity model with internal length scale dependence on grain size,sample size and strain

The internal length scale(ILS)is a dominant parameter in strain gradient plasticity(SGP)theories,which helps to successfully explain the size effect of metals at the microscale.However,the ILS is usually introduced into strain gradient frameworks for dimensional consistency and is model-dependent.Even now,its physical meaning,connection with the microstructure of the material,and dependence on the strain level have not been thoroughly elucidated.In the current work,Aifantis'SGP model is reformulated by incorporating a recently proposed power-law relation for strain-dependent ILS.A further extension of Aifantis'SGP model by including the grain size effect is conducted according to the Hall-Petch formulation,and then the predictions are compared with torsion experiments of thin wires.It is revealed that the ILS depends on the sample size and grain size simultaneously;these dependencies are dominated by the dislocation spacing and can be well described through the strain hardenmg exponent.Furthermore,both the original and generalized Aifantis models provide larger estimated values for the ILS than Fleck-Hutchinson's theory.

Study on mathematical model of cutting force in micromachining

With the development of micromachining technology,it is very important to study the mechanism of micromachining,determine the micromachining parameters and ensure the products’quality during the micromachining process.Combined with the micromechanism between tool and workpiece during micromachining process,the sources of the micro-cutting force were analyzed,the micro-cutting physical model was constructed,and the microstress model interacted between the cutting arc edge of the tool and the material of the workpiece was analyzed.Combined with the surface friction and elastic extrusion mechanism between the cutting tool and workpiece,the micro-cutting force model was constructed from two aspects.The micro-cutting depth is deeper than the minimum cutting depth and the micro-cutting depth is shallower than the minimum cutting depth,then the minimum cutting depth value was calculated.Combined with the dislocation properties and microcrystal structure of workpiece’s material,the internal stress of the micromachining force model based on the gradient plasticity theory was calculated,and the force model of the micro-cutting process was studied too.It is significant to control the precision of micromachining process during the micromachining process by constructing the micromachining process force model through studying the small deformation of the material and the mechanism of micromachining.