A physics-based single crystal plasticity model for crystal orientation and length scale dependence of machining response

Official URL: http://risc01.sabanciuniv.edu/record=b1817027 (Table of Contents)

Recent demands towards the miniaturization raises the importance of micro-machining, which is one of the most flexible manufacturing process. The cutting parameters such as depth of cut, tool diameter etc. have become comparable to the dimensions of the crystals during machining at micro scale which effects on the machining response of the material. Due to the highly anisotropic behavior of single crystals, it is important to consider the effect of the crystallographic orientation on the cutting response. Size-dependency of the cutting response is defined as the non-linear increase in specific cutting energy with the reduction in the uncut chip thickness. Size dependence has to be also considered in machining models since it could affect the chip formation process, cutting forces and the stability. In this work, micro-machining model based on crystal plasticity kinematics and physics based constitutive descriptions is developed for FCC single crystals. The proposed model contains constitutive laws that are based on physics-based material state variables. The size-effect is also incorporated to the physics based constitutive laws as an additional strain hardening term that is a function of the amount of shear and shear plane length. Size dependence is related to the nature of the shearing process being confined to smaller shear planes as the depth of cut decreases and the corresponding increase in the statistically stored dislocation density. In this work the effect of edge radius is not considered and the effect of strain-rate is present. The total work is minimized to find the shear angle for any given crystal orientation and the selected machining parameters. The model is applied simulate the experimental force fluctuations of single crystals of aluminum and copper in Cohen’s work with a reasonably good agreement