FE modeling and simulation of machining Alloy 718 based on ductile continuum damage

A novel model for rigid visco-plastic flow and continuous damage evolution is proposed for the modeling and simulation of chip formation of the Alloy 718. The model draws from a recent thermodynamically consistent damage coupled to elasto-visco-plasticity framework for ductile failure, which is advanced to purely dissipative flow stress problems in the DEFORM 2D (TM) platform. As opposed to standard models with direct damage-plasticity coupling, the present model describes this coupling through a visco-plastic damage driving energy. The effective material response is described by the Johnson-Cook model where onset of damage evolution is controlled by a modified Cockcroft-Latham failure criterion, facilitating a flexible modeling of serrated chip formation. By comparing the proposed continuous damage degradation model to the damage drop method in DEFORM 2D (TM) the role of ductile failure on the chip formation is investigated. The model is calibrated and validated against experimental machining tests, where both continuous and serrated chip formation is observed for the Alloy 718 depending on the cutting speed. From the experiment, cutting forces, chip shapes and tool-chip contact lengths were analyzed and compared to the model response. A good agreement between model and experimental results is obtained.