Modeling of Serrated Chip Formation With a Fracture Locus Approach

A fracture model is of great concern when it comes to chip formation and simulation of localized shear bands that take place in serrated chip formation. Considering the special loading characteristics of the cutting regime, the present paper is intended to evaluate the equivalent fracture strain to be used in the prediction of segmented chip formation and energy evaluation. It is assumed that both the equivalent strain rate and stress triaxiality define the material fracture locus. The stress triaxiality analysis was based on the fracture experiments using flat-grooved specimen conducted by Bai et al. [1]. The effect of the strain rate was estimated based on the strain energy density and stress triaxiality. To ensure model completeness and solution stability, damage evolution was modeled based on the material fracture energy. Numerical simulations of machining AISI steel 1045 with and without friction model were performed. The physical and morphological characteristics of the chip formation were analyzed. The results were found to be in agreement with the experimental data of the actual segmented chip obtained from the literature. The anticipated fluctuation of the cutting force caused by the chip segmentation was observed. It is noted that up to 25% reduction of the total energy required by the system may be achieved by minimizing tool friction using tribological coating and/or metal working fluids.