Modeling of Serrated Chip Formation With a Fracture Locus Approach

Abstract

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.

Material embrittlement in high strain-rate loading

“…Similarly, in their experimental study on the ductile-to-brittle transition of an Ni metal, Mahalingam et al [116] found that the toughness of the metal decreased with an increase in strain rate. Abushawashi et al [117] also studied the influence of strain rate on the fracture strain of a material during a cutting process. The fracture strain was calculated based on the J-C damage model, as shown in equation ( 26)…”

3D FEM simulation of chip breakage in metal cutting

“…For example, Abushawashi et al modified the Rice-Tracey model by incorporating the strain rate impact on ductility in order to simulate serrated chip formation in steel AISI 1045 [27]. The Johnson-Cook damage model was widely applied to simulate serrated chip formation for different materials, for example, Inconel 718 by Singh et al and Sievert et al [28,29], titanium Ti-6Al-4V by Zhang et al [30], or AISI 1045 by Vaziri et al [31].…”