410 Identification of the Constitutive Equation and the Shear Localization Onset based on the Mechanics of Orthogonal Metal Cutting

This paper proposes a methodology to identify the material coefficients of constitutive equation within the practical range of stress, strain, strain rate, and temperature encountered in metal cutting. Besides, it investigates the characterization of the material fracture necessary to the modeling and analysis of the chip segmentation. A methodology is therefore proposed to identify the shear stress at which the fracture occurs and the corresponding strain, strain rate and temperature necessary to define the shear localization onset. Both methodologies are based on analytical modeling of the orthogonal cutting process in conjunction with orthogonal cutting experiments. The basic mechanics governing the primary shear zone have been reevaluated for continuous and segmented chip formation processes. The stress, strain, strain rate and temperature fields have been theoretically derived leading to the expressions of the effective stress, strain, strain rate, and temperature on the main shear plane. Applying the least-square approximation techniques to the continuous chip formation results yields an estimation of the material coefficients of the constitutive equation described herein by a Johnson-Cook model. However, the segmented chip results provide data to characterize the shear localization onset. The identification results of the constitutive equation agree well with those obtained using the Compressive Split Hopkinson Bar technique (CSHB) in the case of 42CD4U steel. The identification of the shear localization onset yields encouraging results in the case of hardened AISI D2 tool steel (62 HRc).