TOWARDS A PHYSICAL COMPREHENSION OF MATERIAL STRENGTHENING FACTORS DURING MACRO TO MICRO-SCALE MILLING
AbstractPresent work highlights the importance of material strain rate hardening characteristics as an influential factor in increasing material strength, as uncut chip thickness decreases from macro to micro-level dimensions during down-cut milling process. It has been found for a strain rate dependent material (A2024-T351) that rake face-chip contact length increases nonlinearly when tool approaches to micro-level of uncut chip thickness. This suggests higher energy consumption due to frictional interaction at tool-chip interface, resulting in higher specific cutting energy. In addition, results depict that increase in cutting speeds are attributed to increased rake face-chip contact lengths. Furthermore, to analyze the contribution of the strain gradient hardening on size effect phenomenon during micro cutting operations, modified Johnson-Cook material model (strain gradient-based approach) of the equivalent stress has been formulated in ABAQUS®/EXPLICIT via its user subroutine VUMAT. The results put forward the significance of strain gradient hardening to fully capture the size effect phenomenon du-ring micro cutting operations, at high cutting speeds for a strain rate dependent material. Finally, milling experiments have been performed to validate the numerical model in terms of specific cutting energy and chip morphology.