MECHANICS OF DUCTILE FRACTURE AND SEGMENTED CHIP FORMATION IN CUTTING OF METALS

We aim to understand the mesoscale mechanics of type 3 (segmented chip formation and underlying deformation/fracture. This is done via in situ observational approach. We characterize the evolution of the deformation field, and the underlying fracture instability in both the nucleation and development stages. Using high-speed imaging, in conjunction with image correlation analysis, the main features of the deformation and fracture processes are described, both in terms of the flow phenomena, and quantitatively via deformation fields. Based on this understanding, we demonstrate control of the deformation/fracture (segmentation) instability. By ‘control’, here, is meant not only suppression of the segmentation but also means to induce it to occur in metals where segmented flow would not be the norm. We also address microstructural origins of the segmented flow, examining contribution of surface features in nucleation of segmentation. Besides its relevance for improving machining processes, improved understanding of segmentation mechanics offers potentially new routes for studying ductile failure in metals.