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Metal peeling refers to the process of forming a thin metal strip from the surface of a rotating feedstock using controlled material removal -- machining under an applied strip tension. In this paper, the mechanics of strip formation process is described, while emphasizing the role of strip tension in ensuring uniformity and quality of the peeled strip. This includes an analysis of the deformation history in the peeling zone and the transport dynamics of the strip as it moves from the cutting edge to the coiler. Using conservation laws, governing equations for strip tension and velocity that incorporate dynamic spatiotemporal interactions between peeling and transport processes are developed. The mechanics of strip formation process is described, while emphasizing the role of strip tension in ensuring uniformity and quality of the peeled strip. This includes an analysis of the deformation history in the peeling zone and the transport dynamics of the strip as it moves from the cutting edge to the coiler. Using conservation laws, governing equations for strip tension and velocity that incorporate dynamic spatiotemporal interactions between peeling and transport processes are developed. Peeling experiments are performed with steel using a prototype experimental platform to evaluate the proposed control approach. Comparisons between two control strategies, with and without tension feedback, are presented and discussed. The importance of real-time tension control for mitigating strip thickness variations and improving other dimensional features of the strip such as flatness and edge waviness is also briefly discussed. 

Tool-chip contact stresses are of major interest in developing a basic understanding of the mechanics of machining. The interfacial and sliding conditions along the tool-chip contact in machining differ significantly from that of conventional, lightly loaded, tribological contacts in two major aspects — the occurrence of plastic flow (in the chip) at the sliding interface and intimate nature of the contact where apparent and real contact areas are the same. In this study, we present an experimental method for direct measurement of the tool-chip contact stresses. This involves the use of sapphire as a cutting tool coupled with digital photoelasticity to obtain full-field principal stress difference (isochromatics) and principal stress directions (isoclinics). This enables direct full-field characterization of the tool-chip contact stresses, as well as stresses within the cutting tool, at a micron-scale resolution not achieved previously. Our results show that the shear stress exhibits a maximum at a small distance from the tool tip, while the normal stress decreases monotonically with increasing distance from the tool tip. The maximum shear stress shows a good correlation with the shear flow stress of the material that is being machined. We also briefly discuss applications of the method to derive the stress distribution at the tool flank face and quantify frictional dissipation at both the contacts — tool-chip contact and flank-machined surface contact. 

Using direct high-speed imaging, we study the transition between different chip formation modes, and the underlying mechanics, in machining of ductile metals. Three distinct chip formation modes — continuous chip, shear-localized chip, and fragmented chip — are effected in a same material system by varying the cutting speed. It is shown using direct observations that shear-localized chip formation is characterized by shear band nucleation at the tool tip and its propagation towards the free surface, which is then followed by plastic slip along the band without fracture. The transition from shear-localized chip to fragmented chip with increasing cutting speed is triggered by crack initiation at the free surface and propagation towards the tool tip. The extent to which crack travels towards the tool determines whether the chip is partially fragmented or fully fragmented (discontinuous). It is shown that shear localization precedes fracture and controls the crack path in fragmented chip formation. Dynamic strain and strain-rate fields underlying the each chip formation mode are quantified through image correlation analysis of high-speed images. Implications for using machining as an experimental tool for fundamental studies of localization and shear fracture in ductile metals are also discussed.