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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.
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Insights into tribology from in situ nanoscale experiments
Tribology—the study of contacting, sliding surfaces—seeks to explain the fundamental mechanisms underlying friction, adhesion, lubrication, and wear, and to apply this knowledge to technologies ranging from transportation and manufacturing to biomedicine and energy. Investigating the contact and sliding of materials is complicated by the fact that the interface is buried from view, inaccessible to conventional experimental tools. In situ investigations are thus critical in visualizing and identifying the underlying physical processes. This article presents key recent advances in the understanding of tribological phenomena made possible by in situ experiments at the nanoscale. Specifically, progress in three key areas is highlighted: (1) direct observation of physical processes in the sliding contact; (2) quantitative analysis of the synergistic action of sliding and chemical reactions (known as tribochemistry) that drives material removal; and (3) understanding the surface and subsurface deformations occurring during sliding of metals. The article also outlines emerging areas where in situ nanoscale investigations can answer critical tribological questions in the future.
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- PAR ID:
- 10167391
- Date Published:
- Journal Name:
- MRS Bulletin
- Volume:
- 44
- Issue:
- 06
- ISSN:
- 0883-7694
- Page Range / eLocation ID:
- 478 to 486
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1557/mrs.2019.122
