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UBC Theses and Dissertations

Analytical modeling of shear localization in machining processes and its effects on the tool-chip interface Fazlali, Mohammad Reza


Advanced metals, such as titanium and nickel alloys, have been widely used in the production of high-value and high-performance components in various industries, including aerospace, biomedical, automotive, etc. Shear localization is the dominant chip formation mechanism in machining of these metallic components, limiting the cutting productivity due to high cutting temperature, rapid tool wear, and tool breakage. The machined surface integrity is also affected by shear localization with wavy topography of the finished surface and residual stress fluctuation. Therefore, it is of practical importance to investigate shear localization and its effects during machining processes. This thesis proposes a new analytical thermo-mechanical model for shear localization by assuming an extended primary deformation zone and complete localization of plastic deformation inside shear bands after their formations. Unlike the classical cutting mechanics, the extended primary deformation zone enables capturing the material behavior from homogeneous deformation, to instability onset, and finally, to localization. It will be shown that localization changes the contact mechanism between the tool and the chip, where both sticking and sliding lengths change with respect to time in each localization cycle. Subsequently, the thermal load on the tool’s rake face is affected by the shear band formation in front of the tool. The model predicts: 1) shear band’s stress, temperature, and strain rate inside the primary deformation zone; 2) shear band spacing (subsequently, cutting force frequency) and width, 3) shear band’s displacement, its distribution and chip morphology; 4) time-varying sticking-sliding contact lengths; 5) time-varying cutting forces; 6) normal stress and shear stress distributions on the tool’s rake face; and 7) transient temperature distribution at the tool-chip interface. It is experimentally shown that: 1) the produced shear bands roll on the cutting tool’s rake face, causing an intimate contact between the tool and high temperature shear band. 2) the large displacement at the shear band’s location (and subsequently, the chip morphology) can be predicted without any fracture assumption and criterion; 3) both sliding and sticking contact lengths change with respect to time in each localization cycle.

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Attribution-NonCommercial-NoDerivatives 4.0 International