Measurement of strain field in the primary deformation zone is of major interest for development of machining as an experimental technique for studying phenomena associated with large strain deformation. A study has been made of the primary deformation zone and tool-chip interface in planestrain (two-dimensional) machining of metals. The use of a high-speed, charge-coupled device (CCD) imaging system in conjunction with an optically transparent, sapphire cutting tool has enabled characteristics of the deformation field such as velocity, strain, and material flow, to be obtained at high spatial and temporal resolution. The velocity distributions in the primary deformation zone and along the tool rake face have been obtained by applying a particle image velocimetry (PIV) technique to sequences of high-speed images of the chip-tool interface taken through the transparent tool, and of the primary deformation zone recorded from a side of the workpiece. A procedure is presented and demonstrated for determining the strain and strain rate distributions in the primary deformation zone. The measurements have provided data about the variations of velocity, strain rate, and strain, in and around the cutting edge and primary deformation zone; confirmed the existence of a region of retarded sliding in the region of intimate contact between tool and chip; and highlighted the occurrence of a region of dead metal ahead of the cutting edge when cutting with a negative rake angle tool.

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A hybrid particle image velocimetry/particle tracking velocimetry (PIV/PTV) method is described for direct measurement of large-strain deformation fields using plane-strain machining as the model system. PIV/PTV is shown to accurately measure displacements and velocities with a spatial resolution of ∼1/10th of a pixel, which is an order of magnitude improvement over a comparable PIV-based method. For the configuration studied here, this translates to about ∼400 nm in terms of displacement and ∼80 µm s−1 in terms of velocity. Furthermore, the method is shown to be able to capture steep gradients in velocity, which are typical of deformation zones in machining. This enables accurate estimation of associated strain rates. Implications of the technique for measuring large-strain fields in deformation processes and indentation tests, and velocity gradients due to friction at sliding interfaces, are briefly discussed.

A novel method using luminescent molecule sensors is described for in situ measurement of fluid film thickness along the tool rake face in machining. The method uses an optically transparent sapphire tool to access the rake face, and measurement of radiation emitted by luminescing molecules dispersed in a machining fluid. By measuring the intensity of the emission, the film thickness is estimated. Implications for tool-chip contact boundary conditions and near-dry machining are discussed.