Direct measurements of severe plastic deformation in machining and equal channel angular pressing
Abstract
Measurement of the strain field in Severe Plastic Deformation (SPD) is of major interest for a number of reasons including validation of process models; development of machining as an experimental technique for studying phenomena associated with large strain deformation; creation of nano structured materials. In this context, a study has been made of the primary deformation zone and tool-chip interface in plane strain (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 deformation zone of various processes. The measurements have provided data about the variations of velocity, strain rate and strain, in and around the cutting edge and the 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. The effect of machining parameters such as undeformed chip thickness and rake angle on the deformation field has been quantified. The PIV based measurement technique has also been used to highlight important aspects of SPD of titanium at ambient temperature by machining. Lastly, an extended application of the PIV, the strain rate and strain distribution in ECAP was investigated. The implications of these results to the use of machining as an SPD method for producing nano structured materials, and estimating material properties under extreme conditions of deformation are discussed.
Degree
Ph.D.
Advisors
Chandrasekar, Purdue University.
Subject Area
Mechanical engineering
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