Preliminary investigation of polarization effects during metal cutting

Abstract

Under certain conditions, the polarization state of infrared light emitted by metal changes when the metal is strained. During cutting, metal is severely strained. Assessing both strain and strain rate is of interest to the metal cutting research community. Over large areas, Digital Image Correlation (DIC) performed on high-speed video can provide approximate values for the average strain and strain rate. However, small areas such as the shear zone are difficult to image with enough resolution to perform DIC. If the thermal radiation emitted by these small areas is polarized, there is the potential to provide valuable information to the metal cutting community. This paper is an initial investigation into that possibility, as well as the use of the polarization information for uncertainty analysis, reflection detection, and region of interest classification. A rotating polarizer is used that triggers a thermal spectrum camera to acquire images at specific polarization angles. When cutting, the metal is constantly moving and the material imaged is different from one moment to the next. At each angle of the polarizer, a sufficiently long integration time is used so the material is severely motion blurred, resulting in an image which estimates the typical intensity for that angle. By comparing the typical intensities, and assuming the light is linearly polarized, the polarization state may be estimated.