Digital Image Correlation at Extreme Temperatures Using Shortwave Ultraviolet (UV-C) Lights and Filters

Abstract

Background

DIC is a widely used optical method that uses cameras to track the motion of an applied random surface pattern to measure the full-field deformation. Due to its non-contacting nature, DIC is very preferable to be used in the areas of high temperature experimental mechanics. One of the biggest challenges of DIC at extreme temperatures is the blackbody radiation emitted from the glowing surface of the specimen. This glow from the blackbody radiation of the specimen is relatively higher at longer wavelengths and lower at shorter wavelengths.    

Objective

Previously, studies have shown the usefulness of using shorter wavelength of lights such as blue filtered light (450 nm) and UV-A filtered light (365 nm) for high temperature measurements. By contrast, this study uses UV-C filtered technique which utilizes even shorter wavelength of filtered light (UV-C, 254 nm) to demonstrate its effectiveness at elevated temperatures.

Methods

Four different DIC techniques using an unfiltered blue light (200–1000 nm), a blue filtered light (450 nm), a UV-A filtered light (365 nm), and a UV-C (254 nm) filtered light have been performed at extreme temperatures in this study. 

Results

It was found that the techniques using unfiltered blue, blue filtered, and UV-A filtered lights could only go up to a temperature of 900 °C, 1200 °C, and 1600 °C respectively before showing significant saturations in the images.

Conclusions

The new UV-C DIC showed no sign of saturation even up to a temperature of 1600 °C while providing comparable axial displacement and coefficient of thermal expansion (CTE) data and therefore demonstrating the usefulness of this method in higher temperatures. We also include helpful recommendations for how to produce speckle patterns having sufficient contrast at UV-C wavelengths.