Elevated Temperature Optical Microscopy DIC

Abstract

When determining the microstructural performance of new materials, such as composites and additively manufactured parts, it is necessary to understand their full-scale behavior. Since non-homogeneous materials are being used more often in critical applications, understanding their microstructural response is becoming more important. Digital Image Correlation (DIC) has proven to be invaluable in characterizing the small-scale performance of non-homogenous materials, but presents a number of challenges for certain tests. One such area is determining the local strain behavior for non-homogeneous micro-scale materials as the part is heated. Using DIC on a sample at elevated temperatures must deal with optical distortions caused by uneven heating of the air above the part. Using DIC at a microstructural level is difficult due to the limited depth of field, which can cause a loss of focus and difficulty in generating an appropriate speckle pattern. To examine the microstructural thermal response both of these difficulties must be overcome simultaneously. Southern Research has developed methods and apparatus to allow optical DIC to be used over a range of temperatures and microscopic fields of view. This paper will address how each of the problems was overcome in the apparatus design and testing method as well as show results validating the technique.