Wednesday  |  Phipps  |  09:20 AM–09:40 AM

#13914, Mitigation of DIC Speckle Pattern Inversion at Extreme Temperature using Color Cameras

During hot fire rocket engine testing, non-contacting measurements are preferable to bonded gauges because they cannot burn, shake loose, or become otherwise damaged during testing. Additionally, when compared to traditional instruments which register at discrete and/or single points, Digital Image Correlation (DIC) has the added benefit in that it collects full-field displacement and strain maps over the duration of the test. However, under some high temperature circumstances, darker portions of the speckle pattern may emit more light compared to the lighter portions of the pattern, resulting in a high temperature pattern which is inverted in comparison with that at room temperature. One of primary factors attributing to the inversion is that the difference in emissivity of high temperature DIC paint and the background of the specimen surface, thus resulting in the uneven emission of light from the speckle pattern.

In past work, we have shown that this inversion effect can be mitigated by subtracting two images: one taken at high temperature with light sources on, which contains both reflected and emitted light, and the other taken at high temperature with light sources off, which contains only emitted light. By subtracting these images, the resulting artificial image contains only reflected light and can thus successfully correlate against a room temperature image which also contains only reflected light. However, one key drawback of this subtraction method is that no motion can occur between the two images being subtracted.

In this new work, we obtain both images to be subtracted by pairing a blue light source with a color camera. The blue channel of the camera records both reflected and emitted light, and is therefore analogous to the “lights on” image. The green channel records only emitted light, making it analogous to the “lights off” image. The images from the two channels are recorded simultaneously and are mapped to common coordinates, making them much more suitable for instantaneous DIC measurements when speckle pattern inversion is present.

Lindsey Rowley   Utah State University
Thinh Thai   Van Lang University
Steven Jarrett   Utah State University
Prasenjit Dewanjee   Utah State University
Ryan Berke   Utah State University