Ultraviolet digital image correlation (UV-DIC) for high temperature applications

Abstract

A method is presented for extending two-dimensional digital image correlation (DIC) to a higher range of temperatures by using ultraviolet (UV) lights and UV optics to minimize the light emitted by specimens at those temperatures. The method, which we refer to as UV-DIC, is compared against DIC using unfiltered white light and DIC using filtered blue light which in the past have been used for high temperature applications. It is shown that at low temperatures for which sample glowing is not an issue all three methods produce the same results. At higher temperatures in our experiments, the unfiltered white light method showed significant glowing between 500 and 600 °C and the blue light between 800 and 900 °C, while the UV-DIC remained minimally affected until the material began nearing its melting point (about 1260 °C). The three methods were then used to obtain the coefficient of thermal expansion as a function of temperature for the nickel superalloy Hastelloy-X. All three methods give similar coefficients at temperatures below which glowing becomes significant, with the values also being comparable to the manufacturers specifications. Similar results were also seen in uniaxial tension tests.

Experimental Investigation of Thermal Strain Caused by Electrical Discharge Machining on Stainless Steel SUS430

“…Therefore, the boundary between the speckle pattern and the material surface must remain intact during deformation. (16) Solutions with bare material surfaces (9,17,18) have been proposed to overcome this issue instead of applying a coating (19) or using paint deposition. (20) By using the natural local features produced from bare material surfaces, the displacement can be directly calculated from the surface features without special surface preparation.…”

“…For this purpose, grit-400 sandpaper is used to manually grind the bare material surface, and the variable gray intensity pattern can be generated at the material surface owing to the different levels of optically rough scattering, (21) in contrast to a speckle pattern generated by painting the surface. (9) The change in contrast was used as a random pattern and the speckle pattern acted as the carrier of surface deformation. Additionally, the ground surface of the sample was benefited by the removal of any residual surface damage.…”

“…However, the traditional strain gauges contact with the material and work in a limited temperature range. (9) Furthermore, the thermal residual strain of the surfaces can be examined by scanning electron microscopy (SEM), (10) X-ray diffraction (XRD), (11) and Raman spectroscopy (12) to study the behavior of material under thermal stress. However, the disadvantages of these methods are their high cost and limited applicability to field use.…”

High Temperature Vibratory Response of Hastelloy-X: Stereo-DIC Measurements and Image Decomposition Analysis

“…Later, Chen et al and Pan et al applied the blue-filtering technique to stereo-DIC -in which two cameras are used to make three-dimensional (3D) measurements -at temperatures up to 1100 and 1200°C, respectively [3,4]. Most recently, Berke and Lambros showed that the temperature range can be extended even further by using ultraviolet lighting and optics, which operate at an even shorter wavelength than blue light [6].…”

“…Motivated by the increasing interest in applications involving significant thermal effects, such as aero-engines, spacecraft re-entry, aircraft hypersonic flight, and nuclear power applications, recent efforts have extended the upper temperature limit of the DIC technique by the use of optical bandpass filters and narrow band lighting, which reduces the influence of light radiated by the specimen at high temperatures [1][2][3][4][5][6]. Grant et al demonstrated this approach for hightemperature DIC by using blue light along with blue range bandpass filters to measure the coefficient of thermal expansion of RR1000 (a nickel-based alloy) at temperatures up to 1000°C with two-dimensional (2D)-DIC [1].…”