Combined thermographic phosphor and digital image correlation (TP + DIC) for simultaneous temperature and strain measurements

Abstract

Thermographic phosphors (TP) are combined with stereo digital image correlation (DIC) in a novel diagnostic, TP + DIC, to measure full-field surface strains and temperatures simultaneously. The TP + DIC method is presented, including corrections for nonlinear CMOS camera detectors and generation of pixel-wise calibration curves to relate the known temperature to the ratio of pixel intensities between two distinct wavelength bands. Additionally, DIC is employed not only for strain measurements but also for accurate image registration between the two cameras for the two-colour ratio method approach of phosphoric thermography. TP + DIC is applied to characterize the thermomechanical response of 304L stainless steel dog bones during tensile testing at different strain rates. The dog bones are patterned for DIC with Mg 3 F 2 GeO 4 : Mn (MFG) via aerosol deposition through a shadow mask. Temperatures up to 425 K (150 C) and strains up to 1.0 mm/mm are measured in the localized necking region, with conservative noise levels of 10 K and 0.01 mm/mm or less. Finally, TP + DIC is compared to the more established method of combining infrared (IR) thermography with DIC (IR + DIC), with results agreeing favourably. Three topics of continued research are identified, including cracking of the aerosol-deposited phosphor DIC features, incomplete illumination for pixels on the border of the phosphor features, and phosphor emission evolution as a function of applied substrate strain. This work demonstrates the combination of phosphor thermography and DIC and lays the foundation for further development of TP + DIC for testing in combined thermo-mechancial environments.

Educational series: characterizing crosslinked polymer networks

“…Beyond advances in new techniques, such as NDS or microrheology, there are also important developments where instruments are being developed with multiple coupled characterization methods. Examples include combined thermal and strain measurements, 171 IR-rheological analysis, 172 and AFM-IR among many others. Without a doubt, this will continue to be an emerging area as techniques are coupled together and automated for facile analysis.…”

Advances in phosphor two-color ratio method thermography for full-field surface temperature measurements

“…In order to generate a robust coating of phosphors that adhered well to the substrate with no need for binders, a tailored process for AD was developed. The AD setup used in this work has been described in [17,18], with additional process development detailed in [19,20]. An overview of the final process is presented here.…”

“…An overview of the final process is presented here. Mg 3 F 2 GeO 4 :Mn (MFG) phosphor powder was obtained from Phosphor Technology Ltd and ball-milled, dried, and then ground with a mortar and pestle and sieved to <180 µm [20]. The powder was aerosolized in helium using a rotating brush generator (RBG) RBG1000isd powder feeder and a particle sizing cyclone, and accelerated to supersonic speeds through a 3D printed Vero polymer DeLaval converging-diverging nozzle into a vacuum to impinge on the sample.…”

“…2 ) were deposited using AD. A laser scanning profilometer was used to determine that the phosphor thickness was approximately 4 µm [19,20].…”

Coupled strain and temperature gradient analysis in curved surfaces

“…In recent work by [6], the suitability of such approaches is shown even for elevated temperatures and high strain rates. Instead of drawing on TG, [7] choose the thermographic phosphor technique and DIC to simultaneously measure temperature and strain information.…”