PSI - Issue 57

Haelie Egbert et al. / Procedia Structural Integrity 57 (2024) 179–190 Haelie Egbert et al. / Structural Integrity Procedia 00 (2019) 000 – 000

182 4

The STB test methodology in general lends itself to optical DIC type measurements on gear specimens as the gear is not rotating and there is plenty of visual accesses to the gear teeth transverse plane. A field of view (FOV) of around 11x8 mm is required to capture images of a single test gear tooth in the SAE J1619 specimen. The specimen allows for 16 tests per gear to be performed, without reusing any tooth, making it a cost-effective platform for evaluating tooth bending fatigue lives in gearing specimens. 3. Optical Crack Measurement Methodology 3.1 High Speed Camera Setup Modifications needed to be incorporated on the test machine to produce a macro image of the tooth with minimal distortion to allow for ease of processing and crack measurement analysis. Fatigue test machines are not designed to accommodate the lighting and backdrops traditionally used for taking high quality images. Extraneous features in the background of the image could result in errors in an image processing routine that defines edges through sharp gradients in the color value of neighboring pixels. The image setup needed to eliminate this and contrast the background with the tooth segment in focus. Figure 2 shows the lighting and camera setup used for imaging the tooth. A matte-black cover dampened glare from the background and created uniformity, eliminating any extraneous background features. High speed cameras have special requirements on lighting such that there is no flicker and there is enough light to create contrast in the image sensor through the small capture times at high frame rates. Two 1000 lumen LED gooseneck lights were used to illuminate the tooth surface and were positioned at an angle to avoid glare. The lens used had a variable focal length which modifies the magnification ratio if any focal length below the maximum was used. A digital calibration technique was used to ensure the final magnification factoris known. The technique was performed for each measurement taken accounting for slight variations in lens settings resulting from test changeovers. A clear front cover was used as a safety feature. Utilization of the cover produced little distortion within the video and negligible refraction of the LED lights, as shown in the resultant macro image in Figure 3.

Figure 2. STBF High Speed Camera Setup