Use of three-dimensional digital image correlation for the experimental characterization of buckling in large, thin, 2024-T3 aluminum, middle-crack tension specimens

The buckling response of wide, thin, center-notch, 2024-T3 aluminum, specimens was investigated. To arrest crack growth in the panels, the notch was terminated in small, 4.76 mm diameter, holes. Panels with widths of 305 mm, 610 mm, and 1016 mm were tested. All panels had a crack length to panel width ratio of 1/3. Full-field surface displacement measurements of the response of the panels to an applied load were made using a three-dimensional digital image correlation technique. Two correlation systems were used to capture both the global response of the sheet and the response near the notch tips. Global areas, from 250 mm x 250 mm to 550 mm x 550 mm, were imaged for each panel. A second imaging system recorded displacements for a small area, 10 mm x 20 mm, ahead of the notch tip. Load and rain displacement data from the test stand was also recorded. Finite element analyses of the panels were run for each of the different panel geometries. The results of the finite element analyses were compared with both the load-displacement data and to the full field data. For the 305-mm and the 610-mm panels it was shown that the finite element predictions match well with the experimental results for the U and W displacements. The finite element analysis under predicted the load-grip displacement response by 5%. The 1016-mm panel, where the finite element analysis did not match the experimental data, demonstrated how knowledge of the experimental full-field response of the panels was instrumental in determining the probable cause of the discrepancy between the data and the predictions. It was shown from the full-field data that the panel was slipping out of the grips during the test. The small amount of slip, 0.5 mm, had a significant effect on the panel's response.