Hickman, William A. & Dow, Norris F. Data on the Compressive Strength of 75S-T6 Aluminum-Alloy Flat Panels Having Small, Thin, Widely Spaced, Longitudinal Extruded Z-Section Stiffeners, report, November 1949; (https://digital.library.unt.edu/ark:/67531/metadc55276/m1/1/: accessed May 27, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .