The relation between the tensile strength and the hardness of metals
A 1930 NACA technical memorandum from the NASA Technical Reports Server, written as an engineering report on metals testing, presenting graphs for engineers and researchers studying how tensile strength relates to hardness. The pictures are plain black-and-white line charts with fitted curves, labelled axes, and plotted data points in dense grids. A designer could take their clean graph structure, layered curves, and tabular grid patterns as abstract linework for technical diagrams.
