The Charpy impact test was used to characterize the toughness of 6061 aluminum and 1018 carbon steel samples at varying temperatures. For aluminum, the impact energy decreased sharply from 33 ft-lbs to 15 ft-lbs as temperature decreased from 50°F to -25°F, while steel impact energy was relatively unaffected by temperature. Steel exhibited a ductile to brittle transition around 0°F as impact energy and shear lip percentage decreased sharply at lower temperatures, while aluminum toughness was unaffected by temperature due to its FCC crystal structure. Both materials showed fracture toughness values independent of temperature.