The ASTM E208 Drop-Weight Test is used primarily to determine the Nil-ductility transition temperature or NDT of ferritic steels of 5/8 inch thickness and over.
It consists of a rectangular coupon with a brittle weld bead deposited on one face. Tests are carried out at a variety of temperatures, the NDTT being defined as the maximum temperature at which the brittle crack spreads completely across one or both of the tension surfaces on either side of the brittle weld bead.