The ASTM E208 drop weight test is used to determine the Nil-ductility transition temperature or NDT of ferritic steels 5/8 inch thick (15.875mm) and over. NDT is the temperature at which the fracture mode of steel changes from ductile to brittle. At temperatures above the NDT a piece of steel will stretch or deform in a ductile manner before fracturing when loaded to its ultimate tensile strength. At temperatures lower then the NDT that same piece of steel will fail in a brittle manner when loaded to its yield strength (roughly half of its ultimate tensile strength). Once a brittle failure begins the crack will continue to grow until it runs out of material, the pressure is released or it encounters steel that is more ductile.
To find a steel’s NDT beam specimens are prepared according to ASTM E208 and subjected to a single impact from a drop weight test system. The Instron Dynatup Model 9250 and the Instron Dynatup Model 8120 are ideal for this test. The Model 9250 is capable of testing specimens with an impact energy up to 18.4 – 1182 ft-lb (25 -1603 J). For steels that require higher impact energies the Model 8120 has an energy range from 104 – 4271 ft-lb (141 - 5792 J). When coupled with the Impulse Data Acquisition System a full load – time – displacement – energy data curve and test results can be captured for each test.