Welding Inspection & Metallurgy API ICP Self Study Notes

10.4.4 Toughness
The toughness is the ability of a metal to absorb energy and deform
plastically before fracturing. An important material property to tank and
pressure vessel designers is the “fracture toughness” of a metal which is
defined as the ability to resist fracture or crack propagation under stress. It is
usually measured by the energy absorbed in a notch impact test. There are
several types of fracture toughness tests. One of the most common is a
notched bar impact test called the Charpy impact test. The Charpy impact test
is a pendulum-type single-blow impact test where the specimen is supported
at both ends as a simple beam and broken by a falling pendulum. The energy
absorbed, as determined by the subsequent rise of the pendulum, is a
measure of the impact strength or notch toughness of a material. The tests
results are usually recorded in foot-pounds.