Total Energy Impact - ASTM D4272
The total failure energy absorbed by a film specimen impacted by a falling dart under specified test conditions. Since impact values are only partially related to specimen thickness, data comparison can only be made between specimens whose thickness differs by up to 15%.
A 38.1 mm (1.5 in) diameter hemispherical head dart is dropped from 66 cm (26 in) and impacts a test specimen. After passing through the test specimen, the dart passes through a speed trap made
of a pair of photoelectric sensors that measure the time it takes for the dart to cover a given distance. The time it takes for the dart to pass through the speed trap after passing through the
specimen is referred to as the test-fall time, while the time through the speed trap without a specimen is called the free-fall time. The energy absorbed by the specimen is equated to the loss of
kinetic energy of the dart and is determined using the formula:
E = (m/2g)[d2(1/t12 + 1/t22) + (g2/4)(t12 - t22)]
where E is the energy required to rupture the specimen (J),
m is the mass of the dart (kg),
g is the gravitational constant (9.81 m/s2),
d is the distance between the photoelectric sensors (m),
t1 is the free-fall time (s), and
t2 is the test-fall time (s).