Energy-Balance Method.

DOE-STD-3014-96

6.3.3.1

a. The objective of the energy-balance method of global response

evaluation is to determine whether the target structure can absorb the

energy that is imparted to it without deforming excessively. This

method uses the principles of conservation of energy and

conservation of momentum, and requires that the energy absorption

capability (SE) of the target be greater than the kinetic energy

imparted to it (Ea). It recognizes that, since a significant portion of the

impact energy is dissipated in deforming the aircraft body, the

effective missile mass is less than the total mass of the aircraft but

more than the mass of the rigid components, such as the engines.

The effective missile mass for calculating the total

kinetic energy of impact (Ei) will depend on the mass of the engines

and the relative rigidity of the aircraft body.

b. To calculate Ei, the effective missile mass (m) can be conservatively

estimated based on Chelapati (Reference 10):

1. For small aircraft with airframes that are flexible relative to the

target structure, m=2 times the combined mass of the engines.

2. For large aircraft, m=8 times the combined mass of the engines.

However, m should not be less than 30 percent, nor more than

the total mass of the aircraft.

c. To calculate Ea, the effective target mass (Me) may conservatively be

taken as the mass of the target structure that is included within d/2 of

the periphery of the impact interface, where d is the thickness of the

target in the direction of missile travel. On the basis of the predicted

deformed shape of the target, less conservative but practical values

may be used if justified. However, Me need not be less than one-

tenth of the total mass of the target structure panel (Reference 10).