Civil Engineering Reference
In-Depth Information
Chapter 14
Determination of a Load Approaches
for Aircraft Impacts
Abstract
As basis for the analysis and verification of building and mechanical
components adequate load approaches for aircraft impacts have to be developed.
Different approaches and mathematical models to derive load-time-functions for
the contact force between airplane and hit structure are presented. Finally the shown
impact load-time functions of the different types of aircraft are compiled for
comparison.
14.1 General Information
The crash of an aircraft on a target is physically an impact problem with largely
non-linear processes. The kinetic energy of a projectile, determined by its mass and
speed, is changed into other forms of energy during impact. For the design of a
structure the contact force between the striking and hit bodies are important. In
principle this is dependent on the ductility of the participating structural elements.
In the case of an aircraft impact a so called soft impact takes place. This is
characterized by the fact that the projectile is very ductile. The kinetic energy is
largely absorbed by the striking body itself in the form of plastic deformation, such
that only a fraction of the energy is introduced into the impacted body. Due to the
large deformations of the projectile on impact the size of the resulting contact force
is practically independent of the behaviour of the impacted structure. This allows a
decoupled examination. In a first step the impact force-time function can be
determined using only the characteristics of the projectile. The impacted structure
can then be loaded with this load function in a dynamic analysis in a second
independent step. The spatial distribution of the load over the whole impact area
with respect to the time sequence is of special interest.
It is necessary to establish the load functions for the aircraft models and
approach scenarios discussed in the previous chapter in order to continue the
analysis of the problem. The first functions were created in the early 1970s: first
