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Evaluation and assessment of the effects of Blast Loading by means of a Ballistic Pendulum

maandag, 5 september, 2011 - 17:00
Campus: Brussels Humanities, Sciences & Engineering campus
D
2.01
Dimitrios Kakogiannis
doctoraatsverdediging

The increasing interest on safety and crashworthiness in structures leads to additional design
requirements in any application where high-energy absorption is required, one of which is the
protection of civil structures under blast loading. The objective of a shielding is to reduce the
peak force and extend the duration of the deformation so the energy absorption is effective.
Several suggestions have been made and different kinds of mechanisms are investigated in
order to absorb energy from the blast wave. Composite unidirectional reinforced tubular
sections are considered as effective energy absorbers due to the failure mechanism which
increases the energy absorption capacity of the structure. The evaluation of the energy
absorbing mechanism under blast load requires an experimental setup from which complete
information about the applied blast load and the impulse that is transmitted to the structure
can be given. Especially in the case of the contact blast loading, that is the worst-case
scenario, it is difficult to measure and investigate the impulse transmission and the blast
mitigation. Attention is turned towards advanced numerical tools like the finite element
methods.

In the present dissertation, the estimation of the blast wave by two types of finite element
methods is investigated: Eulerian multi-material modeling and pure Lagrangian. By using
numerical and analytical methods, based on the rigid body theory of collinear impact, a
ballistic pendulum is designed. A striking mass that is in contact with the specimen is
accelerated by detonating an explosive charge placed on the striking mass. After detonation
the striking mass was accelerated onto the tubular structure in an axial direction compressing
the tubular specimen. Several sensors are placed on the pendulum main body in order to
retrieve as many information as possible measuring the effect of the contact blast on tubular
specimens. Specifically, a force transducer to measure the transmitted force v.s time, an
optical laser sensor to measure the amplitude of the pendulum oscillation and strain gauges
are placed on the ballistic pendulum.

An aluminum tube and a pultruded composite tube unidirectionally rein- forced are subjected
under contact blast loading in order to investigate the im- pulse transmission on the designed
pendulum and compare their response under blast. The transmitted impulse is measured by
the integration of force transducer or the maximum amplitude of the pendulum oscillation and
the two values are compared. The impulse applied by the explosive on the striking mass is
esti- mated and all the experimental configurations are modeled in the finite elements in order
to validate the measured impulsive loads. Finally with the combination of analytical, numerical
and experimental results the contact blast load impulse is define for the examined range of
blast.