Study of a laboratory scale technique for combined blast and fragment impact loading

Improvised explosive devices as well as conventional ammunition, such as grenades, mortars,
bombshells, rockets and missiles generate both a blast wave and the projection of multiple
fragments at high velocity when detonated. The synergistic effect created by the combination
of both loadings on the impacted materials and structures can be greater than the sum of the
effects of each loading separately. Until now, no standardized experimental technique exists
to generate the combined loading condition in a controlled and repeatable manner.
This doctoral dissertation presents an investigation into the dynamic behavior of thin alu-
minum plates subjected to combined blast and fragment impact loading. The primary objec-
tive is to develop a controllable laboratory-scale technique to generate repeatable combined
loading conditions and experimentally and numerically analyse the response of the plates.
The conducted research explores two distinct scenarios in which the sequence of blast wave
arrival time and the moment of fragment impact varies. In the first scenario, fragment
impacts occur before the arrival of the shock wave, while in the second scenario, the shock
wave reaches the structure prior to the fragment(s). In both cases, the blast wave is generated
by an Explosive Driven Shock Tube (EDST).
In the first scenario, the plates are first subjected to ballistically projected fragments before
being blast loaded. The influence of projectile diameter, impact locations and hole spacing
on plate deformation and damage is analysed. The findings demonstrate that cracks develop
in high-strain regions between the holes and that hole spacing has an influence on the damage
mechanism.
In the second scenario, a laboratory-scale technique to generate a repeatable combined
blast and fragment impact loading is proposed and evaluated. The technique is based on
the use of one or more spherical steel projectiles, attached to a given quantity and shape
of plastic explosive. The detonation of the explosive charge generates a blast wave and
propels the projectiles towards the plate. The feasibility study confirms the capacity of the
technique to yield stable projectile flight trajectories. Moreover it allows the blast loading
parameters, projectile flight characteristics and the time interval between the blast wave
and fragment impacts to be monitored and evaluated. Numerical simulations using the LS-
DYNA finite element software have been performed for all of the scenario’s and compared
to the experimental results in order to provide further insights into the technique and the
behaviour of the loaded aluminum plates.
Overall, this doctoral thesis presents and discusses a laboratory-scale technique for evaluating
the response of plates under combined blast wave and fragment impact loading. The research
results in an extensive experimental and numerical database, providing a foundation for future
studies in this field.