Jean-Marc
Petit <petit@obs-nice.fr>
Patrick
Michel <michel@obs-nice.fr>
CNRS,
Observatoire de la Côte d'Azur, BP 4229
06304
Nice Cedex 04, France
Partners
The
following partners have already shown interest in this project: Centre
d'Essai des Landes (CEL), Centre Technique d'Arcueil (CTA), Pr. Willy Benz
(Berne University, Switzerland), Dr. Mario Di Martino (Torino Observatory,
Italy).
Proposed
experiments
We
plan to perform experiments of high-velocity impacts on meter-sized solid
targets. The range of projectile velocities we are interested in goes from
several hundreds m/s to several km/s. The main objective of these experiments
is to improve our knowledge of a wide variety of phenomena occurring during
collisions: fragmentation modes, the size and shape of the fragments, their
rotational and ejection velocity fields, the fraction of impact energy
transfered into fragment kinetic energy. Up to now laboratory experiments
have been performed on targets at most 20 centimeters in size. It has been
realized that it is impossible to simply extrapolate the outcome characteristics
of the collisions to larger target size. The proposed new experiments will
help to constrain the available models, and will allow for the first time
to measure physical quantities (pressure, displacement, temperature, ...)
during the fragmentation process, thus improving our knowledge of the physical
processes at work. They will also lead to industrial developments.
Scientific
Rationale
The
role of collisions is fundamental in different astrophysical fields such
as the origin of our Solar System and the formation of planets, the evolution
of small bodies in the Solar System, and even in the fate of the human
kind, since a collision of a dangerous asteroid on the Earth is a threat
that cannot be neglected.
To
build a coherent model of collisional and dynamical evolution of our Solar
System, and to be able to face the potential threat of an asteroid coming
to the Earth, a good knowledge of the collisional process and of the outcome
characteristics as a function of the impact conditions is required.
Experimental
strategy
Our
project is thus to perform high-velocity impact experiments using targets
in the size range 1-1.5 meters in radius. These experiments will be done
in relation with a tridimensional hydrocode developed by our collaborator
Pr. Willy Benz, using the concept of Smooth Particle Hydrodynamics (SPH),
in order to represent the evolution of stress and strains inside the material
and important physical quantities such as the internal energy of the target
and crack propagation.
Besides
the increase by an order of magnitude of the size of the target, the great
novelty of these experiments, compared to previous ones, will be the possibility
of measuring physical quantities during the fragmentation process. Simulations
with our SPH code will allow first to guide the choice of the experimental
parameters and to estimate the order of magnitudes of these physical quantities.
In turn, the experimental results will allow to calibrate the free parameters
of the numerical models.
Our
first experiments will consist in 6 impacts, 3 at 400 m/s and 3 at 800
m/s, with a projectile mass between about 10 and 100 kg. This allows to
investigate different impact conditions. The projectile will be accelerated
on the 2 km railway available at the CEL. The target will consist in a
sphere of radius as large as 1.5 meter. Both target and projectile should
be made out of concrete.
Industrial
developments
The
industrial developments will basically concern three distinct fields: the
knowledge of the material behavior, the development of measuring instrumentation,
imaging and pattern-recognition technics.
First,
the experiments will provide precious information on the behavior of the
used material during energetic impacts. The results should strongly interest
industries who could then find a motivation to build and provide the targets.
These data will bring an important contribution to the study of the protection
of sensitive infrastructures.
One
of the innovative aspects of the proposed experiments is the possibility
to place several captors on and around the target, allowing to measure
different physical quantities under unusual conditions during the impact
and along the fragmentation phase. This will lead to developments of captors
with fast response time (microsecond to millisecond) and high dynamical
range.
The
effects of the impacts will be filmed by four fast cameras. The images
will be digitalized, and each individual fragment will have to be automatically
detected and identified. The problems of pattern-recognition, of the determination
of topography, and of the following of objects during their motion are
hot topics in the imaging research field. It will require the writing
of new softwares which could then be applied to the study of automatic
control of autonomous mobile engines.
The
results of these experiments will be published in specialized journals.
Industrial ownership of data or technics will however be preserved. The
experiments are available to be used for advertisement by our partners
as they see fit.
Estimated total budget: 1.7 M Euros ( 11 MFrs).