Interpretation of soft impact medium velocity tests on concrete slabs
Titre du congrès :19th International Conference on Structural Mechanics In Reactor Technology (SMIRT 19)
Ville du congrès :Toronto
Date du congrès :12/08/2007
Data from impact tests of "soft" missiles on rigid (i.e. thick steel plate) or deformable (i.e. concrete plates) targets are used to validate and calibrate two different numerical methods : a simplified finite difference model developed by IRSN and the fast dynamic finite element model LS-DYNA. The purpose of this work is to predict the loading forces applied by a commercial plane on a nuclear building and the corresponding behavior of the civil works structure. The tests are performed by VTT in Finland. Two similar tests performed on concrete plates to investigate the scattering of the experimental results have proved to be quite consistent. The repeatability of the first tests then appears to be satisfactory. Comparing equivalent tests performed either with missiles carrying no fluid, or with missiles loaded with water, shows that the loading of the targets is more severe when the missile carries water. The authors think that this result is due to the bouncing of the fluid, which increases the momentum transmitted to the target, as if the impact were not purely "soft" any more but partially "hard". As a consequence, the assessments concerning the behavior of civil structures submitted to the impact of a commercial aircraft carrying a significant load of fuel should take into account loading functions higher than those derived by Riera method, depending on the bouncing amount of the fluid on the impacted structure. Concerning the numerical simulations, the simplified finite difference model developed by IRSN proved to be adapted to the dynamic analysis of a concrete plate behaving like a beam, while the code LSDYNA allows various simulations on any kind of civil structure, with a special effort in choosing the concrete material and mechanical parameters. Based on the first results of the experimental program, other tests are under way varying the experimental conditions. The data gained from these tests should lead to a better understanding of the phenomena that pilot the interaction between a "soft" missile and a deformable target during an impact.