A multibody approach in modelling crash dynamics of vehicles against road safety systems

In the paper the impact dynamics of a vehicle against a road restraint system is studied. The description of an homologation test for crash barriers is, in particular, carried out. According to standards (UNI EN 1317), to get the product homologation, experimental tests have to be passed, during which barriers are crashed by means of vehicles of different size and typology. Usually the design methodology consists in a trial and error approach, having the aim of developing prototypes that have to be tested to be validated. The manufacturer has, indeed, to verify that the dynamical and structural behaviours of the barrier satisfy the standards. Since each test and, hence, each attempt turn out to be very expensive and time consuming for the project development, virtual prototyping FEA based techniques are sometimes employed. In the paper a Multibody-FEA approach is utilised to model the crash test scenario (Vehicle- Barrier model). Of course the advantage of such a description is related to the reduced computational effort needed, if compared with a whole FEA modelling, but it also allows a better representation of the collapse kinematics of the barrier, from functional design point of view. Since the barrier is a structural element that works only once in its life, it has to be designed, indeed, to collapse in a determined way, during operation. A mixed model, consisting of rigid and deformable parts, helps, then, to focus on the desired performance. Moving from data and movies collected during the homologation test of an existing barrier, the fine tuning of the V-B model has been performed. From this model one gets all the needed kinematical and dynamical quantities, beyond that parameters which the norms introduce to evaluate how severe is the impact for vehicle occupants, such as ASI (Acceleration Severity Index) is. The calculation of those parameters is based only on the kinematics of the vehicle. During the tests, indeed, no instrumented dummy is requested to evaluate occupant biological injuries. For this reason another simulation model has been built up, that, from forces acting on the vehicle, evaluated by means of the V-B model, allows to estimate the biological damage on the occupant, due to the impact (Cockpit-Occupant model). The aim of this second model has been to investigate the possibility of correlating ASI with effective injury parameters such as HIC (Head Injury Criterion) is, that could be utilised directly during the homologation procedure.