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Session 13

Wood-steel structure for vehicle restraint systems
Certain roadside safety barriers are structures made of steel and wood. This kind of structure is currently in fashion in location where the safety equipments need to be discreet (mountains, countryside). In Europe, to be installed on the roadside, the vehicle restraint systems have to pass two crash tests, as defined in the European standard EN1317. Our aim is to develop a dynamic model of the multi material structure in order to understand and optimize the safety barriers i.e. to define the best association of the mechanical properties of both materials. The first part of this paper concerns three point bending experimental tests at different energy levels. These laboratory tests were used as a basis for the evaluation of a material constitutive law. Then, a numerical parametric study which takes into account the variation of moisture content and temperature, as observed in the experiment, will be exposed. After that, a model of a roadside safety barrier and a procedure based on variation of failure modes analysis will be presented in order to correlate the numerical model to the real crash test results. Finally, a parametric study, concerning wood mechanical properties, will be performed in order to check the effect of this variation on the device performances.
Optimizing Thermoplastic Parts in Crash Applications - Status and Vision
Prediction of failure on high strength steel in seat mechanisms simulation
Tracks are the mechanisms which enable to translate the seat; they are key contributors in occupant safety as link between seat and car. With the current evolution of ecologic legislation, one of major automotive industry priorities is to decrease the product mass. To reach this objective, the use of high strength steels appears as a good solution with the drawback to be more brittle. In parallel, FEA models have to be more and more predictive in order to reduce the validation cost. In this context, rupture risk prediction appears as a strong need from design office and usual post-processing methods are not accurate enough to bring sufficient support to design teams. The solution chosen is a coupling between Ls-Dyna and the failure criteria crachFEM developed by MatFem Company. The evaluation of this risk is based on plastic strain evolution and stress state of the element. The methodology requires a specific characterization of the material to get information about the failure for different stress states. First application has been launched on ultimate strength subsystem on track. With dual- phase material, primary track failure mode is generally a profile rupture. First results highlighted correctly the area of rupture, but the ultimate strength was generally higher in FEA model than in the hard-test. This gap can be explained by the difference of scale between characterization of failure, which is a very local phenomenon, and the evolution of strain in simulation which is dependant of mesh size. Industrial crash model requirement (best compromise between accuracy and computation time: around 3mm mesh size) doesn’t permit to use mesh size needed for accurate rupture prediction. So “hybrid” modeling has been developed in order to have mesh size appropriate to MatFem analysis in useable computation time. With this approach the ruptures are well identified in term of areas, kinematics & ultimate strengths. Nowadays we are able, on this product, to predict with accuracy a risk of rupture on subsystem or on complete seat crash test.
Comparison of material models for crash simulation - experimental and simulation work
Crashworthiness and Sensitivity Analysis of Structural Composite Inserts in Vehicle Structure
This study is focused on identifying influential parameters in numerical analysis of structural composite inserts in vehicle structure. A 3-point bending test of a simplified steel-composite beam structure is conducted to evaluate the crashworthiness of composite insert in steel structure. Empty sections of the beam structure are filled with composite insert and foam filler. From physical 3-point bending tests, it is identified that the two critical behaviors of composite insert and foam filler greatly affect the strength level of steel-composite beam structure. Some influential parameters to achieve an accurate simulation model are studied. Finally, future steps of research work are indicated.