Effect of plastic deformation and boundary conditions combined with elastic wave propagation on the collapse site of a crash box

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Several papers have been published recently on the crashworthiness studies. The main task was to predict the energy absorption Wp and average collapse force overbar-F in time of sheet steel structures. The main objective of this contribution is to design a component that allows absorbing and dissipating a high energy Wp allowing improvements of the survivability of passengers in vehicles. However, the range of applications is larger since it includes all civil and military applications related to safety of components, or more generally of construction elements being loaded by impacts or explosions. In the present 3D case, the aim of this numerical study on dynamic loading in adiabatic conditions of deformation is to analyze the effect of elastic wave propagation combined with plastic behavior on the collapse site of a rectangular tubular structure made of steel sheet. To demonstrate the strong coupling between the effects of strain-rate sensitivity, accounted for in the constitutive relation that is used in numerical simulations, with the process of elastic wave reflection on the boundary conditions, a series of numerical simulation was performed. It is shown in this numerical study that the strain-rate sensitivity influences the position of the first collapse site. Moreover, the first collapse initiation of a structure defines the level of power absorption. Since the process of folding may be combined with bending of the structure (in particular when a local buckling appears close to the opposite side of impact), in this non-axial case the energy absorption Wp decreases and the effectiveness of the structure to the energy absorption is insufficient.
21 pages, 22 figures.
Crashworthiness, Collapse of a steel crash box, Numerical simulation, Plasticity, Elastic waves
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Thin-Walled Structures, 2008, vol. 46, n. 10, p. 1143-1163