1 Proceedings of International Conference. Transport Means. 2004. Explicit nonlinear Finite element simulation of quasi-static axially crushed thin- walled elements P. Griskevicius*, A. Ziliukas**, J. Holnicki-Szulc*** *Kaunas University of Technology, Kestucio 27, 44025, Kaunas, Lithuania, E-mail: paulius.griskevicius@ktu.lt ** Kaunas University of Technology, Kestucio 27, 44025, Kaunas, Lithuania, E-mail: antanas.ziliukas@ktu.lt ***Institute of Fundamental Technological Research, Swietokrzyska 21, 00-049, Warsaw, Poland, E-mail: holnicki@ippt.gov.pl Abstract To analyse the behaviour of axially crushed thin-walled elements, the quasi-static experimental investigations and numerical simulations were performed. The numerical modelling was performed using computer code LS-DYNA v.960. The explicit FE analysis are used to establish the influence of velocity of deformation to the characteristics of buckling. The selection of velocities and accelerations for quasi-static analyses are discussed. KEY WORDS: crash analysis, buckling, thin-walled, axial impact, stress wave 1. Introduction The main criteria of occupant safety are vehicles deceleration pulses and deformation of the occupant compartment. Longerons are used in vehicles as energy absorption devices to minimize injury to people during the frontal collisions. We consider longerons as the thin-walled elements of different profiles. The management of the absorbed energy allows to increase the vehicles safety. The way of deformation of vehicles construction elements during the frontal impact and the value of the absorbed crash energy depends on vehicle construction, mechanical properties of materials and geometric characteristics of elements sections [1, 2]. A series of approximately 50 axial compression tests of thin-walled cylindrical elements ( 57 24   t d ) were conducted under quasi-static conditions. Tests were carried out on a universal hydraulic 50t tension-compression testing machine, which applied the axial load through flat end platens without any additional fixing. Crosshead speed was approximately s m / 3 . 0 . The load-compression curves were obtained on the machine chart recorder and their typical deformation histories (Fig.1) were observed. Fig.1 Load-compression curve of the axially crushed thin-walled cylindrical shell Using the load-compression curves the main buckling characteristics were established: quantity of energy absorption, average buckling load and wavelength of fold. Energy absorption and mean crushing loads have calculated by measuring the area under the load displacement curves. The numerical model of the buckling of thin-walled cylindrical shells was made and tested in order to set the consistency of buckling characteristics when changing its boundary conditions. The numerical simulation of buckling phenomena was done on the non-linear explicit Finite element (FE) analysis. Some investigators [3-5] have studied the explicit nonlinear Finite element simulation of quasi-static problems. In order to check the created numerical models the experiments with crushing thin-walled elements in this work were made. The aim of the modelling was to find out how the value of absorbed energy and the behaviour of longerons is influenced by the velocity of deformation. 2. The numerical simulation of buckling of thin-walled elements The FE models of the buckling thin-walled elements and longerons (Fig.2) were performed using experimented specimen dimensions. The length of the specimen studied in the work is mm L 300  . The distance of buckling was chosen mm L 200   (to calculate absorbed energy) or mm L cr 40   (to calculate critical force). The aim of the modelling was to repeat the conditions of quasi-static experiments. Rigid plate is moved to the longitudinal direction of specimen. The speed of deformation during the buckling remains the same or increases gradually. Bottom of cylinder constrained in axially z direction. Upper rigid plate can move only in z direction.