BEHAVIOUR OF AN AUTOMOTIVE BUMPER BEAM-LONGITUDINAL SYSTEM AT 40% OFFSET IMPACT: AN EXPERIMENTAL AND NUMERICAL STUDY

Abstract

ASSESSING THE IMPACT PERFORMANCE OF BUMPER BEAM SYSTEMS THROUGH A FULL-SCALE CRASH TEST OF A CAR IS NOT EASY. THEREFORE, IN THE PRESENT STUDY A BUMPER BEAM CONNECTED TO TWO LONGITUDINALS WAS TESTED AT 40% OFFSET IMPACT. LONGITUDINALS OF TWO DIFFERENT ALLOYS (AA7003 AND AA6060) AND TWO TEMPERS (T79 AND T1) WERE TESTED, WHILE USING A SINGLE ALLOY (AA7108 { T6) FOR THE BUMPER BEAM. THE BUMPER BEAM IS A BOX-LIKE STRUCTURE PRODUCED FROM AN ALUMINIUM EXTRUSION THAT IS PLASTICALLY FORMED TO THE REQUIRED CURVATURE BY STRETCH-BENDING IN A SOFT CONDITION, WHICH IS OBTAINED BY SOFT SOLID-SOLUTION HEAT TREATMENT. SUBSEQUENTLY, THE BUMPERS ARE ARTI¯CIALLY AGE-HARDENED TO T6 PEAK HARDNESS CONDITION. WITH AN OBJECTIVE TO DEVELOP MODELLING TOOLS FOR AN AUTOMOTIVE BUMPER SYSTEM SUBJECTED TO IMPACT LOADING CONDITIONS THIS PAPER PRESENTS BOTH THE EXPERIMENTAL AND NUMERICAL RESULTS. EXPERIMENTS WERE PERFORMED USING SIMLAB'S KICKING MACHINE TO PROVIDE HIGH-PRECISION DATA FOR VALIDATION OF NUMERICAL COMPUTATIONS. THE NUMERICAL STUDY WAS CARRIED OUT WITH THE NON-LINEAR FINITE ELEMENT CODE LS-DYNA, SEARCHING FOR AN E±CIENT, NUMERICALLY ROBUST AND ACCURATE REPRESENTATION OF THE OBSERVED SYSTEM BEHAVIOUR. FOR THIS PURPOSE A USER-DE¯NED ELASTO-VISCOPLASTIC MATERIAL MODEL WAS ADOPTED, WHICH INCORPORATES STATE-OF-THE-ART ANISOTROPIC PLASTICITY, AN ISOTROPIC STRAIN AND STRAIN-RATE HARDENING RULE AS WELL AS SOME DUCTILE FAILURE CRITERIA. THE OBTAINED DIFFERENCES IN ENERGY ABSORPTION AND FAILURE MODES CAUSED BY VARYING THE ALLOY AND TEMPER OF THE LONGITUDINALS ARE DISCUSSED IN SOME DETAIL.