In this study, a comparison of dynamic mechanical behaviour of thin sheet boxes (crash energy absorbers) of two different materials (aluminium and steel), submitted to crash tests by means of a large Hopkinson bar, is reported. For the steel boxes, the experimental results show that the first peak load value is higher than the succesive ones; for aluminium boxes the first peak load is almost at the same level of the succesive ones. The study has shown that the material strain rate sensitivity is one of the mechanical parameters which affects especially the first peak load during thin sheet box crash test. This is explained by the stress waves and the innertial effects which are more influent at the beginning of the test when the whole spicemen is submitted to high particle acceleration accompanied by large variation of material strain rate. These phenomena could explain also the difficulty to obtain first peak load values with a classical load cell in the drop hammer test. After many reflections an elastic stress equilibrium is reached and then the mechanical response of the thin sheet material does not change for the succesive fold formation. It is then important to understand the crash behaviour at the beginning of the test especially for strain rate sensitive materials. A too strong first peak load may have dangerous effects on the safety of passengers. The strain gauges glued on the box can be a solution to check the stress value. This can be obtained by reporting the strain values obtained before the plastic deformation to the stress strain curve of the material at the same velocity.
Precision measurements of crashworthiness of automotive longitudinals in aluminium and steel
Genaue Messungen crashrelevanter Eigenschaften von Fahrzeuglängsträgern aus Aluminium und Stahl
1996
7 Seiten, 6 Bilder, 5 Quellen
Conference paper
English
Precision Measurements of Crashworthiness of Automotive Longitudinals in Aluminium and Steel
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