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The dynamic tensile properties of pre-strained (plane strain, uniaxial, biaxial) or cyclic pre-loaded automotive sheet steels have been investigated for crash application. The dynamic denting resistance of sheet steels after small pre-straining has also been investigated. The pre-straining effect is of interest for the full exploitation of the mechanical behaviour of high-strength steels in automotive applications. The cyclic preloading has been carried out in order to evaluate the effect of damage development during service on the component behaviour. Crash boxes in the base, uniaxially pre-strained or pre-loaded condition and hydroformed longitudinal beams have been tested on a drop tower. Dynamic denting properties of minidoors and outer door panels have also been investigated. Increasing pre-straining increases the dynamic strength and energy absorption. Load controlled cyclic pre-loading in the low cycle fatigue range with a load ratio of 0.1 improves the crash performance of sheet steels due to accumulated plastic deformation through possible ratcheting effects. During high strain rate testing of sheet samples, pre-straining and cyclic pre-loading are beneficial with respect to dynamic mechanical properties for all ferritic steels. The TRIP effect for metastable austenitic steel grade 1.4318 is prevented by adiabatic heating at higher strain rate. This results in a significant softening of dynamic strength properties. Higher strain rate and pre-straining reduce the deformation and energy absorption time for crash boxes. Load controlled cyclic pre-loading of crash boxes in bending mode shows no significant influence on the crash properties. This can be explained by very small localised plasticity in the developed set-up which did not provide severe pre-damaging of the component. The dynamic denting resistance of minidoors and outer door panels is mainly controlled by the geometrical stiffness, thickness and strain hardening of the components.

Additional information

Authors: BLECK W, RWTH, Aachen (DE);LAROUR P, RWTH, Aachen (DE);VANDUYNSLAGER P, Arcelor (OCAS), Zelzate (BE);GEOFFROY J L, Arcelor Research, Maizzières-lès-Metz (FR);WEDEMEIER A, Salzgitter, Salzgitter (DE);GOMES M, ISQ, Porto Salvo (PT)
Bibliographic Reference: EUR 22380 EN (2006), 154 pp. Euro: 25
Availability: Katalogue Number: KI-NA-22380-EN-S The paper version can be ordered online and the PDF version downloaded at:
ISBN: ISBN: 92-79-02643-7
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