High strain rate properties of fatigued advanced high strength steel sheets

Abstract
Before a possible crash, energy absorbing structural elements in cars are often subjected to an important number of loading cycles. It is known that the mechanical properties of the material used for these elements can be significantly influenced by an possible fatigue. Therefore, the influence of the fatigue on the impact-dynamic behaviour of three advanced high strength steel sheets is investigated. Next to static experiments, a series of split Hopkinson tensile bar experiments is performed on a dual phase steel (DP600 Z), a TRIP steel (TRIP700 Z) and an austenitic stainless steel (301LN 2B). During these experiments as-received and fatigued material is subjected to strain rates ranging from 250/s to 1200/s. The experiments clearly show that both the deformation properties and the yield stresses, and thus the energy absorbing potential, are strongly influenced by the fatigue. Due to the fatigue, the strength of all materials considered in this study increases considerably, however the material becomes significantly more brittle. The influence of is most pronounced for the austenitic steel.