Dynamic behaviour of high-strength sheet steel in dynamic tension:: experimental and numerical analyses

This paper presents the behaviour of high-strength steel TRIP 700, frequently applied in automotive industries. This material is used to design some car components owing to high stress levels induced by phase transformation. Generally, a pre-plastic deformation is induced in the sheet steel at a low strain rate to transform austenite into martensite. The next step is to design for example a crash box, as described previously by Durrenberger et al. [1], in order to increase the level of energy absorption. The problem with testing this material is the specimen attachment during the tension test, notably at intermediate and high strain rates. A special problem appears when this material is used for crash applications, namely the plastic behaviour at intermediate strain rates 50 s(-1) <= <(epsilon) over dot> <= 3 x 10(2) s(-1) and for the maximum stress level observed at <(epsilon) over dot>(max) 10(3) s(-1) must be defined correctly. In order to evaluate the behaviour of materials for this range of strain rates, servohydraulic machines are used. However, even if the actuator allows for velocities V-0 >= 10 m/s, usually some problems appear during force measurement because the natural frequency of the load cell is too low. Even using a piezoelectric load cell, the material behaviour cannot be defined precisely. In order to obtain more precise information by force measurement, resistance strain gauges are generally used. One possibility is to cement these on to the specimen head. However, using this technique it is necessary to have a good knowledge of the parasite effects as discussed in this paper. Therefore, a coupled experiment-numerical simulation allows some effects due to the specimen design and resistance gauge position to be demonstrated.