Characterisation of the high strain rate behaviour of tubular materials

Abstract

Airbag gas generators used in the automotive industry are often fabricated from tubular materials. The present work deals with the development of split Hopkinson tensile bar (SHTB) tests for tubular samples. Tubular specimens were machined from the tubes. A specific gripping system was designed to install the samples between the incident and transmitter bars. The forces acting on the samplegrip assembly were measured using strain gages mounted on the bars. Strain gages were also placed on the specimen in order to obtain the local strain history. Finite element computations were carried out to assess the validity of the experimental setup. It was observed that, in some cases, a vibration of the gripping system may induce oscillations on the force signals. To limit this phenomenon, pulse shapers [1] were employed in order to obtain a smoother input wave. Several tests were performed for different impact velocities. Strain rates ranging between 100 and 700 s-1 were achieved. Quasi-static tensile tests were also carried out. From the results of the different experiments, it was found that the steel under investigation has significant strain-rate sensitivity. Using inverse analysis, parameters for the Zerilli-Armstrong constitutive model [2] were identified.