Characterisation of the high strain rate behaviour of tubular materials

Camille Caisso,Aboulghit El Malki Alaoui,Younes Demmouche,Nicolas Jacques,Harold Fresnel

doi:10.1051/epjconf/201818302046

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.

Highlights

This study takes place in airbag gas generator industry, where mass reduction and robustness are critical quality factors
split Hopkinson pressure bar (SHPB) tensile tests applied to tubular materials were not described in bibliography
The purpose of the present work is the development of an experimental SHPB setup adapted to tubular materials and of a methodology to characterise the high strain-rate behaviour of this kind of materials

Summary

Introduction

This study takes place in airbag gas generator industry, where mass reduction and robustness are critical quality factors. The material of gas generator chambers is subjected to severe dynamic loading conditions. The design of gas generator requires the characterisation of the High strain-behaviour of their constitutive material. Gas generators are produced from thin walled tube, material characterisation requires the development of specific tests. Different experimental set-ups have been developed to characterize the quasi-static elastic-plastic behaviour of tubular materials [3]. Standard testing machines allow achieving strain-rates close to 1 s-1. To reach higher strain-rates, it is necessary to use high-speed testing machines or split Hopkinson pressure bar (SHPB) systems. Using split Hopkinson pressure bar, strain-rates to 1000 s-1 can be achieved. SHPB tensile tests applied to tubular materials were not described in bibliography

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