Uniaxial tension test on Rubber at constant true strain rate

J.-C Petiteau,E Verron,J.-F Sigrist,R Othman,G Barras,H.L Sourne

doi:10.1051/epjconf/20122601011

Abstract

Elastomers are widely used for damping parts in different industrial contexts because of their remarkable dissipation properties. Indeed, they can undergo severe mechanical loading conditions, i.e., high strain rates and large strains. Nevertheless, the mechanical response of these materials can vary from purely rubber-like to glassy depending on the strain rate undergone. Classically, uniaxial tension tests are made in order to find a relation between the stress and the strain in the material at various strain rates. However, even if the strain rate is searched to be constant, it is the nominal strain rate that is considered. Here we develop a test at constant true strain rate, i.e. the strain rate that is experienced by the material. In order to do such a test, the displacement imposed by the machine is an exponential function of time. This test has been performed with a high speed hydraulic machine for strain rates between 0.01/s and 100/s. A specific specimen has been designed, yielding a uniform strain field (and so a uniform stress field). Furthermore, an instrumented aluminum bar has been used to take into account dynamic effects in the measurement of the applied force. A high speed camera enables the determination of strain in the sample using point tracking technique. Using this method, the stress-strain curve of a rubber-like material during a loading-unloading cycle has been determined, up to a stretch ratio λ = 2.5. The influence of the true strain rate both on stiffness and on dissipation of the material is then discussed.

Highlights

Because of their remarkable dissipative properties, elastomers are widely used as damping parts in industry, especially to absorb shock
The beginning of the experiment presents a wave propagating in the specimen, which means that the strain field is not constant and so we can not prescribe constant true strain rate
We have presented a method to perform tests at constant true strain rate

Summary

Introduction

Because of their remarkable dissipative properties, elastomers are widely used as damping parts in industry, especially to absorb shock They can undergo severe mechanical loading conditions, i.e. both large strain and strain rates. Because of their viscoelastic nature, the mechanical response of these materials can vary from purely rubber-like to glassy depending on the strain rate undergone, as shown by Yi et al [1] or Sarva et al [2]. Roland et al [6] used the same idea and modify a drop weight machine These solutions, interesting, needs a high accuracy on the design of the pulleys and cables in order to achieve an acceptable synchronisation between loads at specimen extremities: the delay between the two loading time must be insignificant compared to the test duration. The three strain-gage signals are analysed by a wave separation technique proposed in Refs. [8, 9] and previously applied to the Hopkinson bar set-up [10, 11]

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Conclusion