Uniaxial tension test on Rubber at constant true strain rate

¹ LUNAM Université, École Centrale de Nantes, GeM, UMR CNRS 6183, BP. 92101, 44321 Nantes Cedex 3, France
² LUNAM Université, Institut Catholique des Arts et Métiers (ICAM), 35 avenue du champ de Manœuvres, 44470 Carquefou, France
³ DGA Techniques Navales, Avenue de la Tour Royale, BP. 40915, 83050 Toulon Cedex, France
⁴ DCNS BU Propulsion, Indret, 44620 La Montagne, France

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.