Abstract: A flywheel tensile testing apparatus for viscoelastic materials is used for high-rate tensile testing to determine the mechanical properties such as the initial modulus, the stress-strain characteristics, energy at break, and void formation of energetic materials such as solid propellants and plastic bonded explosives under deformation rates in excess of 20,000 inches per minute. The tensile tester is comprised of a plurality of support trestles which are mounted on a common base. A flywheel and a light weight engagement wheel are mounted for rotation on the support trestles. A clutch and rotor assembly is located between the flywheel and the light weight engagement wheel so that when the clutch is engaged, the stored energy of the flywheel is transferred to a rotor assembly which in turn drives the light weight engagement wheel. The flywheel is driven by a variable speed motor. The activation of the clutch and rotor assembly are preferably performed in response to an electronic signal.