Finite-element simulation of wave propagation and dispersion in Hopkinson bar test

Hopkinson bar test is a standard method to investigate mechanical properties of materials under high strain rates. In practice, however, wave dispersion distorts pulse shape and may limit the accuracy of results. Using finite element simulation, it is shown in this work that a trapezoidal pulse decreases wave dispersion. Moreover it is also demonstrated that the higher the rise time the lower the wave dispersion. It is known that a trapezoidal pulse with a great rise time may be obtained by inserting a deformable disk (pad) between the projectile and the incident bar. This fact is verified in this work using an appropriate constitutive model for the deformable disk. Optimum characteristics are found for the pad, i.e., the most suitable material and dimensions. The use of deformable pad is also important when brittle materials are tested, this is because the increase in pulse rise time allows a gradual stress application.