On Spurious Reflection Waves in Hopkinson Bar Tensile Tests Using a Collar

Overview & Synopsis

In order to investigate the effect of the spurious waves present in the Hopkinson bar tensile testing technique using a collar, tests are performed with different set-ups (simple and net-shaped collars, normal and cut specimens) and different specimen materials (steel, aluminum and polyethylen). Numerical simulation (using the FD dynamic code AUTODYN-2D) is also done to support the experimental results. The tranfer of the incident compressive pulse through the collar can not be perfect, because of spurious waves which reflect at the end surface between threaded specimen and input bar. They interfere with the measurement signals from the tensile specimen and lead to a (factitious) tensile pre-stress. The cause for this effect is the actual set-up used for the tests having a same length for the input and output bars.