Piezo-driven clamp release for synchronisation and timing of combined direct-shear stress waves

We propose a novel double clamp Tension-Torsion Hopkinson bar (TTHB) technique for measuring material responses under combined direct-shear loading. The proposed method overcomes the limitations of the existing high rate loading techniques by allowing arbitrary loading paths of tension and torsion to be prescribed to the specimen. High speed piezo actuators were employed to enable the synchronisation of direct stress and shear stress waves. The system also allows flexibility of control on the arrival times of torsional and tensile waves, thus enabling the generation of different dynamic loading paths. Direct and shear stress pulses can be generated such a way to achieve synchronised loading, torsion loading followed by tensile loading, and vice versa. The stress pulse histories of three different loading paths are presented to illustrate and validate the technique.