A biaxial split Hopkinson bar for simultaneous torsion and compression

A biaxial split Hopkinson bar which operates in simultaneous compression and torsion is described. The device utilizes torsional stress waves generated by release of a stored torque and compressive waves generated by mechanical impact of a long rod onto a loading bar. The torque is released by capacitive discharge explosion of a thin foil in a holding adhesive joint. The two stress waves travel in opposite directions toward a specimen sandwiched between two rods, arriving at the specimen within 10 μsec of each other. The machine is used on specimens of compact bone, and it is found that plastic deformation without fracture can be achieved under the combined dynamic torsion and compression, whereas it seldom occurs under either of these loading modes alone.