Adaptation of Broadband Simple Shear Device for Constant Volume and Stress-Controlled Testing

We adapted an existing digitally controlled simple shear device, originally designed for drained testing with strain-control, to perform constant height testing under strain-or stress-controlled conditions. The re-designed system provided PID control of horizontal displacements or loads coupled with either vertical force or displacement control (for drained and constant-volume testing, respectively). The new system had substantially similar horizontal displacement control capabilities as the previous system. The tracking error under stress-controlled loading depends on amplitude and frequency of the load; however, its value was almost the same as errors in strain-controlled tests for common shear strain/stress amplitudes. High-precision vertical control was achieved during constant height testing in two respects: (1) height change was small (less than 0.05 % of the specimen height for large shear-strain tests), even at high frequencies; and (2) top cap rocking was small, with the vertical displacements due to rocking at the specimen edge being half or less than average changes in specimen height.