Progress Report 2 on Addition of a High-Speed Drive to High-Pressure, Rotary-Shear Apparatus

Terry E. Tullis

Published August 14, 2018, SCEC Contribution #8560, 2018 SCEC Annual Meeting Poster #177 (PDF)

Rotation of the sample in my rotary-shear, high-pressure machine is driven by two systems. The first uses an electrohydraulic stepping motor providing unlimited displacement at >7 orders of magnitude in speed from 0.001 microns/s to 10 mm/s. The second system rides piggy-back on the rotating table driven by the first system, and is a hydraulic rotary servo with 9 degrees of rotation, allowing effective stiffening of the loading system.

This project involves adding a high-speed servo motor drive to the apparatus to allow rotation of samples at slip speeds up to ~4.5 m/s. This will allow study of high-speed friction weakening mechanisms at effective normal stresses similar to those at which crustal earthquakes occur. The motor will be positioned on the table rotated by the electrohydraulic stepping motor, replacing the present hydraulic rotary servo. This will allow continuous changes in speed of over 9.5 orders of magnitude.

Since our last report 2 years ago we have turned the motor design into a functional motor by fabricating and assembling a large number of fixtures, bearings, etc. We have also assembled and connected several components needed for the motor to function, including a Haskris chiller, a Siemens Simanic S120 motor controller, and a control system that allows LabVIEW control of programed slip speed and displacement sequences. We have built a 27-bit Heidenhain absolute optical encoder into the motor as the feedback device for the Siemens motor controller, allowing tight motor control to a precision corresponding to a nominal sample slip of 1 nanometer; in practice, noise degrades this by a factor of about 8. The controller can use the existing 24-bit resolver in a secondary feedback loop, allowing electronic stiffening of the apparatus as at present, but at higher speeds.

The motor is currently being tested on the bench prior to installing it in the deformation apparatus. Although its performance is impressive, additional tuning of the motor control parameters is needed to attain the precision of speed and displacement control and the accelerations that the system is nominally capable of. A video showing a sequence of motor speed steps will be shown at the poster.
Once the motor is installed and operational, jacketing of the samples at high slip speeds is the next challenge. Elevated temperatures due to frictional heating of the samples will require use of more refractory materials than the present Teflon rings and Viton O-rings.

Citation
Tullis, T. E. (2018, 08). Progress Report 2 on Addition of a High-Speed Drive to High-Pressure, Rotary-Shear Apparatus. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)