Tullis Large Volume, High Pressure Gas Medium, Rotary Shear Deformation Apparatus

Rotary Shear Friction Apparatus

This unique machine [Tullis and Weeks, 1986; Tullis, 1997; Beeler et al., 1996], built in 1980 and undergoing continued use and modification, is a high-pressure conventional triaxial apparatus, similar to those built by Paterson, Brace, and Byerlee [Paterson, 1970; Caristan, 1982; Tullis and Tullis, 1986], with a vertical pressure vessel and a hydraulic ram beneath that moves an uncompensated piston into the pressure vessel (Fig. 5). The unique aspect is that multiple driving systems are added that rotate the piston, thereby allowing torsional strain of samples or rotary shear of sample pairs. To date it has been used nearly exclusively to study friction using rotary shear of annular samples under confining pressure, employing a unique sliding jacket assembly to isolate the pore space from confining pressure. For years, this has been used to produce many meters of slip at confining pressures up to 200 MPa. The pressure vessel bore is 76 mm in dia. and 686 mm long, allowing inclusion of several internal transducers such as load and torque cells, a resolver, and an LVDT to measure relative rotational and vertical motion of sample halves. The pressure vessel is designed to operate at 1.0 GPa confining pressure and has been tested to 1.2 GPa. Independent pore pressure control up to 200 MPa is provided to both halves of the sample. This allows pore fluid flow through the sample for slip amounts of 200 mm. Unlimited displacement with pore pressure is attainable, if only the top sample half is connected. To date only room temperature experiments have been done, but an internal furnace can allow controlled temperatures of 300˚C. Slip speeds from 0.001 microns/s to 10 mm/s are attainable with the long-available drive system, which can include servo control of slip that substantially stiffens the machine. The addition of a 100 kW electric servo motor to the drive system will be completed soon and will increase the slip speed to 4.5 m/s (1800 RPM) with positional motor control of 1 nm of slip [Tullis, 2017] (see Results from Prior NSF Support section, grant 1359596).

Loading; Unloading