Griggs apparatus

The sample assembly is constructed of multiple cylindrical sleeves which are placed in the opening in the pressure vessel or “bomb”.

The outermost sleeve is typically composed from NaCl which is used to transfer the vertical load applied from the steel piston into a confining pressure on the sample at the center of the assembly.

The inner most sleeve which houses the sample along with the upper and lower alumina pistons, is commonly also composed of NaCl.

Temperature is monitored by a side entry thermocouple(s) that penetrate the wall of the graphite furnace and are directly adjacent to the sample, and are typically threaded through protective mullite insulation.

Deviatoric stress is created by a mechanical drive train that is powered by an electric motor that sits on top of the apparatus.

When the electric motor is powered it engages with a set of gears that allow for variable strain rates to be chosen that range from 10−3sec-1 down to 10−8sec-1.