Griggs press

First-generation apparatuses

Based on the piston-cylinder technology, the Griggs-type apparatus has been formerly designed by Prof. David T. Griggs in the 60’s^[1], and then modified by Prof. Jan and Terry Tullis in the following years. The Griggs apparatus is characterized by a metal frame that includes: 1) three horizontal platens mounted on vertical columns, 2) a main hydraulic cylinder (confining pressure ram) suspended to the middle platen and 3) a deformation gear box and piston/actuator fixed on top of the upper platen. The “confining” ram and deformation actuator are each connected to independent pistons that transmit forces to the sample assembly within a pressure vessel. With such a design, deformation can be achieved at confining pressures of up to 2 GPa. Thanks to a resistance furnace (graphite), the sample temperature is increased by Joule effect (up to ≈1300 °C), while the pressure vessel is water cooled on top and bottom. For further details about the Griggs press, the readers are referred to the excellent description of the modified Griggs apparatus design by Rybacky et al.^[2].

A new generation rig^[4]

Arising from a close collaboration between the ISTO, École Normale Supérieure de Paris (ENS Paris, France) and Sanchez Technologies company (Core Lab France), the new generation Griggs-type apparatus is directly based on the design of Prof. Harry W. Green^[3], which includes an end-load system homogenizing stresses in the pressure vessel and permitting to achieve deformation experiments at higher pressures (max. 5 GPa). In this new press, the confining and deformation actuators are driven by servo-controlled hydraulic syringe pumps, while the applied forces and piston displacements are continuously monitored using several sensors and transducers^[4]. The pressure vessel is made of an inner tungsten-carbide (WC) core inserted into a 1° conical steel ring and pre-stressed using the strip winding technique. Together with regular cooling on top and bottom of the pressure vessel, water flows through the steel vessel around the tungsten-carbide core for better cooling. In addition, the deformation apparatus in Orléans employs larger sample size up to 8 mm diameter, so that 1) microstructures can be better developed, 2) the Griggs press and Paterson press share common sample dimensions and 3) higher shear strain can be applied during non-coaxial experiment. This nevertheless requires an increased diameter of the WC bore in the pressure vessel (27 mm instead of 1 inch, i.e., 25.4 mm), reducing the maximum attainable pressure to 3 GPa. Some improvements have been also made to comply with European standards for safety of high-pressure experiments^[4].

The Sample assembly (see video JoVE)

The sample assembly refers to all “consumable” pieces around the sample and required to perform a Griggs-type experiment, irrespective of the press generation. This includes NaCl as the confining medium, a graphite furnace and two copper discs to heat by joule effect, and other pieces (lead, pyrophyllite, alumina pistons, etc.) to increase pressure and transmit forces. Such a sample assembly is fully appropriate to perform either co-axial (pure shear) or non-coaxial (general shear) deformation experiments over the whole range of pressures and temperatures of the Griggs-type apparatus^[4]. While a pure shear experiment typically requires a cored drill sample of a certain length (commonly ≈2 times the sample diameter), a general shear deformation is commonly applied to a zone cut at 45° to the piston axis. The sample material can either be a slice of a core sample or fine-grained powder of a chosen grain size. The shear pistons and sample are wrapped into a metal foil and jacketed within a platinum tube welded (or folded flat) at both sides. The temperature is commonly monitored using either S-type (Pt90%Rd10% alloy) or K-type (Ni alloy) thermocouples.

[1] Griggs, D. J. Hydrolytic weakening of quartz and other silicates. Geophys. J. Int. 14(1-4), 19 – 31, doi:10.1111/j.1365-246X.1967.tb06218.x (1967).
[2] Rybacky, E., Renner, J., Konrad, K., Harbott, W., Rummel, F., Stöckhert, B. A Servohydraulically-controlled Deformation Apparatus for Rock Deformation under Conditions of Ultra-high Pressure Metamorphism. PAGEOPH. 152, 579 – 606, doi:10.1007/s000240050168 (1998).
[3] Green, H. W., and Borch, R. S. A New Molten Salt Cell for Precision Stress Measurements at High Pressure. Eur. J. Mineral. 1(2), 213 – 219, doi:10.1127/ejm/1/2/0213 (1989).
[4] Précigout, J., Stünitz, H., Pinquier, Y., Champallier R., and Schubnel, A. High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus. Journal of Visualized Experiments 134, e56841, doi:103791/56841 (2018).