This study is dedicated to the memory of Prof. Harry W. Green, without whom none of this would have been possible. We also thank J&#246;rg Renner and S&#233;bastien Sanchez for their implications in designing and implementing the apparatus, as well as Andreas K. Kronenberg, Caleb W. Holyoke III and three anonymous reviewers for their fruitful discussions and comments. We are grateful to Jan Tullis for teaching us and numerous students the basics and many useful tricks of solid-medium deformation experiments. This study has been funded by the ERC RHEOLITH (grant 290864), Labex Voltaire (ANR-10-LABX-100-01), Equipex PlaneX (ANR-11-EQPX-0036) and ANR DELF (ANR-12-JS06-0003).

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</ol>

The authors have nothing to disclose.

Initially, the Griggs-type apparatus was designed to perform deformation experiments as slowly as possible to approach geological strain rates closer than other techniques, i.e., over weeks, months or even years9. Thus, Griggs-type experiments may run as long as the electrical supply and water cooling are functioning, particularly overnight when no operator is required. As mentioned before, the Griggs press can also explore most of the range of pressure and temperature encountered in the lithosphere. However, this technique presently is subjected to some limitations that may reduce the accuracy of the stress determination.
The success of a Griggs-type experiment relies on several critical points that mainly include the quality of the thermocouple sheath, the shape of packing rings, and the alignment of shear pistons (only for general shear experiments). Indeed, the thermocouple wires should be well insulated from each other and from the confining medium (NaCl). Otherwise, the temperature recording may be either modified through touching of the two wires outside of the sample chamber, leading to a dramatic increase of temperature (this could break the pressure vessel), or the thermocouple may break and the experiment fails. The top surface of each packing ring (&#963;1 and &#963;3) should be flat and large enough (around half a millimeter). This is required to avoid any lead leak during pressure increase. For general shear experiments, the top and bottom shear pistons should be perfectly aligned, so that no asymmetrical deformation occurs during experiment. If not, the sample may come into contact with the confining medium through a jacket leak, giving rise to possible contamination and sample failure. In addition, such a jacket leak will likely occur in a general shear experiment if the deformation piston is not stopped early enough. The capability of the platinum jacket in being deformed without any breaking may significantly vary from one experiment to another. Nevertheless, although shear deformation has been already achieved at more than gamma = 7 on samples of 2 mm thickness (an example is given in Heilbronner and Tullis24), a gamma = 5 is routinely applied with a good success rate and significantly higher shear strains can be achieved by reducing the sample thickness.
Nowadays, the Griggs press is subject to friction effects that reduce the accuracy of stress measurements, particularly when the &#34;hit point&#34; is defined by curve fitting. Most of the friction occurs while the deformation piston is advancing through the &#963;1 packing ring, lead piece and confining medium (NaCl). This can be seen from the stress-time curve during the &#34;run-in&#34; step of the deformation stage (Figure 9), but also during loading after the hit point. While elastic behavior is not dependent on the sample stiffness, the slope of the loading curve increases with the sample strength in the Griggs-type apparatus. This is mainly due to non-elastic sample strain while the &#963;1 piston pushes through the lead. Indeed, the slope of the load curve before yield stress conditions does not represent pure elastic loading of the sample, but a combination of different components that include friction and some sample deformation/compaction. Unfortunately, this type of behavior is hardly reproducible as it depends on the sample strength, which is low at high temperature, and the error induced by friction that strongly varies from 3 to 9%18. Some other weaker materials like Indium, Bismuth or Tin have been used instead of lead19, but they always give rise to some leak at pressures higher than 1 GPa. In addition, whereas km-scale objects and very slow strain rates (10-15-10-12 s-1) need to be considered for geological purposes, the Griggs-type apparatus - like any other deformation apparatus - is limited in terms of sample size (max. 8 mm diameter for the Griggs press) and strain rate (min. 10-8 s-1). These geological conditions require indeed unrealistic forces and impractical duration of experiment to be applied. Nevertheless, this inevitable gap between deformation experiments and geological circumstances may be partly substituted by numerical models, provided that lab-based mechanical laws are fully valid through extrapolations. This definitely requires developing high-pressure apparatuses with better accuracy, at least as good as the one of the gas-pressure-medium-type apparatus (i.e., &#177; 1 MPa).
At present, only the gas-medium apparatuses are accurate enough to perform rheological experiments, and most of the available mechanical laws come from the Paterson apparatus at confining pressure of 0.3 GPa. The high accuracy on stress measurements mainly relies on the presence of an internal load cell that undergoes the confining pressure, in contrast to an external one that only suffers room pressure, and its combination with a gas pressure vessel, which permitted to apply a specific design that cannot be transferred as-is into a solid-medium press. Today, the solid-medium apparatus only uses an external load cell &#8211; some of them do not even have any load cell &#8211; to measure the differential stress, giving rise to a poor resolution and substantial overestimation because of friction.
In the Griggs-type apparatus, the using of a molten salt assembly may significantly reduce the friction around the sample (by a factor of 3). But as mentioned before, it also gives rise to further issues and the accuracy of stress measurement remains 10 times lower than that in the Paterson apparatus. Another approach would consist in implementing an internal load cell, or something similar, to get rid of the friction effects in the Griggs press. Considering the size and capacities of &#34;regular&#34; load cells, such as found in the industry, it seems unrealistic to include some of them within the sample chamber of the pressure vessel. They could not sustain the confining pressure and a high-capacity load cell (max. 200 kN), such as required for high-pressure experiments in the Griggs-type apparatus, and they would be too large to be included in the sample chamber. However, one possibility would imply using the basal piston of the sample column as an internal load cell25, provided that its deformation can be precisely measured (Andreas K. Kronenberg, personal communications). This requires a room below the base plate to adapt a specific load cell, which has been anticipated in the new Griggs-type apparatus (Figure 1). But today, such an internal load cell in solid-medium deformation apparatus remains to be implemented.

Rock deformation is one of the most important geological processes. It strongly contributes to human-time-scale phenomena, like earthquakes or landslides, but also to the large-scale mass movements of the solid outer shell in telluric planets, including plate tectonics on Earth1. For instance, depending on the rheology of the shell-like lithosphere, which defines the strength of both the crust and sub-solidus mantle (<img alt="Equation" src="/files/ftp_upload/56841/56841eq1.jpg" /> 1200 &#176;C), the scheme of plate tectonics and related features may vary significantly2,3,4,5. On the one hand, the presence of a strong uppermost mantle and/or lower crust is required to sustain mountain belts or stabilize subduction zones6. But on the other hand, numerical models have also shown that plate boundaries cannot develop from mantle convection if the lithosphere is too strong, giving rise to a rigid lid behavior as observed on Venus7. Thus, the strength of the lithosphere as dictated by rock rheology has a direct control on the plate-like behavior of active planets.
For more than half a century, the rock rheology has been investigated at high temperatures (&#62; 300 &#176;C), giving rise to state-of-the-art techniques that mainly differ in the pressure range they can achieve. This includes the gas-medium Paterson-type apparatus8 at relatively low pressures (&#60;0.5 GPa), the solid-medium Griggs-type apparatus9,10,11 at intermediate to high pressures (0.5-5 GPa), and the deformation-Dia apparatus12,13 (DDia: up to ~20 GPa) or diamond anvil cell at very high pressures14 (up to more than 100 GPa). Thus, the pressures and temperatures encountered in the deep Earth can nowadays be achieved experimentally. However, rock deformation also relies on differential stress that needs to be measured with high accuracy and precision, so that constitutive relationships can be formulated. Thanks to its gas-confining medium, the Paterson apparatus is today the only technique able to perform stress measurements with an adequate accuracy (&#177; 1 MPa) to extrapolate the data over 6 orders of magnitude in strain rate, but it can only explore deformation processes at low pressures. Conversely, solid-medium apparatuses can deform rocks at high pressures, but with a lower accuracy of the stress measurements. While stress accuracy has been estimated at &#177; 30 MPa for the Griggs-type apparatus15,16, the synchrotron-based DDia produces mechanical laws with an error of more than &#177; 100 MPa17. In the Griggs-type apparatus, stress could also be overestimated by up to 36% with respect to stress measurements in the Paterson one15. Performing accurate and precise stress measurements at high pressures - and high temperatures - therefore remains a major challenge in Earth Sciences.
Excluding deep subduction slabs where pressures may exceed 5 GPa, the Griggs-type apparatus is presently the more appropriate technique to study deformation processes over the pressure (&#60; 4 GPa) and temperature (<img alt="Equation" src="/files/ftp_upload/56841/56841eq1.jpg" /> 1200 &#176;C) ranges in a large part of the lithosphere. On this basis, significant endeavors have been undertaken in the 1990&#39;s to improve stress measurements, particularly to reduce friction effects by using eutectic salt mixtures as a confining medium around the sample11,18. Such a molten salt assembly gave rise to a better accuracy of the stress measurement, reducing the error from &#177; 30 to &#177; 10 MPa15,19, but additional disadvantages have been encountered when applying this type of assembly. These have a much lower success rate, great difficulties to perform non-coaxial (shear) experiments, and a more complicated sample assembly. Moreover, the accuracy of stress measurements remains ten times lower than that of the low-pressure Paterson-type apparatus. These issues limit the quantification of rheological processes using the Griggs-type apparatus, which today is more commonly applied to explore the deformation processes and their related microstructures. A new approach will be therefore required to perform rheological quantification at high lithospheric pressures.
This paper gives detailed documentation of the &#34;conventional&#34; procedure to perform high-pressure deformation experiments using a newly designed solid-medium Griggs-type apparatus. In the framework of new &#34;Griggs&#34; laboratories implemented at the ISTO (Orl&#233;ans, France) and ENS (Paris, France), the main purpose is to properly illustrate each step of the protocol in details, so that scientists from all fields can decide whether the apparatus is appropriate or not to their aims of study. The critical steps and limitations of this state-of-the-art technique are also discussed, together with new approaches and possible future developments.
The new Griggs-type apparatus
Based on the piston-cylinder technology, the Griggs-type apparatus has been formerly designed by David T. Griggs in the 1960&#39;s9, and then modified by Harry W. Green in the 1980&#39;s11 (mainly to achieve higher pressures during deformation experiments). In both cases, 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 (Figure 1). The &#34;confining&#34; ram and deformation actuator are each connected to independent pistons that transmit forces to the sample assembly within a pressure vessel. With such a vessel, deformation can be achieved at confining pressures of up to 2 or 5 GPa, depending on the apparatus and diameter of the sample assembly.
Thanks to a resistance furnace, the sample temperature is increased by Joule effect (up to &#8776;1300 &#176;C20), while the pressure vessel is water cooled on top and bottom. In Green&#39;s design, the Griggs apparatus also includes an end-load system that homogenizes the pre-stress in the pressure vessel (Figure 1). This permits to achieve deformation experiments at higher pressures (max. 5 GPa), particularly using a small bore in the pressure vessel. 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.19.
Arising from a close collaboration between the Institut des Sciences de la Terre d&#39;Orl&#233;ans (ISTO, France) and &#201;cole Normale Sup&#233;rieure de Paris (ENS Paris, France), the new generation Griggs-type apparatus is directly based on the design from H. W. Green11, but some improvements have been made to comply with European standards for safety of high-pressure experiments. In this new press, the confining and deformation actuators are driven by servo-controlled hydraulic syringe pumps, giving the possibility to perform either constant load or constant displacement experiments at high pressures (up to 5 GPa). The confining (isostatic) pressure, force, and displacement are respectively monitored using oil pressure sensors, a load cell (max. 200 kN) and displacement transducers (Figure 1). The pressure vessel is made of an inner tungsten-carbide (WC) core inserted into a 1&#176; conical steel ring and pre-stressed using the strip winding technique21. For transmitting forces, the pressure vessel and sample assembly lie between WC-removable pistons that include a deformation piston (&#963;1), confining piston (&#963;3), end-load piston and base plate (Figure 1). Together with regular cooling on top and bottom of the pressure vessel, water flows through the steel vessel around the tungsten-carbide core within 6 mm diameter holes for better cooling (Figure 1). The hydraulic cylinder for the confining pressure is also cooled by silicon oil flow. In addition, the deformation apparatus in Orl&#233;ans employs larger sample size up to 8 mm diameter, so that 1) microstructures can be better developed, and 2) the Griggs press and Paterson press share a common sample dimension for future comparisons. This 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.
The present paper describes the procedure to perform an experiment with the new Griggs-type apparatus, which includes the description of all pieces that compose the conventional solid-salt sample assembly using alumina pistons (Figure 2A and 2B), as well as the successive steps to produce them and introduce them into the pressure vessel. This description follows in large parts the routine developed over many years by Prof. Jan Tullis and co-workers at Brown University (R.I., USA). The resulting 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. While a pure shear experiment typically requires a cored drill sample of a certain length (commonly &#8776;2 times the sample diameter), a general shear deformation is commonly applied to a zone cut at 45&#176; to the piston axis (Figure 2B). The sample material can either be a slice of a core sample or fine-grained powder of a chosen grain size. All pieces 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) thermocouple, but only the preparation of an S-type thermocouple using a mullite 2-hole sheathing tube is here described (Figure 2C).

<table><tbody><tr><td>Griggs-type apparatus</td><td>Sanchez Technologies (Corelab)</td><td>TRI-X 6/1500 SD</td><td>Solid-medium Griggs-type deformation apparatus</td></tr><tr><td></td><td>Sanchez Technologies (Corelab)</td><td>Stigma pumps 1000/300 and 100/1500</td><td>hydraulic syringe pumps to apply pressure</td></tr><tr><td>Arbor press</td><td>Schiltz</td><td>PA.WZ.5000.530</td><td>Arbor press required to insert the sample assembly into the pressure vessel</td></tr><tr><td>Low-speed saw</td><td>Presi</td><td>Mecatome T180</td><td>Law-speed saw to cut alumina piston and mullite sheath</td></tr><tr><td></td><td>Presi</td><td>LR02033</td><td>Diamond saw blade</td></tr><tr><td>40 tons hydraulic press</td><td>CompaC</td><td>APA 9040EH1-D</td><td>40-ton hydraulic press to press salt/lead pieces and extract the sample</td></tr><tr><td>Pressure vessel (and pistons)</td><td>STRECON</td><td>vessel A4071&amp;nbsp;</td><td>Inner tungsten-carbide core inserted into a 1&amp;deg; conical steel ring and pre-stressed using the strip winding technique</td></tr><tr><td></td><td>STRECON</td><td>Deformation piston</td><td>Tungsten carbide piston to apply deformation</td></tr><tr><td></td><td>STRECON</td><td>Confining piston</td><td>Tungsten carbide piston to apply confining pressure</td></tr><tr><td></td><td>STRECON</td><td>End-load piston</td><td>Tungsten carbide piston to pre-stress the pressure vessel</td></tr><tr><td>PUK U3</td><td>Lampert</td><td>PUK 5 welding microscope</td><td>Fine welding system to weld the thermocouple and platinum jacket</td></tr><tr><td>Cooling system Ultracool</td><td>Lauda</td><td>UC 4 E1 PI5 SR BSP &amp;deg;C</td><td>Cooler for the pressure vessel</td></tr><tr><td></td><td>Lauda</td><td>Proline RP850</td><td>Cooler for the confining/end-load ram</td></tr><tr><td>Leath</td><td>Schneider electric</td><td>Eurotherm 2704</td><td>Temperature controller</td></tr><tr><td>Milling machine</td><td>Enerpac</td><td>P-142</td><td>Hand pump to lift up the confining/end-load ram</td></tr><tr><td></td><td>HBM</td><td>1-P3TCP/2000 bar</td><td>Pressure transducer</td></tr><tr><td></td><td>HBM</td><td>1-P3TCP/500 bar</td><td>Pressure transducer</td></tr><tr><td></td><td>HBM</td><td>WA/10 mm</td><td>Displacement transducer</td></tr><tr><td></td><td>HBM</td><td>WA/50 mm</td><td>Displacement transducer</td></tr><tr><td></td><td>HBM&amp;nbsp;</td><td>1-C2/200 kN</td><td>Load cell</td></tr><tr><td></td><td>Geoscience instrument</td><td></td><td>Graphite furnace: graphite tube inserted between two pyrophyllite sleeves (custom-made)</td></tr><tr><td></td><td>McDanel</td><td>MRD028330018858</td><td>Mullite Round Double Bore Tubing</td></tr><tr><td></td><td>Morgan Advanced Materials</td><td>WH-Feuerfestkitt</td><td>Ceramic glue</td></tr><tr><td></td><td>PRECIS</td><td>T90 L</td><td>Lathe</td></tr><tr><td></td><td>NSK</td><td>EM-255</td><td>Diamond tool to parallelize alumina piston using the lathe</td></tr><tr><td></td><td>Mecanelec</td><td>CDM &amp;ndash; IP 1 &amp;ndash; 5L/mn</td><td>Flow meter for water cooling (pressure vessel)</td></tr><tr><td></td><td>Hedland</td><td>H602A-0005-F1</td><td>Flow meter for oil cooling (confining/end-load ram)</td></tr><tr><td></td><td>Legris</td><td>S&amp;eacute;rie 21</td><td>double-self-sealing coupler for tube of the water cooling system</td></tr><tr><td></td><td>Corelab</td><td>Falcon</td><td>Software to monitor the hydraulic syringe pumps</td></tr><tr><td></td><td>HBM</td><td>CatmanEasy-HP</td><td>Software to record data</td></tr><tr><td></td><td>Schneider electric</td><td>Eurotherm itools</td><td>Software to set programs for the temperature controller</td></tr><tr><td></td><td>VWR</td><td>410-0114</td><td>Ceramic mortar</td></tr><tr><td></td><td>VWR</td><td>231-2322</td><td>Microspatule</td></tr><tr><td></td><td>VWR</td><td>459-0206</td><td>Ceramic recipient</td></tr><tr><td></td><td>VWR</td><td>AnalaR NORMAPUR 27810.364</td><td>Sodium Chloride 99.9% purity</td></tr><tr><td></td><td>VWR</td><td>Barnstead/Thermoline 48000 furnace</td><td>Benchtop Muffle furnace for melting lead</td></tr><tr><td></td><td>DP/Pr&amp;eacute;cision</td><td>Custom made</td><td>Tools needed to produce the salt and lead pieces</td></tr><tr><td></td><td>Cincinnati</td><td>TYPE PE-5</td><td>Milling machine</td></tr><tr><td></td><td>Memmert</td><td>UNB 400</td><td>Oven to stock salt powder and salt pieces</td></tr><tr><td></td><td>Otelo</td><td>Otelo 65220023</td><td>Tubing cutter for Platinum</td></tr><tr><td></td><td>Otelo</td><td>BAITER 51600202</td><td>File tool</td></tr><tr><td></td><td>Otelo</td><td>VADIUM 65172600</td><td>Diagional micro-cutter</td></tr><tr><td></td><td>Otelo</td><td>VADIUM 65172620</td><td>Flat needle nose micro-pliers</td></tr><tr><td></td><td>SAM</td><td>EMP-13J</td><td>Round screw hollow punch</td></tr><tr><td></td><td>Professional Platic</td><td>Chemfluor MFA Tube</td><td>Minitube for isolating thermocouple wires</td></tr><tr><td></td><td>Radiospar</td><td>RS 370-6717</td><td>S-type flat pin thermocouple connector</td></tr><tr><td></td><td>LEMER</td><td></td><td>Lead (bulk)</td></tr><tr><td></td><td>Goodfellow</td><td>FP301305</td><td>Polyt&amp;eacute;trafluoro&amp;eacute;thyl&amp;egrave;ne - Film ; 0.15 mm thickness</td></tr><tr><td></td><td>Heraeus</td><td>81128696</td><td>Pure Platinum wire</td></tr><tr><td></td><td>Heraeus</td><td>81128743</td><td>Platinum90%/Rhodium10% wire</td></tr><tr><td></td><td>Alfa Aesar</td><td>M11C056</td><td>Nickel foil 0.025 thickness annealed 99.5%</td></tr><tr><td></td><td>DP/precision</td><td></td><td>Tools to produce the salt pieces and lead piece (custom-made)</td></tr><tr><td></td><td>Polyco Bodyguards</td><td>GL890</td><td>Blue Nitrile Medical Examination gloves</td></tr></tbody></table>

high-pressure, high-temperature deformation experiment using the new generation griggs-type apparatus

In order to address geological processes at great depths, rock deformation should ideally be tested at high pressure (&#62; 0.5 GPa) and high temperature (&#62; 300 &#176;C). However, because of the low stress resolution of current solid-pressure-medium apparatuses, high-resolution measurements are today restricted to low-pressure deformation experiments in the gas-pressure-medium apparatus. A new generation of solid-medium piston-cylinder (&#34;Griggs-type&#34;) apparatus is here described. Able to perform high-pressure deformation experiments up to 5 GPa and designed to adapt an internal load cell, such a new apparatus offers the potential to establish a technological basis for high-pressure rheology. This paper provides video-based detailed documentation of the procedure (using the &#34;conventional&#34; solid-salt assembly) to perform high-pressure, high-temperature experiments with the newly designed Griggs-type apparatus. A representative result of a Carrara marble sample deformed at 700 &#176;C, 1.5 GPa and 10-5 s-1 with the new press is also given. The related stress-time curve illustrates all steps of a Griggs-type experiment, from increasing pressure and temperature to sample quenching when deformation is stopped. Together with future developments, the critical steps and limitations of the Griggs apparatus are then discussed.

Figure 9 shows an example of a stress-time curve resulting from the new generation Griggs-type apparatus during pure shear (co-axial) deformation of Carrara marble (8-mm-long core sample) at a strain rate of 10-5 s-1, a temperature of 700 &#176;C and a confining pressure of 1.5 GPa. During such an experiment, both the pressure and temperature are first increased alternatingly, mainly to prevent the NaCl from melting. The molten NaCl is very corrosive for the sample and it may irreversibly damage the thermocouple. All along the successive steps of increasing pressure and temperature - here referred as the &#34;pumping stage&#34; (Figure 9) &#8211; the lead piece has the function of preventing the sample from becoming deformed by transferring stresses from &#963;1 to &#963;3 and conversely, maintaining a more or less isostatic stress state in the sample assembly.
When the target pressure and temperature are achieved, a period of &#34;hot-pressing&#34; may be applied. Although optional, this step &#8211; of commonly 24 h duration &#8211; may be required to sinter the sample powder before deformation, if applicable. The &#963;1 piston/actuator is then advanced to deform the sample, giving rise to the so-called &#34;deformation stage&#34;. This latter is first characterized by a steep-to-gentle increase of differential stress (&#963;1 - &#963;3), which is due to friction induced by 1) the packing rings and 2) the increasing surface of contact between the &#963;1 piston and lead piece while &#963;1 is moving through the lead. This &#34;run-in&#34; section should have a sufficient duration in order to determine the hit point (contact between the &#963;1 piston and top alumina piston) accurately by curve fitting (Figure 9). For this purpose, a significant thickness of lead (&#8805; 2 mm) between the &#963;1 piston and alumina piston is required before starting advancing &#963;1. When approaching the top alumina piston, lead is extruded faster as a thin sample thickness, causing strain hardening in the lead and promoting a progressive stress increase until the &#963;1 piston is pushing on the sample column. The stress curve then increases steeply up to yield stress conditions, which theoretically defines the transition from elastic to plastic behaviors (Figure 9). As required to define the differential stress, the hit point of the experiment is subsequently deduced from the intersection between the extensions of the &#34;elastic&#34; curve and &#34;run-in&#34; curve (Figure 9).
When deformation is finally stopped, the temperature is decreased very quickly (&#8776; 300 &#176;C/min) to preserve microstructures. A substantial drop of pressure necessarily occurs during the &#34;sample quenching&#34;, but following this drop, both the &#963;1 and &#963;3 pistons are moved back slowly by reducing the oil pressure in the hydraulic rams (&#8776; 5 MPa/min). This is required to limit the formation of unloading cracks, although some cracking is inevitable. After experiment, the stress-time curve is subsequently corrected to produce a stress-strain curve of the deformed sample up from the hit point (see inset in Figure 9). These corrections include 1) the stiffness/extension of the apparatus and 2) the friction induced by the packing rings and lead piece15,19. Figure 10 also shows two examples of the post-experiment sample assembly, one containing the core sample of Carrara marble (Figure 10A and 10B) and a second one of an olivine powder sintered, and then deformed in general shear at 900 &#176;C and 1.2 GPa using the former Griggs-type apparatus23 (Figure 10C and 10D).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56841/56841fig1.jpg" /> 
Figure 1: The new generation Griggs-type apparatus. Schematic drawings of the Griggs-type apparatus now available at the Institut des Sciences de la Terre d&#39;Orl&#233;ans (ISTO, France) and &#201;cole Normale Sup&#233;rieure de Paris (ENS Paris, France). While the sample assembly lies within the pressure vessel, high confining pressure and differential stress are applied by independent syringe pumps through hydraulic rams and pistons/actuators. The temperature is increased using a low-voltage/high-amperage electrical current injected from below the assembly (see side view) through a resistive graphite furnace. To preserve the tungsten carbide (WC) die, the pressure vessel is also cooled by water flow from bottom to top through the cooling plates/boxes and the vessel itself. <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56841/56841fig2.jpg" /> 
Figure 2: Sample assembly. Detailed view of the pieces that compose the sample assembly. The &#963;1 piston, &#963;3 piston and base plate are also shown &#8211; part of them in transparency &#8211; to locate the position of each piece with respect to the Griggs-type apparatus. A) Sample assembly of a coaxial experiment. B) Exploded view of the sample assembly, either for a &#34;coaxial&#34; (white) or &#34;general shear&#34; sample (green). The lead piece and lower salt piece are shown in transparency. C) 3D view of a mullite 2-hole sheathing S-type thermocouple used to monitor the temperature during an experiment. WC = tungsten carbide. <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56841/56841fig3.jpg" /> 
Figure 3: Tools required to cold press the outer and inner salt pieces from NaCl powder. A) 3D views during pressing (14 tons for 30 s) and extraction of the outer salt pieces (left), and scaled drawings of the related tool components (right). B) 3D views during pressing (6 tons for 30 s) and extraction of the inner salt piece (left), and scaled drawings of the related tool components (right). Some parts are shown in transparency. <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56841/56841fig4v2.jpg" /> 
Figure 4: Tool required to drill the lower outer salt piece. A) 3D views before (top) and during (bottom) drilling. B) Scaled drawings (3D, top and side views) of the tool (only one part is shown). <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56841/56841fig5.jpg" /> 
Figure 5: Tools required to produce the platinum jacket. A) 3D view (left) and scaled drawings (right) of the tool needed to produce the platinum cups. By pushing on the 10-mm-diameter platinum disc, its outer part is bent up over 1 mm thickness into a cup-shape, so that it can fit into and be welded together with the 8-mm-diameter platinum jacket. B) 3D view (top) and scaled drawings (bottom) of the tool needed to weld a platinum cup to the platinum jacket (only half of the top piece is shown). <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56841/56841fig6.jpg" /> 
Figure 6: Tool required to produce the lead piece. A) 3D view during pressing (4 tons for 30 s) of the molten lead (50 g). The component #2 is shown in transparency. B) 3D view during extraction of the lead piece (the dimensions are shown in the top left inset). C) Scaled drawings of the tool components. <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/56841/56841fig7v2.jpg" /> 
Figure 7: Clamps to fix the basal piston to the pressure vessel. 3D view of the pressure vessel, basal piston and clamps (top), and scaled drawings of the top and bottom parts of one clamp, including a 3D view (bottom). <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/56841/56841fig8.jpg" /> 
Figure 8: Hydraulics of the pumps and cooling systems. Scheme of the hydraulics &#8211; including valves (V), electro-valves (EV) and oil tank (T) &#8211; of the deformation pump (purple), confining pump (orange), cooling system of the pressure vessel (light blue) and cooling system of the confining/end-load ram (yellow). <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/56841/56841fig9.jpg" /> 
Figure 9: Representative result. Example of a stress-time curve of a deformation experiment using the new generation Griggs-type apparatus. This experiment has been performed coaxially on a core sample (8 mm long) of Carrara marble at 700 &#176;C, 1.5 GPa and a strain rate of 10-5 s-1. This result illustrates the successive steps of a Griggs-type experiment, which includes 1) a &#34;pumping stage&#34; to increase pressure and temperature, 2) a &#34;hot-pressing stage&#34; to sinter the sample, if applicable, 3) a &#34;deformation stage&#34; to deform the sample, and 4) a &#34;quenching stage&#34; to decrease pressure and temperature. During deformation, the &#963;1 piston first advances through the lead (&#34;run-in&#34; step), and then pushes on the alumina piston to properly deform the sample (up from the hit point), giving rise to elastic-then-plastic behavior (see text). After correction of the stress-time curve from friction and stiffness/extension of the apparatus, a stress-strain curve is produced up from the hit point (inset). &#963;1 = stress applied by the &#963;1 piston; &#963;3 = stress applied by the &#963;3 piston; P = confining (isostatic) pressure; T = temperature. &#963;1-&#963;3 = differential stress. <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/56841/56841fig10.jpg" /> 
Figure 10: Sample extraction. A) Lower part of the sample assembly extracted after the experiment described in Figure 9. B) Sample of Carrara marble (still wrapped into its platinum jacket) after pure shear deformation at 700 &#176;C and 1.5 GPa in the new Griggs-type apparatus. C) Lower part of a sample assembly containing a sample of olivine powder sintered, and then deformed in general shear at 900 &#176;C and 1.2 GPa with the former Griggs-type apparatus23. D) Olivine sample and alumina shear pistons (still wrapped into the platinum jacket) after extraction from the sample assembly. TC = Thermocouple. <a href="https://cloudflare.jove.com/files/ftp_upload/56841/56841fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus at JoVE.com

High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus

Rock deformation needs to be quantified at high pressure. A description of the procedure to perform deformation experiments in a newly designed solid-medium Griggs-type apparatus is here given. This provides technological basis for future rheological studies at pressures up to 5 GPa.

In order to address geological processes at great depths, rock deformation should ideally be tested at high pressure (&#62; 0.5 GPa) and high temperature ...

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18.8K Views.  Université d’Orléans. Rock deformation needs to be quantified at high pressure. A description of the procedure to perform deformation experiments in a newly designed solid-medium Griggs-type apparatus is here given. This provides technological basis for future rheological studies at pressures up to 5 GPa.

Video: High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Engineering

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from their extraction to the core during terrestrial accretion. Experiments to investigate the partitioning of these elements between metal and silicate melts suggest that the PUM composition is best matched if metal-silicate equilibrium occurred at high pressures and temperatures, in a deep magma ocean environment. The behavior of the most highly siderophile elements (HSEs) during this process however, has remained enigmatic. Silicate run-products from HSE solubility experiments are commonly contaminated by dispersed metal inclusions that hinder the measurement of element concentrations in the melt. The resulting uncertainty over the true solubility and metal-silicate partitioning of these elements has made it difficult to predict their expected depletion in PUM. Recently, several studies have employed changes to the experimental design used for high pressure and temperature solubility experiments in order to suppress the formation of metal inclusions. The addition of Au (Re, Os, Ir, Ru experiments) or elemental Si (Pt experiments) to the sample acts to alter either the geometry or rate of sample reduction respectively, in order to avoid transient metal oversaturation of the silicate melt. This contribution outlines procedures for using the piston-cylinder and multi-anvil apparatus to conduct solubility and metal-silicate partitioning experiments respectively. A protocol is also described for the synthesis of uncontaminated run-products from HSE solubility experiments in which the oxygen fugacity is similar to that during terrestrial core-formation. Time-resolved LA-ICP-MS spectra are presented as evidence for the absence of metal-inclusions in run-products from earlier studies, and also confirm that the technique may be extended to investigate Ru. Examples are also given of how these data may be applied.

We present a procedure to determine the metal-silicate partitioning of siderophile elements, emphasizing techniques that suppress the formation of metal inclusions in experiments for the noble metals. The results of these experiments are used to demonstrate the effect of core-formation on the highly siderophile element composition of the mantle.

Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from ...

Chemistry

High-Sensitivity Nuclear Magnetic Resonance at Giga-Pascal Pressures: A New Tool for Probing Electronic and Chemical Properties of Condensed Matter under Extreme Conditions

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their electronic properties. The application of high pressure enables one to synthesize new materials, but the response of known materials to high pressure is a very useful tool for studying their electronic structure and developing theories. For example, high-pressure synthesis might be at the origin of life; and understanding the behavior of small molecules under extreme pressure will tell us more about fundamental processes in our universe. It is no wonder that there has always been great interest in having NMR available at high pressures. Unfortunately, the desired pressures are often well into the Giga-Pascal (GPa) range and require special anvil cell devices where only very small, secluded volumes are available. This has restricted the use of NMR almost entirely in the past, and only recently, a new approach to high-sensitivity GPa NMR, which has a resonating micro-coil inside the sample chamber, was put forward. This approach enables us to achieve high sensitivity with experiments that bring the power of NMR to Giga-Pascal pressure condensed matter research. First applications, the detection of a topological electronic transition in ordinary aluminum metal and the closing of the pseudo-gap in high-temperature superconductivity, show the power of such an approach. Meanwhile, the range of achievable pressures was increased tremendously with a new generation of anvil cells (up to 10.1 GPa), that fit standard-bore NMR magnets. This approach might become a new, important tool for the investigation of many condensed matter systems, in chemistry, geochemistry, and in physics, since we can now watch structural changes with the eyes of a very versatile probe.

Nuclear magnetic resonance is one of the most important spectroscopic tools. Here, the development of a new approach under high pressure, currently up to 10.1 GPa, is presented. This opens a new window into condensed matter physics and chemistry, where high-pressure research is of great importance.

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their ...

A Method for Studying the Temperature Dependence of Dynamic Fracture and Fragmentation

The dynamic fracture of a body is a late-stage phenomenon typically studied under simplified conditions, in which a sample is deformed under uniform stress and strain rate. This can be produced by evenly loading the inner surface of a cylinder. Due to the axial symmetry, as the cylinder expands the wall is placed into a tensile hoop stress that is uniform around the circumference. While there are various techniques to generate this expansion such as explosives, electromagnetic drive, and existing gas gun techniques they are all limited in the fact that the sample cylinder must be at room temperature. We present a new method using a gas gun that facilitates experiments on cylinders from 150 K to 800 K with a consistent, repeatable loading. These highly diagnosed experiments are used to examine the effect of temperature on the fracture mechanisms responsible for failure, and their resulting influence on fragmentation statistics. The experimental geometry employs a steel ogive located inside the target cylinder, with the tip located about halfway in. A single stage light gas gun is then used to launch a polycarbonate projectile into the cylinder at 1,000 m/sec-1. The projectile impacts and flows around the rigid ogive, driving the sample cylinder from the inside. The use of a non-deforming ogive insert allows us to install temperature control hardware inside the rear of the cylinder. Liquid nitrogen (LN2) is used for cooling and a resistive high current load for heating. Multiple channels of upshifted photon Doppler velocimetry (PDV) track the expansion velocity along the cylinder enabling direct comparison to computer simulations, while High speed imaging is used to measure the strain to failure. The recovered cylinder fragments are also subject to optical and electron microscopy to ascertain the failure mechanism.

Fracture and fragmentation are late stage phenomena in dynamic loading scenarios and are typically studied using explosives. We present a technique for driving expansion using a gas gun which uniquely enables control of both loading rate and sample temperature.

The dynamic fracture of a body is a late-stage phenomenon typically studied under simplified conditions, in which a sample is deformed under uniform ...

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

A Novel Biaxial Testing Apparatus for the Determination of Forming Limit under Hot Stamping Conditions

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional experimental approaches, such as out-of-plane and in-plane tests, are not applicable to the determination of forming limits when heating and rapid cooling processes are introduced prior to forming for tests conducted under hot stamping conditions. A novel in-plane biaxial testing system was designed and used for the determination of forming limits of sheet metals at various strain paths, temperatures, and strain rates after heating and cooling processes in a resistance heating uniaxial testing machine. The core part of the biaxial testing system is a biaxial apparatus, which transfers a uniaxial force provided by the uniaxial testing machine to a biaxial force. One type of cruciform specimen was designed and verified for the formability test of aluminum alloy 6082 using the proposed biaxial testing system. The digital image correlation (DIC) system with a high-speed camera was used for taking strain measurements of a specimen during a deformation. The aim of proposing this biaxial testing system is to enable the forming limits of an alloy to be determined at various temperatures and strain rates under hot stamping conditions.

This protocol proposes a novel biaxial testing system used on a resistance heating uniaxial tensile test machine in order to determine the forming limit diagram (FLD) of sheet metals under hot stamping conditions.

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System

Injecting carbon dioxide (CO2) into a deep coal seam is of great significance for reducing the concentration of greenhouse gases in the atmosphere and increasing the recovery of coalbed methane. A visualized and constant-volume gas-solid coupling system is introduced here to investigate the influence of CO2 sorption on the physical and mechanical properties of coal. Being able to keep a constant volume and monitor the sample using a camera, this system offers the potential to improve instrument accuracy and analyze fracture evolution with a fractal geometry method. This paper provides all steps to perform a uniaxial compression experiment with a briquette sample in different CO2 pressures with the gas-solid coupling test system. A briquette, cold-pressed by raw coal and sodium humate cement, is loaded in high-pressure CO2, and its surface is monitored in real-time using a camera. However, the similarity between the briquette and the raw coal still needs improvement, and a flammable gas such as methane (CH4) cannot be injected for the test. The results show that CO2 sorption leads to peak strength and elastic modulus reduction of the briquette, and the fracture evolution of the briquette in a failure state indicates fractal characteristics. The strength, elastic modulus, and fractal dimension are all correlated with CO2 pressure but not with a linear correlation. The visualized and constant-volume gas-solid coupling test system can serve as a platform for experimental research about rock mechanics considering the multifield coupling effect.

A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System

This protocol demonstrates how to prepare a briquette sample and conduct a uniaxial compression experiment with a briquette in different CO2 pressures using a visualized and constant-volume gas-solid coupling test system. It also aims to investigate changes in terms of coal&#8217;s physical and mechanical properties induced by CO2 adsorption.

Injecting carbon dioxide (CO2) into a deep coal seam is of great significance for reducing the concentration of greenhouse gases in the atmosphere and ...

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is known about the effects of high pressure hydrogen on the polymer sealing and barrier materials also found within these components. More study is required in order to determine the compatibility of common polymer materials found in the components of the hydrogen fuel delivery infrastructure with high pressure hydrogen. As a result, it is important to consider the changes in physical properties such as friction and wear in situ while the polymer is exposed to high pressure hydrogen. In this protocol, we present a method for testing the friction and wear properties of ethylene propylene diene monomer (EPDM) elastomer samples in a 28 MPa high pressure hydrogen environment using a custom-built in situ pin-on-flat linear reciprocating tribometer. Representative results from this testing are presented which indicate that the coefficient of friction between the EPDM sample coupon and steel counter surface is increased in high pressure hydrogen as compared to the coefficient of friction similarly measured in ambient air.

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A test methodology for quantifying tribological properties of polymers used in hydrogen infrastructure service is demonstrated and characteristic results for a common elastomer are discussed.

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is ...

Conducting Elevated Temperature Normal and Combined Pressure-Shear Plate Impact Experiments Via a Breech-end Sabot Heater System

A novel approach for conducting normal and/or combined pressure-shear plate impact experiments at test temperatures up to 1000 &#176;C is presented. The method enables elevated temperature plate-impact experiments aimed towards probing dynamic behavior of materials under thermomechanical extremes, while mitigating several special experimental challenges faced while performing similar experiments using the conventional plate impact approach. Custom adaptations are made to the breech-end of a single-stage gas-gun at Case Western Reserve University; these adaptations include a precision-machined extension piece made from SAE 4340 steel, which is strategically designed to mate the existing gun-barrel while providing a high tolerance match to the bore and keyway. The extension piece contains a vertical cylindrical heater-well, which houses a heater assembly. A resistive coil heater-head, capable of reaching temperatures of up 1200 &#176;C, is attached to a vertical stem with axial/rotational degrees of freedoms; this enables thin metal specimens held at the front-end of a heat-resistant sabot to be heated uniformly across the diameter to the desired test temperatures. By heating the flyer plate (in this case, the sample) at the breech-end of the gun-barrel instead of at the target-end, several critical experimental challenges can be averted. These include: 1) severe changes in the alignment of the target plate during heating due to the thermal expansion of the several constituents of the target holder assembly; 2) challenges that arise due to the diagnostics elements, (i.e., polymer holographic gratings, and optical probes) being too close to the heated target assembly; 3) challenges that arise for target plates with an optical window, where crucial tolerances between the sample, bond layer, and window become increasingly difficult to maintain at high temperatures; 4) in the case of combined compression-shear plate impact experiments, the need for high-temperature resistant diffraction gratings for the measurement of transverse particle velocity at the free surface of the target; and 5) limitations imposed on the impact velocity necessary for unambiguous interpretation of the measured free surface velocity versus time profile due to thermal softening and possibly yielding of the bounding target plates.By utilizing the adaptations mentioned above, we present results from a series of reverse geometry normal plate impact experiments on commercial purity aluminum at a range of sample temperatures. These experiments show decreasing particle velocities in the impacted state, which are indicative of material softening (decrease in post-yield flow stress) with increasing sample temperatures.

Here, we present a detailed protocol of a new approach for conducting elevated temperature reverse normal plate impact, and combined pressure-and-shear plate impact. The approach involves the use of a breech-end resistive coil heater to heat a sample held at the front-end of a heat-resistant sabot to the desired temperature.

A novel approach for conducting normal and/or combined pressure-shear plate impact experiments at test temperatures up to 1000 &#176;C is presented. The ...

High-pressure, High-temperature Deformation Experiment Using the New Generation Griggs-type Apparatus

Summary

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