We kindly acknowledge Marco Albano for providing the video dealing with optical microscope and SEM and Domenico Mannetta for the rock cutting procedure. This research has been supported by the ERC Grant GLASS n&#176; 259256 and TECTONIC n&#176; 835012. This contribution was greatly improved by the comments of three anonymous reviewers and by the editorial production suggestions on the video.

1. Rock sample collection
<ol>
	<li>In a well-exposed outcrop of a natural phyllosilicate-rich fault, select the right exposure (fault rock well preserved along a plane containing fault lineation) where to collect a representative rock sample for the experiments. Take care to select a fault rock with a foliation spacing not larger than a few millimeters. This is done to capture phyllosilicate horizons in rectangular wafers up to 1.5 cm thick that will be sheared during friction experiments.</li>
	<li>Use a hammer and chisel to obtain a fault rock sample with an area of about 10 cm x 10 cm and thickness of more than 3 cm.</li>
	<li>Mark the sense of shear on the rock sample, based on kinematic indicators observed in the field (e.g., slickensides, foliations, drag folds, etc.). 
	NOTE: The area of the sample can be smaller than 10 cm x 10 cm, but it must be larger than 5 cm&#160;x 5 cm that is the dimension of the forcing blocks of the experimental apparatus. 
	&#8203;CAUTION: The foliated rock samples are very friable and therefore after the collection it may be useful to wrap the sample with some tape or a plastic film. It is mandatory that collected samples are not altered by weathering and therefore that these rocks represent the fault rock at seismogenic depth.</li>
</ol>
2. Sample preparation for friction experiments in the double direct shear configuration
<ol>
	<li>Cut the rock sample to obtain rectangular wafers that fit the forcing blocks of the rock deformation apparatus. This is usually achieved in two steps: in the first step, use a standard laboratory saw to obtain a rock sample that is slightly larger than the forcing blocks; secondly use a high precision rotary blade or a hand-grinder to shape wafers 5 cm x 5 cm in area and 0.8-1.2 cm thickness (Figure 1, left). For a standard double-direct shear test, two wafers of the same rock will be required to perform a single experiment. During the cut and shaping procedure, ensure that natural phyllosilicate-rich shear planes contained in the sample are maintained parallel to the surface of the forcing blocks. This means that the foliation is parallel to the 5 cm x 5 cm face of the wafer.</li>
	<li>Use a disk mill to crush the remaining material from the cut of the intact samples and sieve the material to obtain powders with a grain size &#60;125 &#181;m (Figure 1, right).</li>
	<li>Mount two identical wafers on stainless steel forcing blocks with nominal frictional contact area of 5 cm &#215; 5 cm and then assemble them with the central forcing block to compose the symmetric double direct shear configuration. 
	NOTE: It is important that the shear sense imposed by the machine on the sample coincides with the natural sense of shear recorded on the wafer and marked at point 1.3.</li>
	<li>Use the powders to construct two identical rock layers with thickness of about 5 mm and area of 5 cm x 5 cm2. For these powdered rock samples, the natural foliation is destroyed by the sample preparing procedure with a disk-mill. Use a precise leveling jig to obtain a uniform and reproducible rock layer composed of powdered material. Compose the symmetric double direct shear assembly.</li>
</ol>
3. Friction experiments
<ol>
	<li>In a biaxial apparatus27,28 use the horizontal servo-controlled hydraulic piston to apply and maintain a constant normal stress to the rock sample.</li>
	<li>Apply shear stress at constant displacement rate, usually 10 &#956;m/s, via the vertical servo- controlled hydraulic piston. 
	NOTE: Loads are measured via two strain gauge load cells (accuracy 0.03 kN) positioned between the ram and the sample assembly. Horizontal and vertical displacements are measured by LVDT (linear variable differential transducers), with an accuracy of 0.1 &#181;m, referenced at the load frame and the upper side of the ram27,28.</li>
	<li>Characterize all experiments by an initial strain hardening, where the shear stress increases rapidly during elastic loading, before a yield point, followed by shear at a steady-state value of frictional stress.</li>
</ol>
4. Post-experimental sample collection
<ol>
	<li>At the end of the friction test, carefully extract the experimental fault. Rubber bands or adhesive tape can be applied to the sample before load removal to maintain the integrity of the deformed rocks.</li>
	<li>Impregnate with epoxy resin the rock samples. If possible for powder experiments, avoid vacuum impregnation to prevent damage to the original microstructure by the forced flow of the resin into the sample.</li>
	<li>Cut these rock samples parallel to the experimental shear direction. There are several ways to track the experimental shear direction. In our double direct shear configuration, the surfaces of the steel sliding blocks in contact with gouge layers are machined with grooves 0.8 mm high and spaced 1 mm to avoid slip at the interface between gouges and steel and to ensure shear deformation within the gouges, therefore in our experiments the shear direction is perpendicular to grooves.</li>
	<li>Build thin sections from the cuts for microstructural studies.</li>
</ol>
5. Microstructural analysis
<ol>
	<li>Investigate with an optical microscope to characterize the bulk fault zone microstructure.</li>
	<li>Use a scanning electron microscope (SEM) to investigate the main deformation processes.</li>
	<li>Use a transmission electron microscope (TEM) to obtain details on the deformation processes at the nanoscale. Details on how to perform microstructural analysis can be found in previous publications4,5,6,7,8,9,10,29.</li>
</ol>

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The authors have nothing to disclose.

An important point worth mentioning is that with this procedure we characterize the steady state fault frictional strength, measured with experiments at low sliding velocities (i.e., 0.01 &#181;m/s &#60; v &#60; 100 &#181;m/s). The measured low values of friction demonstrate the weakness of phyllosilicate-rich faults resulting from long-term fluid assisted reaction softening and foliation development1,4,5,6,7,8,9,10,11,12,30. This low frictional strength can be used as a proxy to evaluate the fault strength at steady-state or during the pre-seismic phases of the seismic cycle. Therefore, the important dynamic weakening mechanisms that occur at high slip velocities (i.e., &#62; 10 cm/s) and induced by temperature rise33 are not considered in our analysis.
The critical steps in the protocol regard the sample collection and preparation. Since phyllosilicates are characterized by very low tensile strength in the direction perpendicular to the (001) basal planes (i.e., in the direction perpendicular to the foliation), during the work with the hammer and chisel in the field or with the hand-grinder in the lab, quite often the rock samples fall apart and the shaping process has to restart. Therefore, it is strongly recommended to collect more samples than those strictly required to run experiments and arm yourself with patience.
Before integrating mechanical with microstructural data, it is important to check that the frictional sliding along the phyllosilicate-rich foliae observed along natural fault rocks is reproduced in the lab, or in other words that the natural fault rock microstructure is similar to the one obtained from shearing the wafer (Figure 3).
In experiments on solid wafers characterized by thin networks of phyllosilicates, the continuous layers of weak mineral phases can be consumed during significant shearing (displacement &#62; 12 mm). At this stage the deformation is accommodated by a combination of cataclasis of the strong mineral phases and sliding along the phyllosilicates. This coincides with a phase of strain hardening with an increase in friction of about 0.1 or more13.
The majority of rock deformation experiments, aimed at the characterization of the frictional properties of tectonic faults, are performed on millimetric rock layers that are composed by powders obtained by crushing and sieving natural fault rocks24,27 or on fault rocks that are pre-cut34. These types of experiments are fundamental to characterize the frictional properties of faults where the deformation occurs on fault gouges35 or along sharp slipping planes of localized deformation36. For faults rich in phyllosilicates, low friction and hence fault weakness is related to the interconnectivity of the phyllosilicate-rich networks, which in the field is manifested by multiple anastomosing principal slip zones. This indicate that even a small quantity of phyllosilicates can induce significant fault weakening if their interconnectivity is very high37,38. Therefore, the final goal of our laboratory experiments on solid wafers is to preserve the natural continuity of the phyllosilicate-rich layers during friction tests.
Other laboratory experiments on powdered mixtures of strong and weak mineral phases have documented fault weakening with the addition of the weak phases18,19,20,21,22. It has been observed that amounts of 40-50% of phyllosilicates induce a significant reduction in friction because during shearing they become interconnected. This suggests that for large percentages of phyllosilicates (i.e., &#62; 40%), experiments on wafers or powders are similar25.
A compilation of friction tests conducted on a large number of natural fault rocks rich in phyllosilicates, wafers or powdered material with phyllosilicates percentages &#62; 40%, under a wide range of experimental conditions show that friction is in the range of 0.1-0.330. This implies that a significant number of crustal faults are weak.

The overall goal of this procedure is to test the frictional properties of intact phyllosilicate-rich faults sheared in their in situ geometry and to show that their friction is significantly lower than friction obtained from experiments conducted on powders of the same material.
Numerous geological studies have documented fluid-assisted reaction softening during the long-term evolution of tectonic faults. Softening occurs by the replacement of strong minerals, like quartz, feldspar, calcite, dolomite, olivine, pyroxene, with weak phyllosilicates1,2,3,4,5,6,7,8,9,10. This weakening originates at the grain-scale and is mainly due to sliding, at very low friction, along the phyllosilicate foliae that act together to produce a form of lubrication. From the grain-scale, fault weakening is transmitted to the entire fault zone via the interconnectivity of the phyllosilicate-rich zones11. To capture the role of frictional sliding along interconnected phyllosilicate foliae, intact solid wafers of natural fault-rock samples have been sheared in their in situ geometry during rock deformation experiments12,13,14. At the end of the experiment, microstructural studies on the tested samples have been performed to check if effectively the deformation was accommodated by frictional sliding along the phyllosilicate foliae.
In comparison with traditional friction tests performed on powdered materials obtained from crushing and sieving the fault rock, experiments on intact wafers can capture the frictional sliding along the interconnected phyllosilicate-rich layers formed by fluid assisted reaction softening. In fact, during the process of powder preparation, the crushing and sieving of the fault rock disrupts the connectivity of the phyllosilicate layers and when the material is sheared in the laboratory, the absence of continuous phyllosilicate horizons favors a deformation mainly consisting of grain crushing, rotation and translation resulting in high friction.
Experiments on solid wafers show a significantly lower friction in comparison to experiments on powdered material obtained from the same rock type, particularly when the percent of the phyllosilicates is &#60; 40%15. With increasing phyllosilicate abundance, a reduction in friction has been documented also for tests on powdered material, since in this case the large volume of phyllosilicates is sufficient to promote interconnectivity of the weak mineral phases through the entire experimental fault16,17,18,19,20,21,22. Alternatively, to simulate frictional sliding on the interconnected weak layers, other types of friction tests have been performed on powders composed of 100% weak mineral phases23,24,25.
Geometrical fault weakening promoted by rock fabric in deformation experiments at high temperature, and therefore representative of the ductile lithosphere, has been well known for many years26. The results obtained from the procedure presented here indicate that phyllosilicate fabric promotes fault weakening also for a large number of faults contained within the seismogenic upper crust.

<table><tbody><tr><td>disk mill</td><td>Plenty of companies</td><td>none</td><td>Standard disk mills to pulverize rocks</td></tr><tr><td>fault rock</td><td>Natural outcrops</td><td>none</td><td>All the outcrops rich in phyllosilicates worldwide</td></tr><tr><td>hammer and chisel</td><td>Plenty of companies</td><td>none</td><td>Standard hammer and chisel used by geologists</td></tr><tr><td>optical microscope</td><td>Plenty of companies</td><td>none</td><td>Standard microscope used for mineralogy</td></tr><tr><td>rock deformation apparatus</td><td>we use prototypes like BRAVA &amp;amp; BRAVA2.0</td><td>none</td><td>Rock deformation apparatuses (Marone et al., 1998; Collettini et al., 2014)</td></tr><tr><td>saw to cut rocks</td><td>Plenty of companies</td><td>none</td><td>Standard saws to cat fault rocks</td></tr><tr><td>SEM, scanning electron microscope</td><td>Plenty of companies</td><td>none</td><td>Microscope to investigate microstructures at the micron scale</td></tr><tr><td>TEM, transmission electron microscope</td><td>Plenty of companies</td><td>none</td><td>Microscope to investigate microstructures at the nano scale</td></tr></tbody></table>

the role of fabric in frictional properties of phyllosilicate-rich tectonic faults

Many rock deformation experiments used to characterize the frictional properties of tectonic faults are performed on powdered fault rocks or on bare rock surfaces. These experiments have been fundamental to document the frictional properties of granular mineral phases and provide evidence for crustal faults characterized by high friction. However, they cannot entirely capture the frictional properties of faults rich in phyllosilicates.
Numerous studies of natural faults have documented fluid-assisted reaction softening promoting the replacement of strong minerals with phyllosilicates that are distributed into continuous foliations. To study how these foliated fabrics influence the frictional properties of faults we have: 1) collected foliated phyllosilicate-rich rocks from natural faults; 2) cut the fault rock samples to obtain solid wafers 0.8-1.2 cm thick and 5 cm x 5 cm in area with the foliation parallel to the 5x5cm face of the wafer; 3) performed friction tests on both solid wafers sheared in their in situ geometry and powders, obtained by crushing and sieving and therefore disrupting the foliation of the same samples; 4) recovered the samples for microstructural studies from the post experiment rock samples; and 5) performed microstructural analyses via optical microscopy, scanning and transmission electron microscopy. 
Mechanical data show that the solid samples with well-developed foliation show significantly lower friction in comparison to their powdered equivalents. Micro- and nano-structural studies demonstrate that low friction results from sliding along the foliation surfaces composed of phyllosilicates. When the same rocks are powdered, frictional strength is high, because sliding is accommodated by fracturing, grain rotation, translation and associated dilation. Friction tests indicate that foliated fault rocks may have low friction even when phyllosilicates constitute only a small percentage of the total rock volume, implying that a significant number of crustal faults are weak.

In a diagram of normal stress vs. shear stress both solid foliated and powdered samples plot along a line consistent with a brittle failure envelope, but the solid wafers have friction values significantly lower than their powdered analogues30. For example, in the specific case of a talc-rich foliation, foliated fault rocks at each normal stress have a friction coefficient that is 0.2-0.3 lower than the powders made from them (Figure 2 and12). The lower friction is explained by microstructural studies of the tested rocks showing that the sliding surfaces of the foliated solid wafers occur along the pre-existing phyllosilicate-rich foliation. TEM images show that slip is mainly accommodated by (001) easy sliding associated with interlayer delamination. In contrast, experimental microstructures from the powdered material show that significant deformation is accommodated by grain-size reduction and localization.
Although the foliated wafers of intact fault rocks and their powders have identical mineralogical compositions, the foliated samples show friction that is significantly lower than their powdered analogues. Microstructural studies indicate that the lower friction (i.e., fault weakness) of the foliated fault rocks is due to the reactivation of the pre-existing natural phyllosilicate-rich surfaces that are absent in the powdered samples since the sample preparation steps (2.2 - 2.4) disrupt them.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62821/62821fig01.jpg" /> 
Figure 1:&#160;Representative images of the tested fault rocks: solid foliated vs. powdered material. (left) Solid foliated samples sheared parallel to the natural foliation marked by the arrows. (right)&#160;Powders obtained by crushing and sieving the solid foliated rock. <a href="https://www.jove.com/files/ftp_upload/62821/62821fig01large.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/62821/62821fig02.jpg" /> 
Figure 2:&#160;Friction tests on the same material (talc-rich foliation) but solid foliated samples vs. powdered rock. Each dataset plot along a line consistent with a brittle failure envelope, but the solid foliated rocks are characterized by friction significantly lower than their powdered analogue, friction, &#956; = 0.3 and &#956; = 0.57 respectively. <a href="https://www.jove.com/files/ftp_upload/62821/62821fig02large.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/62821/62821fig03.jpg" /> 
Figure 3:&#160;Natural vs. laboratory reactivated foliation. In the left picture an example of a natural talc-rich foliation with surrounding sigmoidal clasts of calcite31. The right picture shows the same foliation at the end of a friction test on wafers32. Note that during the friction test most of the slip occurs by frictional sliding along the phyllosilicate layers and that the original microstructure is preserved. <a href="https://www.jove.com/files/ftp_upload/62821/62821fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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The Role of Fabric in Frictional Properties of Phyllosilicate-Rich Tectonic Faults

Friction of phyllosilicates-rich faults sheared in their in situ geometry is significantly lower than friction of their powdered equivalents.

Many rock deformation experiments used to characterize the frictional properties of tectonic faults are performed on powdered fault rocks or on bare rock ...

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Unit 1

Friction

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3.1K Views.  Sapienza Università di Roma. Het algemene doel van deze procedure is om de wrijvingseigenschappen van fyllosilicaten te testen, met fouten in de in-situ geometrie, en om aan te tonen dat deze wrijving aanzienlijk lager is dan de wrijving van poeders verkregen door hetzelfde materiaal. Tijdens de langetermijnevolutie van tektonische breuken hebben talrijke geologische studies vloeistofondersteunde reactieverzachting gedocumenteerd, die de vervanging van sterke en korrelige mineralen door fyllosilicaten bevordert. Met name...

Video: The Role of Fabric in Frictional Properties of Phyllosilicate-Rich Tectonic Faults

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

Kinematic History of a Salient-recess Junction Explored through a Combined Approach of Field Data and Analog Sandbox Modeling

Within fold-thrust belts, the junctions between salients and recesses may hold critical clues to the overall kinematic history. The deformation history within these junctions is best preserved in areas where thrust sheets extend from a salient through an adjacent recess. We examine one such junction within the Sevier fold-thrust belt (western United States) along the Leamington transverse zone, northern Utah. Deformation within this junction took place by faulting and cataclastic flow. Here, we describe a protocol that examines these fault patterns to better understand the kinematic history of the field area. Fault data is supplemented by analog sandbox experiments. This study suggests that, in detail, deformation within the overlying thrust sheet may not directly reflect the underlying basement structure. We demonstrate that this combined field-experimental approach is easy, accessible, and may provide more details to the deformation preserved in the crust than other more expensive methods, such as computer modeling. In addition, the sandbox model may help to explain why and how these details formed. This method can be applied throughout fold-thrust belts, where upper-crustal rocks are well preserved. In addition, it can be modified to study any part of the upper crust that has been deformed via elastico-frictional mechanisms. Finally, this combined approach may provide more details as to how fold-thrust belts maintain critical-taper and serve as potential targets for natural resource exploration.

Kinematic histories of fold-thrust belts are typically based on careful examinations of high-grade metamorphic rocks within a salient. We provide a novel method of understanding fold-thrust belts by examining salient-recess junctions. We analyze the oft-ignored upper crustal rocks using a combined approach of detailed fault analysis with experimental sandbox modeling.

Within fold-thrust belts, the junctions between salients and recesses may hold critical clues to the overall kinematic history. The deformation history ...

Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone.

The methodology to perform friction force microscopy experiments for contacting brushes is presented: Two polymer brushes that are grafted from (a) substrates and (b) colloidal probes are slid to show that, by using two contacting immiscible brush systems, friction in sliding contacts is reduced compared to miscible brush systems.

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low ...

Engineering

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 ...

Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) coupled with synchrotron X-radiation. A cube-shaped sample assembly is prepared and compressed, at room temperature, by a set of four X-ray transparent sintered diamond anvils and two tungsten carbide anvils, in the lateral and the vertical planes, respectively. All six anvils are housed within a 250-ton hydraulic press and driven inward simultaneously by two wedged guide blocks. A horizontal energy dispersive X-ray beam is projected through and diffracted by the sample assembly. The beam is commonly in the mode of either white or monochromatic X-ray. In the case of white X-ray, the diffracted X-rays are detected by a solid-state detector array that collects the resulting energy dispersive diffraction pattern. In the case of monochromatic X-ray, the diffracted pattern is recorded using a two-dimensional (2-D) detector, such as an imaging plate or a charge-coupled device (CCD) detector. The 2-D diffraction patterns are analyzed to derive lattice spacings. The elastic strains of the sample are derived from the atomic lattice spacing within grains. The stress is then calculated using the predetermined elastic modulus and the elastic strain. Furthermore, the stress distribution in two-dimensions allow for understanding how stress is distributed in different orientations. In addition, a scintillator in the X-ray path yields a visible light image of the sample environment, which allows for the precise measurement of sample length changes during the experiment, yielding a direct measurement of volume strain on the sample. This type of experiment can quantify the stress distribution within geomaterials, which can ultimately shed light on the mechanism responsible for compaction. Such knowledge has the potential to significantly improve our understanding of key processes in rock mechanics, geotechnical engineering, mineral physics, and material science applications where compactive processes are important.

We report detailed procedures for compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus coupled with synchrotron X-radiation. Such experiments allow quantification of the stress distribution within samples, that ultimately sheds light on compaction processes in geomaterials.

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) ...

Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques.
This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions.

The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the ...

Deposition of Porous Sorbents on Fabric Supports

A microwave deposition technique for silanes, previously described for production of oleophobic fabrics, is adapted to provide a fabric support material that can be subsequently treated by dip coating. Dip coating with a sol preparation provides a supported porous layer on the fabric. In this case, the porous layer is a porphyrin functionalized sorbent system based on a powdered material that has been demonstrated previously for the capture and conversion of phosgene. A representative coating is applied to cotton fabric at a loading level of 10 mg/g. This coating has minimal impact on water vapor transport through the fabric (93% of the support fabric rate) while significantly reducing transport of 2-chloroethyl ethyl sulfide (CEES) through the material (7% of support fabric rate). The described approaches are suitable for use with other fabrics providing amine and hydroxyl groups for modification and can be used in combination with other sol preparations to produce varying functionality.

This report details a microwave-initiated approach for deposition of porphyrin functionalized porous organosilicate sorbents on a cotton fabric and demonstrates reduction in 2-chloroethyl ethyl sulfide (CEES) transport through the fabric resulting from this treatment.

A microwave deposition technique for silanes, previously described for production of oleophobic fabrics, is adapted to provide a fabric support material ...

Visualization of Failure and the Associated Grain-Scale Mechanical Behavior of Granular Soils under Shear using Synchrotron X-Ray Micro-Tomography

The rapid development of X-ray imaging techniques with image processing and analysis skills has enabled the acquisition of CT images of granular soils with high-spatial resolutions. Based on such CT images, grain-scale mechanical behavior such as particle kinematics (i.e., particle translations and particle rotations), strain localization and inter-particle contact evolution of granular soils can be quantitatively investigated. However, this is inaccessible using conventional experimental methods. This study demonstrates the exploration of the grain-scale mechanical behavior of a granular soil sample under triaxial compression using synchrotron X-ray micro-tomography (&#956;CT). With this method, a specially fabricated miniature loading apparatus is used to apply confining and axial stresses to the sample during the triaxial test. The apparatus is fitted into a synchrotron X-ray tomography setup so that high-spatial resolution CT images of the sample can be collected at different loading stages of the test without any disturbance to the sample. With the capability of extracting information at the macro scale (e.g., sample boundary stresses and strains from the triaxial apparatus setup) and the grain scale (e.g., grain movements and contact interactions from the CT images), this procedure provides an effective methodology to investigate the multi-scale mechanics of granular soils.

The protocol describes procedures to acquire high-spatial resolution computed tomography (CT) images of a granular soil during triaxial compression, and to apply image processing techniques to these CT images to explore the grain-scale mechanical behavior of the soil under loading.

The rapid development of X-ray imaging techniques with image processing and analysis skills has enabled the acquisition of CT images of granular soils ...

Source: Nicholas Timmons,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, CA

The goal of this experiment is to examine the physical nature of the two types of friction (i.e., static and kinetic). The procedure will include measuring the coefficients of friction for objects sliding horizontally as well as down an inclined plane.
Friction is not completely understood, but it is experimentally determined to be proportional to the normal force exerted on an object. If a microscope zooms in on two surfaces that are in contact, it would reveal that their surfaces are very rough on a small scale. This prevents the surfaces from easily sliding past one another. Combining the effect of rough surfaces with the electric forces between the atoms in the materials may account for the frictional force.
There are two types of friction. Static friction is present when an object is not moving and some force is required to get that object in motion. Kinetic friction is present when an object is already moving but slows down due to the friction between the sliding surfaces.

Friction: Static and Kinetic

Source: Nicholas Timmons,&#160;Asantha Cooray, PhD, Department of Physics &#38; Astronomy, School of Physical Sciences, University of California, Irvine, ...

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Physics

Physics I

Characteristics of Dry Friction

Dry friction occurs when two solid surfaces slide against each other without any lubrication or fluid present. It causes resistance when pushing objects along a surface, like a gardener pushing a wheelbarrow. The force applied to move the cart causes dry friction between the wheel and the ground.
Before the wheelbarrow starts moving, the static frictional force acts tangentially to the contact surface, opposing the force that is about to induce the motion. This frictional force prevents the wheelbarrow from slipping and helps to maintain stability. It is important to note that the static frictional force is only present when there is no relative motion between the two surfaces.
When the wheelbarrow is about to slip, the maximum static frictional force at the interface is directly proportional to the normal force. This relationship is defined by the coefficient of static friction, which depends on the types of materials in contact and the roughness of their surfaces.
Interestingly, the static frictional force is independent of the contact area when the normal pressure is within a specific range that avoids deformation or damage to the contacting surfaces. This means that even if the contact area between the wheel and the ground changes, the static frictional force remains constant as long as the normal pressure stays within this particular range.
Once the wheelbarrow starts slipping and movement occurs, the developed kinetic frictional force comes into play. This force is also proportional to the normal force but is generally lower than the maximum static frictional force. The difference between the two forces can be attributed to the fact that surfaces in relative motion have less time to interlock and create resistance.
However, if the wheelbarrow moves at a very low velocity over the surface, the kinetic frictional force becomes approximately equal to the maximum static frictional force. This is because the slow movement allows for more interaction between the surfaces, leading to increased resistance.
The coefficient of kinetic friction primarily depends on the material&#39;s surface properties and the surrounding environment. Factors such as temperature, humidity, and surface contamination can significantly impact the kinetic frictional force.
By examining the factors that influence the coefficients of static and kinetic friction, one can better understand the relationship between the materials in contact, the roughness of their surfaces, and the surrounding environment. This understanding enables individuals to make informed decisions when designing and selecting materials for specific applications, ultimately enhancing the performance and functionality of various systems and devices.

Dry friction occurs when two solid surfaces slide against each other without any lubrication or fluid present. It causes resistance when pushing objects ...

The Role of Fabric in Frictional Properties of Phyllosilicate-Rich Tectonic Faults

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