Name: conducting elevated temperature normal and combined pressure-shear plate impact experiments via a breech-end sabot heater system
Uploaded: 2018-08-07T12:30:00
Description: Watch this Scientific Journal Video about Conducting Elevated Temperature Normal and Combined Pressure-Shear Plate Impact Experiments Via a Breech-end Sabot Heater System at JoVE.com

The authors would like to acknowledge financial support of the U.S. Department of Energy through the Stewardship Science Academic Alliance DOE/NNSA (DE-NA0001989 and DE-NA0002919) in conducting this research. Finally, the authors would like to thank Los Alamos National Lab for their collaboration in support of undergoing efforts in the current and future investigations.

1. Sample and Target Material Preparation
NOTE: In the following protocol, we will detail the steps necessary for preparing the sample and target materials, which will be later used in a reverse geometry normal plate impact experiment. In this setup, a flyer plate (also the sample), held at the front of a sabot, will be launched via a single stage gas gun and made to impact a stationary target plate housed in the target chamber of the gas gun. A typical flyer and target plate assembly described ...

<ol>
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The method and protocol stated above detailed the procedure for properly performing a reverse geometry normal plate impact experiment at elevated temperatures. In this approach, we make custom modifications to the gun barrel at the high pressure (breech) end of the existing gas gun at Case Western Reserve University, to house a resistive heater coil with axial and rotational degrees of freedom. The resistive heater coil system enables thin aluminum specimens, held at the front-end of a heater resistant sabot, to be heate...

In engineering applications, materials are subjected to a wide range of conditions, which can be static or dynamic in nature, coupled with high levels of deformation and temperatures ranging from room to near the melting point. Under these thermomechanical extremes the material behavior can vary drastically; thus, over nearly a century, several experiments have been developed aimed towards probing the dynamic response and/or other characteristics of material behavior while under controlled loading regimes1,2,3,4,5,6,7,8,9,10,11,12,13,14. For metals loaded at low to intermediate strain rates (10-6-100 /s), servo-hydraulic or precision screw universal testing machines have been used to study the material response subjected to various loading modes and levels of deformation. But as the applied strain rates increase beyond the intermediate strain rates (i.e., &#62;102/s), other experimental techniques become necessary in order to probe the mechanical response. For example, at loading rates of 103/s up to 5 &#215; 104/s full-sized or miniaturized Split-Hopkinson pressure bars enable such measurements to be made8,15.
Traditionally, light gas-guns and/or explosively driven plate impact experiments have been utilized to study the dynamic inelasticity and other phenomenon such as spallation, or phase transformation that occur with very high strain rates (105-107/s)16,17,18,19,20,21,22, or combinations of high pressures and dynamic loading. Customarily, plate impact experiments involve the launch of a flyer plate carried by a sabot initially at the breech-end of the gas-gun, which then travels down the length of the gun-barrel and is made to collide with a carefully aligned stationary target plate at the impact chamber. As a result of the impact, normal and/or combined pressure and shear stresses are generated at the flyer/target interface, which travel through the spatial dimensions of the plates as longitudinal and/or combined longitudinal and transverse stress waves. The arrival of these waves at the rear surface of the target plate affect the instantaneous free surface particle velocity of the target plate, which is monitored typically via interferometric techniques. In order to allow the interpretation of the measured particle velocity versus time history, it is necessary that plane-waves with a front parallel to the impact surface be generated upon impact14,23. To ensure the former, impact must occur with an impact tilt angle on the order of less than one milli-radian12,24, with impact surfaces of flatness better than a couple micrometers5,25.
Plate impact experiments have been adapted to include heating elements which enable investigations of material behavior to extend into thermomechanical extremes26,27,28,29. These adaptations usually involve the addition of an induction coil, or of a resistive heater element to the target-end of the gas-gun; though these adaptations have been shown to be experimentally feasible, the approach inherently leads to special experimental challenges which require careful considerations. Some of these experimental complications include differential thermal expansion of the various constituents of the target holder assembly and/or alignment fixture while heating the target (sample) plate, which requires in-real-time alignment adjustments, usually made with remotely controlled alignment tools with continuous feedback in order to maintain crucial parallelism tolerance between the sample and target plate. In the case of the pressure-shear plate impact experimental scheme, heating the sample requires conventional polymer gratings be replaced by high-temperature resistant metallic gratings in order to monitor transverse particle velocity at the free surface of the target plate. Moreover, heating of the sample can add limitations on the impact velocity that can be employed in certain experimental schemes, such as in the high strain rate combined pressure-and-shear plate impact configuration, where special considerations may be required to prevent unambiguous interpretation of the experimental results, which are calculated using the acoustic impedance of the front and rear target plates which may be temperature dependent. Lastly, for other experimental schemes, which require a target plate with an optical window, tolerances between the sample, bond layer, and/or coatings become increasingly difficult to maintain at high temperatures19.
To alleviate the experimental challenges mentioned above, we have made custom adaptations to the existing single-stage gas-gun located at Case Western Reserve University (CWRU)7,30,31,32. These modifications enable thin metal specimens held at the front-end of a heat-resistant sabot to be heated to temperatures in excess of 1000 &#176;C, prior to firing, which allow high temperature normal and/or combined pressure-shear plate impact experiments to be conducted. In contrast to most of the conventional approaches employed for elevated temperature plate impact studies, this method has been shown to alleviate several of the experimental challenges described above. For example, this approach has been utilized to feasibly achieve tilt angles of less than one milli-radian without the need for remote tilt adjustment30, or additional optical elements for monitoring tilt changes during the experiment. Second, since the target plate remains under ambient temperatures, this method does not require the need for special high-temperature resistant holographic gratings for the measurement of transverse particle velocity in oblique impact experiments; additionally, higher impact velocities can be utilized without the risk of yielding the target plate, and thus, reduce the complexity in the interpretation of the experimental results. To add, this approach can be utilized to perform high temperature reverse-geometry normal plate impact experiments which provide Us-Up relationships for a choice sample material. These can be obtained via impedance matching techniques, or additionally, an analysis of the rarefaction fan from the back surface of the sample which carry information regarding changes in sample shock velocity during unloading33,34. In the elevated temperature combined pressure-shear plate impact configuration, this approach enables the dynamic inelasticity of thin films to be studied up to a wide temperature and plastic deformation range, and strain-rates up to 107/s depending of the thickness of the thin specimen16,27,29.
We will present the protocols necessary for performing a typical elevated temperature plate impact experiment discussed above. This will be followed by a section dedicated to representative results obtained using the present technique. Lastly, a discussion of the results will be presented prior to a conclusion.

<table>
	<tbody>
		<tr>
			<td>99.999% commercial purity polycrystalline aluminum</td>
			<td>Goodfellow</td>
			<td>AL007970</td>
			<td>Material for flyer plate (sample)</td>
		</tr>
		<tr>
			<td>H13 tool steel</td>
			<td>Fabrication Center of CWRU</td>
			<td>N/A</td>
			<td>Material for the sample holder</td>
		</tr>
		<tr>
			<td>Solution treat &#38; age Inconel 718 alloy</td>
			<td>High Temp Metals</td>
			<td>N/A</td>
			<td>(1.005/1.015)&#34; Dia x 24&#34;, Material for target plate</td>
		</tr>
		<tr>
			<td>Photoresist S1805</td>
			<td>MicroChem</td>
			<td>N/A</td>
			<td>Material of the photoresist for holographic grating</td>
		</tr>
		<tr>
			<td>Developer CD-26</td>
			<td>MicroChem</td>
			<td>N/A</td>
			<td>Developer to the photoresist for holographic grating</td>
		</tr>
		<tr>
			<td>Aluminum 6063 tube</td>
			<td>McMaster-Carr</td>
			<td>4568T19</td>
			<td>Material for the ring in target assembly</td>
		</tr>
		<tr>
			<td>Black Delrin (R) Acetal Resin Rod (4-1/2&#34; Dia.)</td>
			<td>McMaster-Carr</td>
			<td>8576K81</td>
			<td>Material for the Delrin holder in target assembly</td>
		</tr>
		<tr>
			<td>White Delrin (R) Acetal Resin Rod (1/4&#34; Dia.)</td>
			<td>McMaster-Carr</td>
			<td>8572K51</td>
			<td>Material for the Delrin pins in target assembly</td>
		</tr>
		<tr>
			<td>Aluminum 6061 tube</td>
			<td>McMaster-Carr</td>
			<td>9056K24</td>
			<td>Material for the body in projectile assembly</td>
		</tr>
		<tr>
			<td>Aluminum 6061 rod</td>
			<td>McMaster-Carr</td>
			<td>8974K88</td>
			<td>Material for the cap in projectile assembly</td>
		</tr>
		<tr>
			<td>Teflon sheet</td>
			<td>McMaster-Carr</td>
			<td>8711K98</td>
			<td>Material for the key</td>
		</tr>
		<tr>
			<td>LAVA-FF - Alumina Silicate disc</td>
			<td>Technical Products</td>
			<td>CWR-033116-1</td>
			<td></td>
		</tr>
		<tr>
			<td>LAVA-FF - Alumina Silicate tube</td>
			<td>Technical Products</td>
			<td>ALR11515</td>
			<td></td>
		</tr>
		<tr>
			<td>Alumina Pan Slotted Head Bolt</td>
			<td>Ceramco</td>
			<td>A83200PANSLT0.500</td>
			<td></td>
		</tr>
		<tr>
			<td>409 N70 Buna-N O-ring</td>
			<td>The O-ring Store</td>
			<td>B70409</td>
			<td></td>
		</tr>
		<tr>
			<td>Loctite Hysol 9412 adhesive</td>
			<td>Loctite</td>
			<td>83107</td>
			<td></td>
		</tr>
		<tr>
			<td>High Temperature Cements</td>
			<td>OMEGA Engineering</td>
			<td>OB-300</td>
			<td></td>
		</tr>
		<tr>
			<td>Extra fast-set epoxy</td>
			<td>Ellsworth</td>
			<td>4001</td>
			<td></td>
		</tr>
		<tr>
			<td>Mylar sheet</td>
			<td>McMaster-Carr</td>
			<td>8567K94</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

An 82.5 mm bore, 6 m length, single-stage gas gun at CWRU capable of accelerating 0.8 kg projectiles to speeds up to 700 m/s was used in conducting the present experiments. Figure 5 shows a photograph of the modified gas-gun facility at CWRU. Prior to firing, the custom designed sabot is housed within the heater extension piece, shown in Figure 6. The extension piece carries a vertical heater-well enabling a resistive coil heater...

Watch this Scientific Journal Video about Conducting Elevated Temperature Normal and Combined Pressure-Shear Plate Impact Experiments Via a Breech-end Sabot Heater System at JoVE.com

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

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 ...

A question of great interest is:How does the dynamic shearing resistance of metals respond to changes in pressure and applied strain rates? This important question in the dynamic material characterization field, and others, could be addressed by this technique which also mitigates several experimental variation sources that are present in the conventional approach. Though this method was was designed primarily for investigations of high temperature compressive and/or shearing resistance of materials, it can also be applied for studies such as dynamic slip and spall.The gas gun at Case Western Reserve University is single-stage, with a six meter length and 82.5 millimeter bore. One section houses a custom modification to the gun for this experiment. The modifications are represented on this schematic.A heating system mates with the existing gun barrel so that the sample held at the front of the custom heat resistant sabot can be heated to desired temperatures in excess of 1000 degrees Celsius. Additional modifications are at the target chamber end. There, a photonic doppler velocimeter probe precisely measures the velocity of the rear surface of the target plate.Trigger and tilt diagnostic signals come from the voltage-biased pins on the front surface of the target plate. The first step is to create the sample and target for the experiment. Create the samples using high purity polycrystalline aluminum.The equi-spaced holes are for securing the sample. Now check the surface flatness. Place the sample in contact with an optical flat then position the two under a green monochromatic light source.Observe light bands that are curved and spaced depending on the surface features. The surface is sufficiently flat if three or fewer light bands are visible across the sample diameter. The experiment also requires a target plate and aluminum ring.Make the target plates from precipitation hardened alloy rod. Section the ring from an aluminum tube and drill six equal-spaced slots in it before polishing it. Put the target plate and the aluminum ring together to produce an assembly similar to this.Next mount the assembly on the target holder ring. When done the assembly will include copper pins for connecting to the trigger and tilt diagnostic circuit. Mount the ring on the target holder.Gather the components of the heat resistant sabot. These include the sample holder, the sample, and the alumina screws. It also includes the alumina silicate lava rock tube and aluminum body tube with its cap.Now work with the cap. The cap has an eye bolt. It's grooves have a sealing O-ring and PTFE key.Run a thermo-couple wire through its bottom. Use epoxy to adhere the cap to the back of the aluminum tube. At the front of the aluminum tube epoxy the lava rock tube.Pull the thermocouple wire from the cap through the tubes to the sample holder and adhere the sample holder to the lava tube. After the cement dries secure the sample to the sample holder with the alumina screws. Before proceeding ensure that the flatness of the front surface of the sample has not changed.Now begin working with the gas gun at the impact chamber. Mount a three-axis motion stage on a rod above the gun barrel. Attach to the stage a prism holder with a precision optical alignment prism.Next tape a first surface mirror over the sample plate. Then position the sabot and the gun barrel with the sample facing out. At the target chamber put a first surface mirror on the target and put the target holder assembly in place.Carefully rotate the prism to be between the target and sample plates and their mirrors. Use a diffused bulb to perform a rough alignment of the plates. Adjust the stage to achieve a single continuous reflected image of the bulb from all surfaces of the prism.Go on to achieve fine alignment with the aid of an auto collimator. Tighten all the positioning screws on the target holder and remove the motion stage, prism, and mirrors. Move the sabot to the breech end of the gas gun and connect the thermocouple to the temperature monitor.At this point set up the doppler velocimeter. This requires an optical fiber focuser probe epoxied into an aluminum tube. Connect the optical focuser to an all-fiber-optic NDI TDI interferometer.Now take the focuser assembly to the target holder. This one is outside of the target chamber for demonstration. Use the attached amount at the rear to support the focuser.Aim the focuser at the rear surface of the target. Turn on the laser and adjust the focuser probe position using the screws on the focuser assembly. Stop after achieving proper light coupling and signal optimization.Adjust the variable ratio coupler to match the intensity of the reference and doppler shifted light to optimize the signal. After all preparations are complete seal the breech target chamber and evacuate the gun barrel to less than 100 millitorr. Move the heater into position and turn it on.Increase its temperature in 100 derees Celsius increments to reach the desired sample temperature. Pressurize the firing dump and load chambers. Also be sure to secure the sabot catcher to the impact chamber.With everything in place turn off the heater and immediately move it upwards toward the heater-well. Record the temperature of the thermocouple at the sample surface. From here continue with the normal firing sequence.This is an example of recorded voltage as a function of time during a typical reversed geometry normal plate impact experiment. The red trace is the trigger signal from the voltage based pins. The difference between the trigger times of the first and last pins allows an estimate of the maximum tilt at impact.A longitudinal wave arrives at the back surface. The black signal is the result of normal motion diagnostics of the free surface using the photon doppler velocimeter. This plot is of the free normal surface velocity for a range of temperatures.Data symbols go from black to red representing the coolest to warmest initial sample temperatures. The initial sharp rise is related to the stress of the aluminum sample at its interface with the target as the shock evolves. The plateau results from the impedance match between the sample and the target.Note that the highest free surface velocity is associated with the lowest temperature and velocities decrease with increasing temperature. This suggests possible thermal softening of the sample under the different test conditions. A more interesting result can be seen in figure 16 which shows the normal free surface particle velocity trace obtained from reverse geometry normal plate impact experiments performed on commercial purity polycrystalline magnesium.The results show monotonically decreasing particle velocities at the shock plateau with increasing temperatures in the range of 23 to 610 degrees Celsius. However at temperatures beyond this level, ie 617 and 630 degrees Celsius, a reversal of this trend can be clearly observed. This increase in particle velocity suggests an increase in the shock impedance of the sample material.Moreover assuming that the elastic constants of the material decrease as a function of increasing temperature then an increase in the shock impedance in this case suggests an increase in the yield strength and/or plastic modulus of the sample material. It can be seen that the increase in particle velocity at the shock plateau is accompanied by an increase in the particle velocity levels throughout the initial rise in the particle velocity trace, which correlates with the stress levels of the sample target interface during the incipient plasticity of the sample material. Figure 17 shows micrographs of cross sections of the impact surface of post-test specimens.The images show two noticeable effects on the microstructure as a result of increasing temperature. First is grain-ripening with increasing sample temperature. The images also show a change in twin band formations.Carefully looking at the images corresponding to temperatures ranging from 23 to 500 degrees Celsius, a clear reduction in twin bands are observed with increasing temperature. However, at higher temperatures, ie 610, 617, and 630 degrees Celsius, a reemergence of these twin bands are observed, which suggests that twin band formation is favored at the latter end of this temperature range. If the test materials are already assembled, once mastered, this technique can be done in about five to six hours.While attempting this procedure it's important to remember to take proper care in preparing the sample materials so that the flatness and parallelism tolerances can be adequately met. Following this procedure similar methods such as oblique plate impact and pressure shear plate impact can also be performed which enable dynamic material behavior to be probed at various loading rates and modes. After watching this video you should have a good understanding of how to perform an elevated temperature plate impact experiment which enables you to alleviate several experimental challenges present in the conventional approach.

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Research

JoVE Journal

Engineering

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators 1,2. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials.
Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides 3, asymmetric split-ring resonators 4, and photonic band gap structures integrated into parallel-plate waveguides 5. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc.
The sensor design we use here is based on a simple parallel-plate waveguide 6,7. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE1) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove 6,8. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index 9.
Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves 10. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.

The procedure for implementing a refractive index sensor for terahertz frequencies based on a grooved parallel-plate waveguide geometry is described here. The method yields a measurement of the refractive index of a small volume of liquid through monitoring of the shift in the resonant frequency of the waveguide structure

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic ...

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

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 ...

Prescribed 3-D Direct Writing of Suspended Micron/Sub-micron Scale Fiber Structures via a Robotic Dispensing System

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer fiber length and orientation is defined by the spatial positioning of the dispensing system 3-axis stages. The fiber diameter is defined by the prescribed dispense time of the dispensing system valve, the feed rate (the speed at which the stage traverses from an initiating to a terminating position), the gauge diameter of the dispensing tip, the viscosity and surface tension of the polymer solution, and the programmed drawing length. The stage feed rate affects the polymer solution&#8217;s evaporation rate and capillary breakup of the filaments. The dispensing system consists of a pneumatic valve controller, a droplet-dispensing valve and a dispensing tip. Characterization of the direct write process to determine the optimum combination of factors leads to repeatedly acquiring the desired range of fiber diameters. The advantage of this robotic dispensing system is the ease of obtaining a precise range of micron/sub-micron fibers onto a desired, programmed location via automated process control. Here, the discussed self-assembled micron/sub-micron scale 3D structures have been employed to fabricate suspended structures to create micron/sub-micron fluidic devices and bioengineered scaffolds.

Here, we present a protocol to fabricate freely-suspended, micron/sub-micron scale polymer fibers and &#8220;web-like&#8221; structures generated via automated direct writing procedure by means of a 3-axis dispensing system.

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

The Modular Design and Production of an Intelligent Robot Based on a Closed-Loop Control Strategy

Intelligent robots are part of a new generation of robots that are able to sense the surrounding environment, plan their own actions and eventually reach their targets. In recent years, reliance upon robots in both daily life and industry has increased. The protocol proposed in this paper describes the design and production of a handling robot with an intelligent search algorithm and an autonomous identification function.
First, the various working modules are mechanically assembled to complete the construction of the work platform and the installation of the robotic manipulator. Then, we design a closed-loop control system and a four-quadrant motor control strategy, with the aid of debugging software, as well as set steering gear identity (ID), baud rate and other working parameters to ensure that the robot achieves the desired dynamic performance and low energy consumption. Next, we debug the sensor to achieve multi-sensor fusion to accurately acquire environmental information. Finally, we implement the relevant algorithm, which can recognize the success of the robot&#39;s function for a given application.
The advantage of this approach is its reliability and flexibility, as the users can develop a variety of hardware construction programs and utilize the comprehensive debugger to implement an intelligent control strategy. This allows users to set personalized requirements based on their needs with high efficiency and robustness.

We present a protocol on modular design and production of intelligent robots to help scientific and technical workers design intelligent robots with special production tasks based on personal needs and individualized design.

Intelligent robots are part of a new generation of robots that are able to sense the surrounding environment, plan their own actions and eventually reach ...

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (&#8804;150 &#176;C) growth of ultrathin films (100-1000 &#197;) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films&#39; optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Thin films (100-1000 &#197;) of vanadium dioxide (VO2) were created by atomic-layer deposition (ALD) on sapphire substrates. Following this, the optical properties were characterized through the metal-insulator transition of VO2. From the measured optical properties, a model was created to describe the tunable refractive index of VO2.

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with ...