Name: a method for studying the temperature dependence of dynamic fracture and fragmentation
Uploaded: 2015-06-28T14:00:00
Description: Watch this Scientific Journal Video about A Method for Studying the Temperature Dependence of Dynamic Fracture and Fragmentation at JoVE.com

The authors gratefully acknowledge continued funding and support for the project from the Atomic Weapons Establishment, AWE Plc. (UK) and Imperial College London.

1. Target Fabrication and Assembly
<ol>
	<li>Machine target cylinder to desired dimensions from solid stock.</li>
	<li>Prepare the cylinder surface by removing machining marks. A uniform diffuse surface is preferable for PDV reflection. Good results have been obtained with a light wet sanding with &#62;1,200 grit.</li>
	<li>Characterize the target constituents, i.e., measure the following: 
	Cylinder length, diameter and wall thickness (at multiple locations) 
	Projectile length, diameter 
	Ogiv...

<ol>
	<li>Jones, D. R., Chapman, D. J., Eakins, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+gas+gun+based+technique+for+studying+the+role+of+temperature+in+dynamic+fracture+and+fragmentation.">A gas gun based technique for studying the role of temperature in dynamic fracture and fragmentation.</a> J. Appl. Phys. 114, 173508 (2013).</li><li>Liao, S. C., Duffy, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adiabatic+shear+bands+in+a+Ti-6Al-4V+titanium+alloy.">Adiabatic shear bands in a Ti-6Al-4V titanium alloy.</a> J. Mech. Phys. Solids. 46 (11), 2201-2231 (1998).</li><li>Mott, N. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fragmentation+of+shell+cases.">Fragmentation of shell cases.</a> Proc. R. Soc. Lond. A. 189 (1018), 300-308 (1947).</li><li>Hoggatt, C. R., Recht, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fracture+behavior+of+tubular+bombs.">Fracture behavior of tubular bombs.</a> J. Appl. Phys. 39 (3), 1856-1862 (1968).</li><li>Banks, E. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fragmentation+behavior+of+thin-walled+metal+cylinders.">The fragmentation behavior of thin-walled metal cylinders.</a> J. Appl. Phys. 40 (1), 437-438 (1969).</li><li>Warnes, R. H., Duffey, T. A., Karpp, R. R., Carden, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+technique+for+determining+dynamic+metal+properties+using+the+expanding+ring.">Improved technique for determining dynamic metal properties using the expanding ring.</a> Los Alamos Scientific Laboratory Report. , (1980).</li><li>Niordson, F. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+unit+for+testing+materials+at+high+strain+rates.">A unit for testing materials at high strain rates.</a> Exp. Mech. 5 (1), 29-32 (1965).</li><li>Grady, D. E., Benson, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fragmentation+of+metal+rings+by+electromagnetic+loading.">Fragmentation of metal rings by electromagnetic loading.</a> Exp. Mech. 23 (4), 393-400 (1983).</li><li>Winter, R. E., Prestidge, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+technique+for+the+measurement+of+the+high+strain+rate+ductility+of+metals.">A technique for the measurement of the high strain rate ductility of metals.</a> J. Mat. Sci. 13 (8), 1835-1837 (1978).</li><li>Vogler, T. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fragmentation+of+materials+in+expanding+tube+experiments.">Fragmentation of materials in expanding tube experiments.</a> Int. J. Imp. Eng. 29, 735-746 (2003).</li><li>Strand, O. T., Goosman, D. R., Martinez, C., Whitworth, T. L., Kuhlow, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compact+system+for+high-speed+velocimetry+using+heterodyne+techniques.">Compact system for high-speed velocimetry using heterodyne techniques.</a> Rev. Sci. Inst. 77, 083108 (2006).</li><li>Ao, T., Dolan, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SIRHEN:+A+data+reduction+program+for+photonic+Doppler+velocimetry+measurements.">SIRHEN: A data reduction program for photonic Doppler velocimetry measurements.</a> Sandia National Laboratories Report. , (2010).</li></ol>

This method enables investigation of materials at high rates of tensile loading over a wide range of temperatures, from cryogenic to ~1,000 K, unique to this design. However, this adds certain challenges to the experimental setup and execution. Firstly, to optimize the temperature control the ogive insert needs to be machined from a suitable material. 4340 steel is used here, although any high-temperature high-hardness steel should suffice. Likewise, as the entire expansion drive is now originating from the polymer proje...

The dynamic failure of a material is an important aspect of its overall mechanical behavior, and has relevance to numerous industries including automotive, aerospace, and military to name a few. While failure at low strain-rates is typically studied through conventional tension tests, in which a long thin sample is loaded in tension from the ends, at high strain rates such a geometry/configuration requires a sample to be very small in order to maintain a pseudo-mechanical equilibrium throughout the test. At the appearance of a single crack, the surrounding material will be relaxed, effectively arresting the development of any adjacent failure sites. This limits the number of fractures that can be simultaneously observed in any one experiment, and prevents important information regarding the statistics of failure to be determined.
The expanding cylinder test is a well-established technique for characterizing the manner in which materials fail and fragment under high speed loading. In the test, a cylinder made of the material of interest is uniformly loaded along its inner circumference, launching a stress wave through the wall and causing the cylinder to expand. Soon this radial wave dissipates and a uniform tensile hoop stress around the circumference dominates. As the stress and strain rate is the same around the cylinder the fracture and fragmentation behavior is governed solely by the material&#8217;s properties. The test alleviates the aforementioned problem as the typically large sample circumferences promote initiation of multiple failure sites under uniform stress 1.
The main aim in developing this experimental technique was to enable the study of the role of temperature in the fracture and fragmentation behavior of an expanding cylinder. The control of the sample temperature will allow for investigation of how the dynamic tensile strength, fracture mechanism, and fragmentation behavior of the material is affected. For example in metals, an increase in temperature can cause a shift from brittle to ductile fracture, accommodating more plastic work before ultimately failing. Some materials such as Ti-6Al-4V can also exhibit adiabatic shear localization 2. While the sample deforms, the plastic work generates heat. If the rate of softening as a result of this temperature increase is greater than the rate of work hardening from the deformation, an instability can form where a large amount of plastic deformation occurs in a very localized band (adiabatic shear band). This response is promoted in Ti-6Al-4V due to its poor thermal conductivity, and can potentially limit its effectiveness for applications such as lightweight armor.
This new testing approach must satisfy two main criteria. Firstly, the method must produce a radial strain rate on the order of 104 sec-1, typically seen in ballistic and impact events, to allow comparison to previous studies employing more traditional loading schemes. Secondly, the drive mechanism needs to be unaffected by the sample temperature to ensure consistency between experiments. Initial cylinder expansion mechanisms used explosive charges, either simply filling the sample cylinder 3-5 directly or using an intermediate driver. In the latter case a buffer is used 6, where the sample is placed over a steel cylinder that in turn contains an explosive charge. The obvious limitation is that as the sample cylinder contains the drive material (in the form of the explosive) heating the cylinder will also heat the charge. While this may not directly cause initiation of the charge many types of explosive contain a polymeric binder material that will melt out from the sample cylinder. Likewise, some explosives become highly sensitive when cooled. This means that explosive drives are not suitable for temperature study. An alternative method uses the Lorentz force for expansion &#8212; the sample is placed over a driver coil 7, 8. A high current is injected into this driver coil (typically heavy gauge copper wire), inducing an opposite current in the sample. These opposing currents have associated magnetic fields which act against each other, the magnetic pressure driving the sample outwards from the inner face. Again, heating the material will adversely affect the copper drive coil inside the sample. Gas guns have been used for cylinder expansion since the late 1970s 9. In these experiments the material used for the insert in the cylinder is a polymer, the drive coming as a result of both the projectile and insert deforming at impact. This insert is typically a rubber or plastic 10, the strength and ductility of which will be severely affected by temperature. Heating will make the insert too soft, and cooling will make it behave in a brittle manner so it fails prematurely.
Unlike previous cylinder expansion techniques, the method described here is the first to provide a repeatable loading drive over a wide range of temperatures (100-1,000 K). Our technique is unique in the fact that the material used for driving the expansion (in our case the projectile) is separate from the cylinder until the point of impact. Consequently, it is unaffected by the initial temperature of the sample cylinder and provides a repeatable load.
The experimental geometry consists of a steel ogive mounted inside the target cylinder, with the tip located about halfway along the length of the cylinder. A single stage light gas gun is then used to launch a polycarbonate projectile with a concave face into the cylinder at velocities up to 1,000 m/sec-1. The axis of the target is cylinder is carefully aligned to the axis of the gas-gun barrel to facilitate a repeatable and uniform load. The impact and subsequent flow of the polycarbonate projectile around the pseudo-rigid steel ogive, drives the cylinder into expansion from the inside wall. The geometry of the ogive insert and the concave face of the projectile were carefully optimized using hydro-code computer simulations to generate the desired expansion of the cylinder. Using 4340 alloy steel for the ogive enables experimentation with the cylinder at temperature as its strength is much higher than the polycarbonate projectile over the temperature range of interest, ensuring the drive mechanism remains consistent. Ogives recovered from heated and cooled experiments only exhibit minimal deformation as a result of the impact.
The heating and cooling of the sample cylinder is accomplished by the installation of temperature control hardware into a machined recess in the rear of the ogive insert. For cooling the sample to cryogenic temperatures (~100 K), the recess in the ogive is sealed with an aluminum cap and liquid nitrogen is flowed through the cavity. As the target cylinder has a large contact area with the ogive the sample is cooled through conduction. To heat the target cylinder to temperatures approaching 1,000 K, a ceramic and NiChrome resistive heater is placed in the ogive recess. A high current power supply provides up to 1 kW, heating the ogive and cylinder. The cylinder and ogive are thermally isolated from the target mount in the single stage gas-gun through the use of MACOR ceramic spacers. The tank is also held under moderate vacuum (&#60;0.5 Torr) during the experiment which aids thermal manipulation.
In order to diagnose the fragmentation process of the cylinder, the experimental design includes multiple channels of frequency-conversion PDV, to measure the expansion velocity at points along the cylinder. PDV is a relatively new 11, optical fiber based interferometry technique which enables the measurement of surface velocities during highly dynamic events. During a PDV measurement, Doppler shifted light reflected from a moving surface of interest using a fiber-optic probe is combined with un-shifted light, creating a beat frequency that is directly proportional to the velocity of the moving surface. Essentially, a PDV system is a fast Michelson interferometer using advances in near-infrared (1,550 nm) communications technology to record beat frequencies in the GHz range. The mounting system for the 100 mm focal length PDV probes used in the current study ensures that they are isolated from the temperature of the cylinder and provides easy alignment. An additional advantage of using the 100 mm focal length probes is that they provide sufficient optical access to enable high speed photography to measure the expansion profile of the whole cylinder. The arrangement and location of the four probes, A-D, along the cylinder is shown in Figure 1. Two high speed cameras are employed here; a high speed video camera Phantom V16.10 operating at 250,000 fps and an IVV UHSi 12/24 framing camera, capturing 24 images. The IVV camera is backlit such that the cylinder is illuminated in silhouette enabling the radially expanding edge of the cylinder to be accurately tracked. The Phantom camera is front illuminated imaging the failure initiation and fragmentation process. The high speed photography can then be correlated with the velocimetry to give strain and strain rate along the full sample. The high speed imaging also allows for an accurate measure of failure strain and the fracture patterns along the surface.
The experimental technique presented in the following protocol section provides a means of controlling the sample temperature in an expanding cylinder experiment, through which different fracture mechanisms may be activated or suppressed. This technique will lead to a more comprehensive understanding of the role of temperature in dynamic loading scenarios.

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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.

The quality of the data will firstly depend on the experimental timing. If the delays from trigger to impact are correct then the flash lamps will be producing enough light when the target cylinder begins to deform, enabling the high speed cameras to produce clear images. In this case the images from the framing camera will have a clear silhouetted edge that can be used to track the deformation of the whole cylinder. Software such as ImageJ can be used to extract lineout data for each frame, producing an image as in <str...

Watch this Scientific Journal Video about A Method for Studying the Temperature Dependence of Dynamic Fracture and Fragmentation at JoVE.com

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

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 ...

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Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

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The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

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This protocol describes the procedure of measuring the temperature dependence of the full set material constants of piezoelectric materials using resonant ultrasound spectroscopy (RUS).

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the ...

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 ...

Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due to fundamental constraints imposed by the hyperpolarized state, exotic imaging and reconstruction techniques are commonly used. A practical system for characterization of dynamic, multi-spectral imaging methods is critically needed. Such a system must reproducibly recapitulate the relevant chemical dynamics of normal and pathological tissues. The most widely utilized substrate to date is hyperpolarized [1-13C]-pyruvate for assessment of cancer metabolism. We describe an enzyme-based phantom system that mediates the conversion of pyruvate to lactate. The reaction is initiated by injection of the hyperpolarized agent into multiple chambers within the phantom, each of which contains varying concentrations of reagents that control the reaction rate. Multiple compartments are necessary to ensure that imaging sequences faithfully capture the spatial and metabolic heterogeneity of tissue. This system will aid the development and validation of advanced imaging strategies by providing chemical dynamics that are not available from conventional phantoms, as well as control and reproducibility that is not possible in vivo.

A multi-compartment dynamic phantom is used to simulate some biology of interest for metabolic studies using hyperpolarized magnet resonance agents.

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due ...

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line ...

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

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 ...

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This technique utilizes wavelengths of 1150 and 1412 nm, at which the absorption coefficient of water is dependent on temperature. Water or a non-turbid aqueous gel containing a 2.0-mm- or 0.5-mm-diameter magnetic sphere is irradiated with 1150 nm or 1412 nm incident light, as selected using a narrow bandpass filter; additionally, two-dimensional absorbance images, which are the transverse projections of the absorption coefficient, are acquired via a near-infrared camera. When the three-dimensional distributions of temperature can be assumed to be spherically symmetric, they are estimated by applying inverse Abel transforms to the absorbance profiles. The temperatures were observed to consistently change according to time and the induction heating power.

A technique utilizing wavelengths of 1150 and 1412 nm to measure the temperature of water surrounding an induction-heated small magnetic sphere is presented.

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This ...

A 100 KW Class Applied-field Magnetoplasmadynamic Thruster

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate plasma to high speed; they have considerable potential for future space applications with the significant advantages of high specific impulse and thrust density. In this paper, we present a series of protocols for designing and manufacturing a 100 kW class of AF-MPD thruster with water-cooling structures, a 130 V maximum discharge voltage, a 800 A maximum discharge current, and a 0.25 T maximum strength of magnetic field. A hollow tantalum tungsten cathode acts as the only propellant inlet to inhibit the radial discharge, and it is positioned axially at the rear of the anode in order to relieve anode starvation. A cylindrical divergent copper anode is employed to decrease anode power deposition, where the length has been reduced to decrease the wall-plasma connecting area. Experiments utilized a vacuum system that can achieve a working vacuum of 0.01 Pa for a total propellant mass flow rate lower than 40 mg/s and a target thrust stand. The thruster tests were carried out to measure the effects of the working parameters such as propellant flow rates, the discharge current, and the strength of applied magnetic field on the performance and to allow appropriate analysis. The thruster could be operated continuously for significant periods of time with little erosion on the hollow cathode surface. The maximum power of the thruster is 100 kW, and the performance of this water-cooled configuration is comparable with that of thrusters reported in the literature.

The goal of this protocol is to introduce the design of a 100 kW class applied-field magnetoplasmadynamic thruster and relevant experimental methods.

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate ...